73704655 thermoplastic elastome

Well-defined Thermoplastic ElastomersReversible networks based on hydrogen bonding

Well-defined Thermoplastic ElastomersReversible networks based on hydrogen bonding

PROEFSCHRIFT

ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr. R.A. van Santen, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op donderdag 30 januari 2003 om 16.00 uur

door

Ronny Mathieu Versteegengeboren te Tegelen

Dit proefschrift is goedgekeurd door de promotoren: prof.dr. E.W. Meijer en prof.dr. C.A. Hunter

Copromotor: dr. R.P. Sijbesma

This research has been financially supported by the Netherlands Organization for Scientific Research (NWO/CW). Omslag: Ron Versteegen, Paul Verspaget Druk: Universiteitsdrukkerij, Technische Universiteit Eindhoven

CIP-DATA LIBRARY TECHNISCHE UNIVERSITEIT EINDHOVEN

Versteegen, Ronny M. Well-defined thermoplastic elastomers : reversible networks based on hydrogen bonding / by Ronny M. Versteegen. Eindhoven : Technische Universiteit Eindhoven, 2003. Proefschrift. ISBN 90-386-2834-X NUR 913 Trefwoorden: supramoleculaire chemie; waterstofbruggen / polymeernetwerken; dendrimeren / polymeerstructuur / thermoplastische rubbers; polyurethanes Subject headings: supramolecular chemistry; hydrogen bond / polymer networks; dendrimers / polymer morphology / thermoplastic rubber; polyurethanes

Table of Contents 1Thermoplastic elastomers and well-defined polymers 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Thermoplastic elastomers Polyurethanes Novel isocyanate chemistry Spider dragline silk Well-defined thermoplastic elastomeric polymers Aim of this thesis Outline of this thesis References and notes 1 2 3 5 7 9 11 12 13

2[n]-Polyurethanes and hyperbranched polyurethanes 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Introduction Synthesis of -amino--alcohols Preparation of [n]-polyurethanes Thermal properties of [n]-polyurethanes Synthesis of hyperbranched polyurethanes Degree of branching of hyperbranched polyurethanes Conclusions Experimental section References and notes 15 16 18 19 22 24 27 29 30 36

3Synthesis and characterization of block copoly(ether urea)s 3.1 Introduction 3.1.1 Thermoplastic elastomers 3.1.2 Urea-based TPEs Molecular design of block copoly(ether urea)s Synthesis of amine-terminated prepolymers 39 40 40 42 43 44

3.2 3.3

3.4 3.5

3.6 3.7 3.8 3.9

Synthesis of heterofunctional pTHF Preparation of block copoly(ether urea)s 3.5.1 Segmented copolymers with one urea group in the hard block 3.5.2 Segmented copolymers with two urea groups in the hard block 3.5.3 Segmented copolymers with three urea groups in the hard block 3.5.4 Segmented copolymers with four urea groups in the hard block 3.5.5 Segmented copolymers with a polydisperse hard block Hydrogen bonding within block copoly(ether urea)s Conclusions Experimental section References and notes

47 50 50 50 52 54 54 55 58 59 63

4Properties and morphology of block copoly(ether urea)s 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Introduction Crystal structure of model bisurea Thermal properties Morphology Mechanical properties Orientation during tensile testing Conclusions Experimental section References and notes 65 66 67 69 74 80 85 90 91 93

5A modular approach to polymer modification and functionalization 5.1 5.2 5.3 5.4 5.5 5.6 Introduction Increase of hard block content Incorporation of dye molecules Conclusions Experimental section References and notes 95 96 97 99 103 104 106

6Block copolymers containing a monodisperse soft block 6.1 6.2 6.3 6.4 6.5 6.6 6.7 Introduction Synthesis of monodisperse pTHF oligomers Synthesis of a block copolymer containing a monodisperse soft block Properties Conclusions and outlook Experimental section References and notes 107 108 110 114 115 118 119 121

7Reversible networks based on dendrimer telechelic association 7.1 7.2 7.3 7.4 Introduction Synthesis of host and guests Complexation of polymeric guests and dendritic host Viscometry of polymeric guest dendritic host complexes 7.4.1 Polydisperse, bifunctional guests 7.4.2 Polydisperse, monofunctional guest 7.4.3 Monodisperse, bifunctional guest 7.4.4 Temperature-dependence Dynamic light scattering Conclusions and outlook Experimental sections References and notes 123 124 127 129 131 132 134 135 136 137 140 142 143 145 147 149 151

7.5 7.6 7.7 7.8

Summary Samenvatting Dankwoord Curriculum Vitae

1Thermoplastic elastomers and well-defined polymersAbstract This introductory chapter reviews some aspects of thermoplastic elastomers and well-defined polymers. Two types of thermoplastic elastomers are described in more detail: spandex, a highly elastic synthetic polyurethane, and spider dragline silk, an exceptionally tough biopolymer. The relationship between the morphologies of both materials and their properties is recognized, and this demonstrates the relevance of well-defined molecular architectures. These considerations served to formulate the aim and outline of this thesis.

1

Chapter 1

1.1 Thermoplastic elastomers Since the 1940s, many industrial research groups from all over the world have been looking for materials that can be used as an alternative for natural rubber. This led to the discovery of several types of thermoplastic elastomers (TPEs).1 TPEs possess many of the physical properties of rubbers, i.e. softness, flexibility, and elasticity; but in contrast to conventional rubbers, they can be processed as thermoplastic materials.2 Natural rubbers are covalently (irreversibly) crosslinked and, therefore, they cannot be processed once the material is shaped and vulcanized. In contrast, the crosslinks in thermoplastic elastomers are reversible in nature, allowing a processing applying conventional techniques for thermoplastics, e.g. injection molding and extrusion. Another advantage is the possibility to recycle scrap. The thermoreversible nature of the crosslinks in TPEs can be various: e.g. phase separation, crystallization, reversible chemical bonding3, hydrogen bonding, metal complexation, or electrostatic interactions.4 TPEs can be roughly divided into three main groups.5 The largest group of TPEs consists of the ABA triblock copolymers, like polystyrene/polydiene (SBS) block copolymers. In these materials, the crosslinking is due to the formation of glassy domains of polystyrene, that are embedded in the amorphous and rubbery polydiene phase.6 The second group consists of thermoplastic polyolefins blended with an elastomer, e.g. a blend of polypropylene and EPDM rubber. The third group concerns the segmented copolymers. These (multi)block copolymers consist of alternating hard and soft blocks (figure 1.1), and in this thesis, we will mainly focus on this type of TPEs.hard soft segment segment

Figure 1.1: Schematic representation of a segmented copolymer.1 In the segmented copolymers, the hard blocks account for the mechanical stability of the material, since they give rise to reversible crosslinks, which are embedded in an amorphous phase with a low glass transition temperature. This phase is mainly composed of the soft segment, and gives the material its flexibility. In many TPEs, the reversible crosslinks are formed by crystalline or glassy domains. Above the melting point or glass transition temperature of these domains, a viscous polymer melt is obtained, that can be processed easily. Next to reversible crosslinks, the hard blocks also act as reinforcing fillers, causing the material to be stiffer at higher hard block content.

2

Thermoplastic elastomers and well-defined polymers

The hard blocks are generally based on polyester1,7, polyamide8, or polyurethane9 segments. At ambient temperatures, the hard blocks are incompatible with the soft blocks. This induces microphase separation by crystallization or liquidliquid demixing. A schematic representation of the morphology of segmented copolymers, as proposed by Cella, is depicted in figure 1.2.10 The ordered arrays are formed by crystallized hard blocks. Hard blocks that are not crystallized are dissolved in the amorphous, soft phase, and this incomplete phase separation leads to an increase of the glass transition temperature of the soft phase, which is undesired for the low temperature flexibility and elasticity of the material.

Figure 1.2: Schematic representation of the morphology of a segmented block copolymer: () hard block, (~~~) soft block. Upon deformation of these materials, irreversible changes in their morphologies may occur. Above the yield point, the hard blocks are disrupted and will reorganize, resulting in energy dissipation and incomplete recovery to their initial dimensions. This hysteresis leads to irreversible changes in the polymer properties, i.e. the Youngs modulus.

1.2 Polyurethanes From the segmented copolymers, the thermoplastic elastomeric polyurethanes (TPUs) are the most well-known. Polyurethanes form a versatile class of polymers, which are used in a broad range of applications2,11, like foams, coatings, fibers, and as biomedical materials12, but also in less down-to-earth applications like the landing pads of the lunar module.13 In fact, polyurethanes are a collective term for all polymers comprising urethane, urea, or other isocyanate derived groups, even if they are only a minor part of the total structure. Both urethane and urea groups are known for their ability to self-associate via hydrogen bonding (figure 1.3).14 The urethane group forms linear hydrogen bonds, and since it is asymmetric, it can do so in either a parallel or an antiparallel fashion. The urea group is symmetric, and forms bifurcated hydrogen bonds, causing the hydrogen bond strength of 3

Chapter 1

ureas to exceed that of urethanes. In principle, urethane and urea groups can form infinite stacks of hydrogen bonded arrays.O N H O N H O N H O N H O N H O N H

Figure 1.3: Hydrogen bonding between urethane (left) and urea groups (right). The properties of polyurethanes depend strongly on their macromolecular structure, i.e. the nature and functionality of their constituting (macro)monomers. Covalently crosslinked networks are thermosets, and are used as both rigid and flexible foams; segmented polyurethanes show thermoplastic elastomeric properties, and are used e.g. in textile fibers, shoe soles, or hoses; linear homopolyurethanes are thermoplastic materials, and can be used in fibers15 or as biodegradable material.16 The world consumption of polyurethanes in 2000 amounted to about 8 million tons, with a global growth averaging around 3 4% a year.2 Pioneering work in the field of polyurethanes was done by O. Bayer since 1937.15 He described the polyaddition of diisocyanates and diols, yielding [m,n]-polyurethanes. Fibers of this polymer, named Perlon-U, were expected to compete with the nylons developed by DuPont several years earlier.17 However, due to their limited thermal stability and inferior mechanical properties, they are no longer of industrial importance. Soon, it was discovered that the performance of the polyurethanes improved dramatically upon replacing the shortchain diol by a long-chain diol, yielding highly elastic fibers. The thermoplastic elastomeric polyurethanes (TPUs) were soon produced on an industrial scale by a number of companies.1 The TPU consists basically of three building blocks (figure 1.4): 1) a long-chain diol, normally with a polyether or polyester backbone, 2) a diisocyanate, mostly an aromatic one, 3) a chain extender, such as a short-chain diol, or a diamine.hard soft segment segment

residue of long chain diol residue of chain extender residue of diisocyanate urethane group

Figure 1.4: Schematic representation of a TPU and its building blocks.

4


They are often prepared in a one pot procedure, in which the long-chain diol is first reacted with an excess of the diisocyanate, to form an isocyanate functionalized prepolymer. The latter is subsequently reacted with the chain extender which results in the formation of the high molecular weight polyurethane. When a diamine is used as chain extender, the TPU also contains urea groups, that increases the melting temperature of the hard block. The urethane (and/or urea) groups in the hard block form hydrogen bonds, which improve the association and crystallization. However, also TPUs containing secondary urethane groups, thus unable of forming hydrogen bonds, have been prepared.18 These polymers showed properties comparable with their hydrogen bonding analogues, since the crystallization of the hard block is not prevented by blocking the hydrogen bonding sites. One of the most interesting TPU fibers is spandex (Elastane, Lycra), which is produced by DuPont. This fiber is employed extensively in ladies garment, and is now expanding into all areas of clothing at an incredible rate.19 The macromolecular structure of this highly elastic material allows the fiber to stretch up to 600% and then relax to its original shape. The structure of one type of spandex is depicted below.20 It is prepared by reacting a prepolymer diol with an aromatic diisocyanate, in this case, methylene diphenylene isocyanate (MDI).3 In the second step, the chain extension, the macrodiisocyanate is reacted with a diamine in a highly polar solvent (e.g. dimethyl acetamide) to give a high molecular weight poly(ether urethane urea). The most frequently used short-chain aliphatic diamines are 1,2-ethylene diamine, 1,2-propylene diamine, or hydrazine. Due to the presence of urea groups, the melting point of the hard blocks is too high to allow melt spinning of the fibers. Therefore, the more expensive dry spinning procedure is used, in which a viscous solution of the polymer in a volatile solvent is spun in hot air, allowing the evaporation of the solvent. Some types of spandex are known to be crosslinked covalently during processing.O CH2 CH2 O x N H CH2 N H O N N H H O N H CH2 N H O O n

spandex

1.3 Novel isocyanate chemistry Isocyanates, the primary building blocks of polyurethanes, can be prepared via several The only route that is practiced on a significant industrial scale is phosgenation of primary amines or their salts (scheme 1.1). The high toxicity of phosgene is only one of its disadvantages; the rather high temperature necessary to decompose the intermediate routes.13,21

5

Chapter 1

carbamoyl chloride, and the poor selectivity toward different nucleophiles are some other drawbacks that limit the synthetic use of phosgene.O R NH2+

O Cl - HCl R N H Cl - HCl R N=C=O

Cl

Scheme 1.1: Preparation of isocyanates via phosgenation of amines. Some other methods which are used on laboratory scale include the Curtius rearrangement of acylazides, the dissociation of blocked isocyanates, the conversion of alkyl halides with alkali cyanates, and the dehydration of carbamic acids (adducts of amines and carbon dioxide).22 Recently, Peerlings reported on the potential of di-tert-butyl tricarbonate 1 as a versatile and mild reagent for the synthesis of isocyanates.23 Di-tert-butyl tricarbonate 1 is synthesized from carbon dioxide, potassium tert-butoxide, and phosgene,24 and is readily obtained in multigram quantities. Upon reaction of aliphatic or some aromatic amines with a stoichiometric amount of 1, a fast reaction occurs, in which the amine functionality is converted to an isocyanate within a few minutes at room temperature via a cascade of reactions (scheme 1.2). The last step of this cascade is the rate determining step, and since this step is slower than the former two steps, amine and isocyanate functionalities are not present simultaneously, preventing the formation of the symmetric urea. During this reaction, two equimolar amounts of both tert-butanol and carbon dioxide are released.O O O O O

O O R NH2 + O O O O O O H + R N H

O-

1

CO2 t-BuOH

O R N

O O H

O

CO2 t-BuOH

R N C O

Scheme 1.2: Mechanism for the formation of isocyanates from di-tert-butyl tricarbonate and primary amines.

6


This synthetic procedure allowed the synthesis of unusual mono- and multiisocyanates with a minimum of side reactions. Some of these isocyanates were inaccessible by conventional methods, e.g. 1,3-propanediisocyanate, trans-1,2-diisocyanato-cyclohexane, and a dendrimer containing 64 terminal isocyanate groups. The only restraint of this reagent is the limited stability at room temperature of 1, especially in polar solvents, like methanol, pyridine or DMSO.

1.4 Spider dragline silk A famous thermoplastic elastomer that is found in Nature, is spider dragline silk.25 This high-performance protein fiber intrinsically combines both high tensile strength and high elasticity.26 The toughness (energy to break) of the spider silk exceeds the values for steel and polyaramids. In addition, the spider silk is produced under ambient conditions from aqueous solution in nature, while steel and polyaramids require a high temperature and a hazardous solvent, respectively, for processing. These properties have generated considerable interest in spider silk, especially in the dragline silk from Nephila clavipes, the golden orb weaver, whose silk is among the strongest (table 1.1). However, due to the small diameter of the fiber (max. 4 m), its strength on a macroscopic level is rather limited. Table 1.1: Tensile properties of some natural and synthetic fibers.25a Material Density Youngs Strength Strain Toughness modulus at break -3 (g/cm ) E (GPa) br (GPa) br (%) (kJ/kg) 1.1 1.4 0.97 7.8a

Nylon 6,6 Kevlar 49 Dyneema Steel Spider silk

5 130 110 200 10

0.95 3.6 3.4 1.5 1.1

18 3 3.5 1 27

73 36 60 0.77 123

1.3

a) Dragline of Araneus diadematus. The outstanding properties of spider silk are a consequence of both the molecular architecture and the amino acid composition. The primary constituents of spider silk are the two simplest amino acids, glycine (42% of the structure) and alanine (25%). The remainder of the fiber consists of bulkier amino acids, with glutamine, serine, tyrosine, and leucine prominently represented.27 Sequencing of the protein, reveals that it consists of repeating units in which a polyalanine block of five to seven residues is followed by a glycine-rich sequence 7

Chapter 1

containing the bulky residues.28 From this point of view, it resembles the molecular structure of a segmented copolymer. The alanine block has been shown to adopt an antiparallel pleated -sheet conformation. After a detailed analysis by SAXS and solid-state 2H-NMR, Jelinski et al. proposed a structural model for the silk fiber, with highly-oriented alanine-rich crystals, and with weakly-oriented isolated -sheets.29 Both are dispersed in an elastic, non-ordered, glycine-rich phase (figure 5.1). Specific residues in the alanine-rich segments cause reversal of the chain direction, via a -hairpin. This inhibits the growth of the -sheet, resulting in the formation of very small crystals of 2 5 6 nm in size.29a Although the crystallinity of the material is quite low (30%), the abundance of these tiny reinforcing fillers accounts for the fibers toughness. This picture is consistent with a theoretical model of spider silk elasticity developed by Termonia.30

fiber axis

Figure 1.5: Schematic representation of a spider dragline silk fiber. Within the past few years, there has been a renewed interest in the use of spider dragline silk for commercial applications. Silk of the silkworm Bombyx mori is produced on large scale by cultivation of the silkworms, allowing the commercial use of this material as textile fiber. Unfortunately, spider silk cannot be produced in this manner due to cannibalism of the spiders. This challenged researchers to prepare the spider silk via (bio)synthetic methods. Laboratory-scale expression of silk proteins is now feasible, in both bacteria and yeasts.31 However, the most promising technique for large scale production is the expressing of silk genes in mammalian species.32 The company Nexia Biotechnologies is currently employing this recombinant DNA technique for the production of large amounts of spider silk (trade name Biosteel), by using transgenic goats that secrete the silk protein in their milk.33 Even though there is still a lot of debate about the morphology of spider dragline silk, it is generally accepted that its unique properties are the result of its well-defined morphology in combination with the spinning process from a liquid crystalline solution in the spiders 8


gland. This example of spider dragline silk offers insight into the behaviour of biomaterials, but more importantly, it teaches us, synthetic chemists, that precise control over the molecular structure and morphology, by applying well-defined building blocks and well-balanced secondary interactions, can give rise to novel materials possessing unique properties.

1.5 Well-defined thermoplastic elastomeric polymers The synthetic procedure to prepare TPUs, as described in section 1.2, has the intrinsic disadvantage that it leads to a distribution in the hard block lengths.34 In addition to this, the prepolymers that are generally used are polydisperse. Both facts result in a quite inhomogeneous chemical composition of the segmented copolymer. The dispersities in hard and soft block length directly influence the material properties of the polymers. The phase separation within these block copolymers is incomplete.1 Part of the hard blocks, in particular the shorter ones, are dissolved in the soft phase, causing an increase in the glass transition temperature, which is undesired for the low temperature flexibility of the material. The polydispersity of the hard block is manifested in a broad melting range and a rubbery plateau that is dependent on temperature. To improve the properties of TPEs, and to get more insight into the structure properties relationship, block copolymers containing hard blocks of uniform length have been prepared.35,36 Several types of uniform hard blocks were used, such as non-hydrogen bonding polyurethanes,35a,b normal polyurethanes,35c-h polyurethane ureas,35i and aramid units.36 In all these studies, the hard blocks were synthesized first. Due to their low solubility, especially of the longer ones, the maximum number of repeating units in the hard blocks is limited to approximately three repeating units. Subsequently, these hard blocks were polymerized with the appropriate soft blocks, to yield the segmented copolymers. The properties of these materials were compared to those of the analogous materials having polydisperse hard blocks, and these studies showed the advantages of the well-defined molecular structure. The materials showed higher crystallinity and better phase separation, causing the properties to be less dependent on temperature. The ultimate properties of the material improved considerably: higher strengths and strains at break were achieved. Some studies were preformed on the influence of the polydispersity of the soft block on the properties of thermoplastic elastomeric polyurethanes.35a,b,i,37 Harrell and Cooper described the synthesis and properties of block copoly(ether urethane)s, in which the urethane part was based on piperazine (figure 1.6). These secondary urethane groups are unable of forming hydrogen bonds. According to the authors, this should facilitate the interpretation of the structureproperties relationship. A pTHF prepolymer of low polydispersity (P.D.=1.1) 9

Chapter 1

was obtained, upon fractionation of a commercially available, polydisperse prepolymer. This was used as a monodisperse soft block, and built-in into the block copolymer. The material properties of this block copolymer were compared to those of an analogous block copolymer containing a polydisperse soft block (P.D.=1.7). The authors concluded that only some minor effects were observed upon lowering the polydispersity of the soft block: both strength and strain at break increased slightly.O CN O O O NCO C4H8O y n NCO C4H8O CN x

Figure 1.6: Block copoly(ether urethane) possessing secondary urethane groups. Shirasaka et al., who studied block copoly(ether urethane urea)s possessing monodisperse soft blocks (P.D.1.1) based on pTHF, found comparable results.35i Although this polymer showed a slightly lower strength and strain at break, the effects observed upon lowering the polydispersity of the soft block to approximately 1.1 were not significant. At this point the question arises, whether it would make sense to use soft blocks with even lower polydispersity, in other words, truly monodisperse soft blocks. Some examples of truly monodisperse polymers or block copolymers are described in literature.38,39 Tirrell et al. studied the liquid crystalline ordering of monodisperse poly(-benzyl ,L-glutamate), that was prepared via protein engineering.38 Polydisperse samples of this rod-like polymer order in a nematic phase, whereas the monodisperse analogue shows the quite rare smectic ordering. Triblock copolymers possessing a monodisperse rod-like block were prepared by Stupp et al.39 Their self-assembly into discrete mushroom-shaped nanosized objects is a direct result of the well-defined character of the triblock copolymer. In conclusion, the examples of Tirrell and Stupp show that truly monodisperse, well-defined polymers may give rise to highly ordered microstructures, which is even manifested on a macroscopic scale. Two examples are reported of segmented block copolymers possessing a uniform distribution in both hard and soft segment length.37 Such block copoly(ether ester)s were prepared by Wegner et al. (figure 1.7).37a,b They synthesized uniform butylene terephthalateoligomers, as well as monodisperse pTHF-oligomers, via a stepwise synthesis. Both building blocks were coupled via a solution polycondensation to avoid transesterification, which would undo the uniformity of the hard blocks. The melting behaviour of the polymers was studied in detail. However, the limited amounts available of these polymers, due to the tedious purifications of the building blocks, hampered the study of their mechanical properties.

10


O C

O

O

O CO C4H8O y n

CO C4H8O C x

Figure 1.7: Block copoly(ether ester)s with uniform segments; x=14, y=12. Eisenbach and Baumgartner prepared block copoly(ether urethane)s comprising both uniform hard and soft segments (figure 1.8),37c using the same procedure as Wegner et al. The uniform block copoly(ether urethane)s were studied in detail with special emphasis on the thermal behaviour and hydrogen bonding. Again, no mechanical properties were discussed, unfortunately. They concluded that these well-defined block copolymers show better phase separation, and hence, sharper phase transitions.O CN H CH2 O O CH2 H O NCO C4H8O y n NCO C4H8O CN x H H

Figure 1.8: Block copoly(ether urethane)s with uniform segments; x=14, y=12.

1.6 Aim of this thesis This introduction gave a brief overview of thermoplastic elastomers, and thermoplastic elastomeric polyurethanes more specifically. The synthetic procedure employed to prepare these materials, results in polymers possessing an inhomogeneous microstructure: both the hard and soft blocks are polydisperse. These features have a negative effect on the material properties. On the other hand, spider dragline silk demonstrates us how exact control over molecular architecture and secondary interactions can give rise to materials with very appealing properties. The aim of this thesis is to prepare well-defined thermoplastic elastomers from uniform and monodisperse building blocks, by implying precisely-controlled supramolecular interactions (hydrogen bonding, electrostatic interactions). By studying their morphology and material properties in detail, more insight should be gained in the structureproperties relationship of these materials. Employing the novel isocyanate chemistry and highlyselective syntheses, we wish to prepare well-defined building blocks for these polymers. In this way, we expect to close the gap between ill-defined synthetic thermoplastic elastomers and well-defined biomaterials.

11

Chapter 1

1.7 Outline of this thesis The potential of the novel isocyanate chemistry, employing di-tert-butyl tricarbonate, in the field of polymer chemistry is described in chapter 2. Starting from -amino--alcohols, the (so far) unknown class of [n]-polyurethanes is developed and successfully characterized. Some properties of these polymers were studied. In addition to that, hyperbranched polyurethanes were synthesized and characterized in detail. This isocyanate chemistry is utilized in the next chapters for the synthesis of thermoplastic elastomers. In chapter 3, the synthesis and modification of pTHF-based prepolymers is described. These were used as the soft segment in block copoly(ether urea)s, possessing uniform hard blocks comprising 1 4 urea groups. A detailed molecular characterization of these polymers was performed, which showed the successful crosslinking by hydrogen bonding between hard blocks comprising two or more urea groups. The block copoly(ether urea)s possess thermoplastic elastomeric properties. The thermal characteristics, the morphology, and the mechanical properties were studied by a variety of experimental techniques in chapter 4. The behaviour of the materials upon deformation was examined and related to the structural changes on the molecular level. Due to the uniformity of the bisureido-butylene hard block, it was possible to anchor molecules containing the complementary bisureido-butylene unit to these polymers. In chapter 5, a modular approach towards polymer modification based on this principle is described by means of two examples. In chapter 6, monodisperse pTHF-oligomers are described that were synthesized via a stepwise procedure on a multigram scale, resulting in a pTHF 13-mer (MW=954 g/mol) of very low polydispersity (P.D.=1.004). This oligomer was used for the preparation of a block copoly(ether urea) possessing a uniform hard and a monodisperse soft block. Its properties are compared to those of its less-defined analogue. Finally, in chapter 7, a novel type of reversible networks is described, based on the association of the end groups of a telechelic polymer and the host groups of a multivalent dendrimer. The solution properties of this system are studied in detail by viscometry and dynamic light scattering. Upon increasing the concentration of the complex, a transition from flower-like structures to a transient network is observed. The influence of the molecular structure of the guest on this transition is investigated.

12


1.8 References and notes1. Legge, N. R., Holden, G. and Schroeder, H. E. Thermoplastic elastomers: A comprehensive review; Carl Hansser Verslag: New York, 1987. 2. Mark, H. F. Encyclopedia of polymer science and technology; 3 ed.; Wiley-Interscience: New York, 2001. 3. a) Kennedy, J. P. and Castner, K. F. J. Pol. Sci. A 1979, 17, 2055; b) Engle, L. P. and Wagener, K. B. J. Macromol. Sci. Rev. 1993, C33, 239. 4. Ullmann Ullmann's Encyclopedia of industrial chemistry; 6 ed.; VCH: Weinheim, 2001. 5. Niesten, M. Ph.D. Thesis, University of Twente (Enschede), 2000. 6. Holden, G., Bishop, E. T. and Legge, N. R. J. Pol. Sci. C 1969, 26, 36. 7. a) Coleman, D. J. Polym. Sci. 1954, 14, 15; b) Witsiepe, W. K. ACS Advances in Chemistry 1973, 129, 39. 8. Deleens, G., Foy, P. and Marechal, E. Eur. Pol. Journal 1977, 13, 337. 9. Bayer, O., Muller, E., Petersen, S., Piepenbrink, H. F. and Windemuth, E. Angew. Chem. 1950, 62, 57. 10. Cella, R. J. J. Polym. Sci.: Symp. 1973, 42, 727. 11. a) Wirpsza, Z. Polyurethanes: Chemistry, Technology and Applications; Ellis Horwood: London, 1993; b) Saunders, J. H. and Frisch, K. C. Polyurethanes : chemistry and technology, part 1 Chemistry; Interscience: New York, 1962; Vol. 16; c) Saunders, J. H. and Frisch, K. C. Polyurethanes : chemistry and technology, part 2 Technology; Interscience: New York, 1964; Vol. 16; d) David, D. J. and Stanley, H. B. Analytical chemistry of polyurethanes, part 3; Wiley-Interscience: New York, 1969; Vol. 16. 12. a) Spaans, C. J. Ph.D. Thesis, University of Groningen (Groningen), 2000; b) Runt, J., Xu, R., Manias, E. and Snyder, A. J. Macromolecules 2001, 34, 337. 13 Ulrich, H. Chemistry and technology of isocyanates; J. Wiley & Sons: Chichester, 1996. 14. a) Etter, M. C., Urbanczyk-Lipkowska, Z., Zia-Ebrahimi, M. and Panunto, T. W. J. Am. Chem. Soc. 1990, 112, 8415; b) Desiraju, G. R. Organic solid state chemistry; Elsevier: Amsterdam, 1987; Vol. 32; c) Carr, A. J., Melendez, R., Geib, S. J. and Hamilton, A. D. Tetrahedron Lett. 1998, 39, 7447; d) Pathirana, H. M. K. K., Weiss, T. J., Reibenspies, J. H., Zingaro, R. A. and Meyers, E. A. Z. Kristallogr. 1994, 209, 696; e) Perez-Folch, J., Subirana, J. A. and Aymami, J. J. Chem. Cryst. 1997, 27, 367. 15. Bayer, O. Angew. Chem. 1947, 59, 257. 16. Bachmann, F., Reimer, J., Ruppenstein, M. and Thiem, J. Macromol. Rapid Commun. 1998, 19, 21. 17. a) Carothers, W. H. (DuPont) Patent US2130948, 1938; b) Carothers, W. H. (DuPont) Patent US2071253, 1937. 18. Witsiepe, W. L. (DuPont) Patent US3377322, 1968. 19. Bhat, G., Chand, S. and Yakopson, S. Thermochim. Acta 2001, 367-368, 161. 20. Reisch, M. Chem. Eng. News 1999, 77, 70. 21. a) Siefken, W. Justus Liebigs Ann. Chem. 1949, 562, 75; b) Ozaki, S. Chem. Rev. 1972, 72, 457. 22. Waldman, T. E. and McGhee, W. D. Chem. Comm. 1994, 8, 957. 23. Peerlings, H. W. I. and Meijer, E. W. Tetrahedron Lett. 1999, 40, 1021. 24. Pope, B. M., Yamamoto, Y. and Tarbell, D. S. Org. Synth. 1978, 57, 45. 25. a) Kubik, S. Angew. Chem. Int. Ed. 2002, 41, 2721; b) Tirrell, D. A. Science 1996, 271, 39. 26. a) Shao, Z. and Vollrath, F. Polymer 1998, 40, 1799; b) Madsen, B., Shao, Z. Z. and Vollrath, F. Int. J. Biol. Macromol. 1999, 24, 301; c) Gosline, J. M., Denny, M. W. and DeMont, M. E. Nature 1984, 309, 551; d) Gosline, J. M., Shadwick, R. E., Demont, M. E. and Denny, M. W. Biol. Synth. Polym. Networks 1988, 57; e) Gosline, J. M., Guerette, P. A. and Ortlepp, C. S. J. Exp. Biol. 1999, 202, 3295; f) Cunniff, P. M., Fossey, S. A., Auerbach, M. A., Song, J. W., Kaplan, D. L., Adams, W. W., Eby, R. K., Mahoney, D. and Vezie, D. L. Polymers for Advanced Technologies 1994, 5, 401. 27. Fukushima, Y. Biopolymers 1998, 45, 269. 28. Xu, M. and Lewis, R. V. Proc. Natl. Acad. Sci. USA 1990, 87, 7120. 29. a) Yang, Z., Grubb, D. T. and Jelinski, L. W. Macromolecules 1997, 30, 8254; b) Simmons, A. H., Michal, C. A. and Jelinski, L. W. Science 1996, 271, 84. 30. a) Termonia, Y. Macromolecules 1994, 27, 7378; b) Termonia, Y. Pergamon Materials Series 2000, 4, 269.

13

Chapter 1

31. a) Fahnestock, S. R. and Irwin, S. L. Appl. Microbiol. Biotechnol. 1997, 47, 23; b) Fahnestock, S. R. and Bedzyk, L. A. Appl. Microbiol. Biotechnol. 1997, 47, 33; c) O'Brien, P., Fahnestock, S. R., Termonia, Y. and Gardner, K. H. Adv. Mater. 1998, 10, 1185; d) Prince, J. T., McGrath, K. P., DiGirolamo, C. M. and Kaplan, D. L. Biochemistry 1995, 34, 10879; e) Arcidiacono, S., Mello, C., Kaplan, D., Cheley, S. and Bayley, H. Appl. Microbiol. Biotechnol. 1998, 49, 31. 32. Cohen, P. New Sci. 1998, 160, 11. 33. For more information see: www.nexiabiotech.com . 34. Sorta, E. and Melis, A. Polymer 1978, 19, 1153. 35. a) Harrell, L. L. Macromolecules 1969, 2, 607; b) Ng, H. N., Allegrezza, A. E., Seymour, R. W. and Cooper, S. L. Polymer 1973, 14, 255; c) Eisenbach, C. D. and Stadler, E. Macromol. Chem. Phys. 1995, 196, 1981; d) Miller, J. A., Shaow, B. L., Hwang, K. K. S., Wu, K. S., Gibson, P. E. and Cooper, S. L. Macromolecules 1985, 18, 32; e) Fu, B., MacKnight, W. J. and Schneider, N. S. Rubber Chem. Technol. 1986, 59, 896; f) Qin, Z. Y., Macosko, C. W. and Wellinghoff, S. T. Macromolecules 1985, 18, 553; g) Furukawa, M., Komiya, M. and Yokoyama, T. Angew. Makromol. Chem. 1996, 240, 205; g) Lai, Y.-C., Quinn, E. T. and Valint, P. L., Jr. J. Pol. Sci. A 1995, 33, 1767; h) Blundell, D. J., Eeckhaut, G., Fuller, W., Mahendrasingam, A. and Martin, C. Polymer 2002, 43, 5197; i) Shirasaka, H., Inoue, S.-i., Asai, K. and Okamoto, H. Macromolecules 2000, 33, 2776. 36. a) Gaymans, R. J. and Haan, J. L. d. Polymer 1993, 34, 4360; b) Niesten, M. C. E. J., Gaymans, R. J. and Brinke, A. t. Polym. Prepr. 1999, 40, 1012; c) Niesten, M. C. E. J., Gaymans, R. J. and Brinke, A. t. Polym. Prepr. 1999, 40, 1012; d) Niesten, M. C. E. J., Harkema, S., van der Heide, E. and Gaymans, R. J. Polymer 2000, 42, 1131; e) Niesten, M. C. E. J., Tol, R. and Gaymans, R. J. Polymer 2000, 42, 931; f) Niesten, M. C. E. J., Feijen, J. and Gaymans, R. J. Polymer 2000, 41, 8487; g) Niesten, M. C. E. J. and Gaymans, R. J. J. Appl. Polym. Sci. 2001, 81, 1372; i) Niesten, M. C. E. J. and Gaymans, R. J. Polymer 2001, 42, 6199. 37. a) Schmidt, H. G. Ph.D. Thesis, University of Freiburg (Freiburg), 1984; b) Wegner, G., in Legge, N. R., Holden, G. and Schroeder, H. E. Thermoplastic elastomers: A comprehensive review; Carl Hansser Verslag: New York, 1987, Section 12/5; c) Eisenbach, C. D., Baumgartner, M. and Gunter, G. Adv. Elastomers Rubber Elasticity, [Proc. Symp.] 1985, 51. 38. a) Yu, S. M., Conticello, V. P., Zhang, G., Kayser, C., Fournier, M. J., Mason, T. L. and Tirrell, D. A. Nature 1997, 389, 167; b) Yu, S. M., Soto, C. M. and Tirrell, D. A. J. Am. Chem. Soc. 2000, 122, 6552. 39. a) Radzilowski, L. H., Wu, J. L. and Stupp, S. I. Macromolecules 1993, 26, 879; b) Radzilowski, L. H. and Stupp, S. I. Macromolecules 1994, 27, 7747; c) Radzilowski, L. H., Carragher, B. O. and Stupp, S. I. Macromolecules 1997, 30, 2110, d) Stupp, S. I., LeBonheur, V., Walker, K., Li, L. S., Huggins, K. E., Keser, M. and Amstutz, A. Science 1997, 276, 384; e) Zubarev, E. R., Pralle, M. U., Li, L. and Stupp, S. I. Science 1999, 283, 523.

14

2[n]-Polyurethanes and hyperbranched polyurethanesAbstract A facile and mild synthetic procedure for the preparation of isocyanates, using di-tert-butyl tricarbonate, is employed to synthesize -isocyanato--alcohols 3 from -amino--alcohols 2. These isocyanato alcohols were polymerized in situ to yield the aliphatic [n]-polyurethanes, polymers that were still unknown as a general class, despite its structural simplicity. The [n]-polyurethanes are highly crystalline, brittle polymers, and show a strong alternation in their melting points with respect to the number of methylene groups in the monomer unit. The polymers with an even number of methylene units, possess a higher melting point than those with an odd number. Using the same synthetic procedure, also aliphatic hyperbranched polyurethanes were prepared, starting from AB2 and A2B monomers. These polymers were obtained in high yields as viscous oils. A detailed 13C-NMR analysis of one of the hyperbranched polyurethanes indicated that its degree of branching is quite low, DB=0.31 0.06. This isocyanate chemistry is utilized in the next chapters for the synthesis of thermoplastic elastomers.

15

Chapter 2

2.1 Introduction Polyurethanes form a versatile class of polymers, which are used in a broad range of applications1, like automotive, foams, coatings, fibers, and biomedical applications.2 The properties of polyurethanes depend strongly on their macromolecular structure, i.e. the nature and functionality of its constituting (macro)monomers. Covalently cross-linked networks are thermosets, and are used as both rigid and flexible foams; segmented polyurethanes show thermoplastic elastomeric properties, and are used e.g. as textile fibers or in hoses; linear homopolyurethanes are thermoplastic materials, and can be used as fibers3 or as biodegradable material.4O HO CH2m

O N H CH2n-2

OH +

OCN

CH2

n-2

NCO

O

N H

O

CH2

m

x

Scheme 2.1: Synthesis of linear [m,n]-polyurethanes. In most, if not all, cases of linear polyurethanes, the macromolecular structure is based on the reaction of dihydroxy-compounds with diisocyanates, yielding A2B2-polymers or the [m,n]-polyurethanes (scheme 2.1). The values of m and n represent the total number of carbon atoms in the monomeric unit of the dihydroxy-compound and the diisocyanate, respectively. A comprehensive study of the parent aliphatic [m,n]-polyurethanes was reported by Otto Bayer in 1947.3H N O

O N H O H N O

H N O

H N O

N H O

H N O O

H N O O

O O N H

H N O O

H N O O

N H O

[m,n]-nylon

[n]-nylon

[m,n]-polyurethane

[n]-polyurethane

Scheme 2.2

16

[n]-Polyurethanes and hyperbranched polyurethanes

These, at that time, novel structures were compared and proposed to compete with the two series of aliphatic polyamides, the [n]- and [m,n]-nylons (scheme 2,2), which were synthesized by Wallace Carothers in the 1930s.5 The [n]-nylons (AB-polyamides) are either synthesized from -amino--carboxylic acids or from cyclic amides; the [m,n]-nylons (A2B2polyamides) are prepared from diamines and dicarboxylic acids. Whereas the disclosure of the [n]-nylons quickly followed Carothers first description of the [m,n]-nylons, the general class of linear aliphatic [n]-polyurethanes is notably absent in the impressive list of linear macromolecules, despite its structural simplicity and strong resemblance to the [n]-nylons. Why is it, that these aliphatic [n]-polyurethanes have not been prepared before, despite their simple structure? Obviously, this is due to the unavailability of the appropriate monomers; both the -isocyanato--alcohols and the cyclic carbamates are not known and synthesized as a general class. As a result the aliphatic series is limited to a few specific structures.6 Only recently, and after our work was published, Hcker et al. described the synthesis of some [n]-polyurethanes, with n=37 using activated -amino--alcohols7, or ring opening polymerization of trimethylene urethane.8 In the past, some oligomers have been synthesized via a stepwise sequence.9 The aromatic poly(1,4-phenylene urethane) has been prepared by polymerization of 4-isocyanato-phenol that was obtained via the Curtius rearrangement of 4-hydroxybenzoyl azide, as was reported by Kinstle and Sepulveda, and by several others.10 However, the much higher nucleophilicity of aliphatic alcohols over phenols requires a much milder conversion of the amino group of -amino--alcohols into an isocyanato--alcohols, followed by a controlled polymerization. Unfortunately, most of the methods known to transform amines into isocyanates e.g. with phosgene or other suitable carbonic acid derivatives are not mild enough and will furnish several side products containing carbonate or urea groups which are the result of uncontrolled reactions of the two nucleophilic species being able to react with the carbonic acid derivative. Peerlings reported on the potential of di-tert-butyl tricarbonate 1, as a versatile and mild reagent for the synthesis of isocyanates.11 Di-tert-butyl tricarbonate 1 is synthesized from carbon dioxide, potassium tert-butoxide, and phosgene,12 and is readily obtained in multigram quantities. Upon reaction of aliphatic or some aromatic amines with a stoichiometric amount of 1, a fast reaction occurs, in which the amine functionality is converted to an isocyanate within a few minutes at room temperature (scheme 2.3), see section 1.3 for more details. During this reaction, two equimolar amounts of both tert-butanol and carbon dioxide are released. This synthetic procedure allowed the synthesis of unusual mono- and multi-isocyanates with a minimum of side reactions. Some of these isocyanates were inaccessible by conventional techniques, e.g. 1,3-propanediisocyanate, trans-1,2diisocyanato-cyclohexane, and a dendrimer containing 64 terminal isocyanate groups. The

17

Chapter 2

only restraint of this reagent is the limited stability at room temperature, especially in polar solvents, like methanol, pyridine or DMSO.O R NH2 + O O O O O O R N C O + 2 CO2 + 2 t-BuOH

1

Scheme 2.3: Synthesis of isocyanates from di-tert-butyl tricarbonate and primary amines. This novel procedure to prepare isocyanates under very mild conditions prompted us to use it for the synthesis of -isocyanato--alcohols, the monomer for the [n]-polyurethanes, starting from -amino--alcohols. In this chapter, a general and convenient route to aliphatic -isocyanato--alcohols and their in situ polymerization into the corresponding [n]-polyurethanes are described.

2.2 Synthesis of -amino--alcohols -Amino--alcohols were used as the starting material for the synthesis of isocyanato--alcohols, the monomer for the [n]-polyurethanes. Short amino alcohols with x = 2 6 are commercially available, in contrast to their longer homologs, which had to be prepared.HO (CH 2) NH 2x

2-(x)

Amino alcohols with x = 9, 10, and 11 were prepared via the Gabriel synthesis13 by the hydrazine deprotection of -phthalimide--alcohols, which were made out of the commercially available -bromo--alcohols (scheme 2.4).O HO (CH 2) Br + K N x O+ _

KBr CH 3CNx

O HO (CH 2) N O N 2H 4 EtOH HO (CH 2 ) NH 2x

2

Scheme 2.4: Synthesis of amino alcohols via the Gabriel synthesis, x = 9, 10, and 11. This synthesis is rather straightforward, and after distillation, the amino alcohols were obtained in moderate yield (60 80%). The products were successfully characterized by 1H-, 13 C-NMR, GC, elemental analysis and their melting points. Amino alcohols with x = 7, 8, and 12 were prepared from the corresponding lactams (scheme 2.5). Acidic hydrolysis of the lactam resulted in the open amino carboxylic acids, 18


which were derivatized to their ethyl esters. Both reactions proceeded in almost quantitative yield. The last step is a reduction of the ester to an alcohol using lithium aluminum hydride. Due to the basic conditions of this reduction, a considerable amount of secondary amide was formed, resulting in a mixture of the product, the starting lactam, and several oligoamides. Distillation of the crude products yielded the amino alcohols in a rather poor yield (30 40%). The products were successfully characterized using the same techniques as described above.O H C Nx-1

(CH2)

HCl 100C

HOOC (CH 2) NH 3Clx-1

SOCl2 EtOH

EtOOC (CH2) NH3 Clx-1

LiAlH 4 HO (CH2 ) NH 2 x THF 2

Scheme 2.5: Synthesis of amino alcohols derived from lactams, x = 7, 8, and 12.

2.3 Preparation of [n]-polyurethanes The high selectivity and reactivity of di-tert-butyl tricarbonate 1 was used to synthesize -isocyanato--alcohols 3 from the prepared -amino--alcohols 2 (scheme 2.6).O HO (CH 2 ) NH 2x

O O 1 O

O O CO 2, t-BuOH CHCl3, 20C

+

2

O

HO (CH 2 ) NCOx

3

Scheme 2.6: Synthesis of -isocyanato--alcohols. This reagent is the key element for the selective formation of the intermediate isocyanato alcohols 3. Reaction of a small excess of 1 with 2 in chloroform at room temperature gave the isocyanato alcohol monomer 3 within 10 minutes. This reaction is accompanied by the formation of two moles of both carbon dioxide and tert-butanol. The former escapes from the solution, while the latter remains in the reaction mixture. Under the conditions employed here, tert-butanol is unreactive to the isocyanate, hence, it is harmless. The amino alcohol-solution was injected under the surface of a stirred solution of 1.05 equivalents of di-tert-butyl tricarbonate to avoid contact of the amino alcohol with carbon dioxide, since this may result in the formation of a carbamic acid which prevents further reaction. This side-reaction is notified by a turbidity in the reaction mixture. After decomposition of the unstable carbamic acid into the initial amino alcohol, the latter reacts with already formed isocyanate, resulting in symmetrical urea. This side reaction distorts the perfect stoichiometry of the AB-type polymerization, and consequently, limits the molecular weight of the polymer. For the short amino alcohols with x = 2 or 3, the synthesis of the respective isocyanato alcohols failed, due to their spontaneous ring closure into cyclic urethanes with five,

19

Chapter 2

respectively six ring-atoms. For the longer amino alcohols, the formation of the isocyanato alcohols was confirmed by infrared and 1H-NMR spectroscopy. In the IR spectrum, a strong absorption corresponding to the N=C=O stretch-vibration at 2274 cm1 was observed for solutions of 3 in chloroform. Figure 2.1b shows the 1H-NMR spectrum of 5-isocyanato-1pentanol after reaction of 5-amino-1-pentanol (Figure 2.1a) with di-tert-butyl tricarbonate.

a)

(ppm)t-BuOH

t-BuOH

b)

H2O

DMSO-d6 urea

c)

Figure 2.1: 1H-NMR spectra of a) 5-amino-1-pentanol, b) 5-isocyanato-1-pentanol, c) [6]polyurethane. Figure 2.1b reveals the absence of any side products, and also proves the relative stability of 3 in solution. However, evaporation to dryness furnished undefined products. The polymerization of monomers 3 is performed in situ by addition of a catalytic amount of zirconium(IV) acetylacetonate or dibutyltin dilaurate (scheme 2.7).O HO (CH2) NCOx Zr(acac)4 CHCl3, 20C

O On

3

(CH 2) N x H 4-(x) x = 4 12

or

HN

O

(CH 2)x x=23

Scheme 2.7: Polymerization of isocyanato alcohols to [n]-polyurethanes. 20


The precipitation of polymers 4 was observed within a few hours. The polymers were isolated by filtration in a yield of about 60% as a white microcrystalline powder. Since the polymerization was performed in solution, a relatively large amount of soluble, cyclic oligomers was formed. ElectroSpray Mass-Spectrometry of the filtrate showed the presence of cyclic dimers up to cyclic hexamers. According to NMR, FT-IR and elemental analyses, all polymers possess a very uniform microstructure and these techniques confirm the assigned structures. With 1H-NMR spectroscopy (figure 2.1c) both the syn and anti carbamate conformations14 are observed. Further, it revealed that the polymers contain a very small amount (less than 2%) of urea linkages, probably formed by hydrolysis of the isocyanate functionality during reaction. The molecular weights of the polymers were determined by both size exclusion chromatography (SEC) and Ubbelohde viscometry. The SEC measurements were performed in N-methyl pyrrolidone (NMP) as solvent, and polystyrene was used as reference. The intrinsic viscosities of the polymers were determined in m-cresol, and the MarkHouwink parameters of the known [m,n]-polyurethanes were used to estimate the molecular weights of these comparable [n]-polyurethanes.1 The data obtained with SEC corresponds nicely with the values found with viscometry (table 2.1). Table 2.1 Characteristics of [n]-polyurethanes 4. x 4 4 5 5 5 5 6 7 8 9 10 11 12 5-co-6 Solvent CHCl3 DMSO CHCl3 CHCl3 THF DMSO CHCl3 CHCl3 CHCl3 CHCl3 CHCl3 CHCl3 CHCl3 CHCl3 T (C) 20 20 20 61 20 20 20 20 20 20 20 20 20 20 Yield (%) 61 63 70 43 65 56 55 61 57 63 59 48 Mw (kg mol1)a 18.9 12.5 22.3 29.5 15.3 10.6 34.4 26.5 30.5 67.4 32.6 20.3 21.4 22.7 Mw/Mna 1.4 1.7 1.5 1.5 1.4 1.3 1.4 1.5 1.6 1.6 1.7 1.5 1.6 1.4 [] (dl g1) 0.16 0.17 Mv (kg mol1)b 16 18

0.22 0.24 0.24 0.43 0.30 0.18 0.26

25 29 29 64 39 19 32

a) Measured by SEC, with NMP as solvent, relative to polystyrene standards. b) Calculated from intrinsic viscosity in m-cresol at 25C; K=1.34*104, a=0.73.

21

Chapter 2

The weight-averaged molecular weights of the polymers, varying between 20 and 70 kg mol , are fairly high to respectable, despite the precipitation of the polymers from the poor solvent during preparation. Performing the polymerization in more polar solvents like THF, or-1

DMSO, or at reflux temperature in chloroform, does not significantly change the molecular weight of the polymers, as investigated. Table 2.1 shows the yields of the [n]-polyurethanes and estimations of their molecular weights. 2.4 Thermal properties of [n]-polyurethanes The thermal properties of the polymers were studied by DSC, indicating that all polymers are highly crystalline. Figure 2.2 displays the second heating and cooling curve of [6]-polyurethane at 10C/min. The thermogram shows a typical curve reminiscent of a semicrystalline polymer with a broad melting peak, and a shoulder at lower temperatures indicative of a recrystallization process prior to melting. The relative value of this recrystallization peak can be altered by changing the cooling rate or by annealing the sample. A small undercooling is observed of about 20-30C for all [n]-polyurethanes, indicating that these polymers have a high rate of crystallization.22 21.5 Heat Flow Endo Up (mW) 21 20.5 20 19.5 19 50 70 90 110 T (C) 130 150 170 190 Tc=100.1C H=38.2 J/g Tm=127.3C H=41.6 J/g

Figure 2.2: DSC curve of [6]-polyurethane. After melting and crystallization of the microcrystalline powders, as obtained after the polymerization, the polymer is obtained as a pale brittle material. Melting points and melting enthalpies of the polymers are depicted in table 2.2, and melting points are plotted in figure 2.3. The melting points are much lower than those of the corresponding [n]-nylons, as is also observed for [m,n]-polyurethanes compared to [m,n]nylons. It is evident from figure 2.3, that the [n]-polyurethanes show a strong odd-even effect in their melting points. In conformity with other polymers, e.g. [n]-nylons,15 the [n]22


polyurethanes with an odd number of methylene units in the monomeric main chain melt at lower temperatures than the [n]-polyurethanes with an even number of methylene units. At first glance it is surprising that it is not the total number of main chain atoms between the hydrogen bonding units that determines the odd-even effect. However, many examples are known in which the number of methylene units determines this effect.16 The alternation of the melting points is caused by the packing of the alkyl spacer in the crystalline phase. Boese et al. studied this behaviour in detail for several homologous series of substituted alkanes.16b-e Their conclusion is that compounds with an even number of methylene units in the alkyl spacers pack more densely than the odd analogues. This results is a higher melting point for the compounds with an even number of methylene units.200 180 Tm(C) 160 140 120 100

4

6

8 x

10

12

Figure 2.3: Melting points of [n]-polyurethanes: (n) experimental, (g) calculated; x denotes the number of methylene units in the monomer unit. The observed melting points are 10 to 20 degrees lower than those predicted by the additive group theory developed by van Krevelen.17 It is noteworthy to mention that the melting points can be raised by approximately 5C when the low molecular weight fraction is removed by extensive Soxhlet extraction with hot methanol. Table 2.2 DSC measurements of [n]-polyurethanes 4; heating rate of 10C min1. x Tm(C) Hm(J/g) 4 194 89.7 5 127 41.6 6 157 102.8 7 114 51.3 8 146 78.8 9 116 56.7 10 148 65.7 11 119 61.9 12 141 68.5

A random copolymer derived from 5-isocyanato-pentanol and 6-isocyanato-hexanol in a 1:1 molar ratio was prepared in the same way as the homopolymers. In contrast to the

23

Chapter 2

homopolymers, the random copolymer is soluble in chloroform, and is completely amorphous with a glass transition temperature of 8C according to DSC. According to thermogravimetric analysis (TGA), all polymers are stable up to 200C (figure 2.4), above which they decompose due to the cleavage of the urethane entities. The small decrease in weight slightly above 100C is believed to be due to loss of water.

60

100

140

180

220

260

300

T (C)

Figure 2.4: TGA of [6]-polyurethane.

2.5 Synthesis of hyperbranched polyurethanes Highly branched polymeric structures have received much attention from both chemists and physicists during the last decade. These structures combine appealing properties like a high degree of functionality, low melt-viscosity, and excellent solubility, thus making them interesting for a broad range of applications.18 In general, two distinct synthetic strategies have been employed for the preparation of such structures. One is a stepwise organic approach in which the macromolecules are built-up layer by layer, either in a convergent or in a divergent approach, resulting in monodisperse polymers with unprecedented structural precision.19 However, the preparation of these macromolecules, so called dendrimers, implies a multi-step synthesis, which hampers their practical use. The other synthetic strategy concerns the self-condensation of a ABx type monomer, with x2, resulting in a so called hyperbranched polymer.20 This polymeric approach has the advantage that it is synthetically more accessible and easy to scale-up in a one-pot synthesis. In contrast to the former approach, this latter approach yields macromolecules with less welldefined structures, having a polydisperse molecular weight distribution, and imperfect branching points. The properties of hyperbranched polymers tend to be intermediate between those of the fully regular dendrimers and those of linear polymers. 24


Due to the random and unpredictable nature of the branching reaction and the polydispersity inherent in all polymerizations, hyperbranched polymers contain a broad variety of molecular architectures. The molecular weight distribution is only one parameter to describe such a complex mixture of structural diversities.21 More architectural information is obtained by determining the degree of branching (DB) within the mixture. For AB2 monomers, this parameter was originally defined by Frchet (equation. 2.1)22: T +D (eq. 2.1) DB = T +D+L In eq. 2.1, T is the number of subunits in the terminal position (both end groups have not reacted), D is the number in a dendritic position (both end groups have reacted), and L is the number in a linear position (only one of the end groups has reacted). Thus, for a linear polymer, DB=0; and for a perfect dendrimer, DB=1. For a hyperbranched polymer, DB is in between both extremes, and the higher it is, the more branched and globular its structure is. In case of an ideal random polymerization of AB2 monomers, in which the reactivities of both Bgroups are equal and independent of one another, DB=0.5. If the reactivity of the second Bgroups is higher than the first one, more dendritic units are formed, and DB will increase. Contrary, a lower reactivity of the second B-group, results in an increase of the number of linear units, hence DB will decrease, and the polymer is less hyperbranched. For complete conversion of functional group A in the AB2 monomer, T and D are equal, and the more general equation 2.2 is obtained:23 L L 2D (eq 2.2) DB = = 1 = 1 N0 2D + L 2D + L were N0=T+D+L, the total number of monomer units. Thus, the degree of branching can be determined if at least one type of branching unit can be quantified. This can be done by using spectroscopic,20a, 25b or chromatographic techniques.24 A large variety of hyperbranched polymers has been reported, namely polyesters, polyureas, polyamides, polyphenylenes, polysiloxanes, polycarbonates, and polyethers.20a,b,25 Although, hyperbranched polyurethanes have been prepared,26 they are all containing aromatic structures, obtained via the Curtius rearrangement of benzoyl azides, or the dissociation of blocked isocyanates. The incorporation of the rigid aromatic rings in the hyperbranched polymers results in an increase of the glass transition temperature to far above room temperature. Fully aliphatic hyperbranched polyurethanes would have a low glass transition temperature, which makes them more easily processable. The synthetic procedure for the preparation of [n]-polyurethanes was also employed for the synthesis of aliphatic hyperbranched polyurethanes by using AB2 (5) and A2B (6) monomers. The monomers were synthesized by performing a Michael addition of acrylonitrile (ACN) to diethanolamine and 3-amino-propanol, respectively (scheme 2.8).

25

Chapter 2

After catalytic hydrogenation of the nitrile groups, aminodiol 5 and diamino alcohol 6 were obtained.OH HN OHACN

OH NC N OHH2, 80 bar Pd/C

OH H 2N 5 N OH

CN HO NH22 ACN

NH2H2, 80 bar Pd/C

HO

N CN

HO

N 6 NH2

Scheme 2.8: Synthesis of monomers for hyperbranched polymers. Reaction of 5 and 6 with di-tert-butyl tricarbonate gave the corresponding isocyanate monomers, and in situ polymerization by adding Zr(acac)4 yields the hyperbranched structures 7, and 8 respectively (scheme 2.9). To prevent side reactions and crosslinking of the isocyanate end groups of hyperbranched polymer 8, they were derivatized by reaction with methanol.OH 5 tricarb. CHCl3 OCN N OH Zr(acac)4 OCN ( N 7 O OH ) n-x O N )n H O NCO 6 tricarb. CHCl3 HO N NCO Zr(acac)4 2) MeOH HO ( N 8 N H N H O O ) CH3 n OCH3 ) n-x

Scheme 2.9: Synthesis of aliphatic hyperbranched polyurethanes 7 and 8. The hyperbranched polyurethanes are very viscous liquids, that are well soluble in i.e. chloroform, methanol, DMSO, and acidic water. Although SEC is not the appropriate technique to measure molecular weights of hyperbranched and dendritic structures, since their conformations are very different from the linear polystyrene, it was used to obtain a rough estimation of the molecular weights. According to SEC in NMP, the weight average 26


molecular weights of 7 and 8, are 6.4*103, and 3.8*103 g/mol, respectively, relative to polystyrene standards. The hyperbranched polyurethanes were characterized by 1H-NMR, 13 C-NMR, and FT-IR, which showed good agreement with the structures proposed.

2.6 Degree of branching of hyperbranched polyurethanes Equations 2.1 and 2.2 show how the degree of branching can be determined if at least one type of branching unit can be quantified. For our hyperbranched polymers 7 and 8, this is not possible by 1H-NMR, due to overlap of the signals attributed to the different branching units. Therefore, we tried to obtain this information from 13C-NMR. This analysis was only successful for hyperbranched polymer 7, since for hyperbranched polymer 8 the chemical difference between the three branching units is not sufficient to differentiate between them. In order to identify the branching units by 13C-NMR, three model compounds were synthesized that represent the three different types of units present in the final structure (figure 2.5).O T O N H OH O O D O N H O N C6H13 H O L O N H O N C6H13 H N OH O N O O N C6H13 H N OH

Figure 2.5: Model compounds for branching units: Terminal, Dendritic, and Linear. Model compound T (terminal) was prepared by reaction of monomer 5 with di-tertbutyl dicarbonate. Reaction of T with two equivalents of hexyl isocyanate gave D (dendritic), a model compound for a dendritic subunit in which both alcohol end groups have reacted. Reaction of T with only one equivalent of hexyl isocyanate yielded a mixture of products T, D and L (linear), in a ratio of 12%:13%:75%, respectively. This composition deviates from 27

Chapter 2

the statistical distribution in favour of the formation of the linear unit. L was separated from this mixture by column chromatography. Detailed NMR analysis allowed for unambiguous assignment of the signals.

T

D

LL D+L D+L+T

D+L

L+T

T

764 62 60 58 (ppm) 56 54 52 50

Figure 2.6: 13C-NMR spectra of the different branching units and of hyperbranched polymer 7. Figure 2.6 shows part of the 13C-NMR spectra of the three model compounds and of hyperbranched polymer 7. The NMR measurement was performed using inverse gated decoupling with a relaxation time of d1=10 s, in order to make integration as accurate as possible. Although there is overlap for most signals corresponding to the different branching units in the hyperbranched polymer, some dispersion is observed for a peak corresponding to linear units at 56.48 ppm, and a peak from terminal units at 56.38 ppm. Deconvolution of the peaks in the spectrum gives an estimation of the relative amounts of the three different branching units, namely 16%:16%:69% for terminal, dendritic, and linear branching units, respectively. The same trend is observed with the synthesis of the model compound for the linear unit L, in which a deviation from a statistical distribution favouring L was observed. Introducing these data in eq. 2.2, yields a degree of branching of DB=0.31 0.06. This is lower than the value of 0.5 that is expected based on statistics. Accordingly, with polymer 7 we have an example of a hyperbranched polymer containing predominantly linear units. Obviously, the reason for this is the lower reactivity of the second alcohol group of the monomer compared to the first one. Potentially, there are several causes for this lower reactivity. Hydrogen bonding between this alcohol group and the neighboring carbamate or 28


tertiary amine functionality lowers its nucleophilicity. Also the steric demand of the catalyst, Zr(acac)4 may be responsible for the reduced nucleophilicity. Indeed, hard metal complexes are known to be very susceptible to steric hindrance, since they act exclusively via a Lewisacid mechanism.27 Until now, no attempts have been done to increase the degree of branching of the hyperbranched polyurethanes, e.g. by using hydrogen bond competing solvents. It was impossible to determine the degree of branching of hyperbranched polymer 8, due to extensive overlap of NMR signals. Nevertheless, the degree of branching of 8 is possibly higher than that of 7, since monomer 6 is less sterically crowded.

2.7 Conclusions A facile and mild synthetic procedure for the preparation of isocyanates is described, starting from a variety of amines and di-tert-butyl tricarbonate. This procedure was used to synthesize -isocyanato--alcohols 3 from -amino--alcohols 2. By addition of a catalyst, the isocyanato alcohols were subsequently polymerized to yield the aliphatic [n]-polyurethanes. This general class of polymers was still unknown, despite its structural simplicity and strong resemblance with the [n]-nylons. The [n]-polyurethanes are highly crystalline polymers, and show a strong alternation in their melting points with respect to the number of methylene groups in the monomer unit. The polymers with an even number of methylene units in the main chain, are higher melting than the odd ones. This effect is known for many other polymers and organic compounds. Since these polymers are brittle materials, and therefore inferior to the analogous nylons, their mechanical properties were not subjected to further investigation. Using the same synthetic procedure, also aliphatic hyperbranched polyurethanes were prepared, starting from AB2 and A2B monomers. These polymers were obtained in high yields as viscous oils. A detailed analysis of hyperbranched polyurethane 7 showed that its degree of branching is quite low, DB=0.31 0.06, indicating that the hyperbranched polymer resembles linear polymers, more than dendrimers. The low degree of branching is caused by a lower reactivity of the second alcohol group of the monomer. A different catalyst, polymerization at higher temperatures, or reaction in a hydrogen bond competing solvent may lead to a higher degree of branching. It was not possible to determine the degree of branching of hyperbranched polymer 8, due to extensive overlap of NMR signals. Finally, this study shows that application of new synthetic methodologies from organic chemistry in the area of polymer synthesis is highly favorable. In the following chapters, the synthetic procedure using di-tert-butyl tricarbonate will be utilized to prepare more complex polymeric architectures, such as block copolymers. 29

Chapter 2

2.8 Experimental SectionMaterials. Di-tert-butyl tricarbonate was prepared according to a literature procedure14. 2-Amino-ethanol, 3amino-propanol, 4-amino-butanol, 6-amino-hexanol, 8-amino-octanoic acid, 9-bromo-nonanol, 10-bromodecanol, 11-bromo-undecanol, laurolactam, hexylisocyanate, potassium phtalimide, and dibutyltin dilaurate were purchased from Aldrich Chemical Co, 5-amino-pentanol, lithium aluminum hydride, acrylonitrile, thionylchloride, di-tert-butyl dicarbonate, and m-cresol from Acros, oenantholactam, hydrazine hydrate, diethanolamine, and zirconium(IV) acetylacetonate, from Fluka, sodiumhydroxide and sodiumsulfate from Merck, and tetrahydrofuran, acetonitrile, methanol, chloroform, dichloromethane, and diethylether from Biosolve. Raney/cobalt was kindly provided by DSM. The amino alcohols were dried over P2O5; THF was distilled over potassium and sodium; chloroform and acetonitrile was dried over molsieves. All polymerizations were carried out under a dry argon atmosphere. Instrumentation. NMR spectra were recorded on a Varian Inova 500 MHz spectrometer, a Bruker 400 MHz spectrometer, and a Varian Gemini 300 MHz spectrometer. For the characterization of the hyperbranched polyurethanes and model compounds with 13C-NMR, the relaxation time d1=10 s, decoupler mode dm=nny, Fouries number fn=262144, number of points np=100000, and number of transients nt=8192. Infrared spectra were measured on a Perkin Elmer 1600 FT-IR. Elemental analyses were carried out using a Perkin Elmer 240. Size exclusion chromatography (SEC) was performed on a Shimadzu LC10-AT, using a Polymer Laboratories Plgel 5m Mixed-D column, a Shimadzu RID-6A detector, and N-methyl-pyrrolidone as eluent. Molecular weights were calculated relative to polystyrene standards. Differential scanning calorimetry (DSC) was performed on a Perkin DSC 7, at a heating rate of 10C min1. Thermogravimetric analysis (TGA) were performed with a Perkin-Elmer TGA 7, samples were heated from 50C to 300C at 10C min1. Solution viscosities were measured with a Schott-Gerte Ubbelohde micro-viscometer with a suspended level bulb of type 538/20: K=0.1 and 538/10: K=0.01. The sample was thermostated with a bath of type CT1450, and elution times were measured with a Schott AVS 350. m-Cresol was distilled prior to use. 7-Amino-heptanoic acid.hydrochloride Oenantholactam (4.00 g, 31.4 mmol) and concentrated hydrochloric acid (50 ml 10M in water, 0.50 mol) were heated under reflux for 3 days. The solution was allowed to cool to room temperature, active charcoal (2 g) was added and the solution was filtered over diatomaceous earth. Subsequently, the solution was evaporated to dryness under reduced pressure and the product was obtained as a slightly yellow solid (5.53 g, 97%). 1H-NMR (400 MHz, Methanol-d4): 2.92 (t, 2H, CH2NH3), 2.32 (m, 2H, CH2COOH), 1.64 (m, 4H, CH2CH2NH3 + CH2CH2COOH), 1.39 (m, 4H, CH2CH2CH2CH2CH2). Ethyl 7-amino-heptanoate.hydrochloride Thionyl chloride (4.49 g; 37.4 mmol) was added dropwise to ethanol (100 ml) cooled on an icebath. The solution was stirred for 10 min and 7-amino-heptanoic acid.hydrochloride (5.53 g, 30.4 mmol) in ethanol (40 ml) was added dropwise, stirred for another 30 min, and heated under relux for 2 h. The solution was evaporated to dryness under reduced pressure, and the product was obtained as a yellow solid (5.73 g, 90%). 1H-NMR (400 MHz, Methanol-d4): 4.10 (q, 2H, CH2O), 2.91 (t, 2H, CH2NH3), 2.33 (t, 2H, CH2COOEt), 1.64 (m, 4H, CH2CH2NH3 + CH2CH2COOEt), 1.40 (m, 4H, CH2CH2CH2CH2CH2), 1.24 (t, 3H, CH3). 7-Amino-1-heptanol, 2-(7) Ethyl 7-amino-heptanoate.hydrochloride (5.73 g; 27.3 mmol) was dissolved in dichloromethane (100 ml) and extracted with sodium hydroxide solution (60 ml 1 M). The aqueous layer was extracted two more times with dichloromethane (50 ml), and the combined organic layers were combined, dried with sodium sulfate and concentrated in vacuo. Lithium aluminumhydride (1.12 g, 29.5 mmol) was suspended in dry THF (100 ml) and cooled to 0C. To this suspension ethyl 7-amino-heptanoate in dry THF (50 ml) was added dropwise, and the solution was stirred for 30 min at 0C under an argon atmosphere, and subsequently heated under reflux for 2 h. The reaction mixture

30


was cooled to 0C, and water (2.5 ml) was added slowly. The reaction mixture was stirred overnight at 20C, filtered, dried with sodium sulfate, and concentrated under reduced pressure. The waxy solid was distilled at 110C and 0.4 mbar, yielding a white solid (0.97 g, 27%). Tm=54C (Lit: 4853C). 1H-NMR (CDCl3, 400MHz): 3.63 (t, 2H, CH2OH, J=6.6 Hz), 2.68 (t, 2H, CH2NH2, J=7.0 Hz), 1.55 (m, 2H, CH2CH2OH), 1.50 1.32 (br.m, 11H, CH2CH2NH2 + CH2CH2CH2CH2CH2 + NH2 + OH). 13C-NMR (CDCl3, 100MHz): 62.32 (CH2OH), 42.04 (CH2NH2), 33.54, 32.70, 29.20, 26.77, 25.72. Ethyl 8-amino-octanoate.hydrochloride 8-Amino-octanoic acid (2.00 g, 12.6 mmol) was dissolved in hydrochloric acid (30 ml 6 M) and the solution was evaporated to dryness under reduced pressure. The same synthetic procedure was followed as described for the synthesis of ethyl 7-amino-heptanoate.hydrochloride. The product was obtained as a yellow solid (2.68 g, 95%). 1H-NMR (400 MHz, Methanol-d4): 4.12 (q, 2H, CH2O), 2.90 (t, 2H, CH2NH3), 2.29 (t, 2H, CH2COOEt), 1.62 (m, 2H, CH2CH2NH3), 1.43 (q, 2H, CH2CH2COOEt), 1.32 (m, 6H, CH2CH2CH2CH2CH2), 1.25 (t, 3H, CH3). 8-Amino-1-octanol, 2-(8) The same synthetic procedure was followed as described for the synthesis of 7-amino-1-heptanol, starting with ethyl 8-amino-octanoate.hydrochloride (2.60 g, 11.6 mmol). The waxy solid was distilled at 100C and 0.8 mbar, yielding a white solid (0.61 g, 36%). Tm=58C (Lit: 54 59C). 1H-NMR (CDCl3, 400MHz): 3.62 (t, 2H, CH2OH, J=6.6 Hz), 2.68 (t, 2H, CH2NH2, J=7.0 Hz), 1.56 (m, 5H, CH2CH2OH + NH2 + OH), 1.44 (m, 2H, CH2CH2NH2), 1.32 (m, 8H, CH2CH2CH2CH2CH2). 13C-NMR (CDCl3, 100MHz): 62.62 (CH2OH), 42.07 (CH2NH2), 33.57, 32.73, 29.36, 29.32, 26.72, 25.66. 9-Phtalimido-1-nonanol 9-Bromo-1-nonanol (2.00 g, 8.96 mmol) and potassium phtalimide (5.11 g, 27.59 mmol) were dissolved in dry acetonitrile (70 ml) and heated under reflux for 27 h. After removal of the solvent under reduced pressure, the solid was suspended in sodium hydroxide solution (40 ml 1M) and extracted with dichloromethane (2 times 30 ml). The combined organic layers were dried with magnesium sulfate and concentrated to dryness. The product was obtained as a beige solid (2.53 g, 98%). 1H-NMR (CDCl3, 300 MHz): 7.85 (d, 2H, H3,6 arom), 7.71 (d, 2H, H4,5 arom), 3.703.63 (m, 4H, CH2N + CH2OH), 1.67 (m, 2H, CH2CH2OH), 1.58 (m, 2H, CH2CH2N), 1.30 (m, 11H, CH2CH2CH2CH2CH2 + OH). 9-Amino-1-nonanol, 2-(9) 9-Phtalimido-1-nonanol (1.30 g, 4.49 mmol) and hydrazine hydrate (0.67 g, 13.5 mmol) were dissolved in ethanol (40 ml) and stirred at 65C overnight. To the turbid reaction mixture, concentrated hydrochloric acid (1 ml) was added and it was stirred at 65C for another 2 h. After filtration, the reaction mixture was concentrated in vacuo, sodium hydroxide solution (30 ml 1M) was added, and this was extracted two times with dichloromethane (30 ml). The combined organic layers were dried with sodium sulfate, and concentrated to dryness. The solid residue was distilled at 100C and 0.5 mbar, yielding a white solid (0.44 g, 62%). Tm=69C (Lit: unknown). 1H-NMR (CDCl3, 300MHz): 3.60 (t, 2H, CH2OH, J=6.6 Hz), 2.67 (t, 2H, CH2NH2, J=7.0 Hz), 1.7 (br.s, NH2 + OH), 1.55 (m, 2H, CH2CH2OH), 1.43 (m, 2H, CH2CH2NH2), 1.30 (m, 10H, CH2CH2CH2CH2CH2). 10-Phtalimido-1-decanol The same synthetic procedure was followed as described for the synthesis of 9-phtalimido-1-nonanol, starting with 10-bromo-1-decanol (1.20 g, 5.19 mmol). The product was obtained as a white solid (1.43 g, 91%). 1HNMR (CDCl3, 400 MHz): 7.84 (d, 2H, H3,6 arom), 7.71 (d, 2H, H4,5 arom), 3.693.61 (m, 4H, CH2N + CH2OH), 1.67 (m, 2H, CH2CH2OH), 1.56 (m, 2H, CH2CH2N), 1.50 (s, 1H, OH), 1.30 (m, 12H, CH2CH2CH2CH2CH2).

31

Chapter 2

10-Amino-1-decanol, 2-(10) The same synthetic procedure was followed as described for the synthesis of 9-amino-1-nonanol, starting with 10-phtalimido-1-decanol (1.30 g, 4.28 mmol). The solid residue was distilled at 125C and 0.6 mbar, yielding a white solid (0.47 g, 63%). Tm=72C (Lit: 72C). 1H-NMR (CDCl3, 300MHz): 3.63 (t, 2H, CH2OH, J=6.6 Hz), 2.67 (t, 2H, CH2NH2, J=6.9 Hz), 1.56 (m, 2H, CH2CH2OH), 1.43 (m, 2H, CH2CH2NH2), 1.29 (m, 15H, CH2CH2CH2CH2CH2 + NH2 + OH). 11-Phtalimido-1-undecanol The same synthetic procedure was followed as described for the synthesis of 9-phtalimido-1-nonanol, starting with 11-bromo-1-undecanol (1.00 g, 4.25 mmol). The product was obtained as a white solid (1.24 g, 92%). 1HNMR (CDCl3, 400 MHz): 7.84 (d, 2H, H3,6 arom), 7.71 (d, 2H, H4,5 arom), 3.693.62 (m, 4H, CH2N + CH2OH), 1.67 (m, 2H, CH2CH2OH), 1.54 (m, 2H, CH2CH2N), 1.321.37 (m, 15H, CH2CH2CH2CH2CH2+ OH). 11-Amino-1-undecanol, 2-(11) The same synthetic procedure was followed as described for the synthesis of 9-amino-1-nonanol, starting with 11-phtalimido-1-undecanol (0.58 g, 1.83 mmol). The white solid product was not distilled (0.27 g, 79%). Tm=85C (Lit: 73C). 1H-NMR (CDCl3, 400MHz): 3.64 (t, 2H, CH2OH, J=6.6 Hz), 2.68 (t, 2H, CH2NH2, J=7.0 Hz), 1.56 (m, 2H, CH2CH2OH), 1.43 (m, 2H, CH2CH2NH2), 1.28 (m, 17H, CH2CH2CH2CH2CH2 + NH2 + OH). 13C-NMR (CDCl3, 100MHz): 62.98 (CH2OH), 42.27 (CH2NH2), 33.86, 32.80, 29.56, 29.48 (m), 29.39, 26.86, 25.72. 12-Amino-dodecanoic acid.hydrochloride Laurolactam (10.00 g, 50.7 mmol) and concentrated hydrochloric acid (200 ml 10M in water, 2.00 mol) were heated under reflux for 4 days. The product crystallized by cooling the solution to 0C, was filtered off, washed with water, and dried in vacuo. The product was obtained as colorless flakes (11.50 g, 90%). 1H-NMR (400 MHz, Methanol-d4): 2.91 (t, 2H, CH2NH3), 2.27 (m, 2H, CH2COOH), 1.66 (m, 2H, CH2CH2NH3), 1.59 (m, 2H, CH2CH2COOH), 1.32 (br. m, 14H, CH2CH2CH2CH2CH2). Ethyl 12-amino-dodecanoate.hydrochloride The same synthetic procedure was followed as described for the synthesis of ethyl 7-aminoheptanoate.hydrochloride, starting with 12-amino-dodecanoic acid.hydrochloride (5.00 g, 19.9 mmol). The product was obtained as a white solid (5.57 g, 100%). 1H-NMR (400 MHz, Methanol-d4): 4.11 (q, 2H, CH2O), 2.90 (t, 2H, CH2NH3), 2.29 (t, 2H, CH2COOEt), 1.661.57 (m, 4H, CH2CH2NH3 + CH2CH2COOEt), 1.31 (m, 14H, CH2CH2CH2CH2CH2 + NH3), 1.24 (t, 3H, CH3). 12-Amino-1-dodecanol, 2-(12) The same synthetic procedure was followed as described for the synthesis of 7-amino-1-heptanol, starting with ethyl 12-amino-dodecanoate.hydrochloride (5.57 g, 19.9 mmol). The waxy solid was distilled at 140C and 0.2 mbar, yielding a white solid (1.52 g, 38%). Tm=77C (Lit: 79 80C). 1H-NMR (CDCl3, 400MHz): 3.64(t, 2H, CH2OH, J=6.8 Hz), 2.68 (t, 2H, CH2NH2, J=7.2 Hz), 1.56 (m, 2H, CH2CH2OH), 1.44 (m, 2H, CH2CH2NH2), 1.27 (m, 19H, CH2CH2CH2CH2CH2 + NH2 + OH). 13C-NMR (CDCl3, 100MHz): 63.00 (CH2OH), 42.27 (CH2NH2), 33.85, 32.79, 29.54, 29.45 (m), 29.38, 26.86, 25.71. [n]-Polyurethane, 4-(x) The synthesis of [6]-polyurethane, 4-(5) is given as a typical example. A solution of 5-amino-1-pentanol (9.69 mmol, 1.00 g) in chloroform (2 ml) was injected by a syringe under the surface of a stirred solution of di-tert-butyl tricarbonate (10.66 mmol, 2.80 g) in chloroform (30 ml). The solution was stirred for 10 min at room temperature under an argon atmosphere. 1H-NMR (400 MHz, CDCl3, 20C, TMS): 3.67 (q, 2H, CH2OH, J=6.0 Hz), 3.32 (t, 2H, CH2NCO, J=6.6 Hz), 1.55 (br.m, 4H, CH2CH2OH + CH2CH2NCO), 1.40 (m, 2H, CH2 CH2CH2CH2 CH2, J=6.7 Hz). IR (CHCl3): 3396 (br.s, OH), 2971 (m, C H), 2274 (s, N=C=O) cm1.

32


Zirconium(IV) acetylacetonate (0.1 mol%) was added, and the polymerization was carried out for 20 h with continuous stirring under argon at room temperature. The turbid reaction mixture was precipitated in diethyl ether (150 ml) and the polymeric product was collected by suction filtration in a yield of 0.81 g (63%). Tm=127C; Tdecomp=200C. 1H-NMR (400 MHz, DMSO-d6, 20C, TMS): 7.04 (br.t, 0.9H, NH anti conformer), 6.72 (br.m, 0.1H, NH syn conformer), 3.89 (t, 2H, CH2O, J=6.2 Hz), 2.95 (q, 2H, CH2N, J=6.0 Hz), 1.50 (m, 2H, CH2CH2O, J=7.2 Hz), 1.40 (m, 2H, CH2CH2N, J=7.7 Hz), 1.28 (m, 2H, CH2 CH2CH2CH2 CH2, J=6.6 Hz), 13C-NMR (DMSO-d6, 100 MHz, 100C): 156.4 (C=O), 63.5 (CH2O), 40.1 (CH2N), 29.4 (CH2CH2O), 28.7 (CH2CH2N), 26.0 (CH2 CH2CH2CH2 CH2). IR (KBr): 3318 (br.s, NH), 2944 (m, CH), 2870 (w), 1684 (s, C=O), 1535 (s, amide II), 1263 (s) cm1. Anal. Calcd. (%) for (C6H11NO2)n: C 55.80, H 8.58, N 10.85. Found (%): C 55.46, H 8.67, N 10.55. [5]-Polyurethane, (C4H8NHCOO)n, 4-(4) H-NMR (400 MHz, DMSO-d6, 20C, TMS): 7.10 (br.t, 0.9H; NH anti conformer), 6.70 (br.m, 0.1H; NH syn conformer), 3.90 (t, 2H; CH2O), 2.96 (q, 2H; CH2N), 1.48 (m, 2H; CH2CH2O), 1.40 (m, 2H; CH2CH2N). IR (KBr): 3317 (br.s), 2954 (m), 1689 (s), 1541 (s), 1271 (s) cm1. Anal. Calcd. (%) for (C5H9NO2)n: C 52.16, H 7.88, N 12.17. Found(%): C 51.79, H 8.03, N 11.92. Tm=194C; Tdecomp=180C.1

[7]-Polyurethane (C6H12NHCOO)n, 4-(6) 1 H-NMR (400 MHz, DMSO-d6, 20C, TMS): 7.03 (br.t, 0.9H; NH anti conformer), 6.75 (br.m, 0.1H; NH syn conformer), 3.90 (t, 2H; CH2O), 2.94 (q, 2H; CH2N), 1.50 (m, 2H; CH2CH2O), 1.37 (m, 2H; CH2CH2N), 1.17 (m, 4H; CH2 CH2CH2CH2 CH2); IR (KBr): 3319 (br.s), 2938 (m), 2860 (w), 1687 (s), 1542 (s), 1257 (s) cm1; Anal. Calcd. (%) for (C7H13NO2)n: C 58.72, H 9.15, N 9.78. Found (%): C 58.67, H 9.21, N 9.57. Tm=157C; Tdecomp=210C. [8]-Polyurethane, (C7H14NHCOO)n, 4-(7) 1 H-NMR (400 MHz, DMSO-d6, 20C, TMS): 7.03 (br.t, 0.9H; NH anti conformer), 6.73 (br.m, 0.1H; NH syn conformer), 3.89 (t, 2H; CH2O), 2.93 (q, 2H; CH2N), 1.48 (m, 2H; CH2CH2O), 1.38 (m, 2H; CH2CH2N), 1.24 (m, 6H; CH2 CH2CH2CH2 CH2); IR (KBr): 3327 (br.s), 2934 (m), 2856 (w), 1687 (s), 1534 (s), 1252 (s) cm1; Anal. Calcd. (%) for (C8H15NO2)n: C 61.12, H 9.62, N 8.91. Found (%): C 60.66, H 10.09, N 8.65. Tm=114C. [9]-Polyurethane, (C8H16NHCOO)n, 4-(8) 1 H-NMR (400 MHz, DMSO-d6, 100C, TMS): 6.47 (br.t, 1H; NH), 3.93 (t, 2H; CH2O), 2.97 (q, 2H; CH2N), 1.51 (m, 2H; CH2CH2O), 1.40 (m, 2H; CH2CH2N), 1.27 (m, 8H; CH2 CH2CH2CH2 CH2); IR (KBr): 3321 (br.s), 2928 (m), 2852 (w), 1686 (s), 1545 (s), 1261 (s) cm1; Anal. Calcd. (%) for (C9H17NO2)n: C 63.13, H 10.01, N 8.18. Found (%): C 62.84, H 10.64, N 7.88. Tm=146C. [10]-Polyurethane, (C9H18NHCOO)n, 4-(9) 1 H-NMR (400 MHz, DMSO-d6, 120C, TMS): 6.43 (br.t, 1H; NH), 3.95 (t, 2H; CH2O), 3.00 (q, 2H; CH2N), 1.56 (m, 2H; CH2CH2O), 1.43 (m, 2H; CH2CH2N), 1.28 (m, 10H; CH2 CH2CH2CH2 CH2); IR (KBr): 3325 (br.s), 2925 (m), 2852 (w), 1686 (s), 1535 (s), 1254 (s) cm1; Anal. Calcd. (%) for (C10H19NO2)n: C 64.83, H 10.34, N 7.56. Found (%): C 64.74, H 10.79, N 7.33. Tm=116C. [11]-Polyurethane, (C10H20NHCOO)n, 4-(10) 1 H-NMR (400 MHz, DMSO-d6, 120C, TMS): (br.t, 1H; NH), 3.95 (t, 2H; CH2O), 3.00 (q, 2H; CH2N), 1.55 (m, 2H; CH2CH2O), 1.43 (m, 2H; CH2CH2N), 1.28 (m, 12H; CH2 CH2CH2CH2 CH2); IR (KBr): 3324 (br.s), 2922 (m), 2851 (w), 1687 (s), 1543 (s), 1250 (s) cm1; Anal. Calcd. (%) for (C11H21NO2)n: C 66.30, H 10.62, N 7.03. Found (%): C 65.86, H 11.01, N 6.82. Tm=148C. [12]-Polyurethane, (C11H22NHCOO)n, 4-(11) 1 H-NMR (400 MHz, DMSO-d6, 100C, TMS): 6.40 (br.t, 1H; NH), 3.92 (t, 2H; CH2O), 2.97 (q, 2H; CH2N), 1.51 (m, 2H; CH2CH2O), 1.40 (m, 2H; CH2CH2N), 1.28 (m, 14H; CH2 CH2CH2CH2 CH2); IR (KBr): 3327

33

Chapter 2

(br.s), 2922 (m), 2851 (w), 1684 (s), 1534 (s), 1246 (s) cm1; Anal. Calcd. (%) for (C12H23NO2)n: C 67.57, H 10.87, N 6.57. Found (%): C 66.98, H 11.16, N 6.22. Tm=119C. [13]-Polyurethane, (C12H24NHCOO)n, 4-(12) 1 H-NMR (400 MHz, DMSO-d6, 100C, TMS): 6.38 (br.t, 1H; NH), 3.92 (t, 2H; CH2O), 2.95 (q, 2H; CH2N), 1.51 (m, 2H; CH2CH2O), 1.40 (m, 2H; CH2CH2N), 1.25 (m, 16H; CH2 CH2CH2CH2 CH2); IR (KBr): 3326 (br.s), 2921 (m), 2850 (w), 1686 (s), 1542 (s), 1242 (s) cm1; Anal. Calcd. (%) for (C13H25NO2)n: C 68.68, H 11.08, N 6.16. Found (%): C 68.25, H 11.40, N 5.93. Tm=141C. [6-co-7]-Polyurethane, (C5H10NHCOO-co-C6H12NHCOO)n 1 H-NMR (400 MHz, DMSO-d6, 20C, TMS): 7.05 (br.t, 0.9H; NH anti conformer), 6.73 (br.m, 0.1H; NH syn conformer), 3.90 (t, 2H; CH2O), 2.94 (q, 2H; CH2N), 1.50 (m, 2H; CH2CH2O), 1.38 (m, 2H; CH2CH2N), 1.27 (m, 3H; CH2 CH2CH2CH2 CH2); IR (KBr): 3324 (br.s), 2941 (m), 2850 (w), 1687 (s), 1540 (s), 1259 (s) cm1; Anal. Calcd. (%) for (C5.5H11NO2)n: C 57.26, H 8.87, N 10.32. Found (%): C 56.84, H 8.94, N 9.98. Tg=8C. N,N-Bis-(2-hydroxyethyl)-amino-propionitrile Diethanolamine (20 g, 0.19 mol) was dissolved in water (100 ml), and cooled on an icebath. Acrylonitrile (53 g, 1.00 mol) was added dropwise, and the reaction mixture was stirred for 1h at 0C, and subsequently heated to 70C for 3 h. After evaporation of water and excess arylonitrile under reduced pressure, the product was obtained as colorless liquid (29.16 g, 97%). 1H-NMR (CDCl3, 400 MHz): 3.85 (br.s, 2H; OH), 3.61 (t, 4H, CH2OH, J=5.2 Hz), 2.91 (t, 2H, NCH2CH2CN, J=6.8 Hz), 2.69 (t, 4H, NCH2CH2OH, J=5.2 Hz), 2.55 (t, 2H, CH2CN, J=6.8 Hz). 13C-NMR (CDCl3,100 MHz): 119.22 (CN), 60.71 (CH2OH), 55.75 (CH2CH2OH), 50.07 (NCH2CH2CN), 16.25 (CH2CN). FT-IR (neat): 3380 (br.s, OH), 2950 (m, CH), 2248 (m, CN), 1642 (m), 1027 (s, CO) cm1. N,N-Bis-(2-hydroxyethyl)-propylenediamine, 5 Raney/cobalt catalyst suspension in water (3 g) was decanted, rinsed two times with methanol and added to a methanolic ammonia solution (100 ml 7 N). N,N-bis-(2-hydroxyethyl)-amino-propionitrile (26 g, 0.16 mol) was added to this suspension, and the reaction mixture was transferred into the Parr-reactor vessel. After closing the reactor, the solution was purged three times with nitrogen, and two times with hydrogen gas. The reaction mixture was mechanically stirred during 2 h at 50C and 85 bar hydrogen pressure. After cooling and releasing pressure, the catalyst was filtered off on a glass filter over a layer of diatomaceous earth, and the reaction mixture was evaporated under reduced pressure until dryness. The brown product was distilled at 180C and 0.05 mbar using a Kugelrohr apparatus. The product was obtained as a colorless liquid (22.11 g, 85%). 1H-NMR (CDCl3, 400 MHz): 3.62 (t, 4H, CH2OH, J=5.4 Hz), 2.84 (t, 2H, CH2NH2, J=6.4 Hz), 2.8 (br. s, 4H, OH + NH2), 2.65 (t, 2H, CH2CH2CH2NH2, J=6.4 Hz), 2.61 (t, 4H, CH2CH2OH, J=5.2 Hz), 1.62 (qui, 2H, CH2CH2CH2, J=6.4 Hz). 13C-NMR (CDCl3, 100 MHz): 59.66 (CH2OH), 56.09 (CH2CH2OH), 52.20 (CH2CH2CH2NH2), 40.13 (CH2NH2), 29.51 (CH2CH2CH2). FT-IR (neat): 3345 and 3289 (br.s, OH + NH2), 2939 (s, CH), 1600 (m), 1036 (s, CO) cm1. N,N-Bis-(2-cyanoethyl)-3-amino-1-propanol The same synthetic procedure was followed as described for the synthesis of N,N-bis-(2-hydroxyethyl)-aminopropionitrile, starting with 3-amino-1-propanol (10.00 g, 0.133 mol). The product was obtained as a colorless oil (24.09 g, 100%). 1H-NMR (CDCl3, 400 MHz): 3.75 (t, 2H, CH2OH), 2.89 (t, 4H, NCH2CH2CN), 2.70 (t, 2H, NCH2CH2CH2OH), 2.60 (br.s, 1H, OH), 2.51 (t, 4H, CH2CN), 1.72 (qui, 2H, CH2CH2CH2). 13C-NMR (CDCl3, 100 MHz): 118.64 (CN), 60.71 (CH2OH), 50.65 (NCH2CH2CH2OH), 49.48 (NCH2CH2CN), 29.45 (CH2CH2CH2) 16.70 (CH2CN). FT-IR (neat): 3424 (br.s, OH), 2950 (m, CH), 2248 (s, CN), 1466 (m), 1421 (m), 1367 (m), 1033 (s, CO) cm1.

34


N,N-Bis-(3-aminopropyl)-3-amino-1-propanol, 6 The same synthetic procedure was followed as described for the synthesis of N,N-bis-(2-hydroxyethyl)propylenediamine, starting with N,N-bis-(2-cyanoethyl)-3-amino-1-propanol (23.33 g, 0.129 mol). The product was obtained as a colorless liquid (20.10 g, 80%). 1H-NMR (CDCl3, 400 MHz): 3.70 (t, 2H, CH2OH, J=5.6 Hz), 2.72 (t, 4H, CH2NH2, J=6.8 Hz), 2.60 (t, 2H, CH2CH2CH2OH, J=6.2 Hz), 2.48 (t, 4H, CH2CH2CH2NH2, J=7.4 Hz), 2.24 (br. s, 5H, OH + NH2), 1.69 (qui, 2H, OCH2CH2CH2N, J=5.8 Hz). 1.62 (m, 4H, NCH2CH2CH2N, J=7.2 Hz). 13C-NMR (CDCl3, 100 MHz): 62.25 (CH2OH), 53.02 (CH2CH2CH2OH), 51.28 (CH2CH2CH2NH2), 39.98 (CH2NH2), 30.17 (NCH2CH2CH2N), 28.14 (OCH2CH2CH2N). FT-IR (neat): 3340 and 3284 (br.s, OH + NH2), 2942 (s, CH), 1599 (m), 1039 (s, CO) cm1. Hyperbranched polymer, 7 In a solution of di-tert-butyl tricarbonate (0.93 g, 3.56 mmol) in dry chloroform (10 ml) was quickly injected a solution of N,N-bis-(2-hydroxyethyl)-propylenediamine (0.55 g, 3.39 mmol) in dry chloroform (2 ml). The solution was stirred for 15 min, zirconium(IV) acetylacetonate (0.1 mol%) was added, and the polymerization was carried out for 20 h with continuous stirring under argon at room temperature. The reaction mixture was evaporated to dryness under reduced pressure. The product was obtained as a yellow visco

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