polymer chemistry - ugent · in2011,wepresentedapromisingacceleratedprotocolforthe...

ISSN 1759-9954

Polymer Chemistry

1759-9954(2013)4:8;1-F

www.rsc.org/polymers Volume 4 | Number 8 | 21 April 2013 | Pages 2373–2616

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Showcasing work from Kyung-Youl Baek’s research group at the Center for Materials Architecturing, Korea Institute of Science and Technology.

Title: Thermoresponsive amphiphilic star block copolymer

photosensitizer: smart BTEX remover

A thermosensitive and water soluble amphiphilic PNIPAM-PS

star block copolymer with a porphyrin core effi ciently captured

environmentally toxic organic compounds such as benzene,

toluene, ethyl benzene, and xylene (BTEX) from water and

decomposed them using the porphyrin core through a

photo-oxidation reaction under UV irradiation. Afterwards,

this star polymer photosensitizer was easily recycled by fi ltration

after simple thermal treatment.

As featured in:

See Kyung-Youl Baek et al.

Polym. Chem., 2013, 4, 2400.

www.rsc.org/polymersRegistered Charity Number 207890 PAPER

Filip E. Du Prez et al.One-pot, additive-free preparation of functionalized polyurethanes via amine–thiol–ene conjugation

PolymerChemistry

PAPER

Polymer Chemistry Research Group, Dep

University, Krijgslaan 281 S4-bis, B-9000

UGent.be

† Electronic supplementary informa10.1039/c3py00004d

Cite this: Polym. Chem., 2013, 4, 2449

Received 2nd January 2013Accepted 15th January 2013

DOI: 10.1039/c3py00004d

www.rsc.org/polymers

This journal is ª The Royal Society of

One-pot, additive-free preparation of functionalizedpolyurethanes via amine–thiol–ene conjugation†

Pieter Espeel, Fabienne Goethals, Frank Driessen, Le-Thu T. Nguyen andFilip E. Du Prez*

A straightforward, isocyanate-free method for the synthesis of functionalized polyurethanes, based on

amine–thiol–ene conjugation, was elaborated. Aminolysis of a readily available AB0-urethane monomer,

containing both an acrylate (A) and a thiolactone unit (B0), facilitates the preparation of various reactive

thiol–acrylates. In situ polymerization via Michael addition proceeds under ambient conditions, yielding

polyurethanes with a large variety of chemical functionalities. Side-chain functionality originates from

the modular use of different amines, allowing for the introduction of pendent functional groups (e.g.

double bond, triple bond, furfuryl, tertiary amine, morpholine) along the polyurethane backbone.

Extensive model studies revealed the kinetic profile of this reaction sequence and excluded the

occurrence of competing reactions, such as aza-Michael addition and disulfide formation. This mild one-

pot reaction requires no additives or external trigger and the obtained polyurethanes remain soluble

throughout the process, enabling post-polymerization modification in the same reaction medium.

Introduction

Facile synthetic and modication procedures of functionalizedpolymers have been the subject of extensive fundamental andapplied research efforts during the last decade. The concept of‘click’ chemistry1–8 induced a transition towards ‘on-demand’preparation of tailored polymeric systems.9 The toolbox ofresearch labs is currently loaded with a variety of established‘click’ reactions, offering ample possibilities formacromoleculardesign and synthesis. Moreover, the development and valoriza-tionofnovelpolymermaterialswithabroad rangeof applications(medicines,10–13 electronics,14–16 bioconjugation,17–21 labeling,22–26

etc.) signicantly promoted interdisciplinary research. The elab-oration of innovative procedures and the combination of existingreactions in multi-step one-pot sequences further exemplify thescientic eagerness to study the possibilities and limitations of‘click’ chemistry to the full extent.27,28

Polyurethanes (PUs) are an essential class of synthetic poly-mers that are applied worldwide on a large scale.29 Large-scaleproduction of these materials mainly relies on feeds of diisocya-nates, diols and/or polyols in the presence of a catalyst. Despitethe wide range of PUs available via step-growth polymerization,the lackof side-chain functionalities limits their scope. Therefore,methods leading to functionalized PUs equipped with reactivegroups along their backbone remain of particular interest. These

artment of Organic Chemistry, Ghent

Ghent, Belgium. E-mail: Filip.DuPrez@

tion (ESI) available. See DOI:

Chemistry 2013

functional groups can be converted using ‘click’ chemistry,providing paths to uniquematerials with enhanced properties forhigh-end applications. The mainstream approach is to directlyincorporate clickable side-groups in linear PUs during the poly-merization process through the addition of a functionalized diolto the diisocyanate–diolmixture. In addition to the high intrinsicreactivity of diisocyanates, the reactive nature of the desiredfunctional group mostly necessitates the use of protection/deprotection strategies, e.g. amine- and maleimide-containingdiols are protected as the corresponding carbamate30 and furan-adduct31 prior to the polymerization. However, various function-alities have also been introduced directly as pendent groups inPUsby careful selection of the appropriate unprotectedmonomerdiol: alkyne-,32–36 alkene-,37–39 hydroxyl-40 and furan41-functional-ized PUs are available via this approach. Subsequent ‘click’modication via copper catalyzed azide–alkyne cyclo-addition(CuAAC),32–36 radical thiol–ene conjugation,37–39 and thiol–mal-eimide conjugation31 enabled themodular and efficient synthesisof tailored PUs. Similarly, the reactive moiety can be introducedthrough a functionalized diisocyanate, demonstrated by thesynthesis of maleimide-functionalized copoly(urethane–urea)s.42

All methods mentioned above lack versatility as they gener-ally only allow for the incorporation of one type of ‘clickable’functional handle. Moreover, the absence of a general syntheticapproach for the preparation of functionalized diols entails arequirement of dedicated multi-step synthesis. Consequently,functionalized PUs not only differ in their reactive pendentmoieties, but also in their backbone, compromising the in-depth comparison of the material properties of the thusobtained materials and derivatives.

Polym. Chem., 2013, 4, 2449–2456 | 2449

Scheme 1 Nucleophilic amine–thiol–ene conjugation: aminolysis of the thio-lactone ring (i), followed by thiol-Michael addition (ii). EWG ¼ electron-with-drawing group.

Polymer Chemistry Paper

In 2011, we presented a promising accelerated protocol for themodular synthesis of polyurethanebasedmaterials, consisting ofa one-pot amine–thiol–ene reaction of a stable AB0-monomer,containing an allyl and thiolactone unit connected by a urethanelinkage. In this approach, a thiolactone entity serves as a thiolprecursor (latent functionality). The thiolactone ring opens uponaminolysis (nucleophilic reaction) and the in situ generated thiolreacts with the allyl double bond in a radical photo-polymeriza-tion reaction.43However, conceptual issues directly related to theradical reaction in the one-pot process impede further extensionof the scope of the method. Important to note is that somefunctional groups (e.g. furan,44–48 double and triple bond), intro-duced via the amine, are incompatible with this radical envi-ronment. Additionally, UV-curing happens upon decompositionof a photoinitiator (e.g. DMPA), but model studies revealed thatsome amines (e.g. benzylamine) react with the formed radicalfragments, thus limiting the use of a photoinitiator.

Therefore, we aimed at the one-pot combination of theaminolysis of a thiolactone unit on one hand and a nucleophilicthiol–ene conjugation (Michael addition) on the other hand,which is considered to be a breakthrough approach for thedevelopment of a direct, additive- and isocyanate-free synthesisstrategy to obtain functionalized polyurethanes. The Michaeladdition between a nucleophile (such as thiol, amine or stabi-lized carbanion) and an activated double bond (e.g. imidazole,acrylate, vinyl sulfone) is known to be an atom-efficient linkingreaction. This versatile method is oen the key step in polymersynthesis and conjugation, especially when complex macro-molecular architectures are targeted.49 The combination of thethiolactone-based strategy for the in situ generation of thiolsand subsequent Michael addition undoubtedly broadens thescope of metal-free multi-step reactions for the design andsynthesis of polymers.

Replacing the allyl double bond in the AB0-monomer with anacrylate function, allowing for the complete absence of radicalspecies during the polymerization, would indeed be a stepforward, although potential orthogonality issues render theconjugation procedure a fundamentally challenging two-stepreaction sequence. Therefore, the chemoselective discrimina-tion between both nucleophiles (amine vs. the generated thiol)is the major focus when employing the nucleophilic amine–thiol–ene conjugation. Potential side reactions such as the aza-Michael addition49 of the amine to the acrylate and disuldeformation are of primary concern.

Prior to the design of a new AB0-monomer, model studiesshould reveal the feasibility of the anticipated one-pot two-stepreaction. In the second stage, aer the large-scale synthesis of areadily available AB0-urethane monomer, containing both anacrylate (A) and a thiolactone unit (B0), several (multi)-func-tionalized PUs will be prepared by the modular use of a varietyof functional amines.

Scheme 2 Model amine–thiol–ene conjugation between n-propylamine 6, g-thiobutyrolactone 7 and n-butyl acrylate 8.

Results and discussionModel and kinetic studies

The feasibility of the proposed amine–thiol–ene conjugationbetween an amine 1, a thiolactone-containing compound 2 and

2450 | Polym. Chem., 2013, 4, 2449–2456

a Michael acceptor 3 entirely relies on the selectivity of theconjugate addition (Scheme 1).

Therefore, the selection of the reaction partners 1 and 3 iscritically important. While maleimides react with both aminesand thiols as Michael donors,49 acrylates are less reactive: atroom temperature and without a catalyst, only secondaryamines readily react with acrylates.50 As a consequence, areaction mixture of a primary amine, a thiolactone and anacrylate in the absence of any catalyst would result in theformation of product 5. The anticipated chemoselectivediscrimination between both heteroatomic nucleophiles(primary amine 1 and the intermediate thiol 4) is based upondifferent reaction rates. The slow aza-Michael addition allowsthe aminolysis of the thiolactone to precede while the subse-quent thiol-Michael addition is known to be relatively fast.51

In order to conrm these hypotheses, a series of modelreactions have been conducted, for which the reaction progresswas monitored by online FT-IR analysis. In a solution (in CHCl3or THF, 0.5 and 1 M respectively) of primary amine, thiol andacrylate, the consumption rate of the thiol and acrylate isidentical (Scheme S1 and Fig. S1†). In a control experiment, onlythe amine and acrylate were mixed at room temperature.Whereas in the previous case the thiol was consumed in lessthan 15 minutes (1 M in THF), only a negligible conversion ofthe acrylate by aza-Michael addition was observed in the sametime frame (Fig. S1†). In a second model reaction, involving athiolactone as latent thiol functionality, the kinetic prole ofthe reaction between n-propylamine 6, g-thiobutyrolactone 7and n-butyl acrylate 8was studied in detail (Scheme 2). It shouldbe stressed that the reaction was performed at room tempera-ture and under air atmosphere.

The 3D online FT-IR waterfall plot illustrates the decreaseand increase of several (C]O)stretch absorption bands as afunction of time (Fig. 1a).

Due to partial overlap of relevant bands in the IR spectrum(1830 to 1490 cm�1, Fig. S2 and S3, Table S1†), a deconvolution

This journal is ª The Royal Society of Chemistry 2013

Fig. 1 Online monitoring of amine–thiol–ene conjugation between n-propylamine 6, g-thiobutyrolactone 7 and n-butyl acrylate 8; (a) 3D FT-IR waterfall plot of(C]O)stretch absorption bands (1830–1490 cm�1) and (b) FT-IR peak intensities as a function of time (kinetic curves and deconvoluted data points).

Paper Polymer Chemistry

process was performed (Table S2, Fig. S5 and S6†). In Fig. 1b,the FT-IR peak intensities, reecting the concentrations of thereactants 7 and 8 and the product 9 as a function of time,are shown. The decrease of the height of the thiolactone(C]O)stretch and the area of the acrylate (CH]CH2)waggingvibrational bands have been used to establish the kinetic prole(Fig. S4†). The formation of the amide (band area at 1540 cm�1,N–Hscissoring and C–Nstretch) is a good indicator for theconsumption of 7. For further conrmation, it is demonstratedthat the area depletion of the deconvoluted thiolactone (C]O, 2sub-bands at 1714 and 1698 cm�1) and acrylate (C]O, at 1728cm�1) bands strongly agrees with the kinetic curves (Fig. 1b).The major conclusion from this model study is that the ami-nolysis is the rate-determining step: the acrylate functions areconsumed as fast as the thiolactone ones. With 1.1 eq. of n-propylamine compared to an equimolar mixture of thiolactone7 and acrylate 8, it takes 9 hours to reach 70% conversion(Fig. S7†). The rate can be increased by adding more amine; forexample with a two-fold excess, the reaction is completed within8 hours (Fig. 1b). An LC-MS analysis of the reaction with 1.1 eq.of n-propylamine shows a clean mixture of starting materialsand product 9. Only a minor fraction of disulde was detected(Fig. S8c†). Disulde formation is more prominent at a higheramine concentration (Fig. S8d†), indicating that the excess ofamine should be limited. As the aminolysis step is rate-deter-mining, a kinetic screening of the ring-opening of

Scheme 3 Rate constants of the aminolysis of g-thiobutyrolactone 7 in the presen


g-thiobutyrolactone 7 in the presence of ten different (func-tional) primary amines was performed. Generally, the ami-nolysis of thiolactones can be described by second orderkinetics.52 Pseudo-rst order conditions were established usinga 50-fold excess of amine in THF. The conversion of 7 as afunction of time has been monitored by GC analysis of peri-odically taken reaction samples (Fig. S9 and S10†). Rateconstants are summarized in Scheme 3.

Stereo-electronic properties of the primary amines are thebasis for the relative rate differences: aliphatic non-functionalamines react faster than amines containing an inductive-with-drawing group. The sterical constraints due to a-branching inJeffamine� M-600 greatly inuence the reaction rate. Theorthogonality of the reaction is proven by the fact that under thesame reaction conditions, i.e. 50-fold excess of the nucleophileand neutral pH, water, alcohols, thiols and anilines are not ableto open the thiolactone ring.

Monomer synthesis

The use of the above studied nucleophilic amine–thiol–eneconjugation in polymer synthesis demands a straightforwardand scalable method for the synthesis of a stable monomer,containing an acrylate (A) and a thiolactone unit (B0). Uponaminolysis, this monomer forms a reactive thiol–acrylate, whichwill be consumed in the same medium by a conjugate addition.

ce of different primary amines with an indication of the relative reaction rates.

Polym. Chem., 2013, 4, 2449–2456 | 2451

Scheme 4 Two approaches for the synthesis of an AB0-monomer, containing onone hand a thiolactone and an acrylate group as reactive entities and on the otherhand a stable urethane linkage.


In order to synthesize such an AB0-monomer, two reactionroutes have been explored (Scheme 4).

In each case, a stable urethane bond connects the reactiveentities. The rst possibility relies on the Sn-catalyzed carba-mate formation between a-cyanato-g-thiolactone 10 53 and anequimolar amount of a hydroxyl-functionalized acrylate.Two acrylates (2-hydroxyethylacrylate 11 and 1,4-cyclo-hexanedimethanol monoacrylate 12) have been converted totheir respective monomers, 13 and 14, with an isolated yield of92%. The inherent instability of 13, as a result of polyacrylateformation, requires radical inhibition, while 14 can be stored asa white powder for months at �20 �C without any inhibitor. Amore scalable route consists of phosgene treatment of thehydroxyl-functionalized acrylate 12 to yield the chloroformate17 and subsequent reaction of the latter with DL-homocysteinethiolactone 15 in the same reaction vessel. This procedureallows for the preparation of a relatively large amount (45 g) ofthe AB0-monomer 14 in a single batch with an overall isolatedyield of 78% (Scheme S3, Fig. S11 and S12†).

Polymerization by amine–thiol–ene conjugation

Although the thiol-Michael addition is generally regarded as areversible reaction and therefore represents an elegant methodfor dynamic covalent chemistry,54–56 thiol–acrylate conjugateaddition has already been employed as the key step for thefabrication of functional polymer materials.51,57–63 As a

Fig. 2 Online monitoring of amine–thiol–ene conjugation (aminolysis and poly-ad(C]O)stretch absorption bands (1830–1360 cm�1) and (b) IR peak intensities as a fu

2452 | Polym. Chem., 2013, 4, 2449–2456

consequence, the polymerization via poly-addition of thiol–acrylates, originating from the aminolysis of AB0-monomers 13and 14, was studied in detail. A rst screening of the reactionconditions (solvent and concentration) was performed in thepresence of 1.1 eq. of n-octylamine, capable of a relatively fastaminolysis reaction (vide supra). The slight excess of aminepotentially catalyzes the Michael addition aer conversion ofthe thiolactone.64,65 Aminolysis of 13 at varying concentrations(0.25, 0.5 and 1 M) in THF resulted in a precipitate of lowmolecular weight (Mn � 2 kDa, determined by SEC). Precipita-tion could be avoided in CHCl3, but only oligomers wereformed. Similar observations were made when changing thesolvent to CH2Cl2 and N,N-dimethylacetamide. Most probably,the thiol–acrylate as a result of the aminolysis of 13 is alsoconsumed by polyacrylate formation, yielding an ill-denedmaterial. Repeating the same conditions, starting from mono-mer 14, pointed out that poly-addition was most prominent inTHF at 0.5 M: linear polymers withMn of 12.0 kDa and Ð of 1.69were isolated by precipitation.

This optimized condition (a 0.5 M solution of 14 in THF atroom temperature) was used for an online FT-IR study of thepolymerization reaction (Table S3, Fig. S14 and S15†). Due to theoverlapping of the urethane, acrylate and thiolactone C]Ovibration bands, the aminolysis of 14 was followed by theincreasing intensity of the amide vibrational band at 1683 cm�1,whereas the conversion of the acrylate double bond was moni-tored by the acrylate scissoring vibration at 1409 cm�1.Deconvolution and curve tting of the obtained spectra in theregion of 1800–1380 cm�1 were performed, such as for themodel reaction (Table S4 and Fig. S16†). Again, a good agree-ment between the measured and deconvoluted band intensitieswas observed (Fig. 2). Although the acrylate is mostly consumedaer 3 h, only a low-molecular weight polymer could be isolatedfrom the reaction mixture at that moment. On the other hand,integration of the acrylate end-group in the 1H-NMR spectrumof the polymer 18 aer 24 h reaction time allowed for thedetermination of the DP (�33) and Mn (�15.5 kDa) (Scheme 5).The optimized conditions were subsequently applied as ageneral protocol for other (functional) amines as shown inTable 1.

Of particular interest is the possibility to introduce doubleand triple bonds and reactive dienes (furan) without

dition) between octylamine and AB0-monomer 14; (a) 3D FT-IR waterfall plot ofnction of time (kinetic curves and deconvoluted data points).


Scheme 5 Aminolysis of AB0-monomer 14 with n-octylamine and the formation of polymer 18 by conjugate addition: 1H-NMR spectra (CDCl3, 500 MHz) of themonomer 14 (top) and the purified polymer 18 (bottom). Signals m** and p** (inset) designate two protons of the acrylate end-group of polymer 18. Spectralassignment of the 1D-1H-NMR of polymer 18 was facilitated by 2D-NMR spectra (Fig. S13†).

Table 1 Obtained molecular weight and dispersity by amine–thiol–ene reactionbetween (combined) primary amines and AB0-monomer 14

Entrya AmineMn

b

(kDa)Mw

b

(kDa) Ðb

Ratioc

(amine I/amine II)

1 n-Octylamine 12.0 20.3 1.69 —2 Allylamine 5.3 8.7 1.63 —3 Propargylamine 1.9 3.1 1.63 —4 Furfurylamine 9.5 15.4 1.62 —5 N,N-Dimethylethylene diamine 3.2 4.9 1.53 —6 3-Morpholinepropylamine 7.6 13.0 1.73 —7 n-Octylamine/

N,N-Dimethylethylene diamine8.8 14.7 1.67 49/51

8 Allylamine/Glycine t-butylester 6.8 11.4 1.67 72/289 Allylamine/Furfurylamine 8.4 13.0 1.54 58/42

a Reaction conditions: entries 1/ 6; monomer 14 in THF (0.5 M) at roomtemperature for 24 h in the presence of 1.1 eq. of amine; entries 7, 8 and9; monomer 14 in THF (0.5 M) at room temperature for 24 h in thepresence of 2 eq. of amine (1 eq. amine I and 1 eq. amine II). b SEC,calibrated with PMMA standards, DMA as the eluent (Fig. S17).c Calculated from the integration of signals, specic for eachindividual amine, in the 1H-NMR spectrum (Fig. S19, S20 and S21).


interference with the polymerization process (entries 2, 3 and 4;Table 1). This renders the polymers accessible for furthermodication, without a protection and deprotection strategybeing necessary. Other functionalities that were tested include atertiary amine (entry 5) and a morpholine moiety (entry 6),enabling the synthesis of metal-complexing polymers.66–68


The presented strategy thus offers an easy-to-perform, one-pot method for the synthesis of functionalized PUs. Mixing thetwo ingredients (monomer 14 and the selected amine) at roomtemperature without any additive or external trigger givesindeed access to a library of such polymers (Table 1).

MALDI-TOF analysis of a narrow-disperse fraction (Fig. S18†)of allyl-functionalized polymer (Table 1, entry 2) conrms thestructural build-up of the PUs and elucidates the nature of theend-groups (Fig. 3).

Two series of signals can be readily assigned: the majordistribution of peaks representing a telechelic material bearingan acrylate and a thiolactone entity as end-groups and a secondminor series attributed to the corresponding thiol–acrylates. Inboth series, signals occur in a repetitive manner, separated by398 Da, i.e. the sum of the molecular weight of allylamine andmonomer 14. The minor series is shied by 57 Da, which isexactly the molecular weight of allylamine. This MALDI-TOFanalysis clearly demonstrates that there were no signicant sidereactions during the polymerization and again conrms thatthe aminolysis is rate-determining.

To extend the potential of this method and to demonstrateits versatility, experiments have been performed utilizing morethan one amine, enabling the random incorporation of multiplefunctionalities. Reaction conditions were similar, except for theuse of 2 eq. of amine (1 eq. of each amine compared to mono-mer 14). The relative amount of the (functional) amines alongthe backbone aer polymerization was calculated via integra-tion of relevant signals in the 1H-NMR spectra (Fig. S19, S20 andS21†) and the values differ from the initial feed ratio. It was

Polym. Chem., 2013, 4, 2449–2456 | 2453

Fig. 3 MALDI-TOF analysis of the allyl-functionalized PU (Table 1, entry 2) including peak assignment.


anticipated that the respective rates of aminolysis would havethe greatest impact on the incorporation ratio. However, entry 8clearly demonstrates that two amines, being equally fast in theaminolysis reaction (Scheme 3), are incorporated in differentamounts. The reactivity difference between the intermediatethiol–acrylates due to sterical factors most likely contributessignicantly to this phenomenon. The results (entries 7, 8 and9) prove that different functionalities can be simultaneouslyincorporated along the PU backbone in a one-pot synthesis.

Fig. 4 Post-polymerization modification in the same medium of the allyl-containingspectra (CDCl3, 300 MHz) after poly-addition (top) and after subsequent thiol–ene mand after thiol–ene modification.

2454 | Polym. Chem., 2013, 4, 2449–2456

TGA-analysis of the obtained polymers (Table 1, entries 1, 2,4 and 9) showed that these materials are thermally stable until250 �C (Fig. S22†).

Post-polymerization modication

Another appealing feature of this method is that, once the poly-additionhasbeen completed, the reactionmixture is essentially asolution of the expected PU with a minor amount of residual

PUs by radical thiol–ene conjugation with 1-octanethiol. (Left) Details of 1H-NMRodification (bottom). (Right) Corresponding SEC traces of reaction samples before



amine. Post-polymerization modication of the introducedfunctional group (via the primary amine) is thus possible in thesame reaction medium. Two metal-free modication reactionswere examined in this context: the radical thiol–ene reactionbetween 1-octanethiol and an alkene-containing polymer and theDiels–Alder reaction between N-methylmaleimide and a furan-containing polymer. Both polymers were synthesized by treat-ment of monomer 14 with allylamine (Table 1, entry 2), andallylamine and furfurylamine (Table 1, entry 9), respectively. Thedisappearance of the distinct signals in the 1H-NMR spectra andtheapparent shiof the SEC traces indeedconrm the successfuloutcome of both modication reactions (Fig. 4 and Fig. S23†).

Conclusions

In conclusion, a one-pot, additive- and isocyanate-free proce-dure for the synthesis of functionalized PUs has been developedbased on the nucleophilic amine–thiol–ene conjugation. Initialmodel studies, monitored via online IR, demonstrated that theaminolysis of a thiolactone in the presence of an equal amountof acrylate is a clean and atom-efficient two-step, one-potconjugation reaction. This important observation encouragedus to explore this concept for the synthesis of functionalizedPUs. Aer the large-scale synthesis of AB0-type monomers,containing both an acrylate and a thiolactone moiety, several(functional) amines were employed to open the thiolactonegroup in the AB0-monomer. The resulting intermediate thiol–acrylate reacts in situ via Michael addition. This highly conve-nient procedure enabled the preparation of various (multi-)functionalized PUs. SEC-, NMR- and MALDI-TOF-analysisconrmed the structure of the PUs. The reaction does notrequire any additive or external trigger and proceeds underambient conditions. As the obtained polymers remainedsoluble in the reaction mixture, the introduced functionalgroups (e.g. double bond or furan) served as functional handlesfor further tailoring through efficient post-polymerizationmodication in the same pot. Due to all these remarkablefeatures, the nucleophilic amine–thiol–ene conjugation basedon thiolactones is considered to be a powerful and elegantaccelerated protocol for the synthesis and modication offunctionalized materials. Therefore, its use is given full atten-tion by us and research towards functionalized cross-linkedmaterials based on the same concept is in progress.

Acknowledgements

Andreia Guimaraes is acknowledged for the MALDI-TOF anal-ysis. All authors are thankful to Ghent University for nancialsupport. F. G. thanks the Research Foundation-Flanders (FWO)for the funding of her PhD fellowship. F. D. thanks the Institutefor the Promotion of Innovation through Science and Tech-nology in Flanders, Belgium (IWT) for the funding of his PhDfellowship. F. D. P. acknowledges the Belgian Program onInteruniversity Attraction Poles initiated by the Belgian State,the Prime Minister's office (P7/05) and the European ScienceFoundation – Precision Polymer Materials (P2M) program fornancial support.


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