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Step Reaction Polymerization
P O L Y M E RAN INTRODUCTION
C H E M I S T R Y
Malcolm P. Stevens
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Distinguishing features of Chain- and Step Polymerizartion Mechanisms
Distinguishing features of Chain- and Step Polymerizartion Mechanisms
Step Polymerizations Chain Polymerizations
Introduction to Polymer Chemistry
Growth occurs only by addition of monomer to active chain
end.
Monomer is present throughout, but its concentration
decreases. Polymer begins to form immediately.
Chain growth is usually very rapid (second to microseconds).
MW and yield depend on mechanism details.
Only monomer and polymer are present during reaction.
Usually (but not always) polymer repeat unit has the sameatoms as had the monomer
Any two molecular species can react.
Monomer disappears early.
Polymer MW rises throughout.
Growth of chains is usually slow (minutes to days). Long reaction times increase MW, but yield of
polymer hardly changes.
All molecular species are present throughout.
Usually (but not always) polymer repeat unit has
fewer atoms than had the monomer.
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Condensation vs. Addition
Condensation vs. Addition
Introduction to Polymer Chemistry
Carothers originally classified polymers based on a comparison of the atoms in the monomer to the atoms in the polymer
repeat unit.
Condensation polymers had fewer atoms in the repeat unit (i.e., some small molecule was emitted during
polymerization).
Addition polymers had the same atoms as their monomers.
Step polymerization by addition of alcohols to diisocyanates to form polyurethanes:
Chain polymerization (ring opening of heterocycle) with loss of CO2 to form polypeptide.
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A. Step-Reaction Polymerization - KineticsA. Step-Reaction Polymerization - Kinetics
Introduction to Polymer Chemistry
Step-Reaction Polymerization
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A. Step-Reaction Polymerization - KineticsA. Step-Reaction Polymerization - Kinetics
Introduction to Polymer Chemistry
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A. Kinetics of Step-Growth PolymerizationA. Kinetics of Step-Growth Polymerization
Introduction to Polymer Chemistry
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A. Kinetics of Step-Growth PolymerizationA. Kinetics of Step-Growth Polymerization
Introduction to Polymer Chemistry
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A. Kinetics of Step-Growth PolymerizationA. Kinetics of Step-Growth Polymerization
Introduction to Polymer Chemistry
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B. Stoichiometric ImbalanceB. Stoichiometric Imbalance
Introduction to Polymer Chemistry
Three ways to limit M. W. in step polymerization
These are polyethers that are processed to an oligomer stage and are subsequently
converted to network polymer by appropriate reactions of terminal epoxyide groups.
With polyimides for fiber applications, molecular weight must often be limited
because too high a viscosity is detrimental to extrusion of filaments through the
fine holes of a spinneret.
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B. Stoichiometric ImbalanceB. Stoichiometric Imbalance
Introduction to Polymer Chemistry
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B. Stoichiometric ImbalanceB. Stoichiometric Imbalance
Introduction to Polymer Chemistry
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B. Stoichiometric ImbalanceB. Stoichiometric Imbalance
Introduction to Polymer Chemistry
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C. Molecular Weight DistributionC. Molecular Weight Distribution
Introduction to Polymer Chemistry
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14Introduction to Polymer Chemistry
C. Molecular Weight DistributionC. Molecular Weight Distribution
Nx
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15Introduction to Polymer Chemistry
C. Molecular Weight DistributionC. Molecular Weight Distribution
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16Introduction to Polymer Chemistry
C. Molecular Weight DistributionC. Molecular Weight Distribution
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17Introduction to Polymer Chemistry
C. Molecular Weight DistributionC. Molecular Weight Distribution
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D. Network Step-Polymerization : Theory of GelationD. Network Step-Polymerization : Theory of Gelation
Introduction to Polymer Chemistry
If monomers containing a functionality greater than two are used in step
polymerization, chain branching results.
If the reaction is carried to a high enough conversion,gelation occurs.
The onset of gelation, orgel point, is accompanied by a sudden increase in viscosity
such that the polymer undergoes an almost instantaneous change from a liquid to a
gel.
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
Branching point
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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D. Network Step PolymerizationD. Network Step Polymerization
Introduction to Polymer Chemistry
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E. Step-Reaction CopolymerizationE. Step-Reaction Copolymerization
Introduction to Polymer Chemistry
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E. Step-Reaction CopolymerizationE. Step-Reaction Copolymerization
Introduction to Polymer Chemistry
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F. Step Polymerization TechniquesF. Step Polymerization Techniques
Introduction to Polymer Chemistry
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30Introduction to Polymer Chemistry
F. Step Polymerization TechniquesF. Step Polymerization Techniques
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31Introduction to Polymer Chemistry
F. Step Polymerization TechniquesF. Step Polymerization Techniques
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32Introduction to Polymer Chemistry
F. Step Polymerization TechniquesF. Step Polymerization Techniques
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33Introduction to Polymer Chemistry
F. Step Polymerization TechniquesF. Step Polymerization Techniques
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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G. Dendritic PolymersG. Dendritic Polymers
Introduction to Polymer Chemistry
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Commerically Important Polymers Prepared by Step-Reaction PolymerizationCommerically Important Polymers Prepared by Step-Reaction Polymerization
Introduction to Polymer Chemistry
Carbonyl addition-elimination
Polyesters, polycarbonates, polyamides,
polyimides...
Aromatic addition-elimination
Polysulfones, polysulfides,
polyetherketones
Carbonyl addition-condensation
Phenol-formaldehyde and related polymersPolymeric heterocycles
Addition to multiple bonds or epoxides
Polyurethanes
Epoxy polymers
Miscellaneous
Oxidative aromatic addition (polyphenylene
oxide)
Acyclic diene metathesis (ADMET)
Aryl-aryl coupling
Reductive coupling (polysilanes)
Hydrolysis coupling (silicones)
Diels-Alder cycloadditionBiradical coupling (polyxylylene)
Friedel-Crafts chemistry
SN2 reactions
and a host of others...
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Carbonyl Addition-Elimination Step Polymerization : I. PolyesterCarbonyl Addition-Elimination Step Polymerization : I. Polyester
Introduction to Polymer Chemistry
Mechanism :
I. PolyesterSynthesis :
Structure-property relationships:
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43Introduction to Polymer Chemistry
Other commercially important polyester:I. PolyesterCarbonyl Addition-Elimination Step Polymerization : I. PolyesterCarbonyl Addition-Elimination Step Polymerization : I. PolyesterPBT
PEN
PET
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44Introduction to Polymer Chemistry
II. PolycarbonatesCarbonyl Addition-Elimination Step PolymerizationCarbonyl Addition-Elimination Step Polymerization
III. Polyamides
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45Introduction to Polymer Chemistry
IV. Polyimide Carbonyl Addition-Elimination Step PolymerizationCarbonyl Addition-Elimination Step Polymerization
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Aromatic Addition-Elimination PolymerizationAromatic Addition-Elimination Polymerization
Introduction to Polymer Chemistry
Mechanism : This reaction is analogous to carbonyl addition-elimination, in that itis a two step process where the negative charge is accomodated by an
electron withdrawing group. To emphasize the simularity, this example
uses a ketone:
Krishnamurthy, S. J. Chem. Ed. 1982, 59, 543.
Monomers :Bisphenols are most often used as the nucleophillic components. The chemistry begins when
a base like NaOH or K2CO3 deprotonatea the bisphenol, as in this example for Bisphenol A:
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Aromatic Addition-Elimination PolymerizationAromatic Addition-Elimination Polymerization
Introduction to Polymer Chemistry
I. Poly(etheretherketone), PEEK
The most common form of PEEK is the one shown, derived from Bisphenol A. This polymer is a
remarkable material, highly crystalline, thermally stable, resistant to many chemicals, very tough. It
can be melt-processed at very high temperatures (>300 C), and is useful for special applications like
pipes in oil refineries and chemical plants, and parts for aerospace, where high price is not a
limitation.
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Aromatic Addition-Elimination PolymerizationAromatic Addition-Elimination Polymerization
Introduction to Polymer Chemistry
II. Polysulfone, PSF
Like polycarbonate, many other polysulfones could be synthesized, but the particular one shown here is
by far the most common commercially, so that the general term "polysulfone" usually refers to this
particular one. Worse, it is seldom called "poly(etherethersulfone)," despite its close structural similarity
to PEEK
Unlike PEEK, poly(etherethersulfone) is completely amorphous, probably a result of the relatively
large size of the sulfonyl group, and the kink in the polymer backbone caused by the narrow C-S-C
bond angle (close to 100). Therefore, it can be processed at lower temperature than PEEK, but the
material is not as resistant to heat and chemicals.
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Carbonyl Addition-Condensation PolymerizationCarbonyl Addition-Condensation Polymerization
Introduction to Polymer Chemistry
III. Phenol-Formaldehyde Polymers IV. Polymeric Heterocycles
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Carbonyl Addition-Condensation PolymerizationCarbonyl Addition-Condensation Polymerization
Introduction to Polymer Chemistry
The phenol-formaldehyde polymers are the oldest commercial synthetic polymers, first introduced around 100
years ago. Their inventor, Leo Bakeland, had no idea what was happening in his reaction kettles, but he was able to
work out conditions to produce a tough, light, rigid, chemically resistant solid from two inexpensive ingredients.
He soon became a rich man, in the same class as the famous industrialists of the time like Alfred Nobel, Henry Ford,
Andrew Carnegie, George Eastman, etc.
The actual chemistry is complicated, and still not competely understood. The polymers are usually thermosetting (i.e.,
crosslinked), and their insolubility limits the analytical techniques that can be brought to bear. The main reaction is
the production of methylene bridges between aromatic rings, as shown below. Many side reactions also occur, and
some of these give phenol-formaldehyde polymer its dark color.
Of course, these crosslinked polymers cannot be melted or dissolved, so their synthesis must be conducted in molds
for the actual product. In practice, the polymerization is usually carried out to somewhere below the gel point in aseparate reactor, and then the "pre-polymer" is transferred to the mold, where the reaction is completed.
Urea or melamine can be substituted for phenol. Methylene bridges can also be formed between the nitrogen atoms,
giving rise to chemical relatives of the phenol-formaldehyde polymers. The urea and melamine based materials have
much less color, and so are useful for decorative applications such as dinner plates and countertop materials
(FormicaTM).
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Addition to Multiple Bonds or EpoxidesAddition to Multiple Bonds or Epoxides
Introduction to Polymer Chemistry
Mechanism :
The urethane linkage (often called carbamate) is usually made by adding an OH across the
C=N of an isocyanate.
The reaction is catalyzed by bases such as tertiary amines or by certain tin salts.
I. Polyurethanes
Many different polyurethanes have been synthesized, giving rise to materials with widely varying
properties. For example, rubbery polyurethanes are used for Spandex fiber and for seat cushions in
furniture and cars, while hard polyurethanes are used for wheels on roller skates, for bowling balls, and for
paints and varnishes. The hydrogen bonds between the NH and CO groups provide toughness to the
polymers.
Polyurethanes are synthesized by the reaction ofdiols with diisocyanates:
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Addition to Multiple Bonds or EpoxidesAddition to Multiple Bonds or Epoxides
Introduction to Polymer Chemistry
II. Epoxy PolymersThese polymers are best known as two component thermosetting adhesives, although linear polymers
can be prepared. The term "epoxy" polymers is something of a misnomer, because the epoxy groups are in
the monomer, not in the polymer. To form the actual polymer, one reacts a multifunctional epoxide with amultifunctional nucleophile. Epoxy monomers based on Bisphenol A are by far the most common
substrates, although others can be used. The nucleophiles are most often amines or phenoxides. The
number of reactive functional groups on the components governs whether the polymer is linear or
crosslinked.
Epoxy Adhesive ChemistryThe resulting network will not dissolve in any solvents,
and resists all but the strongest chemical reagents.
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Addition to Multiple Bonds or EpoxidesAddition to Multiple Bonds or Epoxides
Introduction to Polymer Chemistry
Other Epoxy Polymer
The plurality ofOH groups provides hydrogen
bonding, useful for adhesion to polar surfaces
like glass, wood, etc. Epoxy polymers are often
used to form composite structures filled withglass or carbon fiber.
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Thanks for your attention