Chain-growth polymerization or addition polymerization Step-growth polymerization or condensation polymerization https://www slideshare net/ NikolaiPriezjev
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[PDF] Polymerization - Wright State University
Chain-growth polymerization or addition polymerization Step-growth polymerization or condensation polymerization https://www slideshare net/ NikolaiPriezjev
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Textbook: Plastics: Materials and Processing (Third
Edition), by A. Brent Young (Pearson, NJ, 2006).
Structure and Properties of Engineering Polymers
Lecture: Polymerization Reactions and Techniques
Nikolai V. Priezjev
Polymerization Reactions and Techniques
Chain-growth polymerizationor addition polymerization Step-growth polymerization or condensation polymerizationStep-Growth Polymerization
difunctional each has two reactive functional groups -MW polymer is formed consumed => long reaction timesStep-Growth Polymerization (cont.)
Schematic:
Step-Growth Polymerization (cont.)
Example:
Step-Growth Polymerization (cont.)
Degree of Polymerization:
Xn= average number of monomers per chain
Representative Step-Growth Reactions
Predicting Molar Mass in Step-Growth PolymerizationXn= average number of
monomers per chainStep-Growth Reactions: MW Distribution
MW=Molecular Weight
MWD=Molecular Weight Distribution
Step-Growth Reactions: Molecular Weight Control
1Step-Growth Reactions: Molecular Weight Control
Step-Growth Reactions: Molecular Weight Control
Producing high-MW step-growth polymers requires
High conversions (p > 0.98)
Stoichiometric ratios of functional groups
High-purity monomers
No side reactions
Chain-Growth Polymerization
initiator, a substance that starts the reaction number of initiation sites (free radicals, anions, cations, transition metal complexes) growing chainsChain-Growth Polymerization (cont.)
Schematic:
Chain-Growth Polymerization (cont.)
Example:
Chain-Growth Polymerization (cont.)
Degree of Polymerization:
Representative Chain-Growth Reactions
Chain-Growth Polymerization (cont.)
Chain-Growth Polymerization (cont.)
Chain-Growth Reactions: Molecular Weight Control
Molecular Weight Control (cont.)
Styrene Polymerization: Chain Transfer to Solvent
Adapted from R.A. Gregg & F.R. Mayo,
1947 Disc. Faraday Soc., 2, 328-337
Chain-Growth vs Step-Growth Reactions
Step-GrowthChain-Growth
All molecules present (monomer, oligomer, polymer) can react with any other molecule.During propagation, only monomers react to the
³MŃPLYH VLPH´ MP POH HQG RI POH JURRLQJ ŃOMLQBMonomers exist throughout the reaction, but large
quantities of monomers are consumed early in the reaction.Monomers exist throughout the reaction; its
concentration decreases steadily with time.There is no termination step and the end groups
of the oligomers and polymers are reactive throughout the polymerization process.There are two distinctive mechanisms during
polymerization; these are initiation and propagation.In most cases there is also a termination step.
The reaction proceeds rapidly at the beginning but the molecular weight increases only slowly and highMW's are only attained at the end of the process
by long oligomers reacting with each-other. The reaction speed depends on the concentration of initiator (and co-initiator) and high-molecular weight polymers form throughout the duration of the reaction. Long reaction times are needed for the synthesis of long (high molecular weight) polymers.Long reaction times have high degrees of
conversion but do not affect (much) the (average) molecular weight.Molecular species of any length (oligomers) exist
throughout the reaction, with the length distribution broadening and shifting to higher MW with increasing reaction time.The mixture contains primarily monomers and
polymers, and only small amounts of growing polymer chains;Chain-Growth vs Step-Growth Reactions
Copolymerization
ABCopolymerization: Composition Control
AA BB k 11 k 12k 21 k 22 AB ABCopolymerization: Reactant Ratios
$GMSPHG IURP *B 2GLMQ ³3ULQŃLSOHV RI 3RO\PHUL]MPLRQ´ 4PO (G 2004 SS 4E1-492. AA BB k 11 k 12k 21 k 22 monomer reactivity ratios (rn):BBBBBBBA
Copolymerization: Composition Control
AA BB k 11 k 12k 21 k 22 monomer reactivity ratios (rn):BABABABA
Copolymerization: Composition Control (cont.)
AA BB k 11 k 12k 21 k 22 monomer reactivity ratios (rn):Copolymerization: Composition Control (cont.)
AA BB k 11 k 12k 21 k 22 monomer reactivity ratios (rn): A AAB B BCopolymerization: Composition Control (cont.)
$ā Ą $ $āR11= k11 [ A·] [ A] $ā Ą % %āR12= k12 [ A·] [ B] %ā Ą % %āR22= k22 [ B·] [ B] %ā Ą $ $āR21= k21 [ B·] [ A]Blending two monomers results in four simultaneously occuring propagation reactions with different rate
equations::AA BB k 11 k 12k 21 k 22k21 [B·] [A] = k12 [A·] [B]Symmetry::The rates of monomer
consumption are given: : d[A]/dt = k11 [A·] [A] + k21 [B·] [A] d[B]/dt = k22 [B·] [B] + k12 [A·] [B]r1= k11 / k12 r2= k22 / k21Monomer
reactivity ratios: Divide the first equation by the second equation, we obtain the Mayo-Lewis equation:: d[A]/d[B] = (|A|/|B|)· (r1[A]/[B] + 1) / ([A]/[B] + r2)The mole fraction of unreacted monomerf1(in the feed/reactor) and the mole fraction in an increment of
copolymerF1formed at a given stage in the polymerization process: f1= [A] / ([A] + [B]) = 1 -f2 F1= d[A]/d([A]+[B]) = (r1f12+ f1f2) / (r1f12+ 2f1f2+ r2f22) = 1 ±F2