Chemistry 367L/392N

Macromolecular ChemistryMacromolecular Chemistry

Lecture 12 Lecture 12

10

5

0.5

0.1

Chemistry 367L/392N

Chain Transfer in Free Radical Chain Transfer in Free Radical PolymerizationPolymerization

� A termination and re-initiation reaction

� For Chain Transfer Y• must be able to re-initiate reaction

Chemistry 367L/392N

Chain Transfer Agents (Chain Transfer Agents (CTAsCTAs))

� Thiols are efficient examples

Chemistry 367L/392N

DPDPnn = degree of = degree of polymerisationpolymerisationWITH transfer agentWITH transfer agent

DPDPoo = degree of = degree of polymerisationpolymerisationWITHOUT transfer agentWITHOUT transfer agent

Measurement of Chain Transfer ConstantsMeasurement of Chain Transfer Constants

+=monomer

gentTransfer aCs

DPDPn 0

11

CCSS = Chain Transfer = Chain Transfer ““ constantconstant”” or or ““ coefficientcoefficient””

The Mayo Equation:The Mayo Equation:

Chemistry 367L/392N

1/DP0

Cs

1/D

P

[S]/[M]

Generic Mayo plot

Chemistry 367L/392N

BButylatedutylated HHydroxyydroxyTTolueneoluene� BHT radical will not initiate new chains� So…BHT is an inhibitor, not a CTA

Chemistry 367L/392N

Interesting Interesting ““InhibitorsInhibitors”…”…..

N

O

N

O

PhenylPhenyl--aa--tt--butylnitronebutylnitrone

PBNPBN

TEMPOTEMPO

Chemistry 367L/392N

Chemistry 367L/392N

Chemistry 367L/392N

Free Radical CopolymerizationFree Radical Copolymerization

What happens when we initiate a polymerization in a mixture of monmers???

Random Copolymers Random Copolymers MM11MM22MM11MM11MM22MM22MM22MM11MM11MM22

Block Copolymers Block Copolymers MM11MM11MM11MM11MM22MM22MM22MM22MM22MM22

Alternating Copolymers Alternating Copolymers MM11MM22MM11MM22MM11MM22MM11MM22MM11MM22

MM11 +M+M22 →→ --[([(MM11))xx--(M(M22))yy]]nn--AIBNAIBN

Chemistry 367L/392N

Free Radical CopolymerizationFree Radical Copolymerization

~

~

~

~

~

~

~

~

Assume chain end concentrations are constant at “st eady state”

Free Radical Co-polymerization

Chemistry 367L/392N

a

b

pages 467-469 !!

Do the algebra -see

is a/b

Chemistry 367L/392N

If r1 > 1 means M

If r 1 >1 this means that ~M 1• adds M 1 more readily than M 2. If r 1 is zero then M 1 does not undergo homopolymerization!!

This important relationship can be expressed in This important relationship can be expressed in terms of mole fractions rather than concentrationsterms of mole fractions rather than concentrations

Chemistry 367L/392N

This gives the Instantaneous mole fraction of M 1 in the copolymer

Supplementary Homework!

Chemistry 367L/392N

How does one determine the reactivity rations??

•Fineman Method

•Kelen-Tudos Method

Chemistry 367L/392N

Chemistry 367L/392N

Chemistry 367L/392N

Chemistry 367L/392N

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

A = styreneB = butadienera = 0.75, rb = 1.3

F

a (p

olym

er c

ompo

sitio

n)

fa (monomer composition)

Ideal copolymer

Chemistry 367L/392N

0.0 0.2 0.4 0.6 0.8 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

A = styreneB = maleic anhydridera = 0.05, rb = 0.0

F

a (p

olym

er c

ompo

sitio

n)

fa (monomer composition)

Alternating Copolymer

Chemistry 367L/392N

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

A = vinyl acetateB = styrenera = 0.01, rb = 50

F

a (c

ompo

sitio

n of

pol

ymer

)

fa (Composition of monomer)

Rich in one monomer

Chemistry 367L/392N

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

A = AcrylonitrileB = Butadienera = 0.046, rb = 0.36

F

a (p

olym

er c

ompo

sitio

n)

fa (monomer composition)

Quite typical copolymerisation