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Chemistry 367L/392N

Macromolecular ChemistryMacromolecular Chemistry

Lecture 17 Lecture 17

+++Cationic Polymerization+++

Mitsuo Sawamoto Joseph Kennedy

Chemistry 367L/392N

Assignment 9Assignment 9

Read Odian 374-388 and 403-407

Chemistry 367L/392N

Terminate Anionic PolymerizationTerminate Anionic Polymerization

Dr Ellison’s notes will be posted on the web site

Reactivity of monomers

Group A:

Group B:

Group C:

Group D:CH2 CH CH CH2

CH 2 C(CN) 2 CH 2 C

CN

COOC 2H 5 CH 2 CH

NO 2

> >

CH 2 CHCN CH 2 C

CN

CH 3 CH 2 CH C

O

CH 3> >

CH 2 CH

CO OCH 3

CH 2 C CH 3

COO CH 3

>

CH2 CH CH2 C

CH3

Anionic Polymerization in the Lab

Break seal vs Schlenk ApproachBreak seal is sure but complexSchlenk line is simpler but …..

Break Seal Glassware

In the laboratory

For making stars

● Attack of the initiator or living end at the carbonyl group of the monomer may lead to termination

● Activation of the protons in the αααα position to the carbonyl group may lead to transfer

Potential problems with polar side groups

*

C

OO

CH3

H

Chain transfer in acrylates

OMeO

CO2Me

CO2Me

O

CO2Me

CO2Me

Backbiting

C O

CO2Me

CO2MeOMe

O

CO2Me

CO2Me

Ketene formation

Possible Termination Reactions

● Attack of Monomer Carbonyl Group

● Intermolecular Attack of Carbonyl Group

Possible Termination Reactions

● Termination by backbiting

The efficiency of backbiting depends on the size of the Counteranion, the polarity of the solvent, and on monomer structure

Li+ > Na+ > K+ > Cs+ >

THP > THF > DME

Acrylates > methacrylates > methyl tert-butyl

Additives for Anionic polymerization

Alkoxy Alkoxides

Additives in Anionic Polymerization of Meth(acrylates)

● very inexpensive

● very fast polymerization even in non polar solvents

● no increase of termination reactions

● Well-controlled polymerization of primary acrylates

● Controlled block copolymerization of MMA with primary acrylates ( 2-ethyl acrylates, n-butyl-acrylates)

For a series of para-substituted styrenes,

OCH3 > CH3 > H > Cl

Vinyl ethers

CH2 CHORR'+

R'CH2 CH OR+

R'CH2 CH OR+

XCH2 CH

X

Protic acidswith bulky, non-nucleophilic anionse.g. H2SO4, HClO4, FSO3H, etc, etc

Lewis Acids are “co-catalysts”e.g SnCl4, AlCl3, BF3 when reacted with a nucleophile like water

BF3 OH2+ H+3BF OH

-

ORHAC

+

OR

HA

+

are co-catalysts

…proton source

….cation source

“onium salts”

….much like anionic polymerization

Polar solvents favor free ions

R+

R R

+

+

XCH2 CH2 C+

CH3

CH3

monomer CH2 CH2 C

CH3

CH3

CH2 CH CH

CH3

CH3X+

XCH2 CH CH

CH3

CH3

H:shift+