Organic Chemistry

If the initiator is a Lewis acid or a proton-donating acid, epoxides are polymerized by

a cationic mechanism. Polymerization reactions that involve ring-opening reactions, such

as the polymerization of propylene oxide, are called ring-opening polymerizations.

PROBLEM 9

Explain why when propylene oxide undergoes anionic polymerization, nucleophilic attack

occurs at the less substituted carbon of the epoxide, but when it undergoes cationic po-

lymerization, nucleophilic attack occurs at the more substituted carbon.

PROBLEM 10

Describe the polymerization of 2,2-dimethyloxirane

a. by an anionic mechanism

b. by a cationic mechanism

PROBLEM 11

Which monomer and which type initiator would you use to synthesize each of the follow-

ing polymers?

a. c.

b. d.

PROBLEM 12

Draw a short segment of the polymer formed from cationic polymerization of 3,3-

dimethyloxacyclobutane.

3,3-dimethyloxacyclobutane

CH 3

CH 3

O

COCH 3 COCH 3

OO

CH 2 CH CH 2 CH

N N

CH 2 CH CH 2 CH

¬CH 2 CH 2 OCH 2 CH 2 O¬

CH 3

CH 3

CH 3

CH 3

CH 3

CH 3

CH 2 CCH 2 CCH 2 C

+ H+

O

CH 3

H

O

CH 3

+

H

+O

+ HOCH 2 CH

CH 3

O

O

CH 3

CH 3

+

HOCH 2 CHOCH 2 CH

CH 3 CH 3

O

CH 3

+

HOCH 2 CH

CH 3

O +

CH 3

O

CH 3

+

CH 3

084 CHAPTER 28 Synthetic Polymers