Organic Chemistry

092 CHAPTER 28 Synthetic Polymers

Epoxy Resins

Epoxy resinsare the strongest adhesives known. They can adhere to almost any kind

of surface and are resistant to solvents and to extremes of temperature. When an epoxy

cement is used, a low-molecular-weight prepolymer(the most common is a polymer

of bisphenol A and epichlorohydrin) is mixed with a hardener—a compound that will

react with the prepolymer to form a cross-linked polymer.

PROBLEM 18

a. Propose a mechanism for the formation of the prepolymer formed by bisphenol A and

epichlorohydrin.

b. Propose a mechanism for the reaction of the prepolymer with the hardener.

Tutorial:

Repeating units in

step-growth polymers

O

CO

O

C +

CH 3

CH 3

Cl Cl HO C

bisphenol A

Lexan

a polycarbonate

phosgene

OH

CH 3

CH 3 CH 3

C O

O

CO

CH 3

C O

CH 3

O

C

CH 3

C O

−HCl

n

+

n

n

n

O

HO C OH

CH 3

CH 2

CH 2

CHCH 2 Cl

CH 3

OH

O

O O

C OCH 2 CHCH 2

CH 3

CH 3

CH 2

CH 2

NH

CH 2

CH 2

CH 2

CH 2

NH

CH 2

CH 2

O C OCH 2

CH 3

CH 3

bisphenol A epichlorohydrin

prepolymer

an epoxy resin

NHCH 2 CHCH 2

OH OH

O C OCH 2 CHCH 2

OH

CH 3

CH 3

O C OCH 2 CHCH 2 NH

CH 3

CH 3

NHCH 2 CHCH 2

OH OH

O C OCH 2 CHCH 2

OH

CH 3

CH 3

O C OCH 2 CHCH 2 NH

CH 3

CH 3

H 2 NCH 2 CH 2 NHCH 2 CH 2 NH 2

hardener

−HCl