Building Materials, Third Edition

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It may be defined as the reaction between functional monomer molecules leading to the
formation of a polymer with the elimination of some small molecules such as water, HCl, etc.
The most common is Nylon formed from hexamethylene diamine and adipic acid
(Fig. 16.6 (a)). Phenol formaldehyde resin (Bakelite) shown in Fig. 16.6 (b) is another example.

 





 



Hexamethylene diamine

226 24

2226 24

24 26

Apidic acid

24 26

24 26 2

HN — (CH ) — NH H HO OC — (CH ) — COH

HO + NH — (CH ) — NHCO(CH ) COOH

HOOC — (CH ) — CO OH + H NH — (CH ) — NH —

— CO(CH ) CO OH H NH — (CH ) — HN__H

— OC (CH ) CONH(CH ) NHCO(CH )

bd

426

(^2426) n
CONH(CH ) NH —
—OC(CH ) CONH(CH ) NH —
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Also known as degradation, depolymerisation may occur when used for extended period of
time with steam as in the case of urea-formaldehyde plastic or due to thermal variations dis-
rupting the intramolecular bonds within the molecules of plastic formed at high temperatures.
Depolymerisation is used to its advantage for cracking petroleum into highly combustible
products, light molecules charring of carbohydrates (toast) and of cellulose (charcoal).

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Rubbers also known as elastomers, are high polymers having the unique property of undergoing
large deformations under load and returning to their original shape and dimension on its

Apidic acid

Hexamethylene diamine