Page 337 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

314 BIOMATERIALS

Exotherm

Endotherm Crystallization

Melting

T g T m
FIGURE 13.5 Schematic representation of a DTA curve for crystalline polymer
quenched from melt prior to analysis.

fairly self-explanatory with an alternating pattern of repeat units. Block copolymers consist of
long-chain segments (blocks) of single-repeat units attached to each other. Block polymers most
commonly employ two different repeat units and contain two or three blocks. Block copolymers
are named poly(A-b-B) or simply AB for polymers with two blocks (diblock polymer). A triblock
copolymer would be named poly(A-b-B-b-A) or simply ABA. Graft copolymers consist of a back-
bone with side chains of a different repeat unit and are named poly(A-g-B). (See Fig. 13.6.)
Block and random copolymers are the most common copolymers. An example of a random
copolymer is poly(lactide-co-glycolide), also known as poly(lactic-co-glycolic acid), depending on
the synthesis route. Note that the structure of poly(lactide-co-glycolide) does not specify the type

BBBBBBBB BBBBB
AABBABBAAAABABBAABBBABA
Random

ABABABABABABABABABABABA AAAAAAAAAAAAAAAAAAAAAAAAAA
BBBBB BBBBBBBB
Alternating

AAAAAAABBBBBBBAAAAAAAAA
Block copolymer Graft copolymer
FIGURE 13.6 Schematic diagram showing classes of copolymer.