The effect of molecular structure on the properties of biomedical polymers - Durability and Reliability of Medical Polymers - page 30

to tail' polymerisation. Sometimes it is possible to find 'head to head' and
'tail to tail' (Figs 2.7 and 2.8). these structures are isomers for the position
of R -groups (side chains). in the next example a structural isomerism is
shown (Figs 2.9 and 2.10). these examples include steric isomerism; in
polybutadiene 1-4 the cis - trans configuration is applicable (Okada and
Furuya, 2002).

2.1.2 Copolymers
this class of polymers (heteropolymers) is obtained by the simultaneously
polymerisation of two or more monomers to achieve useful properties. Well
known commercial copolymers for biomedical applications are produced by
Boehringer Ingelheim GmbH, Germany (i.e. Resomer LC 703 S) and Purac,
Netherlands (i.e. Purasorb PDLG). A possible configuration for a random
polymerisation of two monomers (unit A and unit B) is shown in Fig. 2.11.
the fundamental parameters for the characterisation become composition
and disposition. Composition is not too difficult to determine because it
relates to the percentage of a unit inside the structure.
Block copolymers are an interesting class where the disposition is as
shown in Fig. 2.12. By synthesis it is also possible to obtain graft copolymers;

CH 2 CH CH 2 CH CH 2 CH CH 2

R R R

2.7 Head to tail.

CH 2 CH CH CH 2 CH 2 CH CH 2

R R R

￿ ￿ ￿ ￿ ￿ ￿

2.8 Head to head, tail to tail.

— CH 2 — CH = CH — CH 2 — CH = CH — CH 2 —

2.9 1, 4-Polybutadiene.

CH 2 CH CH 2 CH CH 2 CH CH 2

CH CH 2 CH CH 2 CH CH 2

2.10 1, 2-Polybutadiene.

2.11 Random copolymer.