Biomedical Engineering Reference
In-Depth Information
2
The effect of molecular structure on the
properties of biomedical polymers
G. Pertici, industrie Biomediche insubri SA, Switzerland
Abstract:
A review is presented on the effects of the molecular structure of
polymers on their properties. The influence of such variables as molecular
weight, macromolecular conformation and crystallisation, amorphous states
and the glass transition temperature are discussed. Biphasic systems are
explored and the properties of thermoplastic and thermosetting polymers are
investigated.
Key words:
amorphous state, crystallinity, average molecular weight,
polydispersity, glass-transition temperature.
2.1 Introduction: the molecular structure of
polymers
Natural and synthetic polymers are comprised of macromolecules. these
are formed from many concatenated structural units and limited terminal
moieties (Fig. 2.1) (cowie, 1991). the structural units are usually carbon
atoms linked to hydrogen, oxygen or nitrogen, but often it is possible to
find other chemical elements such as: Si, Cl, B, P, F and S. This involves
considerable modification of properties (Figs 2.2-2.4) [Mark and SpringerLink
(Online Service), 2007].
2.1
Polymer representation (A = terminal moiety, B = structural unit).
· · · —CH
2
—CH
2
—CH
2
—CH
2
—CH
2
—CH
2
— · · ·
2.2
Polyethylene (PE).
· · · —CH
2
—CH
2
—O—CH
2
—CH
2
— · · ·
2.3
Polyethylene glycol (PEG) or polyethylene oxide (PEO) or
polyoxyethylene (POE).
· · ·
CH
2
CH
· · ·
Cl
2.4
Polyvinyl chloride (PVC).
30
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