Polyhydroxyalkanoates: Structure, Properties and Sources - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 34

absence of photosensitizers or photoinitiators. Cross-linking of these
PHA MCL is expected to yield useful biomaterials, such as biodegradable
rubbers. In addition, since cross-linked PHAs are less susceptible to PHA
depolymerase than natural PHAs, these polymers can be useful as photo-
sensitive materials for microlithography that are also environmentally
friendly. 87
Graft copolymerization is a technique used to transform the properties of
natural polymers. Block or graft copolymerization is the insertion of differ-
ent polymer segments into an existing polymer backbone or at the side chain
of an existing polymer, respectively.
Due to their biocompatibility, PHAs proved to be good candidates for
biomedical applications including biomedical devices, biodegradable drug
carriers or tissue engineering. However, the intrinsic hydrophobic properties
of PHAs restrict their applications as cell growth supports. So, a graft co-
polymer of PHA and a marine exopolysaccharide (EPS), HE800, were syn-
thesized in order to improve the compatibility between hydrophobic PHBHV
and hydrophilic HE800. In the grafting method, the carboxylic functions of
PHBHV were activated with acyl chloride functions, allowing coupling to the
hydroxyl groups of HE800 (Figure 2.5). 88
Dextran-graft-PHBHV copolymers were prepared using click chemistry.
Well defined and functional dextran backbones containing azide groups had
been prepared by tosylation and a subsequent nucleophilic displacement

d n 2 r 4 n g | 8

.

Figure 2.5 Preparation of the copolymer HE800-g-PHBHV.