Page 40 - Biodegradable Polyesters

18 1 Biodegradable Polyesters: Synthesis, Properties, Applications

styrene), poly(bisphenol-A), polyethylene, polypropylene and natural rubber etc.
Due to the low glass transition temperature, PCL is soft and has high flexibility.
Since its low melting point (Table 1.5), PCL is readily for processing and moulding
[57,97].

Applications Homopolymers of ε-caprolactone and its copolymers with dilactide
or ε-decalactone were prepared for biodegradable controlled drug delivery
systems [108]. Release rates from PCL and related biodegradable polyesters were
studied by Pitt et al. [109]. They investigated several steroids from films and cap-
sules of homopolymers and copolymers of ε-caprolactone, DL-lactic acid and gly-
colicacidweremeasured in vitro and in vivo for up to 500 days. Relatively constant
release rates from capsules were observed only under certain conditions. Release
from PCL and poly(ε-caprolactone-DL-lactic acid) was diffusion controlled.
Release from poly(DL-lactic acid-glycolic acid) was associated with polymer
degradation. Release from poly(DL-lactic acid) was very slow when diffusion
controlled. Owing to the bioerosion and permeability [110], PCL and poly(DL-
lactic acid) as drug carriers were applied in the long-term delivery (1 year) of
levonorgestrel, a contraceptive agent, and the short-term delivery (1–2 months)
of naltrexone, a narcotic antagonist.

1.4
Concluding Remarks

In this short chapter, two giant polymer scientists Staudinger and Carothers
and their contributions to the origin and further development of polymer
science as well as some historical records on the synthesis of polyamides and
polyesters were briefly overviewed. Three well-known biodegradable polyesters,
namely, PLA, PGA, and poly(caprolactone) were selected to described their
synthesis, structures, properties, and applications. Owing to the similarity of the
biodegradable polyesters in synthesis, properties, and applications, this chapter
aims to give readers a general outline about biodegradable polyesters. A few
biodegradable polyesters listed in Table 1.1 are not described in the similar
detail in this chapter. Biodegradable polyesters have intensively been researched
in the last two decades because of their biodegradability and superb physical
properties. Recently, nanomaterials, nanotechnology, and the opportunities for
wider medical applications have resulted in much more attention being directed
to this class of polyesters, as can be concluded from the examples described in
other chapters of this book.

Acknowledgment

The Tianshan Scholar Professorships from Xinjiang University is appreciated for
research and teaching funds. Also for financial support from 9M Ltd New Zealand
while author work and stay in Auckland, New Zealand.