52 R. Tran et al.
In addition to moderate elastomeric properties, the utility of homopolymeric
PTMC as a temporary implant material was hampered by its slow degrada-
tion. Over a 30 week period, the PTMC samples suffered a mass loss of only
9%. However, subcutaneously implanted PTMC samples were rapidly degraded
in vivo, and the implanted samples beyond a 3 week period could not be detected
This was attributed to hydrolytic resistance and enzymatic
cleavage of the carbonate bonds. Co-polymerization with other polymers, primar-
ily degradable polyesters like poly(D,L lactide) (PDLLA) and poly(ε–caprolactone)
(PCL), have been employed to improve the degradability and the mechanical
properties of polycarbonates.
The potential of these co-polymers as scaffolds for heart tissue engineering and
synthetic nerve guides for nerve regeneration have also been evaluated.
also found that high molecular weight PTMC was very ﬂexible and tough due to
the excellent ultimate stress and strain characteristics. These mechanical properties
were attributed to strain induced crystallization of the polymeric network upon
application of high deforming stresses. This phenomenon has also been studied
220.127.116.11 Poly(D,L Lactide–co– 1,3–trimethylene carbonate)
Both high molecular weight and low molecular weight co-polymers of amorphous
poly(D,L–lactide) and PTMC have been studied by different researchers.
In all cases, the co-polymer synthesis was carried out through a bulk ring open
polymerization of the different monomer ratios with stannous octoate as the cata-
lyst. High molecular weight poly(DLLA–co–TMC) co-polymers were obtained by
varying the reaction conditions to reduce the degree of transesteriﬁcation. The low
molecular weight co-polymers were synthesized using 1,3–trimethylene carbonate
with a T
value of −26
As expected, the co-polymerization was able to produce co-polymers, which
had properties that were intermediate to those of the PDLLA and PTMC ho-
mopolymers. The T
temperatures of the co-polymers ranged from −16 − 56
depending on the percentage of lactide units in the chain. Co-polymers with a
greater lactide percentage had higher T
temperatures, and were generally stiffer.
The mechanical properties of the different polymers ranged from weak elastomers
to stiff and rigid materials. TMC–DLLA co-polymers with a higher TMC content
exhibited high elongation at break (600–800%), but were weak (tensile strength ≤
2 MPa) and underwent irreversible deformations upon extension. A higher DLLA
content made the polymers strong (tensile strength 28–33 MPa), but brittle with
low elongation at break (6–7%).
Intermediate co-polymers containing similar molar percentages of both TMC
andDLLAexhibitedgoodelastomericbehavior. For example, a co-polymer
containing equal molar percentages of DLLA and TMC (50%:50% molar ratio)
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