Poly( lactide-co-glycolide):
Lactide and glycolide can be copolymerized to obtain a range of copolymers with various mechanical and biodegradation properties.
Copolymers of glycolide with both L-lactide and DL-lactide have been developed for both device and drug delivery applications. It has been found that there is not a linear relationship between the copolymer composition and the mechanical and degradation properties of the materials. For example, a copolymer of 50% glycolide and 50% DL-lactide degrades faster than both homopolymers . The degradation rate strongly depends on the crystallinity of the copolymers. Copolymers of 25% - 7 0% L-lactide with glycolide are amorphous due to the disruption of the regularity of the polymer chain by the other monomer. Therefore, this copolymer showed a much higher degradation rates than each individual homopolymers. Relationship between the copolymer composition and the mechanical and degradation properties of the materials is non-linear. For example, the degradation time of these copolymers were found to increase in the following order:
PLA100(6. 7months) < PGA100 (5months) < PLA75GA25(2. 5 weeks)
The half-life of the copolymers decreased from 5 months for PGA to 1 week for PLA50PGA50 and rapidly increased to 6. 7 months for PLA100.
4- Poly( propylene fumarate):
Poly( propylene fumarate) (PPF) is an alternative copolymer of propylene glycol and fumaric acid. Briefly, monomer di-(2-hydroxypropyl) fumarate is first synthesized by the reaction of fumaryl chloride with propylene glycol in methylene chloride. Then PPF is synthesized by a transesterification reaction between the monomer di-( 2-hydroxypropyl) fumarate molecules at high temperature .