Poly dissolution rate ratio

In a related study, Pitt and others (1979a) reported release rates of various steroids from monolithic films and capsules made from homopolymeric PCL, poly (D,L-lactide), and copolymers of caprolactone and D,L-lactide (in both 60/40 and 90/10 caprolactone/D,Lrlactide acid ratios), and copolymers of glycolic acid with D,L-lactide. The release rates of the steroids from the caprolactone-co-lactide polymers were similar to the homopolymeric PCL. However, the release rates from the glycolide-co-lactide polymers were much slower than those observed with PCL. Further data analysis revealed that the obseiv ed release kinetics depended upon the steroid dissolution rate (in the polymer) and the polymer cry stallinity. WTiile it is outside the scope of the current discussion, a good background reference on PCL thermodynamics and crystallinity is given by Lebedev (1979) and Chynoweth Stachurscki (1986). 

The structure of itaconic acid bears some resemblance to methacryllc acid. While It Is know that methacryllc acid and methacrylic anhydride do enhance sensitivity when copolymerized with methyl methacrylate, some of the Increase In speed may be due to porosity (7,12). The gas formation may cause a higher rate of dissolution then can be attributed to chain scission alone. Pittman and co-workers have reported G(s) values for poly(methacryllc anhydride) of 0.4 (10) and 1.8 and 2.9 (14) based on gamma radiation experiments. Hiroaka (12) measured G(s) by gas evolution on Irradiation of films with electron beams and established values In the ration 1 2 6 for the methyl methacrylate. A terpolymer with the three components In the molar ratio of 70 15 15 (same three monomers) was selected by Moreau et al (13) on the basis of complete lithographic evaluation. The speed Is 4 to lOx that of PMMA. As aforementioned, an Increase In G(s) may be only partially responsible. 

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