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SynopsisThe degradation of poly(ecapro1actone) in rabbits, rats, and water was studied by measurement of changes in intrinsic viscosity, molecular weight, crystallinity, Young's modulus, and weight. Degradation proceeds by nonenzymatic random hydrolytic cleavage of ester linkages. The process is autocatalytic, and the kinetic relationship M,/Mt = exp(-kt) is observed until the M, has decreased to approximately 5000. Significant weight loss is not observed until this point but, once initiated, the rate of weight loss depends markedly on the particle size. Chain scission is associated with an increase in crystallinity, which partly determines the rate of degradation.

Poly(epsilon-caprolactone) [PEC], a biodegradable aliphatic polyester, undergoes a two-stage degradation process: The first lengthy phase involves nonenzymatic hydrolytic cleavage of ester groups, the second phase beginning when the polymer is more highly crystalline, and of low molecular weight. The cellular events of the second phase were examined by implanting gelatin capsules containing 25 mg of low molecular weight (Mn 3000) PEC powders, 106 to 500 micron, in rats. PEC fragments ultimately were degraded in phagosomes of macrophages and giant cells, the process requiring less than 13 days for completion at some sites. PEC was also identified within fibroblasts. These studies support the intracellular degradation of PEC as the principal pathway of degradation once the molecular weight of the aged polymer is reduced to 3000 or less.

The effect of initiation of ϵ‐caprolactone polymerization with mono‐ and polyfunctional alcohols was investigated. The resulting linear and starshaped polymers were characterized by measurement of the molecular weight and molecular weight distribution. The polymerizations were characterized by (1) rapid initiation, (2) invariance of the number of growing chains corresponding to the amount of initiator, and (3) a dominant role played by ester interchange reactions.

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The maximum steady state flux, diffusion coefficients, and solubilities of five contraceptive steroids in homopolymers and copolymers of epsilon-caprolactone and DL-lactic acid were determined. The permeabilities of polymers of epsilon-caprolactone were comparable to silicone rubber and, by inference, are suitable for the construction of drug delivery devices. Poly(DL-lactic acid) was 10(4) times less permeable, although its permeability was significantly enhanced by additives.