The polymerization of e-caprolactone, (e-CL) using porcine pancreatic lipase (PPL) as the catalyst was studied. Polymerization reactions (4 days, 65 °C) of e-CL at ~10% (w/v) concentrations in dioxane, toluene, and heptane using butanol as an initiating species (monomer/butanol ratio = 14.7) gave poly(e-caprolactone) (PCL) with Mn values (by GPC) of 313, 753, and 1600, respectively. Monomer conversion to PCL for these polymerizations was 33, 55, and 100%, respectively. Mn measurements of PCL products by NMR end group analyses were slightly lower (by a factor of -0.9) than the values obtained by GPC. Polymerizations conducted in heptane at 37, 45, 55, and 65 °C showed the highest extent of monomer conversion at 65 °C. Therefore, subsequent studies were conducted at 65 °C in heptane. For a polymerization carried out with a 15/1 monomer/butanol ratio and ~0.29 mmol of water, ~70 and ~100% of the monomer had been converted to PCL by reaction times of 24 and 96 h, respectively. Polymer molecular weight increased slowly with conversion, suggesting that this is a chain polymerization with rapid initiation and slow propagation. Increases in the e-CL/butanol ratio from 15/1 up to where no butanol was added showed only a modest increase in product molecular weight from 1600 to 2700. This was explained by the fact that the water present in polymerizations was active in chain initiation. Variation in the monomer/butanol ratio at constant water concentration resulted in PCL chains with 0-0.65 mol fraction of butyl ester and 0.33-0.86 mol fraction of carboxylic acid chain end groups (by NMR analyses). The presence of water concentrations in polymerization reactions above that which is strongly enzyme bound is believed to be an important factor which limited the formation of PCL chains of significantly higher molecular weight.

Polylactide (PLA) stereocopolymers with (l) repeat unit contents of 75%, 80%, 82%, 85%, 90%, 91%, 92%, 94%, and 95% were prepared from mixtures of (l)-/(d)-lactide and (l)-/meso-lactide. Compression molding of these products gave amorphous films which, for (l) contents ≥90%, were also annealed above T g to crystallize. Analyses by differential scanning calorimetry and wide angle X-ray scattering gave information on the crystalline order of PLA films. For identical (l) contents, stereocopolymers of (l)-/(d)-lactide had higher crystallinities than those from (l)-/meso-lactide. PLA films were incubated with proteinase K (from Tritirachium album), and the enzyme-catalyzed film weight loss rates were measured. Film crystallinity, chain stereochemical composition, and repeat unit sequence distribution were analyzed as independent variables affecting film enzymatic hydrolysis. Amorphous films from (l)/(d)-lactide copolymerizations with (l) compositions ranging from 80% to 95% exhibited film weight loss rates that were almost identical. Also, amorphous PLA films prepared from (l)-/meso-lactide copolymers for (l) contents of 80−95% showed a similar invariability in weight loss rates. It was concluded that proteinase K has a high degree of tolerance for (d) repeat units. Amorphous PLA films from (l)-lactide/meso-lactide copolymerizations had weight loss rates which were about 43% slower than amorphous PLA films from (l)-/(d)-lactide copolymerizations. These results were analyzed considering differences in chain stereosequence distributions. Proteinase K showed an extraordinarily high sensitivity to film crystalline order. For example, the decrease in the film weight loss rate due to crystalline order for a 95% (l) (l)-/(d)-lactide stereocopolymer was 93%.