The thermal effect of microwave energy on ε-caprolactone (CL) monomer and polymerization reaction mixture of CL with stannous octoate [Sn(Oct)2] intimately depended on the power level of microwaves and the mass scale of materials. When 10g of CL was heated by microwaves at a power of 680W, its temperature increased rapidly from 20 to 355℃ within 5 min after which it was self-regulated to keep constant at 360℃. Heat generation was observed when a polymerization reaction mixture of 10g CL with 0.1% (mol/mol) Sn (Oct) 2 was irradiated at 680W. The exothermic peak was recorded at 2-5min and its temperature was over 300℃, with the maximum at 343℃. During this period the ring-opening polymerization of CL occurred quickly, resulting in poly(ε-caprolactone) with weight-average molecular weight (Mw) of 123,000g/mol and yield of 95%.

Ring-opening polymerization of ∈-caprolactone was carried out smoothly and effectively with constant microwave powers of 170, 340, 510, and 680 W, respectively, with a microwave oven at a frequency of 2.45GHz. The temperature of the polymerization ranged from 80 to 210℃. Poly (∈-caprolactone) (PCL) with a weightaverage molar mass (Mw) of 124,000g/mol and yield of 90% was obtained at 680W for 30min using 0.1%(mol/mol) stannous octanoate as a catalyst. When the polymerization was catalyzed by 1% (w/w) zinc powder, the Mw of PCL was 92,300g/mol after the reaction mixture was irradiated at 680W for 270min.

Poly (∈-caprolactone) was blended with various polylactide-based polymers and processed to films by the solution casting method. Blends of 25/75, 50/50, 75/25, 90/10, and 95/5 (w/w) poly(∈-caprolactone)/poly-(L-lactide), a 95/5 (w/w) blend of poly(∈-caprolactone) with a poly (D-lactide), a 50/50 (w/w) poly (L-lactide)-poly (D-lactide) mixture, and a poly (L-lactide-co-∈-caprolactone) copolymer were considered comparatively. The various phase-separated films were allowed to degrade in the presence of Pseudomonas lipase, biodegradation being monitored by proton nuclear magnetic resonance, size exclusion chromatography, differential scanning calorimetry, X-ray diffraction, and environmental scanning electron microscopy. The formation of separated phases during solvent evaporation and their morphologies are discussed. The introduction of poly(L-lactide) dramatically decreased the degradation rate of poly(∈-caprolactone)/poly (Llactide) blends. The higher the percentage of poly(L-lactide), the slower the degradation, while the presence of cracks and increasing the lipase concentration acted in favor of the enzymatic degradation. Long-term enzymatic degradation of the various 95/5 blends was investigated over 480 h. The poly(∈-caprolactone) phase was enzymatically degraded by the lipase regardless of the blend type, the degradation rate depending on the nature of the co-components.

Solution cast films were prepared from poly (L-lactide) (PLLA) and poly (є-caprolactone) (PCL) as well as from three blends, namely B75, B50, and B25 with PLLA/PCL proportions of 75/25, 50/50, and 25/75, respectively. The enzymatic degradation of square samples (10×10×0.2mm) cut from the films was investigated at 37℃ in a pH (8.6 Tris buffer containing proteinase K or in a pH) 7.0 hosphate buffer containing Pseudomonas lipase. It was confirmed that proteinase K can degrade amorphous domains of PLLA, but cannot degrade crystalline PLLA or PCL. In contrast, Pseudomonas lipase can degrade both amorphous and crystalline PCL but cannot degrade PLLA. The two faces of solution cast films showed different morphologies due to the solvent evaporation process. The lower face appeared more crystalline than the upper face because of the plasticizing effect of solvent entrapped inside which allowed crystallization to proceed. Therefore, the lower face was more resistant to enzymatic attack by proteinase K in the cases of PLLA and the blends. The two polymers in the blends exhibited well separated crystalline domains. PCL seemed to constitute the continuous phase of the blends with formation of large size spherulites when the PCL content was over 50%. The selective degradation of PCL or PLLA components revealed the inner morphology of the blends where microspherelike or islandlike patterns were observed.