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.

Poly(D,L-lactide) with a molar mass of 10 5g

The ring-opening polymerization of ∈-caprolactone (∈-CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly (∈-caprolactone) (PCL) by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight-average molecular weight (Mw) of PCL reached 44,800 g/mol, with a polydispersity index [weight-average molecular weight/number-average molecular weight (Mw/Mn)] of 1.6, when a mixture of ∈-CL and benzoic acid (25/1 molar ratio) was irradiated at 680W for 240min, whereas PCL with Mw 12,100 and Mw/Mn 4.2 was obtained from the same mixture by a conventional heating method at 210℃ for 240min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in Mw of PCL. However, the degradation was hindered by benzoic acid at low concentrations.

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.

The micro construction of poly(e-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) blend films fabricated by solution casting under microwave irradiation was investigated by selective enzymatic degradation and scanning electron microscopy (SEM). The results were totally different from the blends obtained by conventional methods. The blend was more homogeneous and the PCL continuous phase more compact as no spherulites and tiny zone separation were observed from the film surface and no PCL network was observed inside the film, and the degradation of a PCL plank by Pseudomonas lipase was significantly retarded. The distributed PLLA micro spheres were enlarged and amorphous. The thermal behavior of the blend by microwave heating revealed that PCL and PLLA underwent a melting process, which induced the variations of the PCL phase and PLLA spheres.