Two different poly(L-lactides) (PLLAb and PLLAa) were blended with poly(ecaprolactone) (PCL) and an elastic poly(e-caprolactone/L-lactide) P(CL/LLA) copolymer to modify the mechanical properties of PLLA. Blends of both PLLAs with 20 wt.-Yo of PCL were prepared. PLLAa was blended with 20 wt.-% of P(CL/LLA) copolymer, and blends of PLLAb and P(CL/LLA) copolymer were made with copolymer contents of 5, 10, 20 and 30 wt.-'To. The tensile properties and impact and shear strengths were determined as a measure of the mechanical properties. The hydrolytic behavior of the blends was investigated, and the changes in shear strength as a function of hydrolysis were followed. The structure of the hydrolyzed samples was studied by means of scanning electron microscopy (SEM). The properties of PLLA changed considerably when blended with PCL or P(CL/LLA) copolymer. An increasing amount of copolymer in PLLAb decreased tensile modulus and shear strength, but improved the strain and impact strength. In hydrolysis, blends containing PLLAa degraded slower than blends of PLLAb because of the higher initial molar mass and purity of PLLAa. The molar masses of PLLAb blends decreased dramatically, and less than 10% of the initial molar masses and shear strengths were left after 12 weeks in vitro. The morphology of the blends affected the degradation. The blends containing P(CL/LLA) copolymer had a porous structure which facilitated water absorption into the blend.

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SYNOPSISCopolymers of c-CL/L-LA and c-CLIDL-LA were allowed to age in a buffer solution of pH 7 at 23 and 37°C. The effects of time and temperature on the rate of hydrolysis were examined by various techniques including weighing (water absorption and weight loss), SEC (molecular weight and polydispersity), and DSC (thermal properties). For comparison, the hydrolytic behavior of PLLA, PDLLA, and commercial PCL homopolymers was investigated by the same methods. SEC measurements showed that molecular weights of the copolymers and PLA homopolymers started to decrease during the first week of hydrolysis, but significant mass losses occurred only much later. As expected, there was no change in either molecular weight or mass of PCL during the hydrolysis study. The kinetic results for copolymers and homopolymers were calculated to study the degradation mechanism. During hydrolysis, the crystallinity of the initially semicrystalline copolymers increased and some crystallinity appeared in the initially amorphous L-LA-containing copolymers.

SYNOPSISIn polymer blends, the crystallization of the dispersed semicrystalline component depends on the type and distribution of the nucleating heterogeneities and on the level of the dispersion. Either fractionated or coincident crystallization may result. In this study, the effect of compatibilizers on the crystallization of polyamide 6/isotactic polypropylene ( P P ) blends was investigated. The morphology was controlled with 10 w t % of four different commercial compatibilizers-PPgMAH, EBAgFA, SEBSgMAH, and E-EA-GMA-each leading to specific morphology and crystallization behavior. The compatibilized blends show more complex crystallization compared with the corresponding binary blends. In the compatibilized blends, the dispersed PA6 seems to crystallize coincidently with PP, probably due to its small particle size. The crystallization of PP takes place a t temperatures above the bulk value at all compositions in blends compatibilized with PPgMAH and blends without the compatibilizer. By contrast, in blends compatibilized with EBAgFA, SEBSgMAH, and E-EA-GMA, the crystallization takes place either at PP bulk temperature or over the temperature range of 76-87"C a t the cooling rate of 10°C/min. The amount of the shift cannot be explained solely by the size of the PP dispersion. 0 1993

SYNOPSISCopolymers of c-caprolactone and L-lactide (c-CL/L-LA) and c-caprolactone and DL-lactide (c-CL/DL-LA) were synthesized with compositions 80/20,60/40, and 40/60 (wt % in feed). The polymerization temperature was 140°C and Sn(I1)octoate was used as a catalyst. The effect of the comonomer ratio on the thermal and mechanical properties of the copolymers was investigated by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectrometry, and tensile testing. The copolymers differed widely in their physical characteristics, ranging from weak elastomers to tougher thermoplastics according to the ratio of c-CL and LA in the copolymerization. Poly (L-lactide) (PLLA), poly(D1-lactide) (PDLLA), and poly(e-caprolactone) (PCL) homopolymers were studied as references. The tensile modulus and tensile strength were much higher for PLLA, PDLLA, and PCL homopolymers than for the copolymers. The maximum strain was very low for PLLA and PDLLA, whereas the copolymers and PCL exhibited large elongation. 0 1996 John Wiley & Sons, Inc. I NTRO DUCT10 NIn the family of polyesters, PCL occupies a unique position: It is at the same time biodegradable and miscible with a variety of polymers and it crystallizes very readily. A lack of toxicity and great permeability have already found wide use for PCL in medical applications, in which environment it has a useful lifespan approaching 1 yr. PLA has been widely used in medical applications due to the biocompatibility, good mechanical properties, and relatively fast biodegradability. PLA is found in two forms: crystalline PLLA and amorphous PDLLA. '-3 Much current research on biomaterials is focused on copolymers of different types. Copolymer systems exhibit a broad range of properties depending on the type and proportions of their constituent monomers. The diverse possibilities challenge the researcher to optimize properties and produce biomaterials tailormade for specific applications. With their unique