Stereocomplexation, Thermal and Mechanical Properties of Conetworks Composed of Star-Shaped l-Lactide, d-Lactide and ε-Caprolactone Oligomers Utilizing Sugar Alcohols as Core Molecules.

It is important to develop tailor-made biodegradable/biocompatible polymer networks usable for biomaterials whose thermal and mechanical properties are easily controlled by changing the composition. We synthesized sugar-alcohol-based polymer networks (SPN-scLAO/3CLO, = 4, 5 or 6) by the crosslinking reactions of erythritol, xylitol or sorbitol-based -armed star-shaped l-lactide and d-lactide oligomers (HSLLAO and HSDLAO), a glycerol-based 3-armed star-shaped ε-caprolactone oligomer (H3SCLO) and hexamethylene diisocyanate (HDI) at the weight ratios of HSLLAO/HSDLAO = 1/1 and (HSLLAO + HSDLAO)/H3CLO = 100/0, 75/25, 50/50, 25/75 or 0/100). The influence of the arm number on the crystallization behavior, thermal and mechanical properties of SPN-scLAO/3CLOs were systematically investigated by comparing with those of sugar-alcohol-based homochiral polymer network (SPN-LLAO, = 4, 5 or 6) prepared by the reaction of HSLLAO and HDI. Stereocomplex (sc) crystallites are dominantly formed for SPN-scLAO/3CLOs 100/0⁻25/75, whereas SPN-LLAOs were amorphous. The higher order of melting temperature of sc-crystals for SPN-scLAO/3CLOs 100/0⁻25/75 was = 5 > = 6 > = 4. The sc-crystallinities of SPN-4scLAO/3CLOs 100/0⁻50/50 were significantly lower than those of SPN-scLAO/3CLOs 100/0⁻50/50 ( = 5 and 6). The larger order of the sc-spherulite size at crystallization temperature of 110 °C was = 5 > = 6 > = 4 for SPN-scLAO/3CLO 100/0. The size and number of sc-spherulites decreased with increasing crystallization temperature over the range of 110⁻140 °C and with increasing CLO fraction. Among all the networks, SPN-5scLAO/3CLOs 75/25 and 50/50 exhibited the highest and second highest tensile toughnesses (21.4 and 20.3 MJ·m), respectively.