Synthesis of Star-shaped 8 arms Poly(ethylene glycol)-Poly(L-lactide) Block Copolymer and Physicochemical Properties of Its Solution Cast Film as Soft Biomaterial

Biodegradable star-shaped 8 arms PEG-b-PLLA block copolymer was synthesized to create a novel implantable soft material. The differences in physicochemical properties between star-shaped 8 arms PEG10K-b-PLLA35K film and linear 2 arms PEG10K-b-PLLA33K film having same compositions of PEG and PLLA units was investigated to reveal the architecture effects on their physicochemical properties. Thermal analysis of these copolymer films revealed that the crystallinity of PLLA in the 8 arms PEG10K-b-PLLA35K films (1.8%) was drastically low compared with that in the 2 arms PEG10K-b-PLLA33K film (37.5%). Additionally, TEM observation of the copolymer films revealed that the larger PLLA domains (greater than 200 nm) with miscellaneous structure were formed in the 2 arms PEG10K-b-PLLA33K film while the smaller PLLA domains (80 nm) with lamellar structure were formed in the 8 arms PEG10K-b-PLLA35K film. Consequently, the 8 arms PEG10K-b-PLLA35K film showed higher swelling ability, lower tensile strength and higher elongation at break than the 2 arms PEG10K-b-PLLA33K film. Moreover, the 8 arms PEG35K-b-PLLA37K film showed higher elongation at break than the 8 arms PEG10K-b-PLLA35K film because of the fine PLLA domains with highly ordered structure. The 8 arms PEG35K-b-PLLA37K film which having the high swelling ability and desirable mechanical properties such as softness as well as tenacity was available as a novel implantable soft material.