Synthesis and characterization of paramylon propionate-graft- poly(lactic acid) and paramylon propionate-graft-poly(ε-caprolactone)

Paramylon propionate-graft-poly(L-lactic acid) (PaPr-g-PLA) and paramylon propionate-graft-poly(epsilon-caprolactone) (PaPr-g-PCL) were synthesized by grafting L-lactide and epsilon-caprolactone to the residual hydroxy group of paramylon propionate (degree of substitution (DS) of 1.6 or 2.0). The chemical structures of the graft copolymers were characterized by GPC, NMR, and FT-IR measurements. The molecular weight of the copolymers was 2.52-3.11 x 105 and the degree of polymerization of grafted side-chains was determined to be around 10. Meltpressed films were formed from all copolymers but solvent-cast films were brittle and defected. The terminal hydroxy groups of the grafted PLA or PCL side-chains were subsequently acetylated. The acetylated graft copolymers showed good solubility in chloroform and formed self-standing uniform solvent-casted films as well as melt-pressed films. The decomposition temperature of the acetylated graft copolymers was 350 degrees C, which was 50 degrees C higher than that of nonacetylated copolymers, indicating that terminal acetylation dramatically improved the thermal stability of the copolymers. The mechanical properties of the films of the acetylated copolymers were investigated and discussed.

Automated summary

PaPr-g-PLA and PaPr-g-PCL were synthesized by grafting on paramylon propionate, and subsequent acetylation of the grafted side-chains significantly improved the thermal stability of the copolymers. The mechanical properties of the acetylated copolymer films were investigated and discussed.