Synthesis, Characterization And Crystal Properties Of Stereoblock Polylacitc Acid

A series of stereoblock polylactic acid(sb-PLA) were synthesized via a novel method ring opening polymerization-solid state polycondensation(ROP-SSP). Molecular Weight, molecular weight distribution, average block length, thermal properties of products were characterized.Poly(L-lactic acid) and poly(D-lactic acid) with medium molecular weight were obtained via ring opening polymerization which using L-lactic acid as initiator, stannous octoate as catalyst.A series of sb-PLA were obtained via ROP-SSP attained a molecular weight (Mw) as high as 18.7×104, and yield is up to 89.8%. The results showed that solid sate polycondensation was effected by the content of PLLA obviously. Catalyst concentration did not produce remarkable influence on solid sate polycondensation reaction rate in the range of 0.05～0.3 wt%.Stereocomplex crystals in sb-PLA which PLLA contents were 90 wt%,80 wt% and 50 wt%, the time required to complete the crystallization increased, effection enhanced by homochiral crystals, crystallization process was formed by complete independence, some overlap and complete overlap. The results of Ozawa analysis showed that the crystal model of sc crystals in sb PLA with different PLLA contents were different. He and sc crystallization process can fuse under given conditions. Crystallization process after fusing is similar to the PLLA's.