Effect Of Topolygy Architecture On The Crystallization And Degradation Of Polylactide Systems

Polylactides(PLAs)have attracted more and more attention because of their plant origins,biocompatibility,good biodegradability and mechanical properties.It is a promising substitution of petroleum-based polymer.However,the poor heat resistance and inherent brittleness significantly limited its practical applications.The formation of stereocomplex(SC)between the two enantiomer PLA,poly(L-lactide)(PLLA)and poly(D-lactide)(PDLA),can not only significantly increase the crystallization rate of PLA-based materials by acting as a heterogeneous nucleation agent,but also greatly improve the heat resistant of PLA-based materials due to the higher melting temperature.The relevant parameters that affecting the formation of SC have been reported,including molecular architecture and molecular weight of the constituents,mixing ratio,optical purities,and so on.Branched polymers,such as star-shaped polymers,comb-like polymers and hyperbranched polymers,have attracted more and more attention in recent years because their particular molecular architectures can tailor the physical properties effectively.In this work,the effect of topology architecture,molecular weight and blend ratio on the crystallization behavior,spherulite morphology and alkaline degradation of PLA and their blends were investigated.This results provide us a new method for improving the propreties of PLA-based materials.The work mainly inclues the following parts.A serial of linear,star-shaped,comb-like and hyperbranched PDLA with a wide range of molecular weights were synthesized by ring-opening polymerization of D-lactide with polyols and PEO-co-PGL as initiators.The crystallition behavior,spherulite morphology and degradation behavior of star-shaped PDLA have been investigated by differential scanning calorimetry(DSC),wide-angle X-ray diffraction(WAXD),polarized optical microscopy(POM)and gravimetric analysis in detail.The influences of branched architecture and molecular weight on the crystallization and degradation behavior were futher discussed.The blend films of branched PDLA/linear PLLA were prepared by solution casting.The crystallization of blends,especially the effect of architecture on the crystallization of SC and PLA were studies by changing the architecture and composition of PDLA.Interestingly,a special spherulite morphology "interpenetrating spherulite" were found in this blends.The formation of interpenetrating spherulite were investigated in detail.