Study On Design, Synthesis And Crosslinking Of Active Group-terminated Poly(lactic Acid)

Poly(lactic acid)(PLA) was widely investigated concerned because of its good biocompatibility and excellent comprehensive performance. But its application was limited because of its high cost. Direct polymerization to prepare poly lactic acid can reduce the cost. Cross linking modification can improve the performance of poly lactic acid. Therefore, this paper studied the direct melt polycondensation of lactic acid. The end groups of PLAs were modified with pentaerythritol and acrylic acid. Modified poly lactic acid can be crosslinked under high temperature or UV light. It can be used in paint, printing ink etc.In this paper, the different molecular weights of hydroxyl-terminated PLA(OHPLA) were prepared by controlling the reaction time, reaction temperature and the dosage of pentaerythritol. The end double bond of PLA(DPLA) was synthesized by solution polymerization with OHPLA and acrylic acid. The structure and properties of polymer were investigated via the infrered spectra(FTIR), nuclear magnetic resonance(NMR), gel permeation chromatography(GPC), differential scanning calorimeter(DSC) and rotational rheometer. The results showed that the molecular weight of OHPLA and DPLA increased with increasing the molecular weight of the PLA prepolymer. But end capping rate of DPLA would continue to decline. For example end capping rate of DPLA(760) and DPLA(1184) were 73.95% and 55.87%. The thermal properties and rheological properties of OHPLA and DPLA were affected, because of their branched structure. Glass transition temperature, the melting temperature, the complex viscosity and storage can modulus of DPLA and OHPLA were lower than that of pure PLA, but increased the crystallization temperature of polymers. Because DPLA no hydrogen bonding interaction, the glass transition temperature and crystallization temperature and melting temperature of DPLA is lower than that of OHPLA, but polymer crystallinity will increase.Gel content of cured film the dynamic rheological behavior of the heat curing process was studied. The best dosage of DCP was 0.5wt%. Compared with all the poly lactic acid curing membrane(FPLA), the higher the molecular weight of DPLA, the lower the degree of cross-linking, but the higher the degree of hardness. The highest hardness was 3H. The molecular weight of FPLA(760) was much larger than that of the curing front, which showed that the crosslinking process had a certain effect on the chain extension. UV curing and thermal curing were studied. It was found that the gel content of the cured films could be improved by 60%, when the maximum interaction of UV curing and heat curing. The thermal stability and degradation properties of PLA can be improved by the cross linking structure.