High Relative Molecular Mass Of Polylactic Acid Synthesis Technology To Further Optimize Research

In this dissertation,the synthetic processes of polylactic acid(PLA) by ring-opening polymerization of lactide were studied.High purity and yield lactide was prepared by optimal technological conditions of the preparation of lactide.The preparation processes of PLA by ring-opening polymerization of lactide made in lab was studied.For the study of preparing the lactide,the optimal technological conditions of how to prepare high purity and yield lactide were researched.By adding A to reduce the heat transmittance and the amount of carbonization,on the basis of this,taking the yield of product as an assessing standard,the optimal experiment was carried out for obtaining the best technological conditions.Results showed that under the optimal conditions such as using 2mL Sn(Oct)₂ as catalyst,20mL B as dispersant,initial decomposing temperature 150℃,dehydration temperature 180℃,7mL A as diluent,and ultimate decomposing temperature 285℃,the highest yield of crude product of lactide reached 79.6%.When ethanol was used as optimal solvent,the yield of lactide reached 59.7% and its melting point ranged from 127.3℃to 128.1℃after three times of recrystallization.For the study of ring-opening polymerization of lactide to synthesize PLA,on the basis of the previous work,the preparation process of PLA was investigated and good results were obtained:the viscosity average relative molecular weight of PLA reached 1.16×10⁶ when THF was used as solvent for measurement;and the viscosity average relative molecular weight reached 9.39×10⁵ when benzene was used as solvent for measurement.In addition,using the lactide recycled from the mother liquor of recrystallization to synthesize PLA,the viscosity average relative molecular weight of PLA reached 2.59×10⁵.IR and GC were used to characterize the products.The viscosity average relative molecular weight of PLA was more than the value (1.02×10⁶) reported in literature when THF was used as solvent for measurement,but the viscosity average relative molecular weight of PLA was't more than the highest level (9.42×10⁵) reported in literature when benzene was used as solvent for measurement.