Two-step Synthesis Of Aliphatic Polycarbonate Diols By Transesterification And Its Theramal Properties

Aliphatic Polycarbonate diols has good mechanical properties, biocompatibility，and excellent resistance to both oxidation and hydrolysis，so，it is an importantcomponent of polyurethanes in areas such as waterborne polyurethane and biomedicalapplications．At present, the synthesis of polycarbonate diol with dimethyl carbonate（DMC） as raw materials mainly focused on one step continuous transesterificationmethod.But there are some problems such as the molecular weight of uncontrolled,wide molecular weight distribution, and high residued small molecular with thismethod.Here, we reported the synthesis of polycarbonate diol with a two-steptransesterification process. First, excess of methyl carbonate and dihydric alcoholundergo transesterification reaction with sodium methoxide as heterogeneous catalyst.The by-product of methyl alcohol was removed with methyl-carbonate by azeotropicdistillation. After filtration and distillation, methyl-carbonate was recycled and we gotdouble carbonate ester monomer. Then, double carbonate ester monomer and diolundergo transesterification reaction with Ti(OBu)4as homogeneous catalyst to givealiphatic polycarbonate glycol. In this method, methyl-carbonate reacted with fourkinds of diol to give double carbonic acid ester monomer with few dimer, and theexcess methyl-carbonate can be recycled. Second, with different proportion ofmonomer and reactant, we synthesized series of hydroxyl-terminated aliphaticpolycarbonate diols with molecular weight ranging from1400to4000. This process isa simple synthesis method to prepare aliphatic polycarbonate glycol, which featuringlight color, controllable molecule weight, low proportion of small moleculecomponent. we also carried out1H NMR,13C NMR and GPC to characterize thestructure of aliphatic polycarbonate glycol.We carried out DSC to investigate the thermal properties of the aliphaticpolycarbonate diols. And, we found that the polymer molecular weight, the structureand composition of copolymerization monomer affected the Tgand Tm of aliphaticpolycarbonate diols in different levels. These findings suggested that the introductionof new glycol monomer into the molecular chain of hexanediol homopolymerizationtype polycarbonate diols with copolymerization could significantly reduce the Tg.