熔融酯交换法合成聚碳酸酯的研究

采用熔融酯交换法,以碳酸二苯酯(DPC)和双酚A(BPA)为原料合成聚碳酸酯(PC).考察了乙酰丙酮(HACAC)类金属配合物催化剂的活性,以及催化剂活性与相应金属离子螯合配位作用的关系.以不同乙酰丙酮金属配合物为催化剂合成的PC的特性黏数(η])对相应金属离子二苯甲酰甲烷(DBM)配合物的稳定常数的对数值(lgβ1)作图,得到1个双火山型曲线,证明DPC与BPA的熔融酯交换缩聚反应是受乙酰丙酮阴离子的碱性作用和金属离子的螯合配位作用共同影响的.通过比较用各种催化剂合成的PC的性质,发现乙酰丙酮锂(LiACAC)是一种优良的催化剂,可以用来合成分子量超过40000(η]=0.710 dL.g-1)、低支化物(Fries产物)含量、低分散(PDI=2.12)的PC.以LiACAC为催化剂,考察了催化剂用量、反应物配比、酯交换阶段压力以及温度等条件对反应的影响.最佳反应条件为,LiACAC的用量为1.5×10-4mol/mol BPA、原料配比nDPC∶nBPA=1.08、酯交换阶段压力设在4000 Pa、缩聚反应阶段反应温度为260℃.

SYNTHESIS OF POLYCARBONATE BY MELT TRANSESTERIFICATION PROCESS

Polycarbonate is synthesized by melt transesterification of diphenyl carbonate(DPC) with bisphenol A(BPA).The catalytic activity of metal acetylacetonates and the effects of the stronger or weaker bond between the catalyst and the reactant,catalyst concentration,initial monomer molar ratio,initial pressure and temprature are investigated.The logarithms of the stability constants(lgβ1) of dibenzoyl methane(DBM) complexes of the corresponding metal species are regarded as corresponding to the bond strength between metal species(catalyst) and benzoyl group(reactant),which are correlated by double volcanoes-shaped relationship with the intrinsic viscosity(η]) of the PC produed with the corresponding metal acetylacetonates as catalysts.Consequently,the catalytic activity of the metal compounds is affected by the basic of acetylacetonate anion and the chelating capacity of each metal species,which is found to be very useful in forecasting the catalytic activity of the metal compound.In all the catalysts,lithium acetyacetonate(LiACAC) is the best one,by which the sample catalyzed has the lowest fries level and polydispersity index(PDI= 2.12),besides its colorless and high molecular weight(η]= 0.710 dL·g-1).Our study exhibites that the best reagent molar ratio:nBPA∶nDPC∶nLiACAC= 1.0∶1.08∶1.5×10-4,the optimal initial pressure in the transesterification stage:4000 Pa and the optimal melt polymerization temperature 260℃.