稀土催化制备窄分子量分布高顺式聚异戊二烯及聚合反应动力学

由稀土羧酸钕盐(Nd)、三异丁基铝(Al)、含氯活化剂(CE)及醇(OH)组成的均相稀土羧酸盐催化体系,用于异戊二烯(Ip)定向聚合,其中含氯活化剂(CE)为氯代烃(CE1)或氯代羧酸酯(CE2).研究了CE和OH的化学结构及Al用量对Ip聚合及聚异戊二烯(PIp)微观结构、分子量及分子量分布的影响,将原位全反射傅立叶红外光谱(in situ ATR-FTIR)技术应用于研究稀土催化Ip配位聚合反应过程及聚合反应动力学,采用FTIR、GPC、NMR及DSC等测试手段表征PIp的微观结构、分子量及其分布、序列分布及热性能.实验结果表明,在稀土催化异戊二烯聚合反应中,少量的CE2和OH有助于提高催化活性、降低分子量分布和提高顺式含量.聚合速率对单体浓度呈现一级动力学关系,表观增长活化能(Ea)为69.5 kJ/mol.通过调节催化剂组分配比及聚合工艺条件,可制备出顺-1,4结构含量可达98%以上、窄分子量分布(Mw/Mn=1.6～2.4)的高顺式聚异戊二烯.

SYNTHESIS OF POLYISOPRENE WITH HIGH CIS-1,4-CONTENT AND NARROW MOLECULAR WEIGHT DISTRIBUTION AND POLYMERIZATION KINETICS

The stereospecific polymerization of isoprene(Ip) was carried out with a modified rare-earth catalyst system which consisting of neodymium tricarboxylate(Nd),triisobutyl aluminium(Al),chlorinating agent(CE) and alcohol(OH),in which CE includes chlorinated hydrocarbon(CE1) and chlorinated carboxylic ester(CE2).The effect of chemical structure of OH and CE2,molar ratio of Al/RE on Ip polymerization,molecular weight,molecular weight distribution and microstructure of the resulting polymers was investigated.The kinetic study on the polymerization was conducted via in situ characterization by Fourier transform infrared spectroscopy in combination with a diamond tipped attenuated tota1 reflectance immersion probe(ATR-FTIR) during polymerization.Detailed characterizations including microstructure,molecular weight and its distribution,sequence and heat capacity of PIp have been carried out by FTIR,GPC,NMR and DSC.The results show that polymerization rate was first-order with respect to monomer concentration,and the apparent propagation activation energy(Ea) was determined to be 69.5 kJ·mol-1 when polymerization temperature was in the range from 0℃ to 30℃.The catalytic activity and content of cis-1,4 configuration of PIp could be improved and molecular weight distribution could be narrowed by introducing a small amount of CE2 and OH.The monomer conversion increased and molecular weight decreased with increasing Al/RE ratios.Polyisoprene with high cis-1,4-content of more than 98% and narrow molecular weight distribution(Mw/Mn = 1.6 ~2.4) could be achieved by adjusting component ratio and polymerization conditions.