用一稀土催化剂合成高分子量聚苯乙烯

由Nd(oct)3(Nd)、Al(i-Bu)3(Al)和C4H9Cl(BCL)三组分组成稀土催化体系,催化苯乙烯(St)在环己烷溶剂中进行配位聚合,考察Al/Nd摩尔比、BCL/Nd摩尔比、陈化温度、陈化时间、催化剂用量、聚合温度与时间等因素对苯乙烯聚合、催化活性以及聚苯乙烯产物(PS)分子量与分子量分布的影响.当Al/Nd=8-12(摩尔比),BCL/Nd=5-25(摩尔比),Ta=40-50℃,ta=6-20 h,Tp=40-50℃时,可以得到高分子量聚苯乙烯,其中重均分子量可高达7.6×105.聚合产物中不溶于丁酮的聚苯乙烯的熔点高达268℃,主要含有间规结构聚苯乙烯和少量等规结构聚苯乙烯;偏光显微镜观察结果表明,可溶于丁酮的聚苯乙烯也是含有部分立构规整链段的聚合物.

SYNTHESIS OF HIGH MOLECULAR WEIGHT POLYSTYRENE WITH A RARE EARTH CATALYST

The polymerization of styrene(St) with a modified rare earth catalyst system composed of neodymium tricarboxylate(Nd),triisobutyl aluminium(Al) and n-butyl chloride(BCL) was carried out in cyclohexane.The effects of preparation procedure of the catalyst system(the molar ratios of Al/Nd and of BCL/Nd,ageing temperature and ageing time) and reaction conditions(catalyst concentration,polymerization temperature and polymerization time) on St polymerization,catalytic activity,molecular weight and molecular weight distribution of the resultant polymers were investigated.The catalytic activity depended mainly on the molar ratios of Al/Nd and BCL/Nd,the catalyst concentration,the polymerization temperature and time.High molecular weight of polystyrene could be obtained with the catalyst with low Al/Nd and BCL/Nd ratios aged at relatively low temperature for relatively short time.The molecular weight of polymers increased with a decrease in polymerization temperature.The optimum conditions for obtaining high molecular weight polystyrene are as follows:Al/Nd=8-12(molar ratio),BCL/Nd=5-25(molar ratio),T_a=40-50℃,t_a=6～20?h,Nd/St=1.5×10~(-4)-6.0×10~(-4)(molar ratio),T_p=40～50℃.The molecular weight of the polymers reached high weight-average(M_w) values(M_w=7.6×10~5 g mol~(1)) when Al/Nd=10.The molecular weight decreased and molecular weight distribution became broad when excess Al or BCL existed in the catalyst system.The polymer obtained was extracted by 2-butanone and then separated into an insoluble fraction and a soluble fraction.The DSC characterization of the insoluble fraction shows that its melting point is around 268℃,which indicating that the insoluble fraction mainly contains syndiotactic polystyrene.It is shown from polarized optical micrograph that the soluble fraction also contains some segments with high stereo-regularity.