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)

Ta＝40～50℃

ta＝6～20 h

Nd/St＝1.5×10-4～6.0×10-4 (molar ratio)

Tp＝40～50℃.The molecular weight of the polymers reached high weight-average (Mw) values (Mw=7.6×105 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.