改性稀土催化丁苯共聚合——共聚物的合成、表征及反应机理

COPOLYMERIZATION OF BUTADIENE AND STYRENE WITH MODIFIED RARE EARTH CATALYST SYSTEM

采用改性稀土催化体系Nd(oct)_3-Al(i-Bu)_3-CHCl_3(Nd-Al-Cl),以己烷为溶剂,进行了丁二烯(Bd)与苯乙烯(St)的共聚合。当催化剂中Al/Nd=10～20(摩尔比),Cl/Nd=10O～25(摩尔比),陈化温度为20～70℃。陈化时间为2～20h时,在St/Bd=0.7～2.0(摩尔比),聚合温度为30～60℃,聚合时间为10～20h的条件下,经催化聚合可得到Bd链段顺-1,4含量为90％～96％(摩尔),结合St含量为10％～15％(摩尔),[η]为0.8～1.2dL/g的丁苯共聚物。经IR,DSC及TEM检测表征,该丁苯共聚物的序列分布以嵌段为主,兼有无规分布。FRIR和UV研究表明,催化活性中心的形成是先由Cl与Al作用生成Al(i-Bu)_2 Cl,再与Nd进行交换和络合反应;而单体与活性中心的配位,则可能相应形成两种引发中心,并插入增长。

The homopolymerization of styrene (St) and copolymerization of styrene and divinyl benzene with rare earth catalyst system was preliminarily reported . With a current rare earth catalyst , it was difficult to copolymerize butadiene (Bd)and styrene to produce Bd - St copolymer by usingstyrene as solvent . In this study , the copolymerization of butadiene and styrene in hexane was carried out by a modified rare earth catalyst system which consisted of three components , Nd(oct)3(Nd),Al(i-Bu)3(Al)and CHCl3(Cl).It was shown that the butadiene - styrene copolymer containing 10%- 15% (mol)styrene and 85% -90% (mol)butadiene (with 90% - 96% cis- 1,4 configuration)could be synthesized under appropriate conditions . The catalyst system was prepared by joining the three components together with mole ratio Al/Nd= 10-20 ,Cl/Nd= 10 - 25 at aging temperature 20 - 70°C for 2 - 20 h .The polymerization proceeded at 30 - 60 °C for 10 - 20 h with monomer ratio St/Bd = 0.7 - 2.0 (mol).The composition of the copolymers was characterized by IR , DSC and TEM. The results showed that the copolymers contain mainly block sequence and some random sequence . Furthermore , the copolymerization mechanism was studied through analysis of the interactions between components in the catalyst system as well as the interactions between monomers (St and Bd)with catalyst system by FTIR and UV spectroscopy . It was predicted by the experiments that the establishment of active centers was primarily done by the formation of Al(i-Bu)2Cl ,and then was completed by the exchange and coordination reactions between Al(i-Bu)2Cl and Nd (oct )3 . Propagation of polymerization was carried out by insertion of monomers which coordinated with active centers , then created two types of reaction centers respectively .