氢气对负载型Z-N高效催化剂的乙烯-丙烯共聚产物链结构影响

用球形的负载型Ziegler-Natta（Z-N）高效催化剂，经丙烯均聚一乙烯丙烯气相共聚两段串联反应工艺制备的聚丙烯／乙丙共聚物（PP／EPR）合金具有优良的抗冲击性能，是聚丙烯的重要高性能化改性品种，已实现大批量生产，对这类反应器合金的结构表征和结构性能关系的研究表明，其共聚物组分中既有起弹性体作用的乙丙无规共聚物，也含有相当量的乙丙多嵌段共聚物．这种多嵌段共聚物既与无规共聚物（EPR）相容，又与PP基体相容，在合金中起相容剂作用，对材料高抗冲性能的形成起着重要作用．然而，负载型Z-N高效催化剂催化乙丙共聚合的产物结构及其影响因素至今鲜见系统的研究，调控PP／EPR合金中共聚物结构的原理尚不明确．氢气在聚烯烃生产中广泛用作分子量调节剂，在PP／EPR合金的生产中同样要用氢气调节PP和EPR组分的分子量．但是，加氢对共聚物的链结构有何影响则鲜见系统的研究．本文初步研究了用Z—N高效催化剂合成的乙丙共聚物的结构特征，着重考察了聚合体系中加入链转移剂氢气对共聚物结构的影响．

EFFECT OF HYDROGEN ON THE CHAIN STRUCTURE OF ETHYLENE-PROPYLENE COPOLYMER SYNTHESIZED BY SUPPORTED HIGH-ACTIVITY ZIEGLER-NATTA CATALYST

Ethylene-propylene copolymers were synthesized using a TiCl_4/MgCl_2/SiO_2/diester type supported Ziegler-Natta catalyst with or without the presence of hydrogen in a slurry polymerization process.The copolymer was inhomogeneous in composition and can be fractionated into two parts, fractions soluble and insoluble in n-octane at room temperature, respectively.The soluble part is a nearly random copolymer,while the insoluble part is a kind of segmented copolymer,as revealed by ~ 13 C-NMR and DSC analyses.Adding H_2 in the reaction system caused an increase of copolymer yield and a decrease of the insoluble part,but the propylene content and average length of propylene segments of the insoluble part were markedly increased,meanwhile the average length of ethylene segments of the insoluble part was markedly decreased.Copolymer sequence distribution of the soluble part was only slightly changed by H_2. The segmented copolymer fraction present in this ethylene-propylene copolymer has the similar structure as the segmented copolymer fractions found in polypropylene/poly(ethylene-co-propylene) reactor alloy.Mechanism of the hydrogen effect on copolymer structure is discussed.