单茂钪催化月桂烯与苯乙烯共聚合的研究

Copolymerization of Myrcene with Styrene Catalyzed by Half-sandwich Scandium Complexes

采用(C5H5)Sc(CH2SiMe3)2(THF)(1)、(C5Me4SiMe3)Sc(CH2SiMe3)2(THF)(2)2种单茂钪催化剂,分别考察了其催化月桂烯与苯乙烯共聚合的性能,并通过核磁共振(1H-NMR、13C-NMR)、凝胶渗透色谱(GPC)和示差扫描量热法(DSC)对所获共聚物结构和热性能进行表征分析.结果表明,在室温甲苯溶剂中,改变月桂烯和苯乙烯的用量,2种单茂钪催化剂均对月桂烯和苯乙烯共聚合表现了较高的催化活性(10^4 g polymer molSc^–1 h^–1),获得了组成可控(月桂烯含量22 mol%~83 mol%)、高分子量(Mn=4.8×10^4~1.13×10^5)、窄分布(Mw/Mn=1.49~1.99)的苯乙烯-月桂烯共聚物,催化剂结构直接影响共聚物的立体和序列结构.采用单茂钪1催化月桂烯与苯乙烯共聚合,月桂烯先聚合形成高顺式1,4-聚月桂烯嵌段(选择性95%),之后苯乙烯开始聚合形成无规聚苯乙烯嵌段,所获共聚物为高顺式聚月桂烯-无规聚苯乙烯嵌段共聚物.由单茂钪1获得的月桂烯-苯乙烯嵌段共聚物均含有–63和96℃2个玻璃化转变温度(Tg),分别对应高顺式聚月桂烯嵌段和无规聚苯乙烯嵌段的Tg.采用单茂钪2催化月桂烯与苯乙烯共聚合,也是月桂烯优先聚合,随后苯乙烯大量聚合,共聚物中月桂烯的含量呈梯度下降趋势而苯乙烯含量呈梯度上升趋势,共聚物为月桂烯-苯乙烯梯度共聚物,共聚物中月桂烯含有3,4-结构单元(选择性75%)和顺式-1,4-结构单元(选择性25%).由单茂钪2获得的月桂烯-苯乙烯梯度共聚物均含有一个–35℃的Tg和一个254℃的熔点(Tm),分别对应聚月桂烯嵌段的Tg和间规聚苯乙烯嵌段的Tm.

The copolymerization of myrcene with styrene by the half-sandwich scandium complexes(C5H5)Sc(CH2SiMe3)2(THF)(1)and(C5Me4SiMe3)Sc(CH2SiMe3)2(THF)(2)was studied.The structures and thermal properties of the obtained copolymers were characterized by NMR,GPC and DSC.The copolymerization of myrcene with styrene at room temperature had been achieved and the copolymerization activity reached up to 104 g polymer molSc^–1 h^–1.The myrcene-styrene copolymers with controllable compositions(myrcene content=22 mol%–83 mol%),high molecular weight(Mn=4.8×10^4–11.3×10^4)and narrow molecular weight distribution(Mw/Mn=1.49–1.99)were conveniently obtained by changing the feed ratio of myrcene and styrene.Significant influence of catalyst structure on the stereoselectivity and comonomer distribution sequences in the resulting copolymers was observed.In the copolymerization of myrcene and styrene catalyzed by scandium complex 1,styrene started to incorporate into chains after myrene was almost completely consumed,and diblock copolymers containing cis-1,4-polymyrcene(selectivity 95%)block and atactic polystyrene block were obtained.The obtained copolymers with different myrcene contents possessed two glass transition temperatures(Tg,–63 and 96℃),close to those of cis-1,4-polymyrcene and atactic polystyrene.In contrast,in the copolymerization of myrcene and styrene catalyzed by scandium complex 2,myrene content showed a gradient decline accompanied by styrene content increasing gradually,producing gradient copolymers containing 3,4-polymyrcene(3,4-selectivity 75%,cis-1,4-selectivity 25%)and syndiotactic polystyrene.The obtained copolymers with different myrcene contents possessed a Tg at–35℃ and a melting temperature(Tm)at 254℃,originating from polymyrcene block and syndiotactic polystyrene block,respectively.There is a great difference in the reactivity ratios between myrcene and styrene in the copolymerization catalyzed by scandium 1(rMy>>rSt).However,the gap between the reactivity ratios of myrcene and styrene in the copolymerization catalyzed by scandium complex 2 was much smaller(rMy=8.47,rSt=0.76)and gradient copolymers were generated.