合成高分子量无规聚丙烯的研究 Ⅱ.聚丙烯大分子链的微观结构

用１３Ｃ ＮＭＲ测定了由不同单茂基钛化合物／ＭＡＯ催化体系制备的聚丙烯大分子链的立体构型和区域结构．结果表明所得聚丙烯是立体无规的，其立体结构序列分布服从Ｂｅｒｎｏｕｌｉ统计．对三单元区域序列统计分析显示单茂基钛催化剂制备的聚丙烯大分子链具有区域嵌段结构．催化剂茂环上甲基取代氢使所得产物的区域嵌段变短，聚合温度下降聚丙烯产物的区域嵌段增长．

SYNTHESIS OF HIGH-MOLECULAR-WEIGHT ATACTIC POLYPROPYLENE Ⅱ.MICROSTRUCTURE OF THE MACROMOLECULAR CHAIN

Chemical microstructure of the atactic polypropylenes prepared with cyclopentadienyltitanium tribenzyloxide/methylaluminoxane and pentamethylcyclo pentadienyltitanium tribenzyloxide/methylaluminoxane catalysts has been investigated by 13 C NMR spectra.Both catalysts give the polymers with similar stereo structure distributions.A satisfaction of Baernoullian statistics,by mr/(2mm+mr)+mr(2rr+mr)≈1,indicates that the propylene polymerizations are stereochemically obedient to a chain end control.The present polymers are regioirregular and contain a nonnegligible proportion of propylene units arranged in head to head and tail to tail sequences which can be observed in the methine carbon region of the 13 C NMR spectra.From a statistical analysis of the regio triad distribution,it was found that polypropylenes with regioblock structure can be produced with the catalysts.Considering a binary copolymerization of 1,2 orientation monomer and 2,1 orientation monomer,the reactivity ratios,r 1 and r 2,were calculated.The relations of r 1>1,r 2>1 and r 1r 21 indicate that the incoming monomers tend to insert into the metal carbon bonds with the same orientation as the end units.By substituting methyl group for hydrogen in the cyclopentadienyl ring,the titanocene catalyst affords a polypropylene containing shorter regioblocks.The length of the regioblocks increases with reducing the polymerization temperature.