限制几何构型三价钛金属配合物介导的可控自由基聚合

Controlled Radical Polymerization Mediated by Constrained Geometry Construction Trivalent Titanium Complex

三价钛金属配合介导的自由基聚合因其可控性好、所得聚合物无需进一步纯化而受到广泛关注.本工作利用限制几何构型三价钛金属配合物1作为控制剂,分别与1-溴-1-苯乙烷(I_(1))、α,α-二甲基苄溴(I_(2))、1-碘-1-苯乙烷(I_(3))构成引发体系,引发甲基丙烯酸甲酯自由基聚合,研究了引发剂种类对聚合活性及所得聚合物的分子量及分子量分布的影响,进一步以1和I1构成的二元引发体系为模型,研究了聚合动力学,同时对单体与引发剂比例以及聚合温度对单体转化率、所得聚合物分子量及分布的影响进行了研究,结合核磁技术和顺磁共振技术对1和I_(1)反应的跟踪,对聚合机理进行了推测.

Controlled radical polymerization has aroused considerable attentions during the past decades due to its ability to adjust the polymer chain structure such as molecular weight,molecular weight distribution,composition,and topology.Transition metals compounds such as copper,iron,ruthenium,nickel,etc have been extensively explored.While the effect of the auxiliary ligands on the polymerization behaviour was rarely investigated.Especially for titanium complexes,only metallocene titanium chloride Cp_(2)TiCl_(2) was examined under the reduction by Zinc.Herein,the binary systems composed by constrain geometry construction trivalent titanium complex(1)and 1-bromo-1-phenylethane(I_(1)),(2-bromo-2-propanyl)benzene(I_(2))and 1-iodo-1-phenylethane(I_(3)),respectively,were employed to catalyzed radical polymerization of methyl methacrylate(MMA).The influence of initiators on the molecular weight and molecular weight distribution was assayed.The kinetic study of MMA polymerization initiated by 1/I_(1) indicated linear relationship between MMA conversion and polymerization time,suggesting zero order dependent on MMA concentration.While with the increase of monomer conversion,the molecular weights of the afforded polymers have no obvious change.In addition,with the increase of the ratio of MMA to I_(1) while keeping the MMA concentration as constant,the molecular weight of the corresponding polymer increased despite the MMA conversion decreased.Meanwhile,with the decrease of the polymerization temperature,the molecular weight of the afforded polymer increased.These results suggested that the polymerization performed in slow initiation,fast propagation.This is consistent with the typical radical polymerization mechanism,but different from those of atom transfer radical polymerization(ATRP)and organometallic mediated radical polymerization(OMRP)which are mediated by organometallic complexes.The above results indicated that the auxiliary ligand has a significantly effect on a radical polymerization process.bromo-2-propanyl)benzene(I_(2))and 1-iodo-1-phenylethane(I_(3)),respectively,was employed to catalyze radical polymerization of methyl methacrylate.The influence of initiator on the molecular weight and molecular weight distribution was assayed.The kinetic study of MMA polymerization initiated by 1/I_(1) was carried out.The influence of reaction conditions,such as the ratio of MMA to 1,temperature,was also investigated.Combined with the results of monitoring the reaction between 1 and I_(1) by nuclear magnetic resonance(NMR)and electron paramagnetic resonance(EPR),the mechanism was proposed.