烯烃易位法降解顺丁橡胶及制备遥爪低聚物的研究

Metathetic Degradation of Polybutadiene and Formation of Telechelic Oligomers via Cross Metathesis

采用烯烃交叉易位反应,在Grubbs二代催化剂和含有功能基团的链转移剂作用下,研究了工业级高分子量顺丁橡胶的降解以及高附加值遥爪型丁二烯低聚物的制备.涉及的链转移剂主要是轴对称的顺丁烯类衍生物：顺-1,4-二氯-2-丁烯（DCB）、顺-1,4-二乙酰氧基-2-丁烯（DAB）、马来酸二甲酯（DMM）、马来酸二乙酯（DEM）.产物的分子量（Mn）和分子量分布指数（PDI）通过凝胶渗透色谱仪（GPC）测定,产物的分子链段结构和组分通过红外光谱（FTIR）、核磁共振氢谱（1H-NMR）以及高效液相色谱-质谱联用（LC-MS）表征.实验结果表明,通过引入不同的链转移剂,控制顺丁橡胶/链转移剂、顺丁橡胶/催化剂的摩尔投料比以及反应时间,可以有效控制低聚物的Mn和PDI,其Mn变化范围为230-4800,PDI变化范围为1.09-2.82.进一步研究发现,在一定反应条件引入DAB,可以逐一断裂顺丁橡胶的主链,获得丁二烯重复单元仅为1的小分子新结构.

Introduced cross metathesis which has been applied widely by organic chemists and polymer technologists as a green and convenient method for degradation of industrial polybutadiene rubber （PB） with high molecular weight and polydispersity index （Mn = 6.6 × 10^4, PDI = 5.2）. Reactions were performed using Grubbs 2^nd catalyst with several symmetrical olefins including cis-1,4-dichloro-2-butene （ DCB ） , cis-1,4- diaeetoxy-2-butene （DAB）,dimethyl maleate （DMM） and diethyl maleate （DEM） as chain transfer agents （CTAs）. M and PDI of teleehelic oligomers were measured by gel permeation chromatography （GPC）. And the structures and properties were determined by nuclear magnetic resonance spectroscopy （^1H-NMR,^13 C- NMR）,Fourier transform infrared spectroscopy （FTIR） and liquid chromatography-mass spectrometer （LC- MS）. It was shown that M and PDI of telechelic oligomers could be tuned by using different types of monomers as CTAs. Well-defined oligomers with controllable molecular weights ranging from 230 to 4800 and polydispersity indices ranging from 1.09 to 2.82 were realized by changing molar ratios of [ PB ]/[ CTA ], [ PB ] / [ catalyst ], as well as reaction time. When DAB was introduced as a CTA,Mn of the product decreased to 330 with the molar ratio of [ PB]/[ DAB] =2：1 and [ PB]/[ catalyst] = 1000： 1. Increasing molar ratio of [ PB ] / [ DAB ] to 1 ： 1, an almost complete degradation procedure could be reached within a few hours. A new compound with the melting point of 9.37 ℃ bonded with end acetoxy groups, containing only one butadiene repeating unit, was obtained by Column Chromatograph. M, of the new compound was 230 determined by ^1H-NMR end group analyses, which was perfectly consistent with calculated theoretical value. Furthermore, ^13 C- NMR and LC-MS analyses confirmed the structure of the new compound. When using DMM and DEM as CTAs,M of the oligomers were above 1800. The low reactivities of DMM and DEM compared with DCB and DAB in the metathesis reaction could be explained by the formation of non-productive complex between carbonyl oxygen and Ru center that impeded the reaction.