等规聚苯乙烯的高真空阴离子合成及其在一体化橡胶中的应用

【作者】 史丰田；

【导师】 刘力； 韩丙勇；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2011， 博士

【摘要】 本文以叔丁基锂(t-BuLi)为引发剂,十二烷基苯磺酸钠(SDBS)为调节剂,己烷(或环己烷)为溶剂,利用高真空阴离子聚合技术,进行等规聚苯乙烯(iPS)的合成,探讨了引发体系组成、活性中心浓度、温度、调节剂种类等因素对iPS等规度的影响。以1-锂基-1,3-二苯基丁烷(LDPB)和对甲基苯磺酸钠(SMBS)分别作为替代聚苯乙烯基锂(PSLi)和SDBS的模型分子,利用密度泛函理论(DFT)分子模拟技术,对引发体系的分子状态进行了量子化学计算。在上述两方面工作的基础上,结合紫外光谱测试结果、分子本身结构特点以及统计学计算数据,探讨了PSLi/SDBS络合物的可能结构,以及iPS可能的生成机理。最后,借助阴离子活性聚合的优势,本文合成了一系列聚丁二烯-b-等规聚苯乙烯(PB-b-iPS)、聚异戊二烯-b-等规聚苯乙烯(PI-b-iPS)嵌段共聚物,并对其在“一体化橡胶”中的应用进行了初步的研究。实验结果表明：以SDBS为调节剂,在己烷等非极性溶剂中,可于30℃或更高温度下获得iPS,反应时间大幅缩短,单体转化率可认为达到100%。用丁酮对聚合产物进行抽提,可将其分为80℃丁酮不溶部分和25℃丁酮可溶部分。但与以往文献报导不同的是,本实验所得80℃丁酮不溶部分并非完全的高等规,且25℃丁酮可溶部分也并非完全的无规。其中,80℃丁酮不溶部分的mmmm五元组含量只有约50%,而25℃丁酮可溶部分却含有约10%的mmmm五元组结构。SDBS的加入量,对苯乙烯的聚合影响显著,主要表现为：低[SDBS]/[t-BuLi]时,苯乙烯的聚合速率增加,可获得等规聚苯乙烯；高[SDBS]／[t-BuLi]时,对聚合有阻滞作用,且所得产物为无规聚苯乙烯。聚合温度对iPS等规度的影响较大。较为特殊的是,降低温度,iPS的等规度不升反降。活性中心浓度对iPS等规度的影响不大。磺(硫)酸盐类调节剂对iPS等规度的影响有：金属反离子、烷基链的长度对等规度的影响较大,而苯磺酸基与硫酸基均可产生iPS。SDBS与t-BuLi或PSLi的络合能力,要强于甲苯、四苯基乙烯,但弱于四氢呋喃。溶剂对iPS等规度的影响较大。在极性溶剂四氢呋喃中,只能得到无规聚苯乙烯,而在非极性溶剂甲苯、己烷、环己烷中,可得到iPS,其中,以在环己烷中所得iPS的等规度为最高。DFT分子模拟计算结果表明：在LDPB中,由于锂离子与前末端苯环的络合作用,pro-m-LDPB与pro-r-LDPB的能量差异较大,无论是在真空中还是在环己烷中,LDPB倾向于采取pro-r构型。在聚合反应发生的时间尺度之内,pro-m-LDPB与pro-r-LDPB及其相应的二缔体(包括混合二缔体)发生差向异构的速率均是非常缓慢的,而采取pro-(R)或pro-(S)构型的单体的转化却是相当迅速的。pro-m-LDPB和pro-r-LDPB与苯乙烯络合后,仍以pro-r-LDPB-St构型为主。LDPB的二缔体不能与苯乙烯形成稳定的络合物,说明只有单个的离子对才能引发聚合,而PSLi二缔体没有引发活性。单体从阳离子一侧插入聚合物链,较从阴离子一侧插入时所需能量为低。LDPB与SMBS可形成1：1或2：1的络合物,两者无论是在结构上还是在能量上,均相差不大。LDPB与SMBS和苯乙烯络合后,活性中心转而以pro-m构型为主。对SDBS/PSLi络合物结构及iPS生成机理的研究结果表明：SDBS的加入使丁基锂的最大吸收波长明显向长波方向移动。一个SDBS分子可与两个活性中心(t-BuLi或PSLi)络合。在烃类溶剂中,我们认为SDBS与t-BuLi主要可生成三种络合物,其引发活性为：SDBS/(t-BuLi)2> SDBS/t-BuLi> (t-BuLi)2。三种络合物处于相互转化的动态平衡中,并且认为只有与SDBS络合的活性种才能够生成等规聚苯乙烯。对聚苯乙烯样品进行的统计学计算表明：80℃丁酮不溶部分符合Bernoullian统计；而未抽提部分和25℃丁酮可溶部分,既不符合Bemoullian统计,也不符合一级Markov统计。SDBS、PSLi和苯乙烯三元络合后,络合物以pro-m构型为主,单体以固定姿态插入聚合物链,生成相应的等规结构。对于iPS在“一体化橡胶”中的应用,初步的研究结果表明：引发活性中心的改变,对iPS等规度的影响不大。借助阴离子活性聚合的优势,成功合成出PB-b-iPS和PI-b-iPS以及聚丁二烯-b-聚苯乙烯-b-聚丁二烯(BSB)嵌段共聚物。PB-b-iPS和PI-b-iPS可形成以iPS为核,相应软段为壳的纳米级球形胶束,粒径均一且大小可控；BSB经己烷处理后,形成以聚苯乙烯为核,聚丁二烯为壳的球形胶束。对BSB的低温硫化表明,其力学性能较差,主要原因是交联不足。PI-b-iPS充当炭黑,对丁苯胶的补强效果不明显,主要原因是没有产生足够的有效连接——iPS核与丁苯胶基体之间的连接。将PI-b-iPS直接硫化,其性能依然很差,主要原因是起补强作用的iPS核被大量破坏。更多还原

【Abstract】 In this dissertation, based on high vacuum techniques, t-Butyllithium (t-BuLi) were used as initiator, sodium dodecylbenzenesulfonate (SDBS) as structure modifier for the styrene anionic polymerization in hydrocarbon media and their influence on polystyrene microstructure has been investigated. The influence on the stereoregulation of other parameters of this initiating system, such as the ratio of initiator, the concentration of living seeds, reaction temperature as well as that of the type of regulator has also been investigated.1-lithio-1,3-diphenylbutane (LDPB) and sodium 4-methylbenzenesulfonate (SMBS) was used as simplified models of the grow chain (PSLi) and SDBS respectively. The quantum chemistry calculations, density functional theory (DFT), on these two models were performed to stimulate the molecular state of this initiating system. On the basis of both research metioned above, combing with the data from ultra-violet spectrum, the structural features and statistics, the possible structure of PSLi/SDBS complexes and the stereoregualtion mechanisms of isotactic polystyrene (iPS) were discussed. By the anionic polymerization technique for living advantage, diblock copolymers of polybutadiene-block-isotactic polystyrene (PB-b-iPS) and polyisoprene-block-isotactic polystyrene (PI-b-iPS) have been successfully prepared. And their practical application in integrative rubber was also preliminary studied.The experimental results indicated that the iPS can be obtained in nonpolar solvent (e.g. hexane) at 30℃or above in the presence of SDBS. The reaction time was saved dramaticly and the conversion of monomer reached nearly 100%. The PS samples were fractionated by extraction using boiling methyl ethyl ketone (MEK) into 80℃MEK insoluble and 25℃MEK soluble fractions. Unfortunately, the 80℃MEK insoluble fraction was not complete highly isotactic and the 25℃MEK soluble fraction was also not entire atactic polystyrene. The mmmm pentad content of these two fractions was about 50% and 10% respectively. These results clearly differ from those described by other publishers. The SDBS content exerted a great influence on the anionic polymerization of styrene. The low [SDBS]/[t-BuLi] ratio gave a markedly increased polymerization rate and isotactic PS microstructure. While at the high [SDBS]/[t-BuLi] ratio a sharp decrease both in isotactic content and polymerization rete was observed. Reaction temperature showed a significant influence on PS isotacticity. Especially, decreasing the temperature to improve the isotacticity was just the opposite to what we wishes. There was no noticeable change in siotactic content by varying the concentration of living seeds. The influence of sulfonate derivatives on stereoregulation of iPS was characterized by:distinctly influence of metal counterion and the length of alkyl chain, slightly influence of sulfonate and sulfate. The coordination of the SDBS with t-BuLi or PSLi is stronger than with toluene and tetraphenylethylene but weaker with tetrahydrofuran (THF). The solvent displayed obvious influence on PS isotacticity. No other than atactic polystyrene was obtained in THF. However, isotactic PS was observed in toluene, cyclohexane and hexane. The relative highest isotacticity was obtained in cyclohexane.DFT calculations on LDPB indicated that ion pairs of LDPB with the Li position in the pro-meso (pro-m) and pro-racemic (pro-r) differ in energy due to the interaction with the penultimate phenyl group with the pro-r complexes being favored. Furthermore, DFT calculations in vacuum or in cyclohexane on possible inter-or intra-molecular ion pair epimerization of LDPB suggested that these processes were slow on the polymerization time scale. In contrast to the ion pairs, the formation of pro-(S) and pro-(R) monomer presentation may well be reversible and rapid on the polymerization time scale. The calculations of LDPB-styrene complexes indicated a preference for pro-r structures. The calculations also indicated the formation of very stable pro-m or pro-r LDPB dimers that appear unable to form stable styrene complexes consistent with a well known lack of reactivity of PSLi dimers under these conditions indicating that the propagating species is the pro-m or pro-r LDPB (PSLi) monomeric ion pair. The DFT calculations also indicated that the styrene attacks cation-side ("syn") as the corresponding "anti" attack results in much higher energy intermediates. DFT calculations on sodium 4-methylbenzene sulfonate (SMBS) as a model for SDBS indicated that the formation of 2:1 LDPB:SMBS and or 1:1 complexes was indeed plausible. Furthermore, DFT calculations in vacuum and in cyclohexane showed that, in contrast with the model LDPB styrene complexes, the pro-m SMBS-LDPB-styrene complexes are now favored.The research on the structure of SDBS/PSLi complexes and the propagating mechanism of iPS was summarized as below. Addition of SDBS yielded a dramaticly n-butyllithium maximum absorption wavelength shift to long-wave band. In nopolar solvent, one SDBS molecule could interact with two t-BuLi molecules to form the corresponding 2:1 complexes. The highest reactivity of SDBS/t-BuLi was observed in 2:1 complexes and the relative reactivity decreased in the order SDBS/(t-BuLi)2> SDBS/t-BuLi> (t-BuLi)2. The nonassociated PSLi was being in a dynamic equilibrium with a high proportion of associated contact PSLi ion pairs that appear to be the only propagation site resulting the isotactic structure in PS. The statistic calculation on PS samples indicated that the 80℃MEK insoluble was consistent with the Bernoullian statistic but the unfractionated and 25℃MEK soluble fraction was neither in agreement with the Bernoullian statistic nor with the 1st-order Markov statistic. The complexes formed by coordination of styrene with the 1:1 SDBS/PSLi complexes suggested that the pro-m structure was preferred. Repeated pro-(R) or pro-(S) monomer presentation will lead to isotactic polymers.The elementary study on the practical application of iPS in integrative rubber indicated that the change of propagating sites had faint influence on the stereoregulation of PS. In virtue of the living character of the anionic polymerization, PB-b-iPS, PI-b-iPS diblock copolymers have been successfully prepared. The expected structure of the micelle-like aggregates was resulted from an inner iPS block surrounded by the corresponding soft block shell. The size of such an aggregate was nanoscale and easy to control their diameter. The polybutadiene-b-polystyrene-b-polybutadiene (BSB) was also prepared in cyclohexane. After treated with hexane, it also can form micelle-like aggregates composed of an inner PS block surrounded by the PB shell. The low temperature vulcanization of BSB indicated that their mechanical properties are bad due to the insufficient crosslink. The PI-b-iPS used as the replacement of carbon black showed a limited ability of reinforcing the styrene-butadiene rubber (SBR). The main reason was lack of effective crosslink between iPS core and SBR matrix. The PI-b-iPS vulcanized directly still displayed the bad mechanical properties as almost iPS core contributing reinforcement was destroyed.更多还原