【作者】 安粒；

【导师】 付志峰；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2012， 博士

【摘要】 基于不可逆加成-断裂链转移机理的分子量调节剂首次报道出现在上世纪80年代末，并在随后十几年的研究中发现烯丙基结构的化合物在自由基聚合中能充当链转移剂来控制聚合物分子量。通过设计该类链转移剂的分子结构，可以得到对应单体链转移常数不同的分子量调节剂；在本体和溶液自由基聚合中，部分链转移剂在聚合过程中既无阻聚现象发生，又能有效降低聚合物分子量，是理想的链转移剂。基于不可逆加成-断裂链转移机理的分子量调节剂与传统的硫醇等链转移剂相比，克服了烷基硫醇自身令人讨厌的气味，同时又能优化乙烯基类单体的链转移常数，具有一定的应用价值。参阅大量文献，基于不可逆加成-断裂链转移机理的分子量调节剂在本体和溶液聚合的研究甚多，并且得到了大量对于苯乙烯链转移常数不同的分子量调节剂，但是这些分子量调节剂运用于乳液聚合的研究几乎没有。基于此，研究该类链转移剂在乳液聚合的动力学特性，无论对理论的探索还是工业的应用都非常重要。因此，本论文就在如下几个方面展开了研究工作，并得出相应结论。首先，根据文献合成或购买了5种基于烯丙基结构的化合物，它们分别是：正丁基-2-苯基烯丙基硫（BPAS），正十二烷基-2-苯基烯丙基硫（DPAS），α-苯磺酰甲基丙烯酸乙酯（EBSA），α-对甲基苯磺酰甲基丙烯酸乙酯（ETSA）以及2,3-二氯丙烯（DCP）。合成和购买的链转移剂无味且产率较高，通过~~1H NMR对5种有机化合物进行了表征，结果表明结构正确，产物纯净。第二，将5种链转移剂运用于苯乙烯乳液聚合来调节聚合物分子量，研究了各链转移剂存在下的乳液聚合动力学特性，并用~1H NMR对聚合物结构，时间-转化率曲线对聚合速率，激光粒度仪和扫描电镜对乳胶粒子以及GPC对聚合物数均分子量分别进行了表征，结果表明本文所使用的5种分子量调节剂的链转移过程符合不可逆加成-断裂机理；不同链转移常数的分子量调节剂因在乳胶粒子中存在自由基解吸附作用，因此对苯乙烯乳液聚合速率影响各不相同。其中，链转移常数较大的分子量调节剂解吸附明显，聚合速率下降严重。而相对链转移常数较小的链转移剂解吸附速率常数较小，对聚合速率影响轻微。而扩散作用，同样影响聚合速率，分子量较大的链转移剂扩散速度慢，自由基解吸附小，对聚合速率几乎未有影响。不同链转移常数的分子量调节剂对数均分子量的控制上，链转移常数较大的调节剂在前期消耗过快，会出现在聚合中后期难以调节聚苯乙烯分子量。而链转移常数相对较小的调节剂能在整个聚合过程中控制聚苯乙烯分子量。而分子量较大的链转移剂因扩散速率慢难以调节聚合物分子量。经典数学模型模拟的数均分子量能与观测值相匹配。第三，利用BPAS在苯乙烯乳液聚合中进了详细考察，得到了乳胶粒子个数、聚合速率与乳化剂浓度、引发剂浓度以及链转移剂浓度之间的相互关系，其动力学特征符合经典乳液聚合原理和相关动力学数学模型假设；BPAS存在下的苯乙烯乳液聚合，用量较少时，解吸附现象并不严重；BPAS存在下的低温苯乙烯乳液聚合对聚合物分子量调节效率与高温苯乙烯乳液聚合一致，其分子量调节效率与温度几乎无关，扩宽了BPAS作为链转移剂的温度使用范围。第四，不可逆加成-断裂链转移机理的分子量调节剂在乳聚丁苯橡胶的应用同时也进行了研究。聚合动力学特性与其在苯乙烯高温乳液聚合特性有相似之处，即在不考虑链转移剂扩散因素的前提下，链转移常数越大解吸附现象越严重，聚合速率越慢。而链转移常数较小的分子量调节剂难以有效调节聚合物分子量。在乳液聚合中，因自由基解吸附存在，所以聚合速率和分子量调节效率是一对矛盾体，在链转移剂分子设计中应综合考虑以上两个因素，来解决聚合过程中出现的问题。更多还原

【Abstract】 Molecular weight regulators or chain transfer agents (CTAs) based onirreversible addition-fragmentation chain transfer (AFCT) mechanism werefirst reported in the late1980s. Among these CTAs mentioned in thereferences in the following research, some allyl CTAs can be used formolecular weight control. The chain transfer constant for some particularvinyl monomers can be easily changed by designing the structure of theCTAs; It were also found no retardation during polymerization when theseallyl compounds were used in bulk or solution system for molecular weightcontrol of polystyrene. Therefore, they were ideal CTAs in bulk andsolution polymerization. Compared with mercaptans, the advantages ofirreversible AFCT agents are obvious: they have no odors; the chaintransfer constant for particular vinyl monomers can be regulated easily bychanging the activity group. Thus, these CTAs have the prospect for application in the industrial areas. Although various irreversible AFCTagents have been evaluated in bulk and solution polymerization, to the bestof our knowledge, the study on the emulsion polymerization of styrenewith these CTAs has never been published. Therefore, the research on theintrinsic kinetics of emulsion polymerization with irreversible AFCT agentsis important for the application of these new CTAs. This work mainlyfocused on the study of the kinetics for emulsion polymerization withirreversible AFCT agents as following description.Firstly, five kinds of CTAs based on allyl structure were synthesizedaccording to the literature or purchased from the chemical company. Theyare butyl(2-phenylallyl)sulfane (BPAS), dodecyl(2-phenylallyl)sulfane(DPAS), ethyl α-benzenesulfonyl-methylacrylate (EBSA), ethylα-p-toluenesulfonyl-methacrylate (ETSA) and2,3-dichloro-1-propene(DCP). These CTAs can be easily synthesized with high yield and have noobjectionable odors compared with mercaptans. They were alsocharacterized by~1H NMR, and the spectrums of compounds shown that thestructures were correct.Secondly, the emulsion polymerization of styrene with above fivedifferent CTAs based on irreversible AFCT mechanism was carried outusing conventional surfactant (sodium dodecyl sulfate, SDS) and initiator(potassium peroxodisulfate, KPS). The influences of these irreversibleAFCT agents on the rate of polymerization, particle size and average-number molecular weight were investigated. It was found that theintrinsic activity, diffusion and desorption behaviors of the CTAsdetermined the efficiency of molecular weight control, rate ofpolymerization and particle size in the emulsion polymerization. It has beendemonstrated that the irreversible AFCT agents with high chain transferconstant (EBSA and ETSA) decreased the reaction rate and practice size,meanwhile, the molecular weight of the polymers could not be controlledwell, whereas the irreversible AFCT agents with low chain transferconstant (BPAS, DPAS and DCP) had a slight effect on the polymerizationrate and particle size. DPAS failed to control the molecular weight, whichwas attributed to the low rate of diffusion through monomer droplets toaqueous phase. The average number of radicals per particle and thenumber-average molecular weight were calculated by classical radicalemulsion polymerization theory, and the experimental results were in goodagreement with the results of model calculations, when the irreversibleAFCT agents were used as CTAs. The effect of CTAs on the kinetics andnucleation in the emulsion polymerization of styrene can be attributed todesorption of chain-transfered radicals from the polymer particles. Theresults of this work show that BPAS as CTA in emulsion polymerization ofstyrene provides the best balance between the rate of polymerization andthe efficiency for molecular weight control conflicting tendencies.Thirdly, the emulsion polymerizations of styrene in presence of BPAS were carried out using various amount of sodium dodecyl sulfate assurfactant and potassium peroxodisulfate as initiator. The effects ofsurfactant, initiator and BPAS on the course of the emulsion polymerization,and the number-average molecular weight were studied. The relationshipsbetween the rates of polymerization and the number of the particles pervolume with respect to the concentrations of KPS, SDS and BPAS werefound. The obtained relationships can be attributed to the exit of leavinggroup radicals on BPAS from the particle. The experimental values of theaverage number of radicals per particle strongly depended on theconcentration of BPAS and were in good agreement with the theoreticalvalues of model calculations. The number-average molecular weight can becontrolled by BPAS almost over the whole conversion range which is alsoin agreement with a mathematical model. Moreover, BPAS can also beused in the emulsion polymerization at lower temperature, and itsefficiency for molecular weight control is relatively independent of reactiontemperature.Finally, the emulsion polymerizations of styrene-butadiene rubber(E-SBR) were also carried out using three CTAs based on irreversibleAFCT mechanism. The polymerization kinetics is similar with theemulsion polymerization of styrene at high temperature. It was also foundthat the irreversible AFCT agents with high chain transfer constantdecreased the reaction rated of polymerization, due to desorption of chain-transfered radicals from the polymer particles. Meanwhile, CTAswith very low chain transfer constant would obtain a decreased efficiencyfor molecular weight control. Therefore, there is a conflicting tendencybetween the rate of polymerization and the efficiency for molecular weightcontrol in emulsion polymerization.更多还原