【作者】 张健；

【导师】 郑安呐；

【作者基本信息】 华东理工大学 ， 材料学， 2013， 博士

【摘要】 本文主要研究阴离子聚合方法合成含苯乙烯链节遥爪聚合物和含有环氧侧基聚苯乙烯嵌段共聚物,苯乙烯本体阴离子聚合动力学以及聚合过程中相关实验现象的理论解释。首先,分别以正丁基锂(n-BuLi).环己烷和双环氧化合物(丁二醇二缩水甘油醚,BDE和新戊二醇二缩水甘油醚,NGDE)为引发剂、溶剂和封端剂合成含有端环氧基团聚苯乙烯遥爪聚合物。分别研究了封端反应温度、封端剂、滴加方式、封端剂的稀释等因素对端环氧基含量的影响。GPC结果表明,使用双环氧化合物对聚苯乙烯活性种进行封端时,无论采用正向滴加和反向滴加方式,均发生偶合副反应；同样反应条件下,使用NGDE封端比BDE封端得到偶合副产物量稍小。由于合成产物中端环氧基团的相对浓度较低,产物端环氧基团的存在很难使用FT-IR和1H-NMR表征方法证实。产物端环氧基团可以采用盐酸-二氧六环银量法进行测定。使用正向滴加方式时,升温、提高聚苯乙烯活性种分子量和提高封端剂用量有利于降低偶合副产物,但整体偶合副产物的量偏高。使用反向滴加方式和降低温度可以较为有效地降低偶合副产物。使用不同溶剂稀(如THF和甲苯)释封端剂也不能有效提高封端效率,DPE预封端聚苯乙烯活性种增大阴离子空间位阻的方式也未能有效降低偶合副产物。其次,采用环己烷(和甲苯)为溶剂,正丁基锂为引发剂制备聚苯乙烯活性种,然后加入GMA单体继续聚合制备PS-PGMA嵌段共聚物。在常温下,以环己烷为溶剂的聚合体系中,研究了GMA添加量和聚合反应温度的影响。结果表明,加入GMA单体后,部分GMA分子上的环氧基团发生开环反应。GMA添加量增大时,开环反应越显著,特别是在[GMA]/[n-BuLi]≥20时,聚合体系出现交联现象。同时也发现,升高温度不利于环氧基团的保留。降低GMA聚合温度,采用甲苯为溶剂,在聚合体系中引入添加剂LiCl并将聚苯乙烯活性种使用二苯基乙烯(DPE)预封端后加入GMA单体进行聚合,结果可以得到分子量分布指数接近1的含数个环氧侧基的PS-nGMA嵌段共聚物。GPC. FT-IR.1H-NMR.13C-NMR.TLC和盐酸-二氧六环银量法等分析结果表明,环氧基团在聚合过程中保存完好,并未发生开环反应。还发现,当GMA聚合温度高于-40℃时和低于-65℃时,产物分子量分布变宽。升高温度对GMA单体的阴离子聚合副反应控制不利,而温度太低则对聚合产物中GMA链节在甲苯溶剂中的溶解不利。继续增大GMA用量,共聚物中GMA链节溶解性更差,体系粘度增大,产物分子量变宽。加入THF后可降低体系粘度,使产物分子量分布变窄。使用1,4-二溴甲基苯(2-BMB)偶联剂偶联PS-PGMA活性种的方法未能成功制备纯的PS-PGMA-PS三嵌段共聚物,只能得到两嵌段和三嵌段共聚物的混合物。再次,假定聚苯乙烯活性种的二缔合体、六缔合体和缔合数较大的缔合体均能引发苯乙烯单体聚合并假定该聚合过程属于非稳态,建立了苯乙烯本体阴离子聚合的动力学模型。该模型给出了聚合反应转化率和产物分子量分布的各阶矩,并结合实验结果对模型参数(各个聚苯乙烯活性种缔合物之间的平衡转化以及其引发苯乙烯单体聚合的链增长反应速率常数)进行估算。结果表明,二缔合体和六缔合体之间的缔合平衡常数与其引发单体的链增长速率常数数量级相当,故而稳态假定不适用于本体聚合体系。缔合数很大的缔合物与六缔合体之间的平衡转化比二缔合体和六缔合体之间的平衡转化快很多(约1000倍左右)。苯乙烯本体阴离子聚合中,各个活性种缔合物的链增长速率常数与同等温度下溶液聚合的链增长速率数量级基本相同。其中二缔合体的引发活性最低,而缔合数很大的缔合物的引发活性最高,六缔合体次之。最后,使用DFT方法在B3LYP/TZVP//B3LYP/SVP水平上对正丁基锂(n-BuLi)引发体系、聚苯乙烯活性种体系以及P配合物存在下的n-BuLi引发体系和聚苯乙烯活性种体系中可能存在的缔合物几何结构进行优化和能量计算。结果发现,无论在气相和溶剂(苯乙烯和THF)中,正丁基锂的六缔合体最为稳定。在溶剂中,随着溶剂极性的增加,六缔合体稳定的优势逐渐减弱；特别是在THF中,在没有考虑THF与n-BuLi发生缔合的情况下,理论计算结果显示,六缔合体稳定性与四缔合体大致相当。分别使用HStLi和H(St)2Li作为模型化合物对聚苯乙烯活性种所可能存在的缔合物几何结构进行优化和能量计算时均发现二缔合体最为稳定。同时还发现聚苯乙烯活性种末端的锂原子被夹在与其相邻的两个苯环之间,而并非“裸露”在最外面。引入P配合物后,n-BuLi引发体系和聚苯乙烯活性种体系缔合物结构均发生变化,两者的单量体在与P配合物的缔合作用下最为稳定。增加P配合物的摩尔比,则会使得两者的单量体更加稳定,从形成的缔合物中解缔合所需的能量更大。更多还原

【Abstract】 This work is focused on the synthesis of styrenic telechelic polymer and block copolymer with pendent epoxy groups, the derivation of the kinetics of anionic bulk polymerization and the explanation of some experimental phenomena using quantum-chemical computation tools during anionic bulk polymerization of styrene.The end-epoxy functionalized telechelic polystyrene (PS-ep) has been synthesized by end-capping polystyryl precursors using diepoxides (1,4-butanediol diglycidyl ether (BDE) and neopentyl glycol diglycidyl ether (NGDE)). Polystyryl precursors were prepared at0℃using cyclohexane, a small amount of tetrahydrofuran (THF) and n-butyllithium (n-BuLi) as solvent, additives and initiator, respectively. The effects of termination reaction temperature, terminating reagents, normal/reverse addition and dilution of terminating reagent on the content of end-epoxy group in the products were investigated. Results from GPC show the existence of unexpected polystyrene dimers, the major byproduct from both oxirane rings opening reaction, whenever either normal or reverse additions were adopted. Under the same reaction conditions, the dimeric byproduct in the crude PS-ep product prepared using NGDE as terminating reagent is slightly lower compared to that using BDE. The lowest dimeric byproduct content in the product (c.a.20%) was obtained at0℃by reverse addition and molar ratio of NGDE and PSLi being3:1. The oxirane ring cannot be found from FT-IR or1H-NMR spectra owing to its very low concentration in the product. The concentration of epoxy group in PS-ep was determined by end-epoxy group titration (HCl-dioxane argentometry). The content of dimeric byproduct was reduced by increasing the reaction temperature and terminating reagent under normal addition; however, it is always higher than that from reverse addition. Under reverse addition, increasing the amount of terminating reagent resulted in lower dimeric byproduct content. It was also found that diluting the terminating reagents by adding THF, toluene and end-capping the polystyryl precursors by diphenylethylene (DPE) did not significantly reduce the dimer content.PS-PGMA was prepared using cyclohexane and n-BuLi as solvent and initiator, respectively, by adding GMA into polystryl precursors under ambient temperature. The effects of GMA dosage and GMA polymerization temperature have been investigated. It is shown that the oxirane ring opening reaction occurs when more GMA momoners were introduced (e.g. more than10GMA units per polystyrene chain). In particular, if the molar ratio of GMA to n-BuLi is over20, cross-linking takes place during GMA polymerization. The oxirane ring opening reaction of GMA was enhanced by increasing the GMA polymerization temperature. PS-nGMA block copolymers with narrow molecular weight distribution (≈1) have been synthesized in toluene by reducing the GMA polymerization temperature and end-capping the polystyryl precursors with DPE in the presence of LiCl. GPC, FT-IR,1H-NMR,13C-NMR, TLC and chemical titration results show that the oxirane were retained without ring opening reaction during GMA polymerization. It was also found that the molecular weight distribution broadened if the polymerization temperature of GMA was lower than-65℃and greater than-40℃. The reactivity of oxirane ring may increase with temperature and hence ring opening side reaction occurs. At very low temperature (≤-65℃), the solubility of PGMA segments becomes poor in toluene and poorer if larger PGMA segments are introduced. It was also found that the viscosity of PS-PGMA due to the poor solubility of GMA segments may be reduced by introducing THF in the system. PS-PGMA-PS was not successfully prepared using1,4-Bis(Bromomethyl)benzene (2-BMB) to link PS-PGMA anions. Only the mixture of PS-PGMA and PS-PGMA-PS was obtained.The kinetics of anionic bulk polymerization of styrene have been developed under the non-steady state assumption and assuming that all the living species (dimeric, hexameic and very large aggregates of polystyryllithium) can intiate the polymerization of styrene. The dependences of monomer conversion and various moments of molecular weight distribution on the time have been established in terms of model parameters (i.e. equilibrium contants between different aggregates and propogation rate constant of each aggregate). These established relationships were compared with the experimental data to estimate the model parameters. It has been shown that the propogation rate constants of dimeric and hexameric aggregates and equilibrium constants between them are almost of the same order of magnitude. In this context, the steady state assumption is not suitable for the anionic bulk polymerization of styrene. It is also interesting to find that the equilibrium constant between very large aggregates and hexameric aggregates is significantly greater (c.a.1000times) than that between dimeric and hexameric aggregates. The propogation rate constant of each aggregate is of the same order of magnitude with the apparent propogation rate constant in anionic solution polymerization of styrene reported in the literature. Among the propogation rate constants of the three aggregates, the propogation rate constant of very large aggregate is the greatest and that of the dimeric aggregate is the lowest.Quantum-chemical density functional theory (DFT) calculations at B3LYP/TZVP//B3LYP/SVP level of theory were performed to find the most stable aggregates of n-BuLi and PSLi living species during anionic bulk polymerization of styrene. It has been found that the hexamer of n-BuLi is the most stable aggregates in both gas and solution. In addition, dimeric PSLi is the most stable aggregates according to the DFT calculations using both HStLi and H(St)2Li as the models of PSLi. It was also found that the Li atom of monomeric PSLi chain-end is "wrapped" between the two benzene rings adjacent to the Li atom. To interpret the effect of P-ligands on the structure of n-BuLi and PSLi aggregates during the anionic polymerization of styrene, DFT calculations on the possible geometrical structures and relative stabilities of the living species and initiators in the presence of P-ligands were carried out. It was shown that the presence of P-ligands facilitated the deaggregation of the PSLi dimers and n-BuLi hexamers to form more stable mixed aggregates of P-ligands+monomeric n-BuLi and P-ligands+monomeric PSLi. It has also been demonstrated that the higher is the number of P-ligands coordinated with n-BuLi (or PSLi), the higher are their stabilities to bind n-BuLi (or PSLi) and their energies required to disaggregate n-BuLi (or PSLi) from the mixed aggregates.更多还原