【作者】 徐旭；

【导师】 吴一弦；

【作者基本信息】 北京化工大学 ， 高分子化学与物理， 2006， 博士

【摘要】 本论文研究了在给电子体(ED)存在的情况下,H2O/Lewis酸(AlCl3或TiCl4)体系引发异丁烯(IB)碳正离子聚合,分别考察了ED浓度与加入方式、H2O浓度、AlCl3浓度、陈化温度、陈化时间、溶剂极性、聚合温度与聚合时间等因素对异丁烯聚合反应转化率、聚合产物的分子量与分子量分布的影响,采用GPC表征聚合物的分子量及其分布,用电测法和紫外吸收光谱研究引发体系各组分间的相互作用与反应,并首先采用电导(G)电容(C)和紫外吸收光谱来研究活性中心的特性。在聚合反应规律基础上,结合动力学研究和活性中心性质的表征结果,进一步探讨ED的作用与聚合反应机理。实验结果表明：H2O/Lewis酸(AlCl3或TiCl4)体系引发IB传统正离子聚合,链增长活性中心为自由离子,聚合反应速率极快,反应过程难以控制,产物分子量分布较宽。对于AlCl3共引发体系,聚合产物的分子量分布指数为7.74；对于TiCl4共引发体系,聚合产物的分子量分布指数为3.75。然而,很有意义的是,在上述聚合体系中引入适量ED,反应体系中电导降低,可使通过自由离子活性中心引发的链增长反应转化为主要通过离子对活性中心引发的链增长反应,聚合反应速率明显降低,链转移副反应减少甚至抑制,实现控制IB正离子聚合,并得到单峰和较窄分子量分布的聚合产物。对于AlCl3共引发体系,聚合产物的分子量分布指数可达2.07；对于TiCl4共引发体系,聚合产物的分子量分布指数可达1.56。H2O/Lewis酸/ED体系引发IB正离子聚合中，H2O主要起到引发剂的作用,但水过量会促进链转移副反应的发生,导致聚合产物分子量降低,分子量分布变宽。引入适量ED对H2O/Lewis酸体系引发异丁烯实现控制正离子聚合起着极其重要的作用。ED调节聚合的效果与ED的化学结构、给电子性大小(DN值)、空间位阻、用量以及Lewis酸性质有关。ED的给电子性越强,其调节效果越明显,且少量ED即可起到明显的作用。当采用TEA(DN=61.0)作为ED,即使[TEA](0.92×10-3mol/L)<[H2O](1.61×10-3mol/L),也能有效地调节聚合反应,并得到单峰窄分子量分布的产物,分子量分布指数可以达到1.56。当采用Py(DN=33.1)或DMA(DN=27.8)作为ED时,需要[ED]>[H2O]才能消除自由离子的不可控引发,实现离子对活性中心引发的控制聚合,得到单峰分布的聚合产物。但是,若ED用量不足,则聚合体系中可同时存在自由离子和离子对两种活性中心,导致聚合产物呈双峰分子量分布。研究发现,对于TiCl4共引发体系,与通过自由离子活性中心进行链增长相比,通过离子对活性中心进行链增长反应,得到聚合物的分子量相对低,因此随ED用量增加,产物分子量减小；而对于AlCl3共引发体系,随ED用量增加,产物分子量反而增大。研究发现,体系的G、C和紫外吸收光谱特征与活性中心的浓度及松紧程度紧密相关。ED与H2O和Lewis酸在低于-30℃时进行络合反应,5min后即可达到络合平衡,形成活性中心,且在6h内基本保持稳定的活性和相近的引发聚合效果。反应温度高于-30℃,活性中心易被破坏,使IB聚合转化率显著下降。ED加入方式也明显影响对聚合反应的调节效果,与直接将ED加入单体溶液相比,当ED加入引发体系中进行预先反应时,调节效果更加明显,聚合反应速率显著下降,ED的反应级数为负值,对于BO为ED,其反应级数为-4.9,对于CHO为ED,其反应级数为-6.2,且聚合产物分子量明显增大,重均分子量可达74.0×104g/mol,分子量分布明显变窄,主峰呈现较对称分布。在H2O/AlCl3体系引发IB正离子聚合中,ED加入单体溶液中与加入引发体系中所起到的作用不同,可形成两种不同活性的离子对活性中心,进行链增长生成不同分子量的聚合产物,可以通过同时在单体溶液和引发体系中引入适量的ED和Lewis酸(如AlCl3),来调节反应体系中两种活性中心的数目与比例,调节聚合产物中高分子量级分与低分子量级分的相对含量,可在一定范围内调节产物的分子量及其分布,设计合成目标分子量及其分布的聚合物,以期使聚合物兼具良好的力学性能与加工性能。当选用AlCl3作为Lewis酸时,AlCl3在引发体系中的初始浓度[Al]1和在聚合体系中的浓度[Al]都对聚合有显著影响,随[Al]或[Al]1增加,聚合反应速率均明显加快,峰位分子量减小,分子量分布变宽。对于H2O/AlCl3体系引发IB正离子聚合中,聚合度活化能E为负值,随着聚合温度Tp降低,聚合物分子量增加。溶剂极性对聚合的影响与Lewis酸性质有关。溶剂极性增加,其溶剂化作用增强,活性中心离子对解离程度增大,聚合反应速率加快。对于H2O/TiCl4/ED体系引发IB聚合,所得产物分子量相对较低,在CH2Cl2/C6H14混合溶剂中不析出,随溶剂极性增加,聚合反应速率加快,单体转化率提高。对于H2O/AlCl3/ED体系引发IB聚合,所得产物分子量相对较高,在CH2C12/C6H14体积比大于8/2的混合溶剂中,分子量高的部分聚合物容易析出,造成活性中心部分被沉析的聚合物链所包埋,反而使IB转化率下降。更多还原

【Abstract】 In this thesis, the carbocationic polymerization of isobutylene (IB) with H2O/Lewis acid initiating system was carried out in CH2Cl2/C6H14cosolvent. The effects of ED, H2O concentration, AlCl3concentration, ageing temperature, ageing time, solvent polarity, polymerization temperature and polymerization time on polymerization, molecular weight and molecular weight distribution of the resultant polyisobutylene were investigated. The monomer conversion was determined gravimetrically. The molecular weight and molecular weight distribution were characterized by GPC. The reactions between the components in the initiating system and the nature of active species were studied by conductance, capacitance and UV spectrum. The experimental results were indicated as follows.Two types of active species with different activity, i.e., unpaired free ion (Ⅰ) and ion pairs (Ⅱ) existed in the polymerization system initiated by H2O/Lewis acid (AlCl3or TiCl4) in the absence of EDs and in the presence of sufficient EDs respectively. The conventional cationic polymerization of IB initiated by H2O/Lewis acid was extremely fast and led to polymers with broad molecular weight distribution, which is attributed to propagation via free ion active species (I) and to the serious chain transfer reaction to monomer. The controlled cationic polymerization of IB initiated by H2O/Lewis acid could be achieved in the presence of sufficient amount of EDs and polymers with narrow molecular weight distribution were obtained, which is attributed to propagation via ion pairs active species (Ⅱ) and decrease in side reactions, such as chain transfer and termination.Small amount of H2O was initiator in the carbocationic polymerization of isobutylene by H2O/Lewis acid/ED system. However, excessive H2O would promote the side reaction of chain chansfer and termination and lead to low molecular weight and broad molecular weight distribution of the resultant polymers.A small amount of EDs played very important roles in the controlled carbocationic polymerization of IB by H2O/Lewis acid/EDs system. The effectiveness of EDs in preventing the side reasctions and improving initiator efficiency in the controlled carbocationic polymerization of IB was classified according to their electron donicity (DN), chemical structure, concentration and the character of Lewis acid as well. The most effective EDs are those with high electron donicity and high donor number (DN). When TEA (DN=61.0) was introduced into the polymerization system, the polymerization proceeded slowly and polymers with narrow unimodal GPC trace (Mw/Mn=1.56) were obtained even though [TEA](0.92×10-3mol/L)<[H2O](1.61×10-3mol/L). When Py (DN=33.1) and DMA (DN=27.8) was used as ED, the controlled polymerization of IB could be achieved by propagation via ion pairs active species (Ⅱ) when [ED]>[H2O] and polymers with narrow unimodal molecular weight distribution were obtained. However, there existed simultaneously two types of active species with different reactivity in the polymerization system if the concentration of EDs was insufficient, the GPC traces of polymer exhibited broad bimodal distribution.The effect of ED concentration on polymer molecular weight also depended on the coinitiator Lewis acid. The molecular weight of polyisobutylene decreased with increasing [ED] in the IB polymerization by H2O/TiCl4/EDs while increased with increasing [ED] in the IB polymerization by H2O/AICI3/EDS.The concentration and ionicity of active species in initiating system and in polymerization system were determined by conductance, capacitance and the character of UV spectrum respectively. The complex reaction between ED, H2O and Lewis acid (TiCl4or AlC13) would take5min to reach an equilibrium. The active species formed in H2O/AlCl3/ED initiating system could hold high activity within6h when the ageing temperature was lower than-30℃. However, the initiation efficiency decreased when ageing temperature was higher than-30℃.The polymerization rate decreased greatly with an increase in ED concentration. The reaction orders of BO and CHO were determined to be -4.9and-6.2respectively. The ion pairs active specieses formed with different activity by addtion EDs into AlCl3solution and monomer solution respectively. The high molecular weight polymers were obtained by the propagation via the ion pairs active species preformed by adding ED into AlCl3solution. The low molecular weight polymers were obtained by the propagation via the ion pairs active species formed in situ by adding ED into monomer solution. The polymers with a designed molecular weight distribution were obtained by the simultaneous propagation via the preformed and formed in situ ion pairs active specieses respectively.The polymerization of IB was influenced greatly by AlCl3concentration in initiating system and in polymerization system respectively. The polymerization rate increased and molecular weight of polymer resultant decreased with an increase in AICI3concentration. Additionally, molecular weight distribution of polymer became broad.The activation energy for propagation in the cationic polymerization of isobutylene by H2O/AlCl3in the absence of or in the presence of EDs was determined to be negative. The molecular weight increased with decreasing polymerization temperature.The effect of solvent polarity in polymeization system on cationic polymerization of isobutylene depended on the character of the coinitiator Lewis acid. The polyisobutylenes obtained by using H2O/TiCl4/ED system with relatively low molecular weight could dissolve in CH2Cl2/C6H14cosolvent, and thus the monomer conversion and polymerization rate increased with increasing solvent polarity. However, the polyisobutylenes with high molecular weight obtained by H2O/AlCl3/ED system precipitated in cosolvent with CH2Cl2/C6H14>8/2during polymerization and thus monomer conversion decreased in CH2C12or CH2C12/C6H14cosolvent with high polarity.更多还原