环硅氧烷开环聚合研究进展

聚硅氧烷(如硅油、硅橡胶、硅树脂等)具有很多优异的性能,如耐高低温、耐紫外线辐射、耐候、低表面张力、电气绝缘、生理惰性等,已被广泛应用于航空航天、电子电器、化工、机械、建筑、交通、医疗卫生、农业等领域。聚硅氧烷制备方法主要有环硅氧烷开环聚合和硅氧烷缩聚。本文从环硅氧烷阴离子开环聚合、阳离子开环聚合和其它聚合方法等出发,较详细介绍了环硅氧烷开环聚合近年来的研究进展,并指出环硅氧烷开环聚合制备有机硅高分子材料所面临的问题。     

环硅氧烷负离子乳液聚合中活性中心浓度的变化规律

以八甲基环四硅氧烷(D4)为单体,十二烷基二甲基苄基氢氧化铵(BDAH)为乳化剂兼催化剂,进行环硅氧烷负离子乳液聚合,采用凝胶色谱(GPC)测定聚合产物的转化率及分子量.在此基础上,分析基元反应,提出活性中心生成机理,并应用环硅氧烷开环聚合普适动力学模型计算乳液聚合平衡之前的活性中心浓度变化规律.结果发现,聚合温度较低时,活性中心浓度随时间逐渐增加,最终恒定;聚合温度较高时,活性中心浓度随时间仅单调递增.结果与机理相符.     

一氯代八甲基环四硅氧烷阳离子聚合动力学

合成了八甲基环四硅氧烷的一氯取代物,并以其为单体,98%浓硫酸为催化剂,采用称重法研究了一氯代八甲基环四硅氧烷阳离子开环的本体聚合动力学,探讨了温度,催化剂浓度对其聚合速率常数的影响.研究表明:温度,催化剂浓度对一氯代八甲基环四硅氧烷的聚合速率有显著影响,其聚合活化能是40.37kJ.mol-1;与八甲基环四硅氧烷阳离子开环聚合相比,氯代甲基使硅氧烷的开环聚合速率减慢,聚合活化能升高.     

特定乙烯基和硅氢键含量聚硅氧烷的可控制备

以1,3,5-三乙烯基-1,3,5-三甲基环三硅氧烷与六甲基环三硅氧烷为共聚单体,四氢呋喃为溶剂,在正丁基锂引发条件下实现可控阴离子开环共聚,制备特定乙烯基含量的聚硅氧烷;同时,以1,3,5,7-四甲基环四硅氧烷与六甲基环三硅氧烷为共聚单体,四氢呋喃为溶剂,在浓硫酸引发条件下实现可控阳离子开环共聚,制备特定硅氢键含量的聚硅氧烷,为制备具有特定乙烯基和硅氢键含量聚硅氧烷国防专用标准物质奠定了基础。     

亲核性调节剂在异丁烯阳离子聚合中的作用机理

亲核性调节剂在异丁烯活性阳离子聚合中发挥着极其重要的作用 ,其作用机理主要包括 :(1)碳阳离子稳定化作用 ,即亲核性试剂或它们与Lewis酸生成的络合物与增长链的末端结合 ,来降低活性中心阳离子的“阳离子性” ,抑制副反应 ,使聚合反应呈现活性聚合特征 ;(2 )质子捕获作用 ,即亲核性试剂捕获质子 ,抑制质子的不可控引发和链转移反应 ;(3)增长链表观稳定作用 ,即亲核试剂降低了增长速率与引发速率之比 ,提高引发效率 ,降低增长速率 ,降低分子量分布 ;(4)抑制自由离子增长作用 ,即亲核试剂与质子源和Lewis酸反应 ,生成同阴离子 ,产生同离子效应 ,抑制自由离子活性中心的引发增长作用。     

六甲基环三硅氧烷（D3）阴离子开环聚合机理与动力学研究

本文从聚合机理和反应动力学两方面综述了近年来六甲基环三硅氧烷（D3）的阴离子开环聚合研究进展。Frye等人提出在非极性的碳氢溶剂中会形成引发剂的的三种加成物质,在不加入促进剂的情况下不会进行D3的开环聚合,这一开环聚合机理成为随后D3阴离子开环聚合机理研究的基础,研究者采用MALDI-TOF研究聚合机理得到的结论证实了这一机理的正确性,促进剂、溶剂、引发剂的类型和聚合步骤会改变活性链末端的缔合和解缔合的平衡能力,对D3开环过程中的反咬和再分布副反应有显著影响。D3开环聚合增长速率对单体浓度为一级,不同的促进剂和引发剂会显著改变活性链末端的缔合能力,从而显著影响聚合动力学。     

八甲基环四硅氧烷正离子细乳液开环聚合动力学

以十二烷基苯磺酸钠(SDBS)为乳化剂,硫酸或盐酸为催化剂,八甲基环四硅氧烷(D4)为单体,十六烷为共稳定剂,超声预乳化,制备了聚硅氧烷细乳液,研究了超声时间、催化剂用量、乳化剂用量和温度对聚合动力学的影响.结果表明,在一定酸度范围内,聚合速度与硫酸浓度0.81次方、与盐酸浓度1.02次方、与乳化剂浓度-0.66次方成正比,反应的表观活化能为40.56kJ/mol.     

环四硅氧烷乳液聚合制备弹性粒子及其反应动力学的研究

用八甲基环四硅氧烷（Ｍｅ－Ｄ４）与四甲基四乙烯基环四硅氧烷（Ｖｉ－Ｄ４）乳液聚合得到了聚硅氧烷乳液，通过乙烯基的自由基聚合反应得到交联的乳胶粒子从而制备出有机硅弹性粒子．对乳液聚合的动力学和共聚物组成进行了研究，同时讨论了Ｍｅ－Ｄ４和Ｖｉ－Ｄ４残基在聚合链上的分布     

八甲基环四硅氧烷阴离子乳液聚合反应的研究

研究了八甲基环四硅氧烷(D_4)在十二烷基本磺酸(DBSA)及其钠盐(Na-DBSA)作用下的阴离子乳液聚合反应,讨论了温度、乳化剂和催化剂用量对反应速度及聚合物分子量的影响。认为该聚合反应包括D_4的水解开环、D_4和羟基硅氧烷的加成及羟基硅氧烷之间的缩合三类基本反应,乳液颗粒表面是主要反应区。     

在阳离子乳化剂的存在下八甲基环四硅氧烷的乳液聚合

研究了八甲基环四硅氧烷(D_4)在十二烷基二甲基苄基卤化铵及碱存在下乳液聚合的反应机理。聚合分二步进行:D_4先开环生成具有端羟基的聚二甲基硅氧烷,然后再缩合。反应终点有二个平衡反应;不同分子量的羟基封头的聚二甲基硅氧烷的平衡,以及羟基封头的线型聚硅氧烷和环硅氧烷的平衡。平衡时羟基封头的聚硅氧烷的量为87％并提出了主要反应位置是在胶束表面并逐渐转移到随后形成的聚合物颗粒表面,单体液滴是次要反应区。     

Cooperative nucleophilic-electrophilic organocatalysis by ionic liquids

The anionic and the cationic partners of ionic liquids may act cooperatively and independently as nucleophilic and electrophilic catalysts. This ambiphilic propensity was demonstrated by kinetically discriminating the contributions of the anion (nucleophilic catalyst) and of the cation (electrophilic catalyst) to the solvent-free Baylis-Hillman dimerization of cyclohexenone catalysed by ionic liquids.     

Preparation of polyacrylate–polysiloxane core–shell latex particles

Crosslinked polymer seed latexes of butyl acrylate, methyl methacrylate and methacrylic acid were synthesized with ethylene glycol dimethacrylate as a crosslinking agent in a first step. Three different processes of seeded emulsion polymerization were used to prepare an outlayer of polysiloxane on the above seed latex particles: (A) direct anionic polymerization of D₄ (octamethyl tetracyclosiloxane) catalyzed by potassium hydroxide; (B) direct cationic polymerization of D₄ onto the seed catalyzed by dodecylbenzene sulfonic acid; (C) a vinyl-containing polysiloxane prepared by copolymerization of D₄ and vinyl septamethyl tetracyclosiloxane was added before the D₄ cationic polymerization. Characterization by transmission electron microscopy showed that only process C provided satisfactory results. Film hardness was measured, and the latex film from process C demonstrated the lowest hardness of all the films. The mechanism of polymerization is discussed.     

THE EFFECT OF EMULSION COMPOSITION OF ASA ON SIZING PERFORMANCE IN THE PAPER WEB

Effects of emulsifying chemicals and emulsion aging on the sizing performance of alkenyl succinic anhydride (ASA) were investigated. The emulsifying chemicals were nonionic and anionic surfactants and cationic starches. Image analysis in emulsion quality control was applied. It was found that the use of surfactants may deteoriate remarkably the sizing efficiency if the surfactant and its dosage is not carefully chosen. The need for surfactants in emulsification was affected by the properties of ASA and the mixing energy available. The act of cationic starch both as an effective stabilizer and as a retention agent in ASA-sizing systems was established.     

The Highly Controlled and Efficient Polymerization of Ethylene

The highly controlled and efficient polymerization of ethylene is a very attractive but challenging target. Herein we report on a Coordinative Chain Transfer Polymerization catalyst, which combines a high degree of control and very high activity in ethylene oligo- or polymerization with extremely high chain transfer agent (triethylaluminum) to catalyst ratios (catalyst economy). Our Zr catalyst is long living and temperature stable. The chain length of the polyethylene products increases over time under constant ethylene feed or until a certain volume of ethylene is completely consumed to reach the expected molecular weight. Very high activities are observed if the catalyst elongates 60 000 or more alkyl chains and the polydispersity of the strictly linear polyethylene materials obtained are very low. The key for the combination of high control and efficiency seems to be a catalyst stabilized by only one strongly bound monoanionic N-ligand.     

苯乙烯在阴离子型聚氨酯纳米水分散液中聚合过程的研究

采用自乳化法制备出阴离子聚氨酯纳米水分散液,以其作为乳化剂使苯乙烯单体在其中进行聚合,制备出不同聚苯乙烯与聚氨酯质量比的阴离子型PS/PU纳米复合物水分散液;对苯乙烯单体的聚合过程进行了研究;采用光子相关谱仪和透射电镜对其微观结构、粒径及其分布进行了测试,结果表明,该方法能够制备出稳定的具有核壳结构的PS/PU纳米复合物水分散液,但当苯乙烯单体浓度增大到一定程度(PS/PU质量比为50∶100)时,粒子不稳定而发生聚集.     

HSAB principle and desulphuration reaction during ionic coordination polymerization of thiiranes [1]

Desulphuration of trimethylthiirane (TMT), catalyzed by anionic and cationic catalysts for thiirane polymerization, has been studied. The possibility of obtaining polymers having mono-, di- and trisulphide bonds during TMT polymerization by typical cationic catalysts has been shown. Some peculiarities of the desulphuration reaction during the polymerization of thiiranes by ionic catalysts have been found. Differences in their catalytic action, shown by the formation of different quantities of both disulphide SSbonds in polymer chain and alkene, are discussed from the point of view of HSAB principle and symbiotic effect of ligands at the counterion. It is shown that desulphuration reactions during the cationic and anionic polymerization of thiiranes have a similar electronic nature, consisting of increase of coordinative state and the activation of the acceptor orbital of the thiirane sulphur atom. The nucleophilic attack by thiirane (during cationic polymerization) or growing thiolate-ion (during anionic polymerization) on the electrophilic sulphur atom of thiiranium intermediates

respectively, is accompanied by concerted fragmentation of these intermediates, giving the alkene and disulphide fragment. Possible mechanisms have been suggested for thiirane desulphuration and SSbond formation in products of the ionic polymerization of thiiranes. HSAB principle proved to be very useful for discussion of experimental results and other aspects of thiirane polymerization.     

有机硅氧烷乳液粒子粒径及其分布的测定

本文采用甲基环硅氧烷与乙烯基环硅氧烷共聚合的方法,制得了硅油轧液,利用乙烯基双键使聚合物硬化,以固定乳液颗粒,并用电子显微镜观察研究了液珠的组成及分布情况。发现阴离子硅油乳液颗粒较阳离子乳液的粒子细,且粒径分布窄。在阳离子硅油乳液中添加非离子乳化剂,或采用机械后乳化的方法,能消除大粒径的液珠,使其颗粒变小、变匀,从而大大改善阳离子乳液的稳定性。     

Surfactant Mediated Cationic and Anionic Suspension Polymerization of PEG-Based Resins in Silicon Oil: Beaded SPOCC 1500 and POEPOP 1500

A novel surfactant has been synthesized for use in cationic and anionic ring-opening suspension polymerization of PEG-based macromonomers in silicon oil. A polymer of acrylate esters containing pentamethyldisiloxane and PEG was prepared by radical polymerization. The surfactant can stabilize an emulsion of PEG-based macromonomers, initiator, and solvent in silicon oil such that polymer beads are obtained by ring-opening polymerization, initiated either by a Lewis acid (cationic ring opening) or potassium tert-butoxide (anionic ring opening). The average bead size could be controlled by varying the stirring rate and the amount of surfactant and solvent. The surfactant does not interfere with the polymerization and can be removed together with residual silicon oil by a simple washing procedure.     

硅氧烷乳液聚合过程中大颗粒形成机理的研究Ⅱ．聚硅氧烷乳液的耐酸碱稳定性

研究了阴离子型与阳离子型聚硅氧烷乳液的耐酸碱稳定性。发现阴离子型乳液对酸碱都相当稳定，在乳液制备过程中，酸性催化剂不会引起乳液颗粒的凝聚；而阳离子型乳液的耐酸碱稳定性较差，尤其是引起乳液颗粒慢速凝聚的碱浓度下限值很低，碱是制备阳离子型乳液的催化剂，碱引起乳液颗粒的慢速凝聚是阳离子型乳液中大颗粒形成的主要原因。在乳液聚合过程中所发生的相当部分的乳化剂从水相向有机硅相的转移也是影响阳离子型乳液稳定性的一个重要因素。