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。     

氯甲基硅化合物与核酸碱基、核酸碱基衍生物和核苷的反应研究

在接近理论量碳酸钾存在下,并以DMF为溶剂,1,3-双(氯甲基)-1,1,3,3-四甲基二硅氧烷(CMDS)能使核酸碱基、核酸碱基衍生物和核苷甲基化,同时生成八甲基环四硅氧烷(D_4)。初步研究了反应机理,提出甲基化反应是分步进行的。     

高效液相色谱测定蝙蝠葛碱与其酯衍生物的容量因子k′及酯衍生物的水解速率常数

本文测定了蝙蝠蔼碱及其酯衍生物D_2,D_3,D_9,D_(10)在不同的流动相pH时的HPLC反相C_(13)柱容量因子k',并将流动相pH为7.4时测得的Logk'7.4与四个酯衍生物羟基上取代的侧链基团的疏水参数π进行了比较,两者相关性很好。对D,D_3,D_9,D_(10)在pH11.3碱性溶液中的水解动力学亦进行了研究。四个化合物的水解一级反应速率常数主要受羟基取代侧链基团的电子效应参数σ~*及立体参数的影响,而受Logk'或π的影响不显著。     

1,3-双[3-(1-甲氧基-2-羟基丙氧基)丙基]封端聚硅氧烷的合成

以1,3-双[3-(1-甲氧基-2-羟基丙氧基)丙基]四甲基二硅氧烷和八甲基环四硅氧烷(D4)为原料,通过阳离子催化开环聚合制备了1,3-双(3-(1-甲氧基-2-羟基丙氧基)丙基)封端聚硅氧烷,研究了反应温度,反应时间,催化剂种类及加入量对于聚合反应的影响,结果表明,最佳反应条件为:反应温度65℃,反应时间24h,浓硫酸作为催化剂加入量为反应物质量的0.3%,此时反应拥有最高的转化率。通过红外光谱与核磁共振光谱对产物进行了表征。     

硅氧烷改性线性酚醛的合成与性能研究

为了提高酚醛树脂的热稳定性,采用甲基三甲氧基硅烷(MTMS)对线性酚醛树脂(Novolac)进行改性,通过酯交换反应制得分子级硅氧烷改性线性酚醛树脂(SN),研究了催化剂种类、反应时间以及反应温度对SN分子量的影响,结果表明,最佳催化剂为冰醋酸,最佳反应时间为4~6h,最佳减压蒸馏温度为110℃。对SN结构的表征表明,Si—CH3和Si—O—CH3基团成功引入到Novolac的酚羟基上,且硅氧烷单体的一个甲氧基与Novolac的酚羟基发生的反应为主要反应。SN固化物的热稳定性结果表明,相比Novolac,在氮气气氛下,SN100固化物最大分解速率温度提高了80℃,最大分解速率降低了42.94%,1000℃的残碳率提高了8.97%,即是说硅氧烷的引入可显著提高Novolac的热稳定性。     

六甲基环三硅氧烷非平衡聚合的研究

六甲基环三硅氧烷(D_3)在为催化剂,二甲亚砜为促进剂的情况下聚合,得到了分子量分布窄且没有大环体的聚二甲基硅氧烷。本文指出了反应溶液中溶解的氧会降低催化剂的活性。在除去了溶液中的氧以后,聚合反应速度大为加快,D_3转化率几乎达100％,而且得到的聚合物是活性高分子,可以继续进行聚合。同时还研究了在除氧以后D_3非平衡聚合反应的特点。     

有机硅高分子研究的趋向 Ⅰ.聚有机硅氧烷

聚有机硅氧烷具有耐高温和良好的低温及介电性能,工业上有广泛的用途。有机硅氧烷高分子化学包括着单体的水解和缩聚,环状低聚物的聚合,聚合体的解聚,硅氧键的反应等。过去这几个方面的研究工作做得很多,主要的问题基本上得到解决。近几年来对反应的动力学、平衡和机理提出了新的数据和看法。最基本的反应;二甲基二羟基硅烷的缩聚动力学得到了实验的结果。八甲基四硅氧烷(以后简称 D_4)的碱催化聚合机理一般认为是没有什么可以怀疑的,M.库切拉(Kǚcera)举出一系列的事实说明已往的机理有修改的必要。以酸做催化剂聚合 D_4时,B.H.格罗别尔认为这不是酸而是氧化还原的催化作用。不同官能团的缩合反应中的副反应引起人们的注意。热稳定性、耐辐射性和粘度测定分子量的公式有了更准确的数据。多年来没有确定的有机硅的立体反应,L.H.佐默(sommer)等得到肯定的结论。本文总结了1959年以来关于有机硅氧烷的主要文献,从这可以看出近来研究的趋向。一些次要的工作也列在参考文献中。至于其他各类型的有机硅高分子将在以后发表。     

惰化处理硅藻土载体的一种新方法

G.V.Filonenko认为最好的载体惰化方法是化学键合聚合层覆盖法。D_4(八甲基环四硅氧烷)是近年来报道较多的毛细管内壁脱活试剂,但未见其用于硅藻土载体的惰化处理。考虑到氧气气氛中D_4高温化学反应和高温下微量水可能催化硅氧烷聚合,本文提出了一种高温D_4/O_2惰化硅藻土表面的新方法。对比考察了经此法处理的白色硅藻土101(101-AW-D_4/O_2)和商品101-AW-DMCS的色谱性能和对高聚物固定     

维生素D_2类似物的合成及生物活性研究进展

1α,25-二羟基维生素D_2(1α,25-(OH)2-D_2,125D_2)是维生素D_2的活性代谢产物,1α,25-二羟基维生素D_3(125D)则是维生素D_3最具活性的代谢产物。125D因高钙血症副反应而限制其临床应用,而维生素D_2及其类似物一般比相应维生素D_3类化合物副作用小。本文综述了两种临床应用效果较好的维生素D_2类似物度骨化醇及帕立骨化醇的合成新进展,以及侧链修饰、19-去亚甲基、A环C_3位修饰和九重氢同位素标记的维生素D_2类似物的合成及生物活性研究新进展,旨在为新型活性维生素D_2类似物的合成及临床开发提供参考。     

1α,25-双羟基维生素D_3的合成研究——从猪去氧胆酸甲酯合成25-羟基胆固醇

25-羟基维生素D_3(1)和1α,25-双羟基维生素D_3(2)是维生素D_3(3)在体内的两个重要代谢产物。2是目前所知生理活性最强的维生素D.1和2可治疗软骨病,特别用于对肝脏、肾脏功能不全的维生素D缺乏症。最近日本Kureha公司报道,它们还具有抑制白血病细胞和骨髓肿瘤细胞生长的作用。25-羟基胆固醇(4)是合成1和2的关键中间体。文献已有许多关于它的合成报道。     

Ionic polymerization in aqueous emulsion

A kinetic study of the anionic polymerization of octamethylcyclotetrasiloxane (D₄) in aqueous emulsion has been carried out in the presence of ionic additives. The rate of polymerization of several cyclosiloxanes has been compared, leading to additional evidence for an interfacial mechanism of polymerization. The emulsion process has been applied to the cationic polymerization of D₄ and of tetramethylcyclotetrasiloxane (D^H₄) initiated by dodecylbenzenesulfonic acid. Very efficient for the synthesis of linear polymethylhydrogenosiloxanes (PMHS), these conditions did not seem suitable for the polymerization of D₄. The extension of the process to other heterocyclic monomers is discussed through the anionic polymerization of phenylglycidylether.     

己内酰胺与环硅氧烷阴离子开环共聚合——Ⅱ.聚合反应过程研究

 研究探讨了己内酰胺和八甲基环四硅氧烷两种完全不同的环单体的共聚过程。在反应初期,环硅氧烷快于己内酰胺而先聚合,随后己内酰胺很快达高转化率。随聚合反应时间延长和环硅氧烷单体配比的增加,共聚体中的硅氧烷含量都相应增加。研究提出并证实了聚合过程中的一些主要反应,并由此推断了共聚产物的结构表达式。     

硅氧烷乳液聚合的研究Ⅲ.八甲基环四硅氧烷在阳离子乳液聚合过程中乳液颗粒的形成

八甲基环四硅氧烷(D_4)在阳离子乳液聚合过程中,首先被乳化成颗粒较大的“过渡粒子”,在这里以D_4的水解开环和加聚反应为主,然后转变为颗粒较小的稳定乳液粒子。聚合物端基≡SiOH的缩合反应主要在乳液粒子中进行。     

Block copolymers of polystyrene and poly(dimethyl siloxane). I. Synthesis and characterization

The block copolymers of the ABA type, poly(dimethyl siloxane-b-styrene-b-dimethyl siloxane), were synthesized by the anionic polymerization of styrene and cyclic siloxane monomer, hexamethyl cyclotrisiloxane (D₃) or octamethylcyclotetrasiloxane (D₄), with lithium or sodium biphenyl as initiator. The effect of initiator concentration, gegenion, and the polymerization temperature for styrene on molecular weight distribution (MWD) was investigated. Gel permeation chromatography (GPC) data show broader MWD of polystyrene prepared by sodium biphenyl in comparison to that produced by lithium biphenyl. The block copolymers have been characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectra. The influence of dimethylsiloxy units on thermal stability of the copolymers has also been discussed.     

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.     

硅氧烷乳液聚合的研究——Ⅱ.八甲基环四硅氧烷阳离子乳液聚合机理

根据八甲基环四硅氧烷(D_4)在阳离子乳液聚合过程中,聚合物的分子量及数目的变化等特点,提出并证明了D_4在乳液粒子表面进行聚合的机理的假设。     

硅氧烷乳液聚合的研究——Ⅰ.环硅氧烷在阳离子乳化剂存在下的乳化与聚合

<正> 有机硅乳液早已得到广泛应用,但关于有机硅乳液聚合以及反应机理的文献却很少。我们对此做了较为系统的研究,本文首先讨论了单体转化率的测定方法,探讨了乳液的形成过程,比较了不同的环硅氧烷向水相扩散及聚合的速度。     

POLYMERIZATION OF OCTAMETHYLCYCLOTETRASILOXANE WITH HEXAMETHYLDISILAZYL-LITHIUM AS INITIATOR*

 This work focused on the anionic polymerization of octamethylcyclotetrasiloxane (D₄, D = Me₂SiO_2/2) initiated by a new kind of initiator hexamethyldisilazyl-lithium (MM^NLi). ²⁹Si-NMR spectroscopy and gas chromatography (GC) were used to characterize the polymerization products. The process was accelerated by adding a small amount of high activity monomer D₃ and by raising the polymerization temperature. At the end of polymerization more than 95% of the monomer was converted to polymer and only a very small amount ofD₄ and D₅ remained in the polymers.     

Synthesis of saccharidic polymer colloids via free radical mini‐emulsion polymerization

Polymer colloids based on 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG) and butyl acrylate (BA) were prepared via free radical mini‐emulsion polymerization. The kinetic and colloidal features of the copolymerization were investigated. The final particle size (D) of the sugar latexes is inversely proportional to the concentration of the anionic emulsifier (sodium dodecyl sulphate, SDS) and the non‐ionic one (alkyl polyglucoside, APG). It was also found that D is independent of the concentration of either the water‐soluble initiator (potassium persulfate, KPS), or the oil‐soluble initiator (2,2′‐azobisisobutyronitrile, AIBN). The rate of mini‐emulsion polymerization is lower in comparison with the conventional emulsion polymerization under the same conditions. The polymerization rate (R_p) and the total number of particles (N_p) are proportional to the 0.72th and 0.93th power of the SDS, and to the 1.40th and 2.22th of the APG concentration. Following reaction orders, 0.79/0.06 were obtained for R_p/N_p versus the concentration of KPS, and 0.22/?0.01 for AIBN, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Preparation of free‐standing silicone particles in aqueous heterogeneous system

To prepare cross‐linked silicone (silicone rubber) particles in an aqueous medium, we investigated two synthesis methods involving a miniemulsion system. The first method was based on cationic ring‐opening polymerization of cyclic siloxane, which is a common synthetic route for linear silicone oil and uses octamethylcyclotetrasiloxane (D₄) as the monomer and dimeric D₄ (bis‐D₄) as the cross‐linker. Although this method produces silicone particles, the particles do not remain in the particulate state after drying because of low cross‐linking density. The polymerization mechanism of this method was also investigated, which proceeds under the ring‐opening reaction of D₄ in monomer droplets and upon polycondensation of hydrolyzed D₄, which occurs in the water phase (ie, outside the monomer droplets). This mechanism implied that introducing the cross‐linking structure into particles is difficult because of the low solubility of bis‐D₄ in water. To overcome these difficulties, we demonstrated a second method of preparing silicone particles based on the thiol‐Michael addition reaction between thiol‐terminated silicone oil and triacrylate in miniemulsion systems. Transmission electron microscopy images indicated that the silicone particles obtained in the particulate state upon drying and the aggregates of these particles showed elasticity.