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。     

含次环己基的有机硅单体及其低聚体的合成

硅氯仿和环己二烯-1,3进行硅氢加成反应,生成1,3-双(三氯硅基)环己烷,经醇解制得1,3-双(三乙氧硅基)环己烷,与溴化甲基镁反应,制得1,3-双(二乙氧甲硅基)环己环、1-(乙氧二甲硅基)-3-(二乙氧甲硅基)环己烷和1,3-双(乙氧二甲硅基)环己烷,它们在盐酸溶液中分别进行水解,得到各种含次环己基的有机硅低聚体,其中2,2,4,4,11,11,13,13-八甲基-3,12-二氧(杂)-2,4,11,13-四硅(杂)三环[11,3,1,1~(5,9)]十八烷和D_4相似,可能经开环聚合得到聚硅次环己基硅氧烷。     

聚有机硅氧烷的研究——Ⅳ.碱对聚二甲基硅氧烷交联的影响

高分子量的线型聚二甲基硅氧烷,即硅橡胶,可用八甲基环四硅氧烷(简称D_4)在适当催化剂下进行开环聚合。工业上普遍采用的聚合催化剂是氫氧化鉀。为了使催化剂能够均匀地分散在D_4中,可将氫氧化鉀和适量的D_4先行反应,形成合碱量較大的低分子量的聚二甲基硅氧烷(简称碱胶),然后以这种碱胶作为催化剂使D_4聚合。     

多巴胺为前驱体过渡金属与N共同掺杂的碳纳米管催化剂ORR性能研究

采用多巴胺的自氧化聚合在多壁碳纳米管表面进行聚合沉积修饰,经热处理可得到氮掺杂的碳纳米管催化剂,通过调整沉积次数可控制表面聚多巴胺C-N膜的厚度,从而调控N的掺杂量.研究沉积次数对多壁碳纳米管催化剂表面形貌、化学组成及原子结合形态的影响,并考察N掺杂的多壁碳纳米管催化剂的氧还原反应活性.在此基础上,用多巴胺配合Mn、Fe离子进行共同聚合沉积,热处理后得到Mn(Fe)、N共同掺杂的多壁碳纳米管催化剂,对催化剂进行了多种测试和电化学表征.循环伏安和线性扫描的电化学表征表明,N掺杂可有效提高催化剂的氧还原反应(ORR)活性,C-N膜的厚度会影响催化剂性能,Mn(Fe)-N@MWCNTs催化剂的氧还原活性高于只有N掺杂的催化剂,两种催化剂氧还原反应均为4电子反应路径,可直接将氧气还原成H_2O,且F e-N@MWCNTs催化剂表现出较好的抗甲醇能力.SEM照片可以看到聚多巴胺在碳纳米管表面形成C-N膜;R aman分析表明聚多巴胺沉积后提高了催化剂表面的无序性,缺陷增多;XPS表征显示过渡金属的掺杂改变了CN_x的结合状态.     

端基功能化聚烯烃的合成与应用

端基功能化聚烯烃（Cef-PO）在聚烯烃改性和构筑复杂结构聚合物方面有着重要应用。可通过控制烯烃配位聚合过程中的自发链转移反应,得到端基不饱和聚烯烃;或通过引入硼烷、磷烷、苯乙烯及其衍生物/氢气等链转移剂得到不同反应性基团封端的聚烯烃;再经进一步基团转化反应,得到多种不同性能的Cef-PO。另外,活性配位聚合过程中,通过对活性增长聚烯烃链选择性封端处理,或使用功能化的催化剂,也可以用来制备Cef-PO。通过配位链转移聚合,即聚烯烃链在催化剂金属中心和烷基金属链转移剂之间快速可逆链转移的聚合过程,可以直接得到具有高度反应活性的碳-金属键封端的聚烯烃,经化学转化得到Cef-PO。此外,叶立德活性聚合、共轭二烯烃的阴离子活性聚合和环烯烃的开环易位聚合也可以用来制备Cef-PO。向其他聚合方式（活性自由基聚合、活性阴离子聚合等）的转换及与点击化学的结合是Cef-PO应用的明显特点。Cef-PO的应用包括作为聚合物的改性剂以及用于合成具有复杂结构的聚合物。     

氢钼青铜对铂催化氧还原反应的促进作用

采用循环伏安法在玻碳电极上和硫酸溶液中电沉积制备出铂催化剂(Pt)及铂-氢钼青铜复合催化剂(Pt-HxMoO3), 用旋转圆盘电极研究并比较了它们对硫酸溶液中氧还原反应的催化活性. 研究结果表明, HxMoO3能明显地提高Pt对氧还原反应的电催化活性. 通过对静态电极上氧还原的峰电流与扫描速度的关系以及旋转圆盘电极上氧还原电流与旋转速度的关系的分析发现, HxMoO3提高了铂电极氧还原反应电荷传递步骤的传递系数, 因此加快了氧还原的动力学过程.     

微生物燃料电池非生物阴极催化剂的研究进展

在微生物燃料电池（MFC）中,以氧为电子受体具有很多优点,但氧阴极还原的反应动力学慢,会造成阴极电势的损失。 因此,提高阴极对氧还原的电催化活性和降低催化剂的价格是MFC非生物阴极催化剂的研究重点之一。 本文综述了近年来MFC中非生物阴极氧还原催化剂的研究进展。 重点讨论了贵金属Pt、过渡金属大环化合物以及金属氧化物催化剂对氧还原的电催化活性。 其中,非贵金属氧化物及过渡金属大环化合物催化剂具有良好的性能,而且价格低廉,有望成为MFC非生物阴极Pt基催化剂的替代催化剂。     

钯铁合金催化剂的稳定性

分别在酸性和碱性溶液中, 结合旋转圆盘电极技术和电化学石英晶体微天平技术原位考察了钯铁合金催化剂对氧还原反应催化活性的稳定性. 发现在酸性溶液中, 钯铁合金催化剂对氧还原反应的催化活性不稳定, 原因是钯铁合金催化剂在酸性溶液中发生电化学/化学溶解; 在碱性溶液中, 覆盖在电极表面的钯铁合金催化剂的质量及电化学活性面积在电化学扫描过程中不发生明显变化, 保持对氧还原反应的催化活性, 证明钯铁合金催化剂在碱性介质中非常稳定.     

甲基铝氧烷的改性及其对乙烯聚合催化活性的影响

用BCl3为修饰剂制备了改性甲基铝氧烷(BMAO) 以二氯二茂锆为主催化剂、BMAO为助催化剂,考察了影响乙烯聚合活性的各种因素及其聚合动力学行为 与常用的甲基铝氧烷(MAO)相比,BMAO用于催化体系显著提高了乙烯聚合的催化活性.     

硅胶负载型二茂铬催化剂乙烯聚合机理研究

硅胶负载二茂铬是一种无需烷基铝助催化剂的传统工业用乙烯聚合催化剂,但是目前其引发乙烯聚合机理尚不明确.本文通过密度泛函理论方法,基于文献提出的金属环状机理、铬氧环机理以及本文首次提出的铬茂环机理对该催化体系的聚合机理进行了系统研究.结果表明,金属环状机理链引发过程反应能垒较低,约为24.9kcal·mol-1,与实验结...     

Simultaneous Preparation of Multiple Polymer Brushes under Ambient Conditions using Microliter Volumes

The fabrication of well‐defined, multifunctional polymer brushes under ambient conditions is described. This facile method uses light‐mediated, metal‐free atom‐transfer radical polymerization (ATRP) to grow polymer brushes with only microliter volumes required. Key to the success of this strategy is the dual action of N‐phenylphenothiazine (PTH) as both an oxygen scavenger and polymerization catalyst. Use of simple glass cover slips results in a high degree of spatial and temporal control and allows for multiple polymer brushes to be grown simultaneously. The preparation of arbitrary 3D patterns and functional/emissive polymer brushes demonstrates the practicality and versatility of this novel strategy.     

π-Allyl nickel halide–oxygen system as a catalyst for polymerization of butadiene

The π-allyl nickel halide-oxygen system was found to be active as catalyst for stereospecific polymerization of butadiene. The catalyst from π-allyl nickel chloride or π-allyl nickel bromide yields the polymer of 90% cis-1,4 content with high activity, whereas the catalyst from π-allyl nickel iodide affords a polymer of 70% or less cis-1,4 content. The catalyst systems can be fractionated into two parts on the basis of solubility in benzene. It is concluded that the catalyst activity originates essentially from the benzene-insoluble nickel complex which is composed of oxygen, halogen, σ-allyl group, and nickel. The structure of growing polymer terminal is discussed in relation to the mechanism of the stereospecific polymerization.     

Polyisonitriles. II. Heterophasic catalytic synthesis of poly(α-phenylethylisonitrile) and of poly(n-hexylisonitrile)

A three-component catalytic system has been discovered, which successfully polymerizes α-phenylethylisonitrile to high polymer (DP = 200–900) and also polymerizes n-hexylisonitrile. The catalyst components are a strong acid, a free-radical source, and a heterophase and are all necessary in this system. The use of a liquid medium in which the polymer is insoluble promotes the rate of polymerization and total yield. Poly(α-phenylethylisonitrile), formed from monomer in a presence of oxygen and finely ground glass coated with sulfuric acid, can itself serve, in the presence of monomer and oxygen, as a catalyst for this polymerization. Preparative details and discussion of these synthesis factors are given.     

Modulation of the Aerobic Oxidative Polymerization in Phenylazomethine Dendrimers Assembling Copper Complexes

The aerobic oxidative polymerization of phenol derivatives can provide poly(phenylene oxide)s, which are known as engineering plastics. This oxidation can be carried out with atmospheric oxygen molecules as the oxidizing reagent in the presence of copper complexes as the catalyst; however, stoichiometric or excess amounts of bases are also generally required. By using a phenylazomethine dendrimer complexed with several equivalent amounts of copper chloride, the additive (base)‐free polymerization of 2,6‐difluorophenol was successful with a very small amount of the catalyst (0.7 mol % of copper for the monomer) because the dendrimer was composed of many Schiff base units, affording a base and catalyst (copper complex) condensed reaction field. The resulting polymer was nearly linear and the molecular weight was very high. When the equimolar amount of the copper complex in one dendrimer molecule was increased, the polymer obtained under this reaction condition was rather branched, resulting in a higher glass transition temperature.     

Synthesis and characterization of poly-β-hydroxybutyrate. I. Synthesis of crystalline DL-poly-β-hydroxybutyrate from DL-β-butyrolactone

The polymerization of β-butyrolactone was investigated as a possible monomer for a proposed synthesis of the naturally occurring polyester, D -poly-β-hydroxybutyrate (D -PHB). The racemic DL -monomer was used in this initial study to determine the best conditions and catalyst system for use in a subsequent study of the polymerization of optically active β-butyrolactone. In so doing it was found that certain organometallic catalysts (Et₂Zn and Et₃Al) plus a cocatalyst of water produced highly crystalline samples of polyester from the racemic monomer. This paper describes the synthesis and characterization of the racemic polymer obtained using these catalyst systems, and compares the results obtained with certain other catalysts that were also investigated for this purpose. Examination of the DL -PHB by infrared, NMR, x-ray, and electron microscopy shows that it is possible to synthesize a crystalline racemic polymer that is virtually identical (excepting optical activity) to the naturally occurring polymer, D -PHB.     

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。     

单茂金属烯烃聚合催化剂*

本文综述了近年来带有给电子配体的单茂金属化合物应用于烯烃聚合的研究。带有给电子配体的单茂金属化合物是目前烯烃配位聚合催化剂的研究热点之一。作为新型的聚合催化剂,这类催化剂具有合成简单、结构清晰的特点,用于催化烯烃聚合,可得到高聚合活性,同时聚合物可得到高的分子量。用于共聚时,具有很好的共聚能力。通过共聚,可以得到Zieler-Natta催化剂和传统茂金属催化剂不能得到的新共聚物。通过调整催化剂上茂配体和给电子配体的结构,可以方便地调节聚合行为,从而调整聚合物的结构。文中涉及了乙烯、alpha-烯烃的均聚与共聚,乙烯与环烯烃共聚合,苯乙烯聚合等方面的研究。     

Syndiospecific polymerization of styrene with embedded metallocene catalysts

Syndiotactic polystyrene (sPS) is a highly crystalline polymer with high melting point (270°C). The syndiospecific polymerization of styrene to sPS with metallocene catalysts is characterized by significant phase changes that lead to global gelation. Since sPS does not dissolve in styrene or solvents such as toluene and n-heptane, sPS precipitates out immediately from the liquid phase with the start of polymerization. The polymer crystallites aggregate to primary particles and they develop to a gel. The gelation is not due to cross-linking polymerization but due to strong molecular interactions between the polymer and monomer molecules. In this work, homogeneous Cp*Ti(OMe)₃ catalyst is heterogenized or embedded into sPS prepolymer particles. The embedded catalyst has been tested in a laboratory scale diluent slurry process to illustrate the feasibility of slurry phase polymerization for the synthesis of sPS particles.     

Synthesis and characterization of poly-β-hydroxybutyrate. II. Synthesis of D-poly-β-hydroxybutyrate and the mechanism of ring-opening polymerization of β-butyrolactone

Synthesis of the naturally occurring polyester, D -poly-β-hydroxybutyrate (PHB) was accomplished by using an optically active monomer. Polymerization of D -(+)-β-butyrolactone (β-BL) of 73% optical purity with a catalyst system of Et₃Al–H₂O produced a polymer with a similar optical activity and essentially identical to the natural polymer as isolated from bacterial cells. This paper describes the synthesis and characterization of this optically active polyester along with a suggested mechanism to account for the observed stereospecific polymerization of β-BL with this catalyst system.     

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.