共查询到19条相似文献,搜索用时 62 毫秒
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制备高质量的环氧化聚合物的关键是采用合适的催化剂。在我国 ,对环氧化物聚合催化剂的研究还处于研制开发阶段 ,本文提到的聚合方法各有其局限性 ,阳离子聚合能制造出许多有商业价值的高分子材料 ,但副反应多 ,分子量不易控制 ,一直未能实现工业化。阴离子聚合过程中往往存在转移反应 ,会生成低分子量齐聚物。配位聚合虽然在一定程度上可以实现聚合产物的立体结构调控 ,但反应机理复杂、反应过程难以控制、催化剂价格昂贵 ,目前还不能实现工业化。因此 ,尽快研究开发出一系列合适催化剂用来合成高质量的环氧化聚合物 ,必将带来巨大的经济效益和社会效益。 相似文献
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合成了希夫碱催化剂,并成功地催化丙交酯本体开环聚合。结果表明,希夫碱催化剂催化合成聚乳酸可达到较高的转化率(高于95%)。研究了单体与催化剂物质的量比、聚合时间及聚合温度对该催化剂催化丙交酯本体开环聚合反应的转化率及所得聚乳酸相对分子质量的影响。当单体与催化剂物质的量比为400,聚合时间24h,聚合温度140℃时,可得到黏均相对分子质量Mq=8.439×10^4的聚乳酸。 相似文献
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介绍了环氧化物阳离子开环聚合的机理,主要包括活性链端机理和活性单体机理等。活性链端机理认为聚合的活性中心位于聚合增长链的链端,聚合单体与活性链端接触发生聚合反应实现链增长;活性单体机理认为聚合的活性中心位于单体分子,在活性单体向聚合链端羟基增加的过程中实现链增长。两者相结合可较成功地解释环氧化物开环聚合的实验现象。 相似文献
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“双碳”背景下,利用CO2与环氧化合物为原料制备聚醚碳酸酯多元醇是CO2化工利用的有效途径。高效的催化剂能够促进CO2与环氧化物反应,制备更高性能的聚合物产品。本文详细介绍了近3年CO2与环氧化合物开环共聚催化剂研究的主要进展。文中从非均相催化剂和均相催化剂两个方面,分别对金属羧酸盐、双金属氰化物、金属Salen、金属卟啉以及新型有机催化剂进行归类和综述。低廉的非均相催化剂仍是工业化实验的首选,但如何通过催化剂制备工艺控制活性位点分布,从而控制聚合物产品质量,是未来需要研究的重点。金属Salen催化剂是目前最热门的研究方向,其有机配体结构的多样性赋予多种金属组合配位的可能,期待开发更高效低廉的催化剂。 相似文献
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Shigeki Habaue Momoko AsaiMasatake Morita Yoshio OkamotoHiroshi Uyama Shiro Kobayashi 《Polymer》2003,44(18):5195-5200
α-Methylenemacrolides having various groups, such as aromatic, ether, and amine, were enzymatically, anionically, and radically polymerized. The polymerization with the lipase catalyst successfully afforded polymers only through the ring-opening process, whereas the vinyl polymerizations selectively proceeded by using anionic and radical initiators. The polyesters obtained by the enzymatic polymerization have a polymerizable methacrylic methylene group in the main-chain, in addition to the aromatic and polar groups, and were further radically polymerized to quantitatively produce a cross-linked polymer gel. 相似文献
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Julian Chojnowski 《Journal of Inorganic and Organometallic Polymers》1991,1(3):299-323
Some basic aspects of the kinetics and mechanisms of anionic and cationic ring-opening polymerization of cyclic siloxanes are discussed in connection with their use in polymer synthesis. The emphasis is put on the polymerization of strained ring monomers, such as cyclic trisiloxanes, since these provide the possibility of tailoring the polymer structure. Much attention is devoted to association phenomena and to oligomer formation processes.This review is from the Second International Topical Workshop, Advances in Silicon-Based Polymer Science. 相似文献
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This paper reviews the recent discoveries that were achieved by our group in the field of particle synthesis via ring-opening metathesis polymerization (ROMP). Both polynorbornene and polybutadiene-based particles were prepared by the respective ROMP of norbornene and cyclooctadiene initiated by (PCy3)2Cl2RuCHPh using several methods of polymerization in dispersed media, such as dispersion, suspension and miniemulsion. Depending upon the process implemented, particles size was found to range from 300 nm to 20 μm. 相似文献
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Li-Bong W. Lee 《Polymer》2004,45(19):6479-6485
‘Living’ ring-opening metathesis polymerization (ROMP) permits the synthesis of narrow-distribution homopolymers and well-defined block copolymers - provided no side reactions occur. However, acyclic metathesis between the chain end and double bonds in the polymer backbone competes with propagation during ROMP of cyclopentene, even with a mild Mo catalyst, though the rate constant is some 1600-fold smaller. ‘Dead’ chains in the reaction mixture can also be attacked; the products of acyclic metathesis are tagged by quenching the ROMP reaction with pyrenecarboxaldehyde. The extent of acyclic metathesis can be minimized through proper choice of reaction conditions, permitting the synthesis of narrow-distribution polycyclopentene with 100 kg/mol molecular weight. 相似文献
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Comb-shaped graft copolymers with poly(methyl acrylate) as a handle were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) techniques in three steps. First, copolymers of poly(styrene-co-chloromethyl styrene), poly(St-co-CMS), were prepared by RAFT copolymerization of St and CMS using 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate (EPDTB) as RAFT agent. Second, the polymerization of MA using poly(St-co-CMS)-SC(S)Ph as macromolecular chain transfer agent produced block copolymer poly(St-co-CMS)-b-PMA. Third, cationic ring-opening polymerization of THF was performed using poly(St-co-CMS)-b-PMA/AgClO4 as initiating system to produce comb-shaped copolymers. The structures of the poly(St-co-CMS), poly(St-co-CMS)-b-PMA and final comb-shaped copolymers were characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). 相似文献
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The rapid development of biodegradable and biocompatible materials for biomedical applications is reflected in the search for new methods for aliphatic polyester modification applicable in this field. One possible approach is modification by changes to the polymer topology.This review covers the main methods of synthesis of branched aliphatic biodegradable and biocompatible (co)polyesters, where the ring-opening polymerization (ROP) of cyclic esters or cyclic carbonates is the leading process. First, literature examples of ring-opening multibranching polymerization (ROMBP) of AB2-type hydroxyl-substituted cyclic lactones, lactides and carbonates are cited followed by the presentation of the application of AB-type cyclic esters and additionally AB2 cyclic ethers or esters as “branching monomers” for the synthesis of branched polyesters based on polycaprolactone (PCL), polylactide (PLA) and polyglycolide (PGA). In the following part, methods involving the combination of the ROP of AB-type cyclic esters and condensation processes leading to branched structures are summarized. Other related strategies leading to “dendri-star” or “core–shell” copolyesters are also discussed. Several examples of approaches to PCL and PLA graft copolymer syntheses are also shown. The advantages and disadvantages of the presented methodologies of branched polyester synthesis are highlighted. Finally, the influence of the branched structure on the properties of the presented class of polyesters, important from the application point of view, is considered. 相似文献
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The polymerization of 7-, 8- and 11-membered lactones, 6-methylene-1,4-oxathiepan-7-one, 3-methylene-1,5-oxathiocan-2-one and 3-methylene-1-oxa-5-thiacycloundecan-2-one in benzene at 70, 40–70 and 40–65 °C, respectively, is presented. All polymerizations proceeded with complete ring-opening up to approximately 25% conversion, where insoluble polymer was formed. Evidence is given attributing polymer double bond loss to crosslinking, although redistribution of the molecular weights via addition to polymer double bonds followed by β-fragmentation also appears to occur for polymerizations of the 8- and 11-membered lactones. Michael adducts of lactones with 2-methyl-2-propanethiol were prepared as models for chain-transfer products of hydrogen abstraction by carbon-centred radicals. Polymerization rates were found to increase marginally with ring size. Arrhenius parameters obtained for the polymerizations of the 8- and 11-membered lactones indicated that the addition step was more important than fragmentation in determining the rate of propagation. 相似文献
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Sijiu Jiang 《Polymer》2010,51(18):4087-4094
A kinetic study on the ring-opening polymerization (ROP) of octamethylcyclotetrasiloxane (D4) in miniemulsion is presented in this work. The polymerization is initiated by dodecylbenzenesulfonic acid (DBSA) which also serves as the surfactant (inisurf). The influence of the size of monomer droplet and the concentration of DBSA on the polymerization rate were studied. Since the main place for the ROP of D4 was confirmed to be at the oil/water interface, a three-layer interface model was proposed to analyze the distribution of molecules at the interface and the effects of DBSA. A kinetic equation is then developed based on this model. In the equation, the polymerization rate (Rp) is related to the initial monomer concentration ([D4]0), the droplet radius (r), the coverage of DBSA on monomer droplets surface (x). The polymerization rate can be predicted from the kinetic equation feeding all parameters with their experimental values. Finally, the equation gave a good accordance between the predicted polymerization rate data and the experimental results under different polymerization conditions. 相似文献