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1.
In tetrahydrofuran, with Na+ as counter-ion, the anionic polymerization of acrolein involves numerous transfer reactions to monomer and to polymer; on the other hand, termination of growing chains does not occur. The use of initiators, like carbanions or oxanions, does not affect the polymerization rate. The kinetic order of the reaction is unity for monomer and unity for initiator; these results indicate that the living ends are not associated at the studied concentrations of initiator. Without stating precisely the mechanism of the transfer reactions, we have proposed a kinetic scheme.In tetrahydrofuran, with Na+ as counter-ion, the anionic polymerization of acrolein involves numerous transfer reactions to monomer and to polymer; on the other hand, termination of growing chains does not occur. The use of initiators, like carbanions or oxanions, does not affect the polymerization rate. The kinetic order of the reaction is unity for monomer and unity for initiator; these results indicate that the living ends are not associated at the studied concentrations of initiator. Without stating precisely the mechanism of the transfer reactions, we have proposed a kinetic scheme. 相似文献
2.
Ben-Ami Feit Eri Heller Albert Zilkha 《Journal of polymer science. Part A, Polymer chemistry》1966,4(5):1151-1161
The anionic heterogeneous polymerization of methacrylonitrile by butyllithium in petroleum ether was investigated. The polymerization was of the “living” type, as seen from the linear dependence of the molecular weights on [MAN]/[BuLi]. This behavior was further supported by block polymerization experiments in which the monomer was added in two portions and the molecular weights obtained were directly proportional to the total monomer concentration. The initiator efficiency was low, and initiator consumption was only about 2%. This fact, together with the results of the block polymerizations showed that there was preferential addition of monomer to the growing chain ends rather than to the initiator. The molecular weights were independent of the rate of monomer addition. This as well as the “living” behavior of the polymerization of methacrylonitrile on a wide range of monomer and catalyst concentrations and the absence of chain transfer to monomer was essentially different from that of the similar heterogeneous polymerization of acrylonitrile by butyllithium previously investigated. This is due to the absence of an α-acidic hydrogen in methacrylonitrile. 相似文献
3.
Funian Zhao Ali Reza Mahdavian Mohammad Bagher Teimouri Eric S. Daniels Andrew Klein Mohamed S. El-Aasser 《Colloid and polymer science》2012,290(13):1247-1255
The preparation of poly(vinyl acetate) with well-controlled structure has received a great deal of interest in recent years because of a large number of developments in living radical polymerization techniques. Among these techniques, the use of reversible addition–fragmentation chain transfer (RAFT)-mediated polymerization has been employed for the controlled polymerization of vinyl acetate due to the high susceptibility of this monomer towards chain transfer reactions. Here, a novel water-soluble N,N-dialkyl dithiocarbamate RAFT agent has been prepared and employed in the emulsion polymerization of vinyl acetate. The kinetic results reveal that the polymerization nucleation mechanism changes from homogeneous to micellar and RAFT-generated radicals can change the kinetic behavior from conventional emulsion polymerization to living radical polymerization. At higher concentrations of the modified RAFT agent, as a result of an aqueous phase reaction between RAFT and sulfate radicals, relatively more hydrophobic radicals are generated, which favors entry and propagation into micelles swollen with monomer. This observation was determined from the investigation of the polymerization rate and measurements of the average particle diameter and the number of particles per liter of the aqueous phase. Molecular weight analysis also demonstrated the participation of the RAFT agent in the polymerization in such a way as to restrict chain transfer reactions. This was determined by examining the evolution of polymer chain length and attaining higher molecular weights, even up to 50?% greater than the samples obtained from the conventional emulsion polymerization of vinyl acetate in the absence of the synthesized modified RAFT agent. 相似文献
4.
A living functionalization method has been investigated for group transfer polymerization (GTP) of poly(alkyl methacrylates) using ethyl 2-phenyl-2-butenoate (EPB). The end-capping reactions of EPB to living trimethylsilyl ketene acetal-ended poly(methyl methacrylate) (PMMA) chain ends have been systematically studied and characterized by SEC, VPO, UV-visible spectrosocopy, 1H and 13c NMR spectroscopy. The results of sequential monomer addition, varying stoichiometry and copolymerization indicate that EPB effects efficient chain end functionalization only at stoichiometric concentrations; chain transfer reactions (chain transfer constant = 0.4) occur with excess EPB and during copolymerization with MMA. Chain transfer reactions (chain transfer constant = 0.1) also occur when copolymerizing ethyl 2-methyl-2-butenoate with MMA. 相似文献
5.
Modeling and Experimentation of RAFT Solution Copolymerization of Styrene and Butyl Acrylate,Effect of Chain Transfer Reactions on Polymer Molecular Weight Distribution
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Chain transfer reactions widely exist in the free radical polymerization and controlled radical polymerization, which can significantly influence polymer molecular weight and molecular weight distribution. In this work, the chain transfer reactions in modeling the reversible addition–fragmentation transfer (RAFT) solution copolymerization are included and the effects of chain transfer rate constant, monomer concentration, and comonomer ratio on the polymerization kinetics and polymer molecular weight development are investigated. The model is verified with the experimental RAFT solution copolymerization of styrene and butyl acrylate, with good agreements achieved. This work has demonstrated that the chain transfer reactions to monomer and solvent can have significant impacts on the number‐average molecular weight (Mn) and dispersity (Ð). 相似文献
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Shigeru Yamago Prof. Dr. Takeshi Yamada Dr. Manabu Togai Yuu Ukai Eiichi Kayahara Na Pan Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(4):1018-1029
Several organostibine chain‐transfer agents possessing polar functional groups have been prepared by the reactions of azo initiators and tetramethyldistibine ( 1 ). Carbon‐centered radicals thermally generated from the azo initiators were trapped by 1 to yield the corresponding organostibine chain‐transfer agents. The high yields observed in the synthesis of the chain‐transfer agents strongly suggest that distibines have excellent radicophilic reactivity. As the reactions proceeded under neutral conditions, functional groups that are incompatible with ionic conditions were incorporated into the chain‐transfer agents. The chain‐transfer agents were used in living radical polymerization to synthesize the corresponding α‐functionalized polymers. As the functional groups in the chain‐transfer agents did not interfere with the polymerization reaction, well‐controlled polymers possessing number‐average molecular weights (Mns) predetermined by the monomer/transfer agent ratios were synthesized with low polydispersity indices (PDIs). The organostibanyl ω‐polymer ends were transformed into a number of different functional groups by radical‐coupling, radical‐addition, and oxidation reactions. Therefore, it was possible to synthesize well‐controlled telechelic polymers with the same and also with different functional groups at their α‐ and ω‐polymer ends. Distibine 1 was also found to increase PDI control in the living radical polymerization of styrene and methyl methacrylate (MMA) using a purified organostibine chain‐transfer agent. Well‐controlled poly(methyl methacrylate)s with Mn values ranging from 10 000 to 120 000 with low PDIs (1.05–1.15) were synthesized by the addition of a catalytic amount of 1 . The results have been attributed to the high reactivity of distibine 1 towards polymer‐end radicals, which are spontaneously deactivated to yield organostibine dormant species. 相似文献
8.
简述了可控聚合技术的发展和分散剂作用机理,分别介绍了氮氧稳定自由基聚合、原子转移自由基聚合和可逆加成―断裂链转移自由基聚合的可控机理和适用环境,重点描述了可控聚合技术在颜料分散剂开发中的研究现状和市场前景。 相似文献
9.
F. P. Boettcher 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5-7):665-678
Application of anionic polymerization and group transfer polymerization to the synthesis of methacrylate polymers with one or two functional endgroups and with functional groups in the side chain is described. Success in the preparation of end-functional polymers depends largely on the absence of chain transfer and chain termination reactions. The higher stability of living chains in group transfer polymerization at temperatures as high as 100°C makes it the preferred route to functional polymers. 相似文献
10.
The polymerization kinetics of n-lauryl acrylate have been investigated in ethyl acetate and n-heptane at 40°C. A high monomer order, 1.6(5), was found in both solvents. Corresponding initiator orders, determined using Azdn and lauroyl peroxide, were slightly less than the usual value of 0.5. Although the chain termination reaction is undoubtedly diffusion controlled from the start of polymerization, diffusion effects dependent on monomer concentration only partly account for the high monomer order. Other possible explanations based on primary radical termination, “cage-effects,” degradative chain transfer, and radical complexing are also not applicable. Contrary to observations with lower acrylate esters, autoacceleration effects do not occur in the high conversion polymerization of n-lauryl acrylate. Ths probably reflects the reduced importance of radical branching reactions with this monomer. 相似文献
11.
Galina I. Litvinenko Alexander A. Arest-Yakubovich 《Macromolecular theory and simulations》1992,1(5):321-331
A new theoretical consideration of chain transfer to monomer in the anionic polymerization of hydrocarbon monomers is presented. It is shown that the kinetic scheme used in theoretical studies reported previously contradicts the widespread views on the chemical mechanism of carbanionic reactions. It is suggested that the most probable path of the transfer reaction is the proton abstraction from the side group of the monomer; the terminal double bond of the monomer molecule remains unchanged, and therefore the intermediate species can participate in succeeding reactions as a macromonomer. The molecular characteristics of polymer formed in processes with monomer transfer by side-group substitution are determined. At high conversion, the polymer formed in such a process is shown to possess a number-average degree of polymerization, P̄n, approaching the theoretical value for living polymers, and a P̄w exceeding it the more the higher the intensity of transfer. Furthermore, it shows a broad molecular weight distribution and a fairly noticeable degree of branching. These results considerably differ from those previously reported. 相似文献
12.
Stéphane Carlotti Cyrille Billouard Emilie Gautriaud Philippe Desbois Alain Deffieux 《Macromolecular Symposia》2005,226(1):61-68
The anionic polymerization of propylene oxide (PO) initiated by alkali metal alkoxides is in non polar solvents a very slow and non controlled reaction process. Transfer reaction to monomer is predominant, allowing only the preparation of low molar masses PPO. The influence of the addition of trialkylaluminium to either an alkali metal alkoxide or a tetraalkylammonium salt used as initiator for PO polymerization in hydrocarbon media was investigated. A strong enhancement of the polymerization rate accompanied by a drastic decrease of the transfer reactions is observed, allowing the synthesis of PPO with well controlled molar masses. At constant monomer and alkali metal alkoxide concentrations, the polymerization rate increases with increasing trialkylaluminium concentration. Results indicate that the trialkylaluminium derivative is involved in the formation of two distinct complexes, one with the alkali metal alkoxide or the tetraalkylammonium salt and another one with the PO monomer which is strongly activated towards nucleophilic active species. Significant differences between the alkali metal and tetraalkylammonium based initiators are observed. In particular much less trialkylaluminum activator is needed with the ammonium salt to get the same rate of propagation and controlled polymerization. 相似文献
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Ping Zhao Qi‐Dan Ling Wei‐Zhi Wang Jie Ru Sheng‐Biao Li Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(2):242-252
The controlled/living radical polymerization of 2‐(N‐carbazolyl)ethyl methacrylate (CzEMA) and 4‐(5‐(4‐tert‐butylphenyl‐1,3,4‐oxadiazol‐2‐yl)phenyl) methacrylate (t‐Bu‐OxaMA) via reversible addition‐fragmentation chain transfer polymerization has been studied. Functional polymers with hole‐ or electron‐transfer ability were synthesized with cumyl dithiobenzoate as a chain transfer agent (CTA) and AIBN as an initiator in a benzene solution. Good control of the polymerization was confirmed by the linear increase in the molecular weight (MW) with the conversion. The dependence of MW and polydispersity index (PDI) of the resulting polymers on the molar ratio of monomer to CTA, monomer concentration, and molar ratio of CTA to initiator has also been investigated. The MW and PDI of the resulting polymers were well controlled as being revealed by GPC measurements. The resulting polymers were further characterized by NMR, UV‐vis spectroscopy, and cyclic voltammetry. The polymers functionalized with carbazole group or 1,3,4‐oxadiazole group exhibited good thermal stability, with an onset decomposition temperature of about 305 and 323 °C, respectively, as determined by thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 242–252, 2007 相似文献
16.
Electroinitiated polymerization of acrolein has been achieved by controlled potential electrolysis at the reduction peak potential of the monomer for direct electron transfer. Kinetics and type of mechanism of the polymerization have been investigated. the structure of the polymer has also been examined by IR spectroscopy. in a separate experiment, a small amount of CCI4 was added to a polymerization system. Since the reduction peak potential of CCI4 appears at a more anodic region than that of acrolein on mercurized platinum, initiation proceeds via the electrolytic product of CCI4. the direct and indirect initiation mechanisms are compared. It is found that electroinitiated polymerization of acrolein carried out by direct electron transfer from cathode to monomer (in the absence of CCI4) proceeds simultaneously via radical and anionic mechanism. 相似文献
17.
J. M. Pujol J. Brossas J. M. Catala 《Journal of polymer science. Part A, Polymer chemistry》1988,26(6):1573-1586
The anionic synthesis of polybutadiene–polysulphide polymers from butadiene, elemental sulphur, and sodium was studied in a polar solvent (THF). The polycondensation results from the combination of three reactions: initiation of the monomer by the alkali metals, anionic propagation, and deactivation of the dianionic species on elemental sulphur. From the characterization of the resulting polymers it has been shown that the sulphur rank of the polymer can be adjusted by varying the ratio K = [sodium]/[sulphur]. The degree of polymerization of the organic chain can be controlled by changing the temperature or the monomer concentration. From the thiol content, it has been concluded that the polysulphide polymers are principally in a cyclic form. It was also observed that the formation of the 1,4-structure for the butadiene unit is quantitative when the deactivation of the corresponding carbanions occurs on elemental sulphur. 相似文献
18.
Summary. The anionic polymerization of four bis-functionalized styrene derivatives with α-alkylvinyl groups have been carried out in
THF at −78°C with the initiator prepared from oligo(α-methylstyryl)lithium and potassium tert-butoxide. The four monomers herein used are 4-isopropenylstyrene (4), 3-isopropenylstyrene (5), 2-isopropenylstyrene (6), and 4-(α-isopropylvinyl)styrene (7). It was found that under such polymerization conditions, the vinyl groups of both 4 and 7 are selectively polymerized and the isopropenyl and α-isopropylvinyl groups remain completely intact to afford stable living
anionic polymers. As expected, the resulting polymers possessed precisely controlled chain lengths and narrow molecular weight
distributions. More importantly, they also possessed the pendant isopropenyl and α-isopropylvinyl group in each monomer unit
possible for further modification. On the other hand, the anionic polymerization of either 5 or 6 proceeded more or less along with the unwanted side reactions leading to chain-branching, followed by cross-linking. The
positional effect of isopropenyl group on the polymerization and the cause of possible side reactions were discussed. 相似文献
19.
A new kinetic scheme for chain transfer to monomer in the anionic polymerization of hydrocarbon monomers is presented. The scheme agrees with generally accepted views on the chemical mechanism of carbanionic reactions better than the one used previously. It is suggested that the most probable path of the transfer reaction is the proton abstraction from the side group of the monomer, the terminal double bond of the monomer molecule remains unchanged, and therefore the intermediate species can participate in succeeding reactions as a macromonomer. The discrepancy between the predictions of the proposed scheme and of the previous one concerning the molar characteristics of polymers are discussed and the ways to establish the true mechanism of transfer in particular systems are suggested. 相似文献
20.
L. H. Tung G. Y. S. Lo J. A. Griggs 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1551-1568
A new method of block polymer preparation using combined anionic and free radical polymerization was investigated. In the method the first monomer was polymerized anionically. The resulting polymeric anions were then reacted with an episulfide to form a polymer with mercaptan end-groups. This mercapto—polymer was mixed with a second monomer(s) in an inert solvent for the free radical polymerization. Conventional free radical initiation methods were used to initiate the polymerization of the second monomer but because of the high chain transfer constant of the mercaptan groups, a large number of the free radical chains would grow from the first polymer to form a block polymer. Block polymers difficult or impossible to make by direct anionic polymerization can thus be prepared. Several block polymers, including the new thermoplastic elastomers, poly[(styrene-co-acrylonitrile)-b-butadiene-b-(styrene-co-acrylonitrile)] and poly(bromostyrene-b-butadiene-b-bromostyrene) were prepared by this method. 相似文献