可逆加成-断裂链转移(RAFT)聚合的研究进展

自可逆加成-断裂链转移自由基聚合技术在1998年发明以来,就逐渐成为聚合研究者的一种非常强大的合成工具,并在研究与应用领域得到很快的发展。文章综述了可逆加成-断裂链转移聚合的RAFT试剂的分类、聚合机理及聚合中的阻滞现象,简要说明了RAFT技术应用的研究进展。     

基于RAFT过程的丙烯酸可控自由基聚合

以2-{[(十二烷基硫基)硫代甲酰基]硫烷基}琥珀酸(DCTSS)为链转移剂(CTA)在水溶液中调控丙烯酸(AA)进行可逆加成-断裂链转移自由基聚合(RAFT)。考察了引发剂种类、聚合温度、n(引发剂)/n(CTA)、n(AA)/n(CTA)、时间对丙烯酸聚合的影响。结果表明,以4,4′-偶氮二(4-氰基戊酸)(V501)为引发剂,聚合反应具有活性可控聚合的特征,聚合动力学呈线性关系,聚合物的黏均相对分子质量(以下简称黏均分子量)随转化率的增加而线性增加,得到分子量可控、分布为1.50左右的聚合物;升高温度可以加快反应速率,使黏均分子量分布降低,反应更加可控;降低n(V501)/n(CTA)值可以使聚合产物的黏均分子量升高,但聚合速率也会降低;随着n(AA)/n(CTA)值的增加,聚合产物的黏均分子量也增加,并且基本呈线性关系;最佳反应时间为2h;用所得聚合物作为大分子RAFT试剂,丙烯酸正丁酯(BA)为单体进行扩链反应,得到聚丙烯酸-b-聚丙烯酸正丁酯;用核磁共振氢谱、傅立叶变换红外光谱对产物结构进行了表征。     

可逆加成-断裂链转移自由基聚合的新进展

可逆加成-断裂链转移(RAFT)自由基聚合的适用单体范围广,反应条件温和,没有聚合实施方法如本体、溶液、乳液和悬浮聚合的限制,因而引起了研究者的广泛兴趣,取得了许多新的研究成果。主要对近年来RAFT聚合中使用的最新链转移剂、单体及相关合成与使用情况以及几种新型RAFT反应体系进行了介绍。     

可逆加成断裂链转移聚合及 链转移剂的制备进展

20世纪以来国内外学者使用可逆加成-断裂链转移(RAFT)聚合法进行了有机合成和分子设计,并探索了满足RAFT聚合条件的RAFT试剂,成功得到了RAFT聚合产物。本文介绍了RAFT聚合法的机理、优势与缺陷,并在对RAFT聚合成果进行系统总结的基础上,简要综述了整体的国内外研究现状,介绍了RAFT试剂的合成案例,并提出了水溶性RAFT试剂的合成思路,展望了RAFT聚合体系未来的发展方向。     

通过RAFT聚合制备经GMA偶联的PMMA/TiO2杂化纳米复合物

利用表面修饰法合成了常用单体甲基丙烯酸缩水甘油酯(GMA)修饰的TiO2纳米粒子。以甲基丙烯酸甲酯(MMA)为单体,S-1-十二烷基-S′-(α,α′-二甲基-α″-乙酸)三硫代碳酸酯(DDACT)为RAFT试剂,在纳米TiO2表面进行可逆加成-断裂链转移(RAFT)接枝聚合,PMMA"经表面接枝到(grafting through)"改性后的纳米TiO2表面。结果表明,随聚合时间的增加,纳米TiO2表面接枝聚合物PMMA的量增加,颗粒的团聚得到明显减缓。     

可逆加成-裂解链转移聚合研究进展

可逆加成-裂解链转移(RAFT)自由基聚合技术自20世纪末提出以来,已成为活性自由基聚合最重要的方法之一,并在研究与应用领域得到很快的发展。简要综述了RAFT技术应用的研究进展。     

活性自由基聚合法合成偶氮聚合物研究进展

偶氮聚合物具有的光致顺反异构和光学各向异性使之在光电信息技术领域具有重要的潜在应用前景。利用活性自由基聚合的方法可以在温和的条件下合成到特定结构与预定相对分子质量的偶氮聚合物,本文综述了该技术领域的最新研究进展,并对近年来出现的聚合体系与方法作了简要的评述。     

聚丙烯酸-b-聚丙烯酸丁酯的RAFT水溶液聚合及其性能

该研究首先以2-{[(十二烷基硫基)硫代甲酰基]硫烷基}琥珀酸为链转移剂(CTA)在水溶液中调控丙烯酸(AA)进行可逆加成-断裂链转移自由基聚合(RAFT),再以得到的聚丙烯酸为大分子RAFT试剂,丙烯酸正丁酯(BA)为单体,进行扩链反应,得到聚丙烯酸-b-聚丙烯酸正丁酯。用红外光谱对产物结构进行了表征。考察了合成条件n(V501)/n(CTA)、n(AA)/n(CTA)、n(V501)/n(PAA-RAFT)、n(BA)/n(PAA-RAFT)对聚合物的表面张力、乳化性、起泡性和泡沫稳定性的影响。结果表明,当n(V501)/n(CTA)=0.2、n(AA)/n(CTA)=20、n(V501)/n(PAA-RAFT)=0.1、n(BA)/n(PAA-RAFT)=20时,得到的聚丙烯酸-b-聚丙烯酸正丁酯的水溶液表面活性最大,表面张力最低为30.89 N/m,乳化性最强,乳状液稳定时间达到1 082 s,起泡性和泡沫稳定性最弱,泡沫高度为17.01 mm,稳定时间为210 s。     

RAFT法合成超分散剂PS-b-PAA及其分散性能研究

以苯乙烯(St)和丙烯酸(AA)为单体,二硫代苯甲酸苄酯为链转移剂,偶氮二异丁腈(AIBN)作为引发剂,采用可逆加成-断裂链转移(RAFT)活性自由基聚合方法合成了两亲性嵌段共聚物分散剂聚苯乙烯-b-聚丙烯酸(PS-b-PAA),探讨了影响聚合反应的主要因素,用GPC、IR、1H NMR对其结构进行了表征.结果表明,用RAFT法制得的共聚物分子量分布为1.1～1.3,聚合反应在80℃下24h内转化率达95%.进一步的分散性能研究表明,超分散剂PS-b-PAA对SiO2粉体在水中有着较好的分散效果.     

可逆加成—断裂链转移自由基聚合研究

可逆加成-断裂链转移(Reversible addition-fragmentation chain transfer,RAFT)自由基聚合是最近发展起来的一种活性可控自由基聚合技术。该技术对聚合调控效果好、聚合条件相对温和、适用单体范围广等优点而备受关注,已成为一种有效的聚合物分子设计手段,文章介绍了RAFT聚合的机理、优点及应用。     

分散聚合反应的研究进展

介绍了分散聚合反应及其成核和稳定机理,并对分散聚合反应的研究进展情况进行了概述.     

水分散体系中原子转移自由基聚合研究进展

水分散体系中原子转移自由基聚合(ATRP)具有自由基聚合、乳液聚合和活性/可控聚合的优点,因此近年来关于水分散体系中ATRP的研究日益增多。本文综述了近年来水分散体系(包括乳液体系、细乳液体系、微乳液体系)中原子转移自由基聚合的研究进展,对应用在水分散体系中的几种ATRP反应机理做了简要介绍,包括正向AT-RP、反向ATRP(RATRP)、正向/反向同时进行的(SR&NI)ATRP、电子转移活化剂(AGET)ATRP,并对RATRP、SR&NI、ATRPAGET ATRP的优缺点进行了总结。     

丙烯酰胺分散聚合研究进展

简介分散聚合成核与稳定机理、分散聚合动力学及反应参数对产品质量的影响,重点介绍分散聚合研究进展及其应用领域。     

Synthesis and characterization of H-shaped copolymers by combination of RAFT polymerization and CROP

A novel trithiocarbonate, S,S′-bis(1-(((5-ethyl-2,2-dimethyl-1,3-dioxane-5-yl)methoxy)carbonyl)propyl) trithiocarbonate (CTA-H), was synthesized in the presence of the anion-exchange resin with OH⁻ form. And then it was used as the chain transfer agent in RAFT polymerizations of styrene (St), the polymers with controllable molecular weights and narrow molecular weight distributions were synthesized. After the terminal acetonide groups was deprotected in the presence of a cation-exchange resin with H⁺ form, the polystyrene (PSt) with two hydroxyl groups in both chain ends was easily afforded. Then it was used as macro initiator in the cation ring open polymerization (CROP) of 1,3-dioxepane (DOP), and the well-defined H-shaped block copolymers, (PDOP)₂PSt(PDOP)₂, were successfully prepared. The H-shaped structure was characterized by its IR, GPC and ¹H NMR spectra, and also those of the hydrolysis products.     

Dihydroxyl-terminated telechelic polymers prepared by RAFT polymerization using functional trithiocarbonate as chain transfer agent

A novel reversible addition-fragmentation chain transfer (RAFT) agent, S,S′-bis(2-hydroxylethyl-2′-butyrate)trithiocarbonate (BHEBT), was first successfully synthesized in the presence of an anion-exchange resin with OH⁻ form, and then it was used as chain transfer agent in RAFT polymerizations of styrene or methyl acrylate, the dihydroxyl-terminated polymers with controlled molecular weights and narrow molecular weight distributions were produced, which was confirmed by GPC, ¹H NMR spectra and kinetic analysis. Furthermore, these obtained telechelic polymers with trithiocarbonate group in the middle of the chains were used as macro chain transfer agents in the further RAFT polymerizations, and well-defined telechelic dihydroxyl-terminated triblock copolymers have been prepared successively. The structures were confirmed by their IR and ¹H NMR spectra.     

Self-healing linear polymers based on RAFT polymerization

Self-healing polystyrene (PS) composites were fabricated, in which glycidyl methacrylate (GMA)-loaded microcapsules were embedded. Because the matrix PS was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, it kept living characteristics and was able to resume the polymerization so long as monomers were available. Upon damage of the composites, the GMA released from the broken capsules infiltrated into the cracks and was copolymerized with the matrix PS according to the above mechanism. As a result, the cracked planes were covalently re-bonded, offering recovery of impact strength. Compared to the self-healing system based on atom transfer radical polymerization (ATRP), which is also an approach of living polymerization, the current one possesses robust vitality in air and eliminates the possibility of acceleration of matrix degradation aroused by metal ions. Additionally, the resultant self-healing PS composites have an advantage in coloration, which is important for satisfying esthetic requirement in practice.     

RAFT with Bulk and Solution Polymerization: An Approach to Mathematical Modelling and Validation

Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization is a novel technique used to impart a living character in free radical polymerization. A mathematical model accounting for the concentrations of the propagating, intermediate, dormant and dead chains is developed based on their reaction pathways. The kinetic scheme used includes initiation, propagation, pre-equilibrium, core-equilibrium and termination of the propagating radicals along with termination reactions of the carbon-centered intermediate radical. This model is combined with chain-length dependant termination model in order to account for the decreased termination rate. The model has been validated against experimental data for solution polymerization of styrene with dithiobenzoate at 80°C. The fragmentation rate coefficient was used as a model parameter and a value equal to 6×10⁴ sec^?1 was found to provide a good agreement with the experimental data. The model predictions indicate that the observed retardation can be attributed to the cross termination of the intermediate radical and, to some extent, to the RAFT effect on increasing the average termination rate coefficient. The hypothesised irreversible self termination was found to have a negligible effect on the polymerization rate. While the linear growth of the number average molecular weight along with the low polydispersity, reveal the living nature of RAFT agent and the importance of the transfer constant in controlling these properties.     

Effect of comonomer composition on the controlled free-radical copolymerization of styrene and maleic anhydride by reversible addition-fragmentation chain transfer (RAFT)

Controlled free-radical copolymerization of styrene and maleic anhydride was performed in 1,4-dioxane or tetrahydrofurane solution at 60 °C using the RAFT technique. The effect of monomer feed ratio on copolymerization kinetics and on control over molar mass distribution was examined. It was shown that polymerization was faster and quality of control was poorer when the proportion of maleic anhydride in the monomer feed was larger. These features were assigned to a decrease in the chain transfer constant of the polymeric RAFT agent, most probably due to an increase in the apparent rate constant of propagation with the proportion of maleic anhydride.