RAFT乳液聚合

高分子材料性能追本朔源主要由分子链微结构决定。以RAFT聚合为代表的"活性"/可控自由基聚合结合了传统自由基聚合和活性阴离子聚合各自的优点,提供了一种有效调控聚合物分子链微结构的聚合方法。RAFT乳液聚合作为"活性"/可控自由基聚合中具有工业应用前景的聚合方法,在过去二十年受到了学术界的广泛关注。本文总结了RAFT乳液聚合乳液失稳机理、聚合动力学、链结构的可控性等方面的进展。在此基础上,介绍了通过RAFT乳液聚合这一可控制备聚合物新材料的平台制备得到的新型嵌段共聚物、梯度共聚物,并展望了RAFT乳液聚合在高分子合成材料领域的应用前景。     

两亲性RAFT试剂存在下丙烯酸六氟丁醋和苯乙烯的无皂乳液聚合

合成了具有两亲性结构的可逆加成断裂链转移(RAFT)试剂,在RAFT试剂的作用下,通过无皂乳液聚合方法合成了丙烯酸六氟丁酯与苯乙烯的共聚物.研究了RAFT试剂浓度和聚合温度对聚合动力学、聚合反应可控性及乳胶粒粒径的影响.通过红外光谱(FTIR)、核磁共振谱(1H NMR)、示差扫描量热仪(DSC)、凝胶渗透色谱仪(GPC)及表面张力仪表征了共聚物的结构、玻璃化转变温度(Tg)、分子量和分子量分布及乳胶膜表面性能.结果表明,得到的苯乙烯和丙烯酸六氟丁酯共聚物无皂乳液的乳胶粒粒径在100 nm左右且呈单分散分布.当RAFT试剂浓度高于0.016 mol/L时聚合体系有较好的可控性.共聚物乳液的乳胶膜对水和二碘甲烷的接触角都很高.     

乳液体系中“活性”/控制自由基聚合研究进展

"活性"/控制自由基聚合(CRP)可用于合成具有精确结构和窄分子量分布的聚合物.乳液聚合具有环保、经济、易控的优点,但乳液体系为多相体系,控制试剂的相间分配和迁移较均相系统复杂,这使乳液"活性"/控制自由基聚合面临一些挑战,诸如控制聚合特征差、乳液稳定性下降等.本文介绍了近年来乳液体系中的原子转移自由基聚合(ATRP)和可逆加成-断裂链转移聚合(RAFT)的研究进展,包括体系的特性、面临的挑战、解决的方法,以及工程与商业运用的前景和需要解决的问题.     

RAFT种子乳液聚合反应初期的Monte Carlo模拟

自由基聚合是制备聚合物材料最为重要的技术 .但由于自由基极易进行双基终止 ,一般很难对其结构进行精确的控制 ,所得产物分子量宽 ,组成分布不易控制 ,很难制备嵌段共聚物 . 2 0世纪 90年代出现的活性自由基聚合技术 (RAFT)克服了上述缺点 ,成为高分子化学研究的热点[1] .RAFT聚合以其适用单体广、聚合条件温和以及活性高而成为最具前途的活性自由基聚合技术之一 .迄今为止 ,RAFT的研究大多集中在溶液和本体等均相聚合体系 [2～ 5] .乳液聚合有聚合速率快、环境友好、体系粘度低等优点 ,是活性自由基聚合工业化首选工艺 ,因而近年来活…     

可逆加成-断裂链转移(RAFT)聚合在星形聚合物合成中的应用

可逆加成-断裂链转移(RAFT)聚合作为一种新型活性自由基聚合,由于其具有单体适用面广、操作条件温和、实施聚合的方法多--本体、溶液、乳液、悬浮聚合均可的优点已经在分子设计方面取得了广泛的应用.星形聚合物作为一种特殊结构的聚合物,由于其具有较低的结晶度、较小的流体动力学体积等独特的性质,越来越引起研究者的重视.本文综述了近几年来采用RAFT法合成星形聚合物的研究进展.根据合成星形聚合物所用的RAFT多官能团试剂种类,对RAFT法合成星形聚合物的反应进行了分类.     

乳液聚合的最新进展（上）

本文对近１０多年中发展起来的与乳液聚合相关的聚合技术，如无皂乳液聚合、细乳液聚合、微乳液聚合、分散聚合等，也对其实施方法、理论研究结果和应用作了介绍；还针对近年来已经成为热点的核壳乳液、单分散聚合物微球及表面官能化的乳液微球的制备方法及应用进行了综述。     

可逆加成-断裂链转移自由基共聚合研究进展

与其它可控/活性自由基聚合相比,可逆加成-断裂链转移(RAFT)自由基聚合具有适用单体范围广、反应条件温和、不受聚合实施方法的限制等优点,因此成为目前高分子合成研究最为活跃的领域之一.通过它不但实现了广泛单体的可控/活性聚合,还合成了嵌段、接枝、梳型、星型、无规及梯度等结构的聚合物.本文综述了RAFT自由基共聚合领域的研究进展,内容主要包括已报道的RAFT自由基共聚合反应体系和RAFT过程对共聚产物组成的影响.     

苯乙烯RAFT细乳液聚合

活性自由基聚合研究在上世纪90年代取得突破，受到研究者的广泛关注．现今，已形成NMP(Nitroxide-medjated polymerization)、ATRP(Atom transfer radical polymerization)、RAFT(Reversible addition／fragmentation transfer)聚合等3种高效活性自由基聚合体系，其各自的聚合机理已基本探明。     

苯乙烯微乳液种子聚合

通过观测苯乙烯微乳液种子聚合前后体系内聚合物粒子大小及其分布的变化发现,无论是γ射线还是KPS引发,聚合过程中都没有新的聚合物粒子生成。尽管聚合前体系中存在单体溶胀的胶束,但在聚合过程中这些胶束主要充当单体仓库,自己成核聚合的几率很低。由于微乳液种子聚合体系内,单体量相对较低,聚合物粒子数目很大,其聚合动力学明显不同于常规乳液种子聚合。     

两亲性RAFT试剂存在下丙烯酸六氟丁醋和苯乙烯的无皂乳液聚合

合成了具有两亲性结构的可逆加成断裂链转移(RAFT)试剂,在RAFT试剂的作用下,通过无皂乳液聚合方法合成了丙烯酸六氟丁酯与苯乙烯的共聚物.研究了RAFT试剂浓度和聚合温度对聚合动力学、聚合反应可控性及乳胶粒粒径的影响.通过红外光谱(FTIR)、核磁共振谱(1H NMR)、示差扫描量热仪(DSC)、凝胶渗透色谱仪(GP...     

Reversible addition–fragmentation chain transfer/miniemulsion polymerization of butyl methacrylate in the presence of β‐cyclodextrin

In the presence of β‐cyclodextrin (β‐CD), reversible addition–fragmentation chain transfer (RAFT) polymerization has been successfully applied to control the molecular weight and polydispersity [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] in the miniemulsion polymerization of butyl methacrylate, with 2‐cyanoprop‐2‐yl dithiobenzoate as a chain‐transfer agent (or RAFT agent) and 2,2′‐azoisobutyronitrile (AIBN) as an initiator. β‐CD acted as both a stabilizer and a solubilizer, assisting the transportation of the water‐insoluble, low‐molecular‐weight RAFT agent into the polymerization loca (i.e., droplets or latex particles) and thereby ensuring that the RAFT agent was homogeneous in the polymerization loca. The polymers produced in the system of β‐CD exhibited narrower polydispersity (1.2 < M_w/M_n < 1.3) than those without β‐CD. Moreover, the number‐average molecular weight in the former case could be controlled by a definite amount of the RAFT agent. Significantly, β‐CD was proved to have a favorable effect on the stability of polymer latex, and no coagulum was observed. The effects of the concentrations of the RAFT agent and AIBN on the conversion, the molecular weight and its distribution, and the particle size of latices were investigated in detail. Furthermore, the influences of the variations of the surfactant (sodium dodecyl sulfate) and costabilizer (hexadecane) on the RAFT/miniemulsion polymerization were also studied. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2931–2940, 2005     

Solution and aqueous miniemulsion polymerization of vinyl chloride mediated by a fluorinated xanthate

Solution and aqueous miniemulsion polymerizations of vinyl chloride (VC) mediated by (3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl‐2‐((ethoxycarbonothioyl)thio) propanoate) (X1) were studied. The living characters of X1‐mediated solution and miniemulsion polymerizations of VC were confirmed by polymerization kinetics. The miniemulsion polymerization exhibits higher rate than solution polymerization. Final conversions of VC in the reversible addition‐fragmentation chain transfer (RAFT) miniemulsion polymerization reach as high as 87% and are independent of X1 concentration. Initiation process of X1‐mediated RAFT miniemulsion polymerization is controlled by the diffusion–adsorption process of prime radicals. Due to the heterogeneity of polymerization environments and concentration fluctuation of RAFT agent in droplets or latex particles, PVCs prepared in RAFT miniemulsion exhibit relatively broad molecular weight distribution. Furthermore, chain extensions of living PVC (PVC‐X) with VC, vinyl acetate (VAc), and N‐vinylpyrrolidone (NVP) reveal that PVC‐X can be reinitiated and extended, further confirming the living nature of VC RAFT polymerization. PVC‐b‐PVAc diblock copolymer is successfully synthesized by the chain extension of PVC‐X in RAFT miniemulsion polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2092–2101     

Living radical miniemulsion polymerization by RAFT in the presence of beta-cyclodextrin

Living radical polymerization of styrene in a miniemulsion by reversible addition–fragmentation chain transfer (RAFT) was successfully realized in the presence of beta-cyclodextrin (CD), using sodium dodecyl sulfate and hexadecane as surfactant and costabilizer, respectively. The drawback of instability (red layer formation) encountered in the living radical polymerization in emulsion or miniemulsion was overcome. The linear relationship between the monomer conversion and the molecular weight, as well as lower molecular weight distribution (MWD), shows that the polymerization process was under control. The addition of CD was found to have little influence on the polymerization rate. However, MWD of the polymer synthesized is obviously decreased. The mechanism of stability and controllability improvement in the presence of CD proposed that the complex formation between CD and RAFT agent or RAFT agent-ended oligomer increased their diffusion ability from monomer droplet to polymerization locus and improved the homogeneity of the RAFT agent level among the polymerization loci.     

Butyl acrylate RAFT polymerization in miniemulsion

Few successes about butyl acrylate (BA) RAFT miniemulsion homopolymerization were reported, even though styrene, methyl methacrylate, and vinyl acetate had been successfully applied in reversible addition fragmentation transfer (RAFT) miniemulsion polymerization. In this article, four types of RAFT agent with various designed R and Z groups [benzyl dithioisobutyrate (BDIB), 1-phenylethyl phenyldithioacetate (PEPDTA), cumyl dithioisobutyrate (CDIB), benzyl dithiobenzoate] were used to mediate BA miniemulsion polymerization using the conditions (5 wt % hexadance and sodium dodecyl sulfate) effective for styrene and methyl methacrylate systems. All four types of the RAFT agents effectively control over the bulk polymerization. In contrast, only BDIB resulted in a rather narrow molecular weight distribution in the miniemulsion polymerization. A pronounced inhibition and rate retardation were observed in both bulk and miniemulsion polymerizations mediated by CDIB and benzyl dithiobenzoate. When compared with the bulk polymerization, a much longer inhibition period (over eight times) was observed in the CDIB-mediated miniemulsion polymerization. It was concluded that only the RAFT agent with the primary R group and Z group with less stabilizing ability to the intermediate radicals is effective to mediate BA miniemulsion polymerization in terms of achieving a narrow molecular weight distribution and short inhibition period. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2304–2315, 2007     

β-CD存在下MMA细乳液体系的RAFT聚合

近年来，活性自由基聚合已成为高分子合成领域中的一个热门课题．Rizzardo研究小组提出了一种新型活性自由基聚合反应，即RAFT(Reversible addition-fragmentation chain transfer)聚合．RAFT反应在传统的自由基聚合中加入了具有高链转移常数和特定结构的链转移剂——双硫酯类化合物．当链转移剂的浓度足够大时，链转移反应由不可逆变为可逆，聚合反应也随之发生质的变化，由不可控     

AB and ABA type butyl acrylate and styrene block copolymers via RAFT‐mediated miniemulsion polymerization

Two trithiocarbonate reversible addition fragmentation chain transfer (RAFT) agents are compared in miniemulsion polymerization of styrene and butyl acrylate and the formation of seeded emulsion block copolymers. The order of block synthesis and the number of block segments per polymer are discussed. The use of nonionic surfactants is examined and the type of surfactant in relation to the monomer used is found to have a significant affect on latex formation. Conditions are shown by which AB and ABA type block copolymers can be successfully prepared via a seeded RAFT‐mediated emulsion polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 588–604, 2007     

Reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in emulsion

Theoretical simulations showed that for controlled/living radical polymerization in an emulsion system, some of the earliest born particles could be superswollen to a size close to 1 μm. We hypothesized that the superswelling of these particles would lead to colloidal instability. Under the guidance of the simulation results, reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) was carried out. Experimental results showed that increasing the initiation rate, surfactant level, and targeted molecular weight could improve the colloidal stability of the RAFT polymerization of MMA in an emulsion. The experimental results were in full accord with the theoretical predictions. The poor control of the molecular weight and polydispersity index was found to have a close relationship with the colloidal instability. For the first time, we demonstrated that RAFT polymerization could successfully be implemented with little coagulum, good control of the molecular weight, and a low polydispersity index with the same process used for traditional emulsion polymerization but with higher surfactant levels and initiation rates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:2837–2847, 2006     

Recent advances in controlled/living radical polymerization in emulsion and dispersion

Effective ways to conduct controlled/living radical polymerization (CRP) in emulsion systems are necessary for commercial latex production without significant modification of current industrial facilities. Conducting CRP in emulsion media is more complicated and more challenging than its application in homogeneous bulk. These challenges come from the intrinsic kinetics of emulsion polymerization. They include mass transport, slow chain growth mechanism, and exit of short radicals from polymeric particles. This review describes the recent developments of CRP in heterogeneous dispersion, including miniemulsion, microemulsion, dispersion, and especially emulsion. Various approaches for conducting emulsion CRP are detailed, including controlled seeded emulsion polymerization, nanoprecipitation, use of short oligomers as macroinitiators for in situ block copolymerization, and RAFT‐mediated self‐assembly. In addition many remaining challenges of the current methods barring wide spread industrial application of emulsion CRP are also suggested. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6983–7001, 2008