RAFT方法合成两亲性嵌段共聚物的研究进展

可逆加成一断裂链转移(RAFT)聚合是制备嵌段共聚物的重要方法之一,介绍了队RAFT聚合方法的基本原理及其所用的RAFT链转移剂基础上,综述了国内外利用RAFT聚合方法合成两亲性嵌段共聚物的研究现状.     

复杂聚合物链结构的可控制备与新材料

自由基聚合与配位聚合的产物通常为宽分子量分布的均聚物或无规共聚物。近二十年来,活性/可控自由基聚合、活性/可控配位聚合、链穿梭聚合的研究取得突破。这些方法使得几乎所有的乙烯基单体,特别是廉价易得的单体,都可用作原料来制备原来无法制备得到的两嵌段、多嵌段共聚物、梯度共聚物等更为复杂聚合链结构。合理设计这些复杂的链结构,有望得到高性能、高附加值合成材料。介绍了这些新型聚合原理的机理、新进展,讨论了它们潜在的应用前景。     

ATRP法制备含氟嵌段共聚物P(MMA-HEMA-BA)-b-PFMA

原子转移自由基聚合(ATRP)法克服了传统自由基聚合法的这种缺陷,因而合成的聚合物可具备更加优异的性能。含氟嵌段共聚物的疏水性能优于含氟无规共聚物,目前ATRP法制备的含氟嵌段共聚物大多采用单一丙烯酸酯类单体与含氟单体制备而成,其涂膜性能较差,本文通过ATRP法,利用两步聚合先制备P(MMA-HEMA-BA)-Br大分子引发剂,再利用该大分子引发剂引发含氟单体聚合生成P(MMA-HEMA-BA)-b-PFMA,最终合成的含氟嵌段共聚物分子量分布为1.21,这表明该聚合过程可控性好。     

PCL-b-PNAGA嵌段共聚物的制备及表征

聚己内酯(PCL)是一种性能优良的生物相容性及降解性良好生物材料,在生物医药方面有着巨大的潜能,但其具有很强的疏水性。本文利用N-丙烯酰基甘氨酰胺(NAGA)的亲水性通过可逆加成-断裂链转移聚合(RAFT)制备嵌段共聚物PCL-b-PNAGA,并通过FI-IR和1H-NMR表征证明了各个产物的成功制备。结果表明:成功制备了单体NAGA,大分子链转移剂PCL-CTA和嵌段共聚物PCL-b-PNAGA。     

基于RAFT聚合策略合成功能化聚烯烃嵌段聚合物的研究进展

首先介绍了可逆加成-断裂链转移聚合（RAFT）的聚合机理及其常用的RAFT试剂,并与其它两种活性可控自由基聚合[氮氧化合物媒介的自由基聚合（NMP）和原子转移自由基聚合（ATRP）]进行了简单的优缺点对比。其次,介绍了近些年在基于RAFT聚合制备功能化聚烯烃嵌段聚合物研究中取得的进展,重点综述了制备功能化聚烯烃嵌段聚合物时所采用的6种方法,包括①烯烃配位聚合与RAFT聚合相结合;②阴离子聚合与RAFT聚合相结合;③阳离子聚合与RAFT聚合相结合;④Click反应与RAFT聚合相结合;⑤开环聚合与RAFT聚合相结合;⑥叶立德活性聚合与RAFT聚合相结合。最后,对基于RAFT聚合策略设计合成功能化聚烯烃嵌段聚合物的研究前景与实际应用进行了展望。     

PGMA-b-PS二嵌段共聚物的RAFT/细乳液合成及表征

以2-(十二烷基三硫代碳酸酯)-2-甲基丙烯酸为链转移剂,利用RAFT/细乳液联合技术合成了相对分子质量分布较窄(PDI=1.53)的大分子链转移剂聚甲基丙烯酸缩水甘油酯。再以该大分子为可逆加成-断裂链转移(RAFT)试剂,通过连续加料的方式加入苯乙烯后进一步引发聚合,得到PGMA-b-PS二嵌段共聚物。采用GPC、FT-IR、1H-NMR、DSC等方法对聚合产物进行了表征。结果表明:合成的聚合物为线型二嵌段共聚物,相对分子质量分布为1.87,该聚合过程具有活性/可控特征。DSC测得二嵌段共聚物具有2个玻璃化转变温度(Tg),分别为77.33℃和98.30℃。此外,还考察了单体加料顺序对聚合过程的影响。     

光引发聚合诱导自组装制备二嵌段共聚物组装体

以N,N-二甲基丙烯酰胺(DMA)为单体,2-甲基-2-(十二烷基三硫代碳酸酯基)丙酸(DDMAT)为链转移剂,通过可逆加成-断裂链转移(RAFT)聚合合成大分子RAFT试剂PDMA-DDMAT。再以N-异丙基丙烯酰胺(NIPAM)为成核单体,N-烯丙基丙烯酰胺(ALAM)为原位交联剂,通过光引发聚合诱导自组装制备具有不同形貌的交联二嵌段共聚物组装体。结果表明,组装体的形貌受大分子RAFT试剂分子量、第二嵌段聚合度、反应温度、固含量及原位交联剂使用量的影响。     

开环易位聚合法制备功能化聚烯烃研究进展

综述了近年来利用开环易位聚合法制备功能化聚烯烃的研究进展,包括无规共聚物、嵌段共聚物和接枝共聚物的制备及其相关性能的研究。开环易位聚合催化剂的耐受性较好,可用于催化多种单体的聚合,从而制备含有多种官能团的聚烯烃,所制聚烯烃具有较为优异的力学性能、表面性能和热性能。通过引入特定功能化取代基还可以赋予聚烯烃优异的光学性能、介电性能、生物性能等。     

梯度共聚物的可控制备及其性能

梯度共聚物是近年来伴随着活性聚合方法而发展起来的一种新型共聚物,其特点在于单体单元组成沿着分子链方向逐渐变化,链结构界于常见的无规共聚物和嵌段共聚物之间。本文从梯度共聚物的结构特点入手,总结了其可控制备方法、表征手段、物化性质以及应用前景。基于共聚动力学模型控制单体加料速率的半连续活性/可控自由基聚合可实现梯度共聚物的结构定制,基于多步单体进料方式的RAFT乳液聚合则由于其简单和高效将成为梯度共聚物可控制备的重要方法。梯度共聚物的自组装行为和微观聚集态不同于嵌段共聚物,表现出独特的界面活性、热学特性和力学性能,组成梯度结构有望成为调控高分子材料性能的新参数,梯度共聚物有望在乳化剂、相相容剂、阻尼材料、多形状记忆材料等领域得到应用。     

双亲性嵌段共聚物的RAFT合成及其胶束化行为研究

以二硫化二异丙基黄原酸酯(DIP)为链转移剂,AIBN为引发剂,通过可逆加成-断裂链转移(RAFT)自由基聚合的方法制备得到大分子链转移剂聚醋酸乙烯酯(PVAc)。进而引发第二单体N-乙烯基乙酰胺(NVA)进行RAFT反应制备得到不同嵌段比的双亲性嵌段共聚物PVAc-bPNVA。红外光谱(FT-IR)、核磁共振氢谱(1 H NMR)和凝胶渗透色谱(GPC)分析表明,所得聚合物结构明确,且分子量分布较窄,符合活性聚合特征。进而使PVAc-b-PNVA在选择性溶剂(DMF/H2O)中自组装形成胶束,研究了不同初始浓度和链段比对胶束粒径和形态的影响。     

可逆加成-断裂链转移聚合制备聚氯乙烯-b-聚乙二醇-b-聚氯乙烯共聚物

合成了含黄原酸酯端基的聚乙二醇（X-PEG-X）大分子链转移剂,并以其为可逆加成-断裂链转移试剂调控氯乙烯（VC）溶液和悬浮聚合,合成聚氯乙烯-b-聚乙二醇-b-聚氯乙烯（PVC-b-PEG-b-PVC）三嵌段共聚物。X-PEG-X调控VC溶液聚合得到的共聚物的分子量随聚合时间增加而增大,分子量分布指数小于1.65。X-PEG-X具有水/油两相分配和可显著降低水/油界面张力的特性,以X-PEG-X为链转移剂和分散剂,通过自稳定悬浮聚合也可合成PVC-b-PEG-b-PVC共聚物,共聚物颗粒无皮膜结构,分子量随聚合时间增加而增大;由于VC悬浮聚合具有聚合物富相和单体富相两相聚合特性,共聚物分子量分布指数略大于溶液聚合共聚物。通过乙酸乙烯酯（VAc）扩链反应进一步证实了PVC-b-PEG-b-PVC的“活性”,并合成PVAc-b-PVC-b-PEG-b-PVC-b-PVAc共聚物。水接触角测试表明PVC-b-PEG-b-PVC的亲水性优于PVC。     

Preparation of well‐defined block copolymer having one polystyrene segment and another poly(styrene‐alt‐maleic anhydride) segment with RAFT polymerization

Block copolymers, polystyrene‐b‐poly(styrene‐co‐maleic anhydride), have been prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization technique using three different approaches: 1‐phenylethyl phenyldithioacetate (PEPDTA) directly as RAFT agent, mediated polystyrene (PS) block as the macromolecular PS‐RAFT agent and mediated poly(styrene‐maleic anhydride) (SMA) block with alternating sequence as the macromolecular SMA‐RAFT agent. Copolymers synthesized in the one‐step method using PEPDTA as RAFT agent possess one PS block and one SMA block with gradient structure. When the macromolecular RAFT agents are employed, copolymers with one PS block and one alternating SMA block can be produced. However, block copolymers with narrow molecular weight distribution (MWD) can only be obtained using the PS‐RAFT agent. The MWD deviates considerably from the typical RAFT polymerization system when the SMA is used as the RAFT agent. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymer vectors via controlled/living radical polymerization for gene delivery

The design of efficient gene delivery vectors is a challenging task in gene therapy. Recent progress in living/controlled radical polymerizations (LRPs), in particular atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization providing a means for the design and synthesis of new polymeric gene vectors with well-defined compositions, architectures and functionalities is reviewed here. Polymeric gene vectors with different architectures, including homopolymers, block copolymers, graft copolymers, and star-shaped polymers, are conveniently prepared via ATRP and RAFT polymerization. The corresponding synthesis strategies are described in detail. The recent research activities indicate that ATRP and RAFT polymerization have become essential tools for the design and synthesis of advanced, noble and novel gene carriers.     

One-step synthesis of poly(2-oxazoline)-based amphiphilic block copolymers using a dual initiator for RAFT polymerization and CROP

A range of poly(2-oxazoline) (POx)-based amphiphilic block copolymers were synthesized using 4-cyano-4-(dodecylthiocarbonothioylthio)pentyl-4-methylbenzenesulfonate (CDPS) as a dual initiator for reversible addition-fragmentation chain transfer (RAFT) polymerization and cationic ring-opening polymerization (CROP) in a one-step procedure. Methyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, and N-isopropylacrylamide were polymerized for the hydrophobic block, and 2-methyl-2-oxazoline and 2-ethyl-2-oxazoline were used as the hydrophilic block. RAFT polymerization and CROP proceeded independently in a controlled manner and resulted in amphiphilic block copolymers with a narrow molecular weight distribution. CDPS was found to be a useful dual initiator for the one-step synthesis of POx-based amphiphilic block copolymers via a combination of RAFT polymerization and CROP.     

Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate core based on amphiphilic block copolymers by RAFT polymerization and palladium-catalyzed coupling reactions

Well-defined amphiphilic block copolymers composed of S-vinyl sulfides and N-isopropyl acrylamide (NIPAM) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate cores were obtained by in situ cross-linking reactions between 4-bromophenyl moieties in the block copolymers and diboronic acids or a diamine compound in the presence of a palladium catalyst following micelle formation in ethanol/H₂O or ethanol. We initially investigated RAFT polymerization of two S-vinyl sulfide derivatives, namely phenyl vinyl sulfide (PVS) and 4-bromophenyl vinyl sulfide (BPVS), using a dithiocarbamate-type chain transfer agent (CTA). Then, RAFT polymerization of NIPAM using poly(S-vinyl sulfide) macro-CTAs was conducted to synthesize the amphiphilic block copolymers. Suzuki and Buchwald-Hartwig coupling reactions were found to be effective in the preparation of core–shell nanoparticles with thermoresponsive shells and cross-linked optoelectronic cores. The resulting nanoparticles showed characteristic thermoresponsive properties, as confirmed by turbidity and dynamic light scattering measurements. Stable and uniform core cross-linked nanoparticles were successfully prepared by the in situ palladium-catalyzed coupling reactions, and the optoelectronic and thermoresponsive properties of the nanoparticles could be tuned depending on the nature of the difunctional coupling agents, reaction conditions, and comonomer composition of the block copolymers.     

Multiblock copolymers synthesized in aqueous dispersions using multifunctional RAFT agents

Triblock copolymers were synthesized in aqueous dispersions in two polymerization steps using a low molar mass difunctional dithiocarbamate-based RAFT agent, and in merely one polymerization step using a macromolecular difunctional dithiocarbamate-based RAFT agent. Segmented block copolymers containing several alternating blocks of different polarities were synthesized in miniemulsion in merely two polymerization steps by applying multifunctional, dithiocarbamate-based RAFT agents. All polymerizations showed a linear increase of with monomer conversion. Evidence that this novel synthetic concept resulted in the formation of (multi)block copolymers was obtained by combining normal gel permeation chromatography with gradient polymer elution chromatography.     

原子转移自由基聚合的近期研究进展

对原子转移自由基聚合(ATRP)的引发体系、催化体系及反应介质进行了全面的综述。介绍了四种不同催化剂脱除技术;结合最新的研究成果,介绍了ATRP在进行聚合物分子设计尤其是在制备嵌段共聚物方面的进展。     

Synthesis of PCL-b-PVAc block copolymers by combination of click chemistry, ROP, and RAFT polymerizations

Abstract  

The synthesis of new poly(ε-caprolactone)(PCL)-b-poly(vinyl acetate)(PVAc) block copolymers was investigated using different combinations of click chemistry, reversible addition-fragmentation transfer (RAFT), and ring opening polymerization (ROP) techniques. Two approaches, “coupling” and “macroinitiator” routes were studied. For the coupling approach, a chain transfer agent comprising an azide function was synthesized and used as initiator for the VAc polymerization. PCL containing an alkyne termination was obtained from a bifunctional initiator bearing an alkyne function and an hydroxyl group. These two functionalized precursors, PVAc and PCL, were coupled by a 1,3 cyclo addition reaction “click chemistry” in order to obtain the corresponding block copolymer. For the macroinitiator approach, PCL-b-PVAc block copolymers were synthesized using a two-step procedure: at first, a PCL macroinitiator with a xanthate end group was prepared by coordinated anionic polymerization of ε-caprolactone; then, the RAFT polymerization of VAc was initiated from the PCL, for the preparation of PCL-b-PVAc block copolymers. Whatever the method used, no detectable quantities of unreacted PVAc or PCL were observed. ¹H NMR and size exclusion chromatography analyses indicated successful synthesis of the block copolymers with well-defined structures.