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。     

用大分子引发剂法制备嵌段共聚物

主要介绍了用大分子引发剂法制备嵌段共聚物的方法。大分子引发剂是从已商品化的功能聚合物制得或用其它活性聚合方法合成。从单封端的端羟基聚合物、其它单官能团或双官能团聚合物以及双功能基团缩聚物制得大分子引发剂．然后用于原子转移自由基聚合(ATRP)、氮氧稳定自由基聚合以及可逆加成裂解链转移(RAFT)聚合等．可制得结构可控、分子量分布窄的嵌段共聚物。     

可逆加成-断裂链转移自由基聚合研究进展

RAFT(Reversible addition-fragmentation chain transfer,可逆加成-断裂链转移)自由基存在链增长自由基与链转移剂(RAFT试剂)之间的可逆蜕化转移,现已广泛应用于聚合物分子结构设计及众多功能高分子材料的合成,受到众多高分子研究者的关注,是一种发展较快的可控/活性聚合技术.本文在简要介绍了RAFT聚合发展历程基础上,综述了RAFT聚合反应机理,RAFT试剂的结构及其对聚合性能的影响,RAFT试剂与单体的匹配性,RAFT聚合实施方法等.同时也对RAFT聚合反应的发展进行了展望.     

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.     

两亲性超支化聚合物的研究进展

两亲性超支化聚合物作为一种新型功能性材料.近年来引起了人们的广泛关注.两亲性超支化聚合物的合成丰要是利用不同亲水性的链段对超支化聚合物端基进行改性,或者首先在超支化聚合物末端产生活性位点,再利用超支化分f作为大分子引发剂引发烯类单体进行斤环聚合、原子转移自由基聚合等得到以超支化聚合物为核的两亲性超支化共聚物;这些分子由...     

RAFT聚合在聚合物分子结构设计中的应用

可逆加成-断裂链转移(reversible addition-fragmentation chain transfer,RAFT)聚合是一种新型的活性/可控自由基聚合方法,在制备窄分子量聚合物和设计聚合物分子结构方面具有独特的优势。本文首先介绍RAFT活性自由基聚合的机理、体系、特点及链转移(RAFT)试剂的选择,然后总结了近年来国内外利用RAFT聚合技术在设计无规和交替共聚物方面的应用,详细介绍了该方法在制备特殊结构共聚物,如嵌段、梯度、接枝、星形、树形和梳形结构聚合物的新应用,并对RAFT聚合技术在今后的研究重点和应用前景做了展望。     

超支化聚苯乙烯-线型聚苯乙烯-超支化聚甲基丙烯酸甲酯三嵌段聚合物的合成与表征

合成了超支化聚苯乙烯-线型聚苯乙烯-超支化聚甲基丙烯酸甲酯三嵌段聚合物(HPS-b-LPS-b-HPMMA). 首先分别合成了带有炔基和溴的三硫代碳酸酯(ATC和BTC), 然后通过苯乙烯(St)的可逆加成-断裂链转移(RAFT)聚合, 制得端炔基和端基溴的线型聚苯乙烯大分子RAFT试剂, 然后将大分子RAFT试剂的溴末端转化为叠氮末端. 接着在大分子RAFT试剂存在情况下, 通过自缩合原子转移自由基共聚合(SCATRCP)分别制得端炔基超支化聚苯乙烯-线型聚苯乙烯(HPS-b-LPS)和端叠氮基超支化聚甲基丙烯酸甲酯-线型聚苯乙烯(HPMMA-b-LPS)两嵌段聚合物. 最后将两种两嵌段聚合物通过点击(click)反应偶合, 得到不对称的超支化-线型-超支化三嵌段聚合物HPS-b-LPS-b-HPMMA. 核磁共振氢谱(¹H NMR)、凝胶渗透色谱(GPC)结果表明, 所得产物分子量可控, 得到了预期结构的聚合物.     

可逆加成-断裂链转移(RAFT)分散聚合

RAFT分散聚合是在分散体系中实施RAFT聚合的一种非均相聚合方法。RAFT分散聚合的最大特点是它可以直接制备聚合物分子量可控、分子量分布窄的聚合物粒子。本文简要介绍了在小分子RAFT试剂和大分子RAFT试剂(Macro-RAFT)存在下,RAFT分散聚合的聚合动力学、聚合物的成核和粒子的增长。小分子RAFT试剂存在下的RAFT分散聚合是一个与普通的分散聚合类似,可以看作为非均相条件下的RAFT聚合,它可以制备微米尺度的聚合物粒子。Macro-RAFT存在下的RAFT分散聚合,是制备高浓度、纳米尺度的嵌段共聚物胶体的重要方法,它包含嵌段共聚物胶束化之前的均相聚合和嵌段共聚物胶束化后的非均相聚合两个阶段。     

可控自由基聚合系列实验教学中的一些尝试与经验*

设计了基于可控自由基聚合的系列实验教学,包括:单体和引发剂精制、RAFT试剂合成、不同单体的RAFT/ATRP聚合、RAFT聚合制备嵌段聚合物、ATRP制备嵌段聚合物等。这些实验环环相扣,互相支撑,又有着明显的对比效果。这种尝试有效改进和扩充了常规高分子合成教学中的自由基聚合部分,有效激发了学生的主动性,提高了其分析问题、解决问题的能力。     

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.     

可逆加成-断裂链转移自由基聚合研究进展

综述了活性/可控自由基聚合中的可逆加成-断裂链转移(RAFT)自由基聚合研究进展;总结了RAFT试剂、RAFT聚合反应条件、RAFT聚合物及其结构形貌的最新研究进展;指出RAFT自由基聚合反应已被作为重要方法之一用于合成具有特定分子结构的聚合物.     

异丁基乙烯基醚与受电子单体的可控自由基共聚合

近年来发展起来的“活性” 可控自由基聚合越来越为人们所关注 ,其原因在于采用这种方法不仅可以设计聚合物的分子量 ,得到窄分布聚合物 ,而且聚合条件不象活性离子型聚合那样严格 ,单体适用范围相对较广 .关于烯类单体的活性自由基聚合迄今主要有 :氮氧自由基调控的稳定自由基聚合 (Ｓｔａｂｌｅｆｒｅｅｒａｄｉｃａｌｐｏｌｙｍｅｒｉｚａｔｉｏｎ ,简称ＳＦＲＰ) [1] 、原子转移自由基聚合 (Ａｔｏｍｔｒａｎｓｆｅｒｒａｄｉｃａｌｐｏｌｙｍｅｒｉｚａｔｉｏｎ ,简称ＡＴＲＰ) [2 ] 以及以后发展起来的自由基可逆加成 断链链转移聚合…     

聚醋酸乙烯酯的光引发可控合成——介绍一个高分子化学综合实验

本实验开展了醋酸乙烯酯的可逆加成-断裂链转移自由基聚合(RAFT),分别运用偶氮二异丁腈(AIBN)引发和可见光引发两种方式进行了聚合反应,运用核磁共振和凝胶色谱等多种手段对所得聚合物结构进行了表征与分析。通过比较AIBN引发与光引发所获得聚合物端基结构的异同,加深了学生对RAFT聚合方法原理的理解。同时,运用该方法实现了聚合物两端端基结构的高度功能化,深入体会聚合物合成设计概念。本综合实验教学不仅通过对比法加深了学生对实验原理和专业知识的理解,提升了学生创新研究能力,而且训练了学生的实验操作技能、大型仪器使用能力和结果分析能力,提升了综合素质。     

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.     

Ab initio Emulsion Polymerization by RAFT (Reversible Addition–Fragmentation Chain Transfer) through the Addition of Cyclodextrins

A novel process to produce homo‐ and copolymers by RAFT polymerization in emulsion is presented. It is known that RAFT‐controlled radical polymerization can be conducted in emulsion polymerization without disturbing the radical segregation characteristic of this process, thus leading to polymerization rates identical to those encountered in the corresponding nonliving systems. However, RAFT agents are often characterized by very low water solubility and, therefore, they diffuse very slowly from the monomer droplets, where they are initially solubilized, to the reaction loci, i.e., the polymer particles. Accordingly, when used in emulsion polymerization, they are practically excluded from the reaction. In this work, we show that cyclodextrins, well‐known for their ability to form water‐soluble complexes with hydrophobic molecules, facilitate the transport across the H₂O phase of the RAFT agent to the polymer particles. Accordingly, chains grow through the entire process in a controlled way. This leads to the production of low‐polydispersity polymers with well‐defined structure and end functionalities as well as to the possibility of synthesizing block copolymers by a radical mechanism.     

Controlled Bimodal Molecular‐Weight‐Distribution Polymers: Facile Synthesis by RAFT Polymerization

The RAFT agents RAFT‐1 and RAFT‐2 were used for RAFT polymerization to synthesize well‐defined bimodal molecular‐weight‐distribution (MWD) polymers. The system showed excellent controllability and “living” characteristics toward both the higher‐ and lower‐molecular‐weight fractions. It is important that bimodal higher‐molecular‐weight (HMW) polymers and block copolymers with both well‐controlled molecular weight (MW) and MWD could be prepared easily due to the “living” features of RAFT polymerization. The strategy realized a mixture of higher/lower‐molecular‐weight polymers at the molecular level but also preserved the features of living radical polymerization (LRP) of the RAFT polymerization.     

Reversible Addition Fragmentation Chain Transfer Mediated Dispersion Polymerization of Styrene

Polystyrene microspheres have been synthesized by the reversible addition-fragmentation chain transfer (RAFT) mediated dispersion polymerization in an alcoholic media in the presence of poly(N-vinylpyrrolidone) as stabilizer and 2,2′-azobisisobutyronitrile as a conventional radical initiator. In order to obtain monodisperse polystyrene particles with controlled architecture, the post–addition of RAFT agent was employed to replace the weak point from the pre-addition of RAFT. The feature of preaddition and postaddition of RAFT agent was studied on the polymerization kinetics, particle size and its distribution and on the particle stability. The living polymerization behavior as well as the particle stability was observed only in the postaddition of RAFT. The effects of different concentration on the postaddition of RAFT agent were investigated in terms of molecular weight, molecular weight distribution, particle size and its distribution. The final polydispersity index (PDI) value, particle size and the stability of the dispersion system were found to be greatly influenced by the RAFT agent. This result showed that the postaddition of RAFT agent in the dispersion polymerization not only controls the molecular weight and PDI but also produces stable monodisperse polymer particles.     

R‐RAFT approach for the polymerization of N‐isopropylacrylamide with a star poly(ε‐caprolactone) core

Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods, providing a reactive thiocarbonylthio end group. A series of well‐defined star diblock [poly(ε‐caprolactone)‐b‐poly(N‐isopropylacrylamide)]₄ (SPCLNIP) copolymers were synthesized by R‐RAFT polymerization of N‐isopropylacrylamide (NIPAAm) using [PCL‐DDAT]₄ (SPCL‐DDAT) as a star macro‐RAFT agent (DDAT: S‐1‐dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate). The R‐RAFT polymerization showed a controlled/“living” character, proceeding with pseudo‐first‐order kinetics. All these star polymers with different molecular weights exhibited narrow molecular weight distributions of less than 1.2. The effect of polymerization temperature and molecular weight of the star macro‐RAFT agent on the polymerization kinetics of NIPAAm monomers was also addressed. Hardly any radical–radical coupling by‐products were detected, while linear side products were kept to a minimum by careful control over polymerization conditions. The trithiocarbonate groups were transferred to polymer chain ends by R‐RAFT polymerization, providing potential possibility of further modification by thiocarbonylthio chemistry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011