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.     

原子转移自由基聚合与高分子构筑

活性聚合反应是目前高分子合成研究最为活跃的领域之一，原子转移自由基聚合反应（ATRP）是实现活性聚合的一种有效途径，可实现多种单体的活性聚合和可控自由基聚合。本文介绍了原子转移自由基聚合反应机理，重点综述了原子转移自由基聚合在高分子合成中的应用。     

γ-射线辐射活性自由基聚合研究

本文对γ- 射线辐射条件下的活性自由基聚合反应研究及进展进行了综述。虽然γ- 射线辐射引发聚合反应通常是不可控的,但在有机硫化物,如二硫代羧酸酯或三硫代碳酸酯存在下,则成功地实现了可控/活性自由基聚合。聚合过程中聚合物分子量随单体转化率线性增长,不但可控,且分布窄,也可以用于合成嵌段共聚物。有机硫化物对聚合反应控制起着关键性作用,硫化物的结构对于γ- 射线辐射活性自由基聚合行为的影响显著。γ- 射线辐射聚合的突出优点是可在室温或更低的温度下实施,且不需要加入引发剂。在环硫化合物存在下,获得了环形聚合物;而且使热和光敏感的叠氮类单体实现了活性聚合。     

Mechanism-based invention of high-speed living radical polymerization using organotellurium compounds and azo-initiators

Kinetic analysis reveals the existence of two competing pathways in the organotellurium-mediated living radical polymerization (TERP) at elevated temperature. The rate-determining step, namely, the thermal dissociation process, could be bypassed by the addition of conventional radical initiators, and the polymerization proceeded at low temperature by the degenerative transfer-mediated polymerization. The polymerization conditions are applicable to a variety of vinyl monomers, and the desired polymers form in a highly controlled manner.     

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.     

Polymerization of methyl methacrylate in the presence of 2,5-di-tert-butyl-p-benzoquinone

Polymerization of methyl methacrylate in the presence of 2,5-di-tert-butyl-p-benzoquinone is a combination of two processes: inhibited and controlled radical polymerization. The adduct of chain propagation radicals and p-quinone formed due to the inhibited polymerization is a macroinitiator of controlled radical polymerization. The fraction of the pseudo-living process is determined by the concentration of p-quinone in the starting polymerized composition. Post-polymerization proceeds via the reversible inhibition mechanism.

     

Living/controlled copolymerization of acrylates with nonactivated alkenes

The living/controlled copolymerization of methyl acrylate with 1‐alkenes and norbornene derivatives through several radical polymerization techniques has been achieved. These techniques include atom transfer radical polymerization, reversible addition–fragmentation transfer polymerization, nitroxide‐mediated polymerization, and degenerative transfer polymerization. These systems display many of the characteristics of a living polymerization process: the molecular weight increases linearly with the overall conversion, but the polydispersity remains low. Novel block copolymers have been synthesized through the sequential addition of monomers or chain extension. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6175–6192, 2004     

Jacketed polymers: Controlled synthesis of mesogen‐jacketed polymers and block copolymers

The controlled radical polymerization of mesogen‐jacketed liquid crystalline polymers has triggered great interests in synthesis of complex structures as well as well‐defined linear homopolymers with controlled molecular weight and narrow molecular weight distributions. This review highlights the synthetic strategies of controlled radical polymerization of linear homopolymers, star polymers, superbranched polymers, graft polymers, block copolymers, star block copolymers, and so on. The employed living methods include nitroxide‐mediated radical polymerization and atom transfer radical polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 319–330, 2009     

Oxygen‐Initiated and Regulated Controlled Radical Polymerization under Ambient Conditions

A rapid oxygen‐initiated and ‐regulated controlled radical polymerization was conducted under ambient temperature and atmosphere. The reaction between triethylborane and oxygen provides ethyl radicals, which initiate and mediate the radical polymerization. The controlled radical polymerization was achieved using RAFT chain transfer agents (CTA) without any process of removing oxygen, providing well‐defined polymers with almost full conversion (>95 %) in a short period (15 min). High‐throughput screening was used to discover the suitable conditions for various CTA and monomers. To show the versatility of this method, a polymer library containing 25 well‐defined polymers with different compositions (block and statistical copolymers) and molecular weights were synthesized in 1 h via high‐throughput synthesis technique. A polymer‐painting technique was developed using this method, forming films with spatial control and excellent control in molecular weight and dispersity.     

可控自由基聚合与其它活性聚合方法结合制备嵌段共聚物

可控自由基聚合与其它聚合方法结合,可以制备多种类型的嵌段共聚物,因此得到了广泛关注。本文着重介绍可控自由基聚合与离子开环聚合、阴离子聚合、烯类单体的阳离子聚合及其它活性聚合方法结合制备嵌段共聚物的研究现状和进展。     

由平面合成聚合物刷--表面引发原子转移自由基聚合研究进展

原子转移自由基聚合反应(ATRP)是实现活性聚合,获得可控聚合物的一种有效途径。通过表面引发原子转移自由基聚合,在材料表面合成聚合物刷,是改变材料表面特征的有效方法。本文综述了表面引发原子转移自由基聚合合成聚合物刷及其最新进展。     

Copper(0)-mediated radical polymerization of styrene at room temperature

The “living’/controlled radical polymerization (LRP) of styrene (St) at room temperature is rarely reported. In this work, copper(0) (Cu(0))-mediated radical polymerization of St at room temperature was investigated in detail. Dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) as well as a binary solvent, tetrahydrofuran/1,1,1,3,3,3-hexafluoro-2-propanol were used as the solvents, respectively. Methyl-2-bromopropionate and ethyl 2-bromoisobutyrate were used as the initiators, respectively. The polymerization proceeded smoothly with moderate conversions at room temperature. It was found that DMF was a good solvent with the essential features of LRP, while DMSO was a poor solvent with uncontrollable molecular weights. Besides, the match among the initiator, solvent and molar ratios of reactants can modulate the livingness of the polymerization, and the proper selection of ligand was also crucial to a controlled process. This work provided a first example of Cu(0)-mediated radical polymerization of St at room temperature, which would enrich and strength the LRP technique.     

From “Living” Carbocationic to “Living” Radical Polymerization

Abstract

“Living” carbocationic polymerization is compared to the “living” radical process. Similarities and differences are discussed. “Living” radical polymerization of vinyl acetate and methyl methacrylate to provide polymers with controlled molecular weights and narrow molecular weight distribution (M_w/M_n < 1.2) are presented.     

丙烯腈可控/"活性"自由基聚合研究进展

可控/"活性"自由基聚合能有效控制聚合物的分子量及其分布,并且能调控其微观拓扑结构。聚丙烯腈及其共聚物具有良好的成纤成膜性能,是一类应用十分广泛的聚合物。本文综述了可控/"活性"自由基聚合法合成聚丙烯腈及其共聚物的研究现状与进展,从氮氧自由基法(NMP)、引发转移终止剂法(iniferter)、原子转移自由基聚合(ATRP)和可逆加成-断裂链转移(RAFT)聚合等方面对丙烯腈均聚物和共聚物的合成研究作了全面的总结,提出了存在的问题,并且对今后的研究方向作了展望。     

Synthesis of block copolymers consisting of liquid crystalline and amorphous segments by living/controlled radical polymerization

Living polymerization is most often observed in systems where the growing species are ions. In such systems the chain ends do not react to each other due to elestrostactic repulsion, but only to monomers allowing, this way, the control in structure of the formed polymer. Free radicals, which are the growing species in the radical polymerization, easely undergo combination and prevent a living radical polymerization. Thus, a great challenge to polymer science was in meeting a system that offered to the radical polymerization a radical stabillization alike in ionic polymerizations. At the same time, the radicals should undergo rapid propagation and should not be able to initiate new chains, in a controlled reaction. Some succesfull techniques of living/controlled radical polymerization, such as stable free radical polymerization (SFRP), mediated by nitroxide, INIFERTER and atom transfer polymerization (ATRP) will be overviewed here, as well as their application to the synthesis of liquid crystalline polymers.     

可控聚合技术在颜料分散剂开发中的应用

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。     

A New Additive for Controlled Radical Polymerization

A new versatile additive for the controlled radical polymerization of numerous vinyl monomers under mild conditions is presented. The addition of 1,1‐diphenylethene (DPE) to a conventional radical polymerization system consisting of initiator and monomer results in a controlled behavior of the polymerization. Block copolymers are obtained by simply heating the resulting polymers in the presence of a second monomer.     

Tailoring macromolecular architecture with imidazole functionality: A perspective for controlled polymerization processes

Controlled radical polymerization (CRP) allows for the design and synthesis of functional polymers with tailored composition and unique macromolecular architectures. Synthetic methods that are readily available for controlled radical polymerization include nitroxide-mediated polymerization, reversible addition–fragmentation chain transfer polymerization, and atom transfer radical polymerization. N-Vinyl monomers that are typically amenable to free radical methods are often difficult to synthesize in a controlled manner to high molecular weight due to the lack of resonance stabilization of the propagating radical. However, recent advances in the field of CRP have resulted in successful controlled polymerization of various N-vinyl heterocyclic monomers including N-vinylcarbazole, N-vinylpyrrolidone, N-vinylphthalimide, and N-vinylindole. The incorporation of the imidazole ring into homopolymers and copolymers using conventional free radical polymerization of N-vinylimidazole monomer is particularly widespread and advantageous due to facile functionalization, high thermal stability, and the relevance of the imidazole ring to many biomacromolecules. Copolymers prepared with methyl methacrylate displayed random incorporation according to differential scanning calorimetry and amorphous morphologies according to X-ray scattering. Imidazole- and imidazolium-containing monomers have shown recent success for CRP; however, the controlled polymerization of N-vinylimidazole has remained relatively unexplored. Future efforts focus on the development of tailored imidazole-containing copolymers with well-defined architectures for emerging biomedical, electronic and membrane applications.     

Free-radical polymerization of methyl methacrylate in the presence of dithiobenzoates as reversible addition-fragmentation chain transfer agents

The pseudoliving radical polymerization of methyl methacrylate in bulk mediated by dithiobenzoates with various leaving groups as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that polymerization proceeds under conditions of the low steady-state concentration of radical intermediates; as a result, the steady-state of the process is rapidly achieved even at low conversions. Retardation of polymerization observed at high concentrations of reversible addition-fragmentation chain-transfer agents is apparently associated with the occurrence of chain termination reactions involving intermediates, as evidenced by the model reaction. The autoacceleration of polymerization is suppressed with an increase in the concentration of reversible addition-fragmentation chain-transfer agents. An efficient approach to the synthesis of a narrow-dispersed PMMA with the controlled molecular mass has been suggested.     

Regiospecific radical polymerization of a tetrasubstituted ethylene monomer with molecular oxygen for the synthesis of a new degradable polymer

A new class of degradable polymers is obtained from a diene monomer and molecular oxygen as the starting materials via a highly controlled radical copolymerization process. We now report the regiospecific copolymerization of a tetrasubstituted ethylene monomer with oxygen. Theoretical calculations support the highly selective propagations observed during the polymerization. The key steps are the regiospecific reactions of a peroxy radical to diene monomers and an allyl radical to molecular oxygen. The well-controlled molecular structure of the resulting polymer leads to the aldehyde-free degradation products during degradation by various stimuli, such as heating.