苯乙烯可逆加成-断裂链转移聚合动力学

为了实现可逆加成-断裂链转移(RAFT)聚合过程中,苯乙烯均聚、高分子量聚苯乙烯的合成及苯乙烯与其他单体共聚时,对苯乙烯转化率、共聚时组成和分子量大小的控制,进行了二硫代苯乙酸-1-苯基乙酯(PEPDTA)调控苯乙烯本体和细乳液聚合动力学分析。在本体聚合中,反应速率慢,链增长自由基与"中间态"自由基的终止反应对聚合速率影响较小,很难合成窄分布、高转化率、高分子量的聚苯乙烯;在细乳液聚合中,反应速率快、转化率高,随着PEPDTA含量增加,乳胶粒数量减少、粒径分布变宽,诱导期和缓聚现象明显;聚合物的数均分子量随转化率线性增长,RAFT试剂浓度越高,分子量分布越窄,反应时间越长,分布越宽。以Smith-Ewart方程为基础,建立了苯乙烯RAFT细乳液聚合动力学模型,模型动力学曲线与实验数据相符合,能较好地预测实验过程。     

Synthesis of 9H-fluoren-9-yl benzodithioates and their application as reversible addition–fragmentation chain transfer agents in living radical polymerization of styrene

The reversible addition–fragmentation chain transfer (RAFT) polymerization is one of living radical polymerizations. In this study, four different 9H-fluoren-9-yl benzodithiolates (FBDTs) were synthesized, and used along with azobis(isobutyronitrile) (AIBN), a radical initiator, in polymerization of styrene (ST) at the molar ratio of 3:1. This new transfer agent exhibited the typical characteristic living free radical polymerization behaviors such as good control of molecule weight and narrow molecule weight distribution. It was concluded that the FBDTs can be used as the RAFT agents in free radical polymerization of vinyl monomers.     

Modeling analysis of chain transfer in reversible addition‐fragmentation chain transfer polymerization

The validity of simplifying the reversible addition‐fragmentation chain transfer (RAFT) polymerization as a degenerative chain transfer process was verified in this work. The simplified chain transfer mechanism enabled the direct modeling investigation of chain transfer coefficient in the RAFT polymerization. It also gave the analytical expressions for concentration, chain length, and polydispersity of various chain species. The comparison between the simulations based on chain transfer mechanism and those from general RAFT mechanism showed that this simplified mechanism can accurately predict RAFT polymerization in the absence of side reactions to adduct radicals other than fragmentation. However, significant errors are introduced at high conversion when side reactions to adduct are present. The chain transfer coefficient of RAFT agent is the key factor in RAFT polymerization. The polydispersity is more sensitive to chain transfer coefficient at low conversion. At high conversion, however, the polydispersity is mainly determined by termination, which can be controlled by RAFT agent concentration and the selection of initiator. At last, an analytical equation is derived to directly estimate chain transfer coefficient of RAFT agent from the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Synthesis and characterization of diethyl-dithiocarbamic acid 2-[4-(2-diethylthiocarbamoylsulfanyl-2-phenyl-acetyl)-2,5-dioxo-piperazin-1-yl]-2-oxo-1-phenyl-ethyl ester as new reversible addition-fragmentation chain transfer agent for polymerization of ethyl methacrylate

Diethyl-dithiocarbamic acid 2-[4-(2-diethylthiocarbamoylsulfanyl-2-phenyl-acetyl)-2,5-dioxo-piperazin-1-yl]-2-oxo-1-phenyl-ethyl ester as a novel di-functional reversible addition–fragmentation chain transfer (RAFT) agent was synthesized based on 2,5-diketopiperazine. The RAFT agent was designed based on the propagating core (R group) approach and characterized by ¹H NMR, ¹³C NMR, FT-IR, elemental analysis, and melting point technique. Then, ethyl methacrylate was synthesized via free radical and RAFT polymerizations. To investigate the effect of the RAFT agent on the kinetic of polymerization, molecular weight, and polydispersity index (PDI) of polymers and also monomer conversion were monitored. Also, synthesized polymers were characterized by ¹H NMR, ¹³C NMR, FT-IR, and TGA. Characterization analyses of synthesized RAFT agent were consistent with the structure. NMR and FTIR analyses confirmed end group incorporation of RAFT agent into polymer structure. According to results, poly(ethyl methacrylate) with low PDI (1.14) was obtained. Kinetic study indicated well-controlled polymerization of ethyl methacrylate by synthesized RAFT agent. TGA results showed that RAFT agent could reduce termination reactions and so reduce head-to-head bonds and chain-end unsaturation by keeping the concentration of radicals low enough.     

A 20th anniversary perspective on the life of RAFT (RAFT coming of age)

RAFT (reversible addition–fragmentation chain transfer) polymerization, making use of thiocarbonylthio transfer agents, was announced to the world just over 21 years ago. RAFT arose out of a desire to achieve perfection in polymers (or at least to define and limit the imperfections) and to invent living radical polymerization. However, living radical polymerization cannot be and never was. This perspective looks at RAFT after 21 years of development. Is RAFT a mature technology? We briefly summarize areas of current interest focusing on what is happening at CSIRO and point to where RAFT is going in areas such as RAFT free from exogenous initiators (photoRAFT, PET‐RAFT, eRAFT), new RAFT agents, RAFT for sequence‐defined polymers and RAFT single unit monomer insertion, RAFT emulsion polymerization and RAFT polymerization‐induced self‐assembly (PISA), RAFT‐crosslinking polymerization and the industrial applications of RAFT. © 2019 Society of Chemical Industry     

甲基丙烯酸酯/二甲基丙烯酸酯自由基共聚合体系中的自加速和凝胶行为

对甲基丙烯酸聚乙二醇单醚酯/二甲基丙烯酸聚乙二醇酯共聚体系分别实施常规自由基聚合（FRP）,原子转移自由基聚合（ATRP）和可逆加成-断裂链转移（RAFT）自由基聚合,通过观察聚合速率、双键转化率、凝胶点以及交联网络的发展,比较FRP、ATRP和RAFT共聚合体系的反应动力学和交联行为。3个聚合体系均出现了自加速现象,ATRP体系的自加速由扩散控制的自由基脱活造成,RAFT体系的自加速来自于扩散控制的自由基加成。在ATRP和RAFT交联体系中,初级链的缓慢增长和充分松弛减少了分子内环化,抑制了微凝胶形成,因此其凝胶点远低于FRP体系。ATRP和RAFT交联网络通过凝胶自由基与单体加成以及支化链的结合而不断发展,导致凝胶含量和交联网络密度随转化率不断增大。     

Poly(vinyl acetate) and Poly(vinyl propionate) Star Polymers via Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization

Summary Poly(vinyl acetate) and poly(vinyl propionate) star polymers with four arms were produced via reversible addition fragmentation chain transfer (RAFT) polymerization, employing a tetra-functional xanthate as the RAFT agent, in which the stabilizing groups are linked to the core. These novel star-like RAFT agents induced living/controlled behavior in both the vinyl acetate polymerization at 60 °C and in the vinyl propionate polymerization at 90 °C, respectively, leading to star polymers with minimum polydispersities of 1.2 and maximum apparent number average molecular weights of about 50,000 g·mol^-1. The microstructure of the star polymers was confirmed by electrospray ionization mass spectrometry.     

纳米纤维素晶须表面接枝及其液晶性能研究进展

作为一种新兴的纳米生物材料,纳米纤维素日益受到各界的广泛关注,对其进行表面接枝改性并开发新的功能是十分必要的。本文综述了纳米纤维素晶须表面接枝的技术及研究进展,主要介绍了传统自由基聚合、离子和开环聚合及活性自由基聚合技术,包括氮氧自由基调控活性聚合、原子转移自由基聚合、可逆加成-断裂链转移聚合、单电子转移活性自由基聚合,讨论了各种接枝聚合方法的适用范围和优缺点。简述了点击化学在纳米纤维素晶须表面接枝的应用。通过各种聚合方法改性得到的纳米纤维素晶须接枝共聚物往往具有一些特殊的功能,某些接枝共聚物在适当的溶剂中可以形成液晶态,本文重点介绍了接枝改性的纳米纤维素晶须的液晶性能及其形成机理和影响因素等。     

Side-Chain Metallocene-Containing Polymers by Living and Controlled Polymerizations

This review summarizes recent work on side-chain metallocene-containing polymers prepared by controlled and living polymerizations, which include living anionic polymerization (LAP), ring-opening metathesis polymerization (ROMP) and controlled radical polymerization (CRP) such as atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer polymerization (RAFT), and nitroxide-mediated polymerization (NMP). The majority of efforts in the field are focused on side-chain ferrocene-containing polymers, while cobaltocenium-containing polymers have recently started to draw attention. Future direction on the development of other metallocene-containing polymers is discussed.     

Particle Size Limits of RAFT Living Emulsion Polymerization,with Xanthate-Based Transfer Agent

With a xanthate-based low activity RAFT (reversible addition–fragmentation chain transfer) agent, the living emulsion polymerization system follows zero-one kinetics and particles are smaller than their characteristic cross over diameter. The size and kinetic limitations in RAFT emulsion were investigated by using the concept of crossover size, based on a mechanistic approach. The main reason for these limitations is attributed to the low transfer constant, which tends to render desorption of a radical from particles difficult, the incoming z-mer has a higher probability to propagate relative to the addition process in RAFT equilibrium. In contrast, the living mini-emulsion polymerization follows either zero-one or pseudo-bulk kinetics, depending on the initial droplet size and reaction conditions.     

Nitroxide-mediated radical polymerization in nanoreactors: Factors influencing compartmentalization effects on bimolecular termination

Modeling and simulations of nitroxide-mediated radical polymerization (NMP) in dispersed systems have been performed to elucidate what factors dictate the magnitude of the segregation effect on bimolecular termination between propagating radicals generated from alkoxyamine activation. The reduction in termination rate due to segregation cannot be predicted merely based on the average number of propagating radicals per particle . This is because the magnitude of the segregation effect is also governed by the distribution of propagating radicals between particles, which is influenced by both the termination (k_t) and the deactivation (k_deact) rate coefficients. The results have implications with regards to improvement of livingness (end-functionality) in NMP by exploitation of particle size, and are expected to apply (qualitatively) to other controlled/living systems based on the persistent radical effect (e.g. atom transfer radical polymerization).     

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。     

Morpholine‐based RAFT agents for the reversible deactivation radical polymerization of vinyl acetate and N‐vinylimidazole

Reversible addition–fragmentation chain transfer (RAFT) polymerization of less‐activated monomers in a controlled fashion is challenging due to the high reactivity and instability of the propagating radicals. We have designed dithiocarbamate‐based RAFT agents with morpholine as activating ‘Z’ group and benzyl, ethyl(1‐ethanoate)yl, ethyl(2‐propanoate)yl and cyanomethyl as ‘R’ leaving groups and investigated them for the reversible deactivation radical polymerization of vinyl acetate (VAc) and N‐vinylimidazole (N‐VIm). RAFT polymerization of VAc and N‐VIm at 70 °C using azobisisobutyronitrile as a free radical initiator proceeded in a controlled fashion as demonstrated by a linear increase in molar mass with conversion. Interestingly, the polymerization of VAc followed fast kinetics (approx. 60 min) with good to moderate control affording high‐molar‐mass poly(VAc) polymers. Furthermore, the synthesized chain transfer agents were able to polymerize N‐VIm under controlled conditions. The morpholine RAFT agents bearing cyanomethyl and ethyl(2‐propanoate)yl leaving groups showed better control of the polymerization of VAc and N‐VIm compared to the others. © 2020 Society of Chemical Industry     

RAFT Polymerization of Methyl Acrylate in Carbon Dioxide

Summary: Reversible addition fragmentation chain transfer (RAFT) polymerizations of methyl acrylate (MA) in solution containing either 22 vol.‐% CO₂ or toluene were performed at 80 °C and 300 bar using cumyl dithiobenzoate (CDB) at concentrations between 1.8 × 10^?3 to 2.5 × 10^?2 mol · L^?1 as the RAFT agent. Product molecular weight distributions and average molecular weights indicated the successful control of MA polymerization in CO₂, even at low CDB concentrations. RAFT polymerization rates were strongly retarded by CDB and were lower in CO₂ than in toluene solution. The enhanced fluidity associated with the addition of CO₂ to the polymerizing system provided access to mechanistic details of RAFT polymerization. The data of the present study into MA, together with our recent results on RAFT polymerization of styrene in solution of CO₂ and of toluene, suggest that self‐termination of intermediate RAFT radicals is responsible for retardation in case of high concentrations of this intermediate and in case of enhanced fluidity, which may be achieved by polymerization in solution of CO₂.

     

Photo-induced controlled radical polymerization with new Photocatalyst

Photo-induced electron transfer reversible addition-fragmentation chain transfer (PET RAFT) of methyl methacrylate (MMA) was investigated at 25 °C with rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein) (RB) as photoredox catalyst under visible light irradiation. The traditional chain transfer agent 4-cyanopentanoic acid dithiobenzoate (CPADB) was employed in this study. The kinetic curve of the photo-induced PET RAFT polymerization exhibited a good linear behavior. The number average molecular weights (M_n,GPC) of the poly(methyl methacrylate) (PMMA) increased linearly with respect to monomer consumption and they were in good agreement with the calculated values (M_n,th). At the same time the molecular weight distribution (M_w/M_n) was narrow. Temporal control of PET RAFT polymerization of MMA was demonstrated by “ON/OFF” experiments. The resulting PMMA was characterized by ¹H–NMR, and GPC. The resultant PMMA could be used as macro-chain transfer agents for the PET RAFT radical polymerization. The chain experiments were successfully carried out and the living characteristics were demonstrated. The probable mechanism was discussed.     

RAFT (Reversible addition–fragmentation chain transfer) crosslinking (co)polymerization of multi‐olefinic monomers to form polymer networks

The use of reversible addition–fragmentation chain transfer (RAFT) crosslinking (co)polymerization of multi‐olefinic monomers to produce three‐dimensional polymer networks is reviewed. We give specific attention to differences between RAFT and conventional processes, differences between RAFT and other forms of reversible deactivation radical polymerization (such as atom transfer radical and nitroxide‐mediated polymerizations) and the dependence of the polymerization process and network properties on RAFT agent structure. This knowledge is important in network optimization for applications as dynamic covalent polymers (in self‐healing polymers), as porous polymer monoliths or gels (used as chromatographic media, flow reactors, controlled release media, drug delivery vehicles and in molecular imprinting) and as coatings. © 2014 Society of Chemical Industry     

Electro‐optical properties of polymer dispersed liquid crystal prepared by successively controlled living radical polymerization

Polymer dispersed liquid crystal (PDLC) films were obtained by successive controlled living radical polymerizations: starting polystyrene (M1) was obtained by reversible addition‐fragmentation polymerization (RAFT), M1 was converted to P‐chloromethylated polystyrene (M2) which was grafted with polystyrene branches by atom transfer radical polymerization (ATRP) to yield RAFT‐initiating graft polymer containing trithiocarbonate moieties in the backbone (M3, RAFT‐active grafted polystyrene), and then PDLC films were prepared by photo‐induced RAFT copolymerization of methyl acrylate with M3 in the presence of a nematic liquid crystal. The electro‐optical properties of the films were investigated for the purpose to apply them to optical devices. Experimental results showed that preferable properties could be acquired by controlling the amount of M3 and the liquid crystal E7 in the polymer matrix of PDLC films. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Modeling RAFT polymerization kinetics via Monte Carlo methods: cumyl dithiobenzoate mediated methyl acrylate polymerization

Cumyl dithiobenzoate (CDB) mediated methyl acrylate (MA) bulk polymerizations at 80 °C, using CDB concentrations between 1.5×10⁻² and 5.0×10⁻² mol L⁻¹, were modeled via a novel Monte Carlo simulation procedure with respect to experimental time-dependent conversions, X, number average molecular weights, M_n, and weight average molecular weights, M_w. The simulations were based upon individual treatment of 5×10⁸ discrete molecules in accordance to their actual reaction pathways. The kinetic scheme employed includes termination reactions of intermediate RAFT radicals with propagating radicals and reaction steps of the RAFT pre-equilibrium, which are different from those of the RAFT main equilibrium. The equilibrium constant of the main equilibrium of the CDB/MA system at 80 °C was found to be K=1.2×10⁴ L mol⁻¹, indicating a relatively stable intermediate radical. The concentration of the intermediate RAFT radical, although not employed as experimental input data for the modeling, was calculated by using the obtained set of kinetic parameters as being in excellent agreement with experimental electron spin resonance spectroscopic data.     

Molecular composite materials formed from block copolymers containing a side-chain liquid crystalline segment and an amorphous styrene/maleic anhydride segment

Side-chain liquid crystalline block polymers containing a poly[6-[4-(4′-methoxyphenyl)phenoxy]hexyl methacrylate] (PMMA-LC) segment and a styrene-co-maleic anhydride segment (alternating structure) were prepared via reversible addition fragmentation chain transfer (RAFT) polymerization. PMMA-LC was initially prepared via RAFT polymerization mediated by 2-(2-cyanopropyl)dithiobenzoate (CPDB). The resulting polymer was subsequently isolated and used to re-initiate styrene/maleic anhydride alternating copolymerization. The block copolymerization proceeded to intermediate conversions with narrow polydispersities, however at higher conversions some molecular weight broadening was observed and this was attributed to radical-radical termination reactions. The resulting polymers were analyzed via size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Microporous honeycomb structured films were cast from solutions of the block copolymers to form porous molecular composites.     

End‐functional polymers,thiocarbonylthio group removal/transformation and reversible addition–fragmentation–chain transfer (RAFT) polymerization

This review focuses on processes for thiocarbonylthio group removal/transformation of polymers synthesized by radical polymerization with reversible addition‐fragmentation‐chain transfer (RAFT). A variety of processes have now been reported in this context. These include reactions with nucleophiles, radical‐induced reactions, thermolysis, electrocyclic reactions and ‘click’ processes. We also consider the use of RAFT‐synthesized polymers in the construction of block or graft copolymers, functional nanoparticles and biopolymer conjugates where transformation of the thiocarbonylthio group is an integral part of the process. This includes the use of RAFT‐synthesized polymers in other forms of radical polymerization such as atom transfer radical polymerization or nitroxide‐mediated polymerization, and the ‘switching’ of thiocarbonylthio groups to enable control over polymerization of a wider range of monomers in the RAFT process. With each process we provide information on the scope and, where known, indicate the mechanism, advantages and limitations. Copyright © 2011 Society of Chemical Industry