“活性”/可控自由基聚合在蛋白质杂化体制备中的应用研究进展

"活性"/可控自由基聚合(LPR)诞生于20世纪60年代,其当前主要包含引发链转移终止剂法(Iniferter)、氮-氧稳定的自由基聚合(NMP)、原子转移自由基聚合(ATRP)、可逆加成-断裂链转移聚合(RAFT),特别是近年来将"活性"/可控自由基聚合(LPR)所得聚合物以共价键耦合到蛋白质杂化体中的应用特别多。根据一些国内外的最新研究,概述了这4种LPR体系在蛋白质上应用的基本原理和发展历程,及在蛋白质杂化制备中的应用研究进展。     

活性自由基聚合的分类及原子转移自由基聚合的研究进展

阐述了活性自由基聚合的产生背景和基本概念,介绍了活性自由基聚合的分类,描述了原子转移自由基聚合的研究进展。     

活性”自由基聚合法合成支链结构可控的SBS-g-PMMA

通过“活性”／可控自由基聚合合成了支链结构可控的ＳＢＳ－ｇ－ＰＭＭＡ接枝共聚物。首先以ＳＢＳ与Ｎ－－溴代丁二酰亚胺反应合成省代ＳＢＳ（ＳＢＳ－Ｂｒ）,并对ＳＢＳ－Ｂｒ中烯丙基溴（－Ｂｒ）的含量进行定量分析。然后以此ＳＢＳ－Ｂｒ为大分子引发剂在ＣｕＸ／ｂｐｙ（Ｘ＝Ｃｌ,Ｂｒ－Ｂｒ：ＣｕＸ：ｂｐｙ＝１：１：３）存在下引发ＭＭＡ进行接枝共聚。在此ＣｕＣｌ／ｂｐｙ体系催化的接枝共聚合中,动力学特性为一级,     

原子转移自由基聚合负载化催化剂研究进展

综述了几种原子转移自由基聚合(ATRP)用负载化催化体系的组成及应用,主要包括硅胶或石英、交联聚苯乙烯或其它聚合物为载体进行的催化剂负载化,它们都能够部分解决催化剂残留问题,但却有一定的局限性;负载/可溶性混杂催化体系成为解决这一问题的新方法,而且它与传统的均相催化体系相比,可控性没有明显差异,有希望作为未来解决催化剂残留的有效方法.最后展望了ATRP负载化催化荆的发展方向.     

氯乙烯活性自由基聚合研究进展

活性自由基聚合(LRP)是一种有效的高分子设计手段,氯乙烯(VC)属于非活性单体,实施LRP较为困难。综述了目前成功应用于VC聚合的LRP体系,即SET-LRP、NMP和RAFT,详细介绍了其调控机理和控制效果,探讨了各法的优缺点,并展望了VC-LRP未来的发展方向。     

异戊二烯阻聚剂的研究

本文用膨胀计法研究抗氧剂二乙基羟胺、对叔丁基邻苯二酚和2,2,6,6,-四甲基-4-氧-哌啶氮氧自由基对过氧化二碳酸二(2-乙基已基)酯引发异戊二烯聚合的阻聚作用.     

活性自由基聚合研究的新动态

介绍了基于可逆链转移思想的“活性”／控制自由基合聚合。着重介绍澳大利亚Ｒｉｚｚａｒｄｏ研究小组的最新研究成果：以双硫酯类化合物为链转移剂的可逆加成－断裂链转移自由基聚合。分析其活性特征,并阐明其反应机理。     

原子转移“活性”可控自由基聚合引发体系的研究进展

原子转移自由基聚合反应(ATRP)是实现活性聚合的一种颇为有效的途径, 可以合成分子量可控、分子量分布窄的各种形状的聚合物.本文介绍了"活性"可控ATRP的研究进展, 包括RATRP、SR&NI ATRP、AGET ATRP、假卤素转移自由基聚合以及一些新催化剂体系下的新型ATRP,并说明了各种引发体系ATRP的反应机理.     

可控自由基聚合技术在涂料树脂合成中的应用

可控自由基聚合技术（CRP）作为一种能够实现对产品分子结构控制的新型聚合方法,对于合成高性能树脂和高分子助剂而言,具有特别重要的意义。本文对主要的可控聚合方法反应机理进行简述,并介绍可控聚合法在高固体分涂料树脂、功能型涂料树脂和水性树脂合成中的应用。     

Controlled/living radical polymerization of styrene catalyzed by cobaltocene

Controlled/living radical polymerization of styrene has been achieved by atom transfer radical polymerization (ATRP) catalyzed by cobaltocene (PDI = 1.27-1.41). The effects of the initiators, temperatures and solvents were studied. The end group of PS-Br was characterized by ¹H NMR. Block copolymerization proved that the polymer end is still living and the PMMA-b-PSt block copolymer was synthesized.     

Molecularly imprinted polymers via living radical polymerization: Relating increased structural homogeneity to improved template binding parameters

This work examined imprinted polymer networks prepared via controlled/living radical polymerization (LRP) and conventional radical polymerization (CRP) on chain growth, network formation, and efficiency of producing molecularly imprinted, macromolecular memory sites for the template molecule, diclofenac sodium. LRP extended the reaction-controlled regime of the polymerization reaction and formed more homogeneous polymer chains and networks with smaller mesh sizes. In addition, LRP negated the effect of the template on polymer chain growth resulting in polymers with a more consistent PDI independent of template concentration in the pre-polymerization solution. Improved network homogeneity within imprinted poly(HEMA-co-DEAEM-co-PEG200DMA) networks prepared via LRP resulted in a 38% increase in template binding affinity and 43% increase in the template binding over imprinted networks prepared via CRP and a 97% increase in affinity and 130% increase in capacity over non-imprinted networks prepared by LRP. By varying certain parameters, it was possible to create imprinted networks with even higher template binding affinities (155% over non-imprinted) and capacities (261% over non-imprinted). This work is the first to conclusively demonstrate that the observed improvement in binding parameters in weakly crosslinked, imprinted polymer networks could be explained by the more uniform molecular weight evolution associated with the LRP mechanism and the longer lifetime of an active polymer chain relative to the total polymerization time, which allowed for the formation of a more homogenous imprinted polymer network.     

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)₂-PEO-(PMMA)₂ has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)₂-CHCOOCH₂CH₂OH with an active hydroxyl group. The chlorine was removed to yield the (PS)₂-CHCOOCH₂CH₂OH ((PS)₂-OH). The hydroxyl group of the (PS)₂-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)₂-PEO-OH. The (PS)₂-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)₂-PEO-OCCHCl₂ ((PS)₂-PEO-DCA). The asymmetric H-shaped block polymer (PS)₂-PEO-(PMMA)₂ was prepared via ATRP of MMA at 130 °C using (PS)₂-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)₂-PEO-(PMMA)₂, were confirmed by ¹H NMR, GPC and FT-IR.     

Reversible chain transfer catalyzed polymerization (RTCP): A new class of living radical polymerization

This article introduces the new family of living radical polymerizations with germanium (Ge), tin (Sn), phosphorus (P), and nitrogen (N) catalysts which we recently developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity polymers are obtained in the homopolymerizations and random and block copolymerizations of styrene, methyl methacrylate, and functional methacrylates. The background, performance, and kinetic features of the polymerizations are described. Attractive features of the catalysts include their high reactivity, low toxicity (Ge, P, and N), low cost (P and N), and ease of handling (robustness).     

Probing the reaction kinetics of vinyl acetate free radical polymerization via living free radical polymerization (MADIX)

Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI^® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of k_t is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of k_t as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of k_t with conversion is more pronounced at increased chain lengths, with a strong decrease in k_t exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800.     

Synthesis of thermosensitive gel by living free radical polymerization mediated by an alkoxyamine inimer

Thermosensitive gel is synthesized through controlled/“living” free radical copolymerization of styrene and DVB mediated by an alkoxyamine inimer, 2,2,6,6-tetramethyl-1-(1′-phenylethoxy)-4-(4′-vinylbenzyloxy)-piperidine (V-ET). The inimer plays the role of both incorporating “T-shaped” inter-chain linkages and mediating the polymerization. First order kinetics is observed for crosslinking polymerizations before gel point, indicating a constant concentration of propagating radicals. Monomer conversion at the gel point depends on the feed ratio of DVB to V-ET. Higher amount of V-ET results in later gel point due to smaller molecular weight of the primary chains that depends inversely on the concentration of nitroxide. The resulting gel contains permanent and labile crosslinking points formed by DVB units and alkoxyamine moieties, respectively. Therefore, the gels exhibit gel-sol transition within a narrow temperature range. The gel properties, such as the swelling ratio and gel-sol transition temperature, can be controlled by changing the feed ratio of DVB to V-ET. The microenvironments in different gels, or at different temperatures, are investigated by ESR spectroscopy.     

High-pressure atom transfer radical polymerization of methyl methacrylate for well-defined ultrahigh molecular-weight polymers

The feasibility of high-pressure atom transfer radical polymerization (ATRP) for synthesizing well-defined polymers of extraordinarily high molecular weights was demonstrated. ATRP of methyl methacrylate (MMA) under pressures up to 500 MPa was investigated at 60 °C. The addition of a small amount of a Cu(II)Cl₂/ligand complex along with the general benefits of high pressure of enhancing propagation and suppressing termination brought about an excellent control of polymerization even with an extremely low concentration of ATRP initiator. For example, there was produced PMMA with a number-average molecular weight M_n of 3.6 × 10⁶ and a polydispersity index of 1.24, which had never been achieved by conventional ATRP.     

Synthesis of amphiphilic triblock copolymer of polystyrene and poly(4-vinylbenzyl glucoside) via TEMPO-mediated living radical polymerization

4-Vinylbenzyl glucoside peracetate 1 was polymerized with α,α′-bis(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)-1,4-diethylbenzene 2 in chlorobenzene using (1S)-(+)-10-camphorsulfonic acid anhydrous (CSA) as an accelerator ([1]=0.4 M,[1]/[2]/[CSA]=75/1/1.3) at 125 °C for 5 h. The polymerization afforded poly(4-vinylbenzyl glucoside peracetate) having TEMPO moieties on both sides of the chain ends, 3, with a molecular weight (M_w,SLS) of 8500, a polydispersity index (M_w/M_n) of 1.09, and an average degree of polymerization of the 1 unit (x) of 17. Styrene (St) was polymerized with 3 in chlorobenzene at 125 °C (St/chlorobenzene=1/2, w/w). The polymerization successfully afforded polystyrene-poly(4-vinyl glucoside peracetate)-polystyrene, 4, when the polymerization time was below about 2 h. Polymer 4 with the M_w,SLS of 12,500, 17,900, and 29,400, the compositions (y-x-y) of 20-17-20, 45-17-45, and 100-17-100, and the M_w/M_n of 1.12, 1.14 and 1.17 were modified by deacetylation using sodium methoxide in dry-THF into polystyrene-poly(4-vinyl glucoside peracetate)-polystyrene, 5. The solubility of polymer 5 was examined using a good solvent for polystyrene such as toluene and for the saccharide such as H₂O.     

Synthesis of random and block copolymers of styrene and styrenesulfonic acid with low polydispersity using nitroxide-mediated living radical polymerization technique

Poly(styrene-ran-styrenesulfonic acid) and poly(styrene-block-styrenesulfonic acid) with low polydispersity were prepared using nitroxide-mediated living radical polymerization technique. Random or block copolymerization of styrene and neopentyl p-styrenesulfonate smoothly proceeded by AIBN/2,2,5,5-tetramethyl-4-diethylphosphono-3-azahexane-3-nitroxide initiating system. Transformation of the sulfonate ester to sulfonic acid was carried out by the reaction with trimethylsilyl iodide or by thermolysis at 150 °C. Those polymers showed amphiphilic characters.     

Living radical polymerization of styrene mediated by a piperidinyl-N-oxyl radical having very bulky substituents

A new cyclic nitroxide 1 and the corresponding alkoxyamines 9 and 10 were synthesized and the polymerization of styrene (St) initiated with 10 was investigated. The NO-C bond of 9 is very weak, cleaving at room temperature. On the other hand, alkoxyamine 10 is stable at room temperature and the A_act and E_act for the NO-C bond homolysis were determined to be 1.4 × 10¹⁵ s⁻¹ and 124.5 kJ mol⁻¹, respectively. When the polymerization of St was carried out at 70 °C, the resultant poly(St) showed narrow polydispersities below 1.25. In the polymerization at 90 °C, the resulting poly(St) showed narrow polydispersity until 60% conversion, but M_w/M_n was rapidly increased above 60% conversion. On the other hand, the polymerization at 120 °C gave poly(St) with broad polydispersities. The unusual polymerization behavior was discussed on the basis of the SEC and ESR results.