以二硫键连接的两嵌段共聚物的制备新方法

报道了一种制备二硫键连接的两嵌段共聚物的新方法.以可逆加成-断裂链转移自由基聚合(RAFT)制备聚苯乙烯大分子链转移剂(PS-RAFT),经伯胺还原得到巯基封端的PS(PS-SH).PS-SH与原子转移自由基聚合(ATRP)引发剂2-溴-2-甲基丙酸-2-(2-吡啶基二硫)乙酯发生交换反应,得到含有二硫键的聚苯乙烯大分子ATRP引发剂(PS-S-S-Br).以PS-S-S-Br引发甲基丙烯酸-2-羟基乙酯(HEMA)的ATRP聚合反应,合成了由二硫键连接的两嵌段共聚物PS-S-S-PHEMA.将PS-S-S-PHEMA可在甲醇中自组装形成以PS为核,PHEMA为壳的球形聚合物胶束,为制备新型含二硫键聚合物提供了新的合成方法.     

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。     

用双硫酯链转移法合成嵌段聚合物

研究了以双硫酯为链转移剂进行的均聚和嵌段共聚物的合成。首先合成大分子链转移剂,得到分子量可控、多分散性系数（PDI）较小（＜1.30）的均聚物。用末端带有双硫酯基因的PSt,PBMA和PBA为链转移剂,加入第二单体聚合得到分子量可控、且PDI较小的两嵌段聚合物。嵌段聚合时必须加入微量的自由基引发剂以形成大分子自由基,达到较好的控制聚合效果。     

丙烯腈-苯乙烯嵌段共聚物的RAFT聚合与表征

以S,S'-二(α,α '-二甲基-α″-乙酸)三硫代碳酸酯(TRIT)为链转移剂,利用可逆加成断裂链转移自由基聚合(RAFT)制备了窄分布的端羧基大分子链转移剂——聚苯乙烯和聚丙烯腈.以大分子链转移剂为RAFT试剂,引发苯乙烯或丙烯腈单体的RAFT聚合,进一步得到聚丙烯腈-聚苯乙烯-聚丙烯腈(PAN-b-PS-b-PAN)和聚苯乙烯-聚丙烯腈-聚苯乙烯(PS-b-PAN-b-PS)三嵌段共聚物.通过1 H-NMR、FT-IR、凝胶渗透色谱(GPC)对所得产物的结构和分子量进行了袁征,通过原子力显微镜(AFM)和拉曼光谱(Raman)研究了嵌段共聚物薄膜的微相分离结构与热解行为.结果表明:所得产物中除PAN-b-PS-b-PAN外,分子量分布均小于1.2.嵌段共聚物薄膜经250℃热稳定化与600℃热解处理后,碳化并形成了规整的石墨结构,微区尺寸在75 nm左右.     

用双硫酯链转移法合成嵌段聚合物

研究了以双硫酯为链转移剂进行的均聚和嵌段共聚物的合成 .首先合成大分子链转移剂 ,得到分子量可控、多分散性系数较小的均聚物PMMA、PBMA、PEMA、PEA、PBA、PMA、PSt,多分散性系数一般小于 1 30 .在相同的条件下 ,甲基丙烯酸酯类的聚合速度最快 ,苯乙烯其次 ,丙烯酸酯类最慢 .用末端带有双硫酯基团的PSt、PBMA、PBA为链转移剂 ,加入多种第二单体聚合得到实测分子量与理论分子量接近 ,且多分散性系数较小的两嵌段聚合物 .在链转移剂和引发剂的比例为 3∶1～ 6∶1的范围内 ,聚苯乙烯同样可以作为第一嵌段得到和其它酯类单体的两嵌段聚合物 .1 H NMR方法证明了聚合物的末端带有双硫酯基团 .嵌段聚合时必须加入微量的自由基引发剂以形成大分子自由基 ,达到较好的控制聚合效果     

以双硫酯为链转移剂的活性自由基聚合

合成并研究了两种双硫酯链转移剂的纯化方法 ,进行了多种单体以双硫酯为链转移剂的活性自由基聚合及嵌段共聚 .发现以PhC(S)SC(CH3) 2 Ph为链转移剂的效果比PhC(S)SCH(CH3)Ph好 ,聚合产物的多分散性系数较小 .引发剂与链转移剂的摩尔数比为 1∶3 5～ 1∶4 2时 ,得到多分散性系数小 ,实测分子量与理论分子量相近的聚合产物 .聚合物的分子量随时间和转化率的增加而增加 ,加入第二单体形成嵌段共聚物 ,具有活性聚合特征 .聚甲基丙烯酸酯大分子引发剂引发丙烯酸酯单体聚合时 ,聚合速度最快 .     

机理转移法合成聚丁二烯-b-聚(甲基丙烯酸N,N-二甲氨基乙酯)两亲性嵌段共聚物

将活性负离子聚合与原子转移自由基聚合(ATRP)技术相结合,运用机理转移法制备了一种两亲性材料聚丁二烯-b-聚(甲基丙烯酸N,N-二甲氨基乙酯)(PB-b-PDMAEMA)嵌段共聚物.首先通过负离子聚合方法设计合成聚丁二烯,用环氧丙烷封端,2-溴异丁酰溴作酯化剂,合成具有活性端基溴的聚丁二烯大分子引发剂(PB-B r),再用其引发亲水性单体DMAEMA进行原子转移自由基聚合,聚合动力学证实了该聚合反应具有典型的活性/可控自由基聚合的特征.通过差示扫描量热法(DSC)研究嵌段共聚物的微相分离行为.制备的大分子引发剂及两亲性嵌段共聚物经凝胶色谱、红外和核磁表征证实了预定的结构.     

支化PEG-b-PCL嵌段共聚合物的合成

以聚乙二醇甲基丙烯酸酯(PEGMA)为大分子引发剂进行ε-己内酯的酶催化开环聚合, 合成出嵌段共聚物, 然后将其转化成大分子引发剂型单体(Macroinimer), 最后通过原子转移自由基聚合(ATRP)制备出一种新型结构的嵌段型支化聚合物.     

超临界CO2中苯乙烯RAFT分散聚合

以末端带有三硫代碳酸酯的聚二甲基硅氧烷(PDMS-TTC)为大分子链转移剂,在超临界CO2中通过苯乙烯的可逆加成-断裂链转移(RAFT)聚合制备了聚二甲基硅氧烷-b-聚苯乙烯(PDMS-b-PS)嵌段共聚物,对聚合反应动力学以及产物的组成、分子量和形貌等进行了表征.由于PDMS链段可溶于超临界CO2而PS链段不溶,因此在超临界CO2中制备PDMS-b-PS嵌段共聚物的过程是以嵌段共聚物自身作为分散稳定剂的RAFT分散聚合,产物为粒径较均一的球形颗粒.     

化学酶法合成五嵌段聚合物及其自组装行为的研究

用酶促开环聚合与ATRP方法相结合,制备了聚甲基丙烯酸六氟丁酯-聚己内酯-聚乙二醇-聚己内酯-聚甲基丙烯酸六氟丁酯(PHFMA-b-PCL-b-PEG-b-PCL-b-PHFMA)五嵌段聚合物.首先用Novozym e 435作为催化剂合成了聚己内酯-聚乙二醇-聚己内酯三嵌段聚合物,然后通过端基官能化法合成了大分子引发剂,并用其引发甲基丙烯酸六氟丁酯(HFMA)的ATRP反应,合成了五嵌段聚合物.通过核磁和GPC证明了大分子引发剂和五嵌段共聚物的结构,五嵌段共聚物的GPC分析表明这种合成方法的可行.共聚物胶束的直径和大小通过动态光散射方法和原子力显微镜测试,五嵌段共聚物在水中的的自组装行为也被研究.结果证明胶束是球形,其平均直径为77 nm.聚合物在四氢呋喃中的浓度对聚合物的聚集形貌有很大的影响.     

原子转移自由基聚合制备聚(甲基丙烯酸甲酯-b-苯乙烯)时单体聚合顺序对嵌段效率的影响

采用原子转移自由基聚合研究了聚（ 甲基丙烯酸甲酯 ｂ 苯乙烯） 嵌段共聚物的合成,实验结果表明,当先进行甲基丙烯酸甲酯的聚合,然后再进行苯乙烯的聚合时,得到了完全的嵌段共聚物;反之,如果改变单体的聚合顺序,则嵌段效率很低．用聚合物末端Ｃ—Ｘ（Ｘ＝ Ｃｌ,Ｂｒ） 键的断裂能对实验结果进行了解释．     

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4‐(2‐bromo‐2‐methylpropionyloxy)‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Br‐TEMPO), was synthesized by the reaction of 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy with 2‐bromo‐2‐methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br‐TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω‐end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006     

The TIT-Inifer Method of synthesis of block copolymers

A two-step free radical method of synthesis of block copolymers, called TIT-Inifer Method is proposed. In the method, specially designed initiators/transfer agents of the general formula TIT (called herein: TIT-Inifers) are used, where: T represents transfer groups, I is an initiator fragment, and SPACER is any skeleton, that separates the radical center formed at T during transfer reaction from interaction with the initiator fragment. In the first step of the method, a monomer A is polymerized in the presence of a TIT-Inifer at some temperature T₁, at which the initiator fragment of the inifer is stable. In that step the TIT-Inifer acts as a transfer agent, so that the initiator fragment gets incorporated into polymer chain to yield a macroinitiator. In the second step of the method, the macroinitiator is used to initiate polymerization of a monomer B at a temperature T₂, at which the initiator groups of the macroinitiator cleave. Depending of the mode of termination of growing polymer chains, AB-type or ABA-type block copolymers are obtained as the major product, altogether with some amount of homopolymers resulting from side reactions of macroradicals. Two example TIT-Inifers were designed and their application for synthesis of block copolymers was studied. It was found that the TIT-Inifer Method was effective for preparation of block copolymers. Aspects of the mechanism by which the TIT-Inifers attach initiator groups to polymer chains and applicability of the TIT-Inifer Method for large-scale production of block copolymers are discussed. © 1996 John Wiley & Sons, Inc.     

Ambient temperature ATRP of benzyl methacrylate as a tool for the synthesis of block copolymers with styrene

The rapid atom transfer radical polymerization (ATRP) of benzyl methacrylate (BnMA) at ambient temperature was used to synthesize block copolymers with styrene as the second monomer. Various block copolymers such as AB diblock, BAB symmetric and asymmetric triblock, and ABABA pentablock copolymers were synthesized in which the polymerization of one of the blocks namely BnMA was performed at ambient temperature. It is demonstrated that the block copolymerization can be performed in a controlled manner, regardless of the sequence of monomer addition via halogen exchange technique. Using this reaction condition, the composition (ratio) of one block (here BnMA) can be varied from 1 to 100. It is further demonstrated that in the multiblock copolymer syntheses involving styrene and benzyl methacrylate, it is better to start from the PS macroinitiator compared with PBnMA macroinitiator. The polymers synthesized are relatively narrow dispersed (<1.5). It is identified that the ATRP of BnMA is limited to certain molecular weights of the PS macroinitiator. Additionally, a preliminary report about the synthesis of the block copolymer of BnMA‐methyl methacrylate (MMA), both at ambient temperature, is demonstrated. Subsequent deprotection of the benzyl group using Pd/C? H₂ results in methacrylic acid (MAA)–methyl methacrylate (MAA–MMA) amphiphilic block copolymer. GPC, IR, and NMR are used to characterize the synthesized polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2848–2861, 2006     

Synthesis of Well-Defined Dendritic-Linear Diblock and Triblock Copolymers by Controlled Free Radical Polymerization

Recently, significant progress has been made in the field of living free radical polymerization such as nitroxide-mediated stable free radical polymerization, atom transfer radical polymerization (ATRP), reverse ATRP and reversible addition-fragmentation chain transfer1. Among them, ATRP has been successfully applied to the synthesis of well-defined comb, gradient, star and dendritic macromolecules. Recent advances have been carried toward new initiators, metals and ligands. As a new cl…     

Synthesis and Characterization of Four-Arm Star Poly(ϵ-caprolactone)-Block-Poly(cyclic-carbonate methacrylate) Copolymers by Combining Ring-Opening Polymerization With Atom Transfer Radical Polymerization

Well-defined four-arm star poly(?-caprolactone)-block-poly(cyclic carbonate methacrylate) (PCL-b-PCCMA) copolymers were synthesized by combining ring-opening polymerization (ROP) with atom transfer radical polymerization (ATRP). First, a four-arm poly(?-caprolactone) (PCL) macroinitiator [(PCL-Br)₄] was prepared by the ROP of ?-CL catalyzed by stannous octoate at 110°C in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2-bromoisobutyryl bromide. The sequential ATRP of CCMA monomer was carried out by using the (PCL-Br)₄ tetrafunctional macroinitiator (MI) and in the presence of CuBr/2, 2′-bipyridyl system in DMF at 80°C with [(MI)]:[CuBr]:[bipyridyl] = 1:1:3 to yield block polymers with controlled molecular weights (M_n (NMR) = 10700 to 27300 g/mol) by varying block lengths and with moderately narrow polydispersities (M_w/M_n = 1.2–1.4). Block copolymers with different PCL: PCCMA copolymer composition such as 50:50, 70:30 and 74:26 were prepared with good yields (48-74%). All these block copolymers were well characterized by NMR, FTIR and GPC and tested their thermal properties by DSC and TGA.     

Block copolymer preparation by atom transfer radical polymerization under emulsion conditions using a nanoprecipitation technique

Living‐radical polymerization of acrylates were performed under emulsion atom transfer radical polymerization (ATRP) conditions using latexes prepared by a nanoprecipitation technique previously employed and optimized for the polymerization of styrene. A macroinitiator of poly(n‐butyl acrylate) prepared under bulk ATRP was dissolved in acetone and precipitated in an aqueous solution of Brij 98 to preform latex particles, which were then swollen with monomer and heated. Various monomers (i.e. n‐butyl acrylate, styrene, and tert‐butyl acrylate) were used to swell the particles to prepare homo‐ and block copolymers from the poly(n‐butyl acrylate) macroinitiator. Under these conditions latexes with a relatively good colloidal stability were obtained. Furthermore, amphiphilic block copolymers were prepared by hydrolysis of the tert‐butyl groups and the resulting block copolymers were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The bulk morphologies of the polystyrene‐b‐poly(n‐butyl acrylate) and poly(n‐butyl acrylate)‐b‐poly(acrylic acid) copolymers were investigated by atomic force microscopy (AFM) and small angle X‐ray scattering (SAXS). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 625–635, 2008     

Controlled/“living” atom transfer radical polymerization of methyl methacrylate in the synthesis of triblock copolymers from a poly(oxyethylene) macroinitiator

Atom transfer radical polymerization of methyl methacrylate initiated by a poly(oxyethylene) macroinitiator by the esterification of PEG 1500 with 2-chloro propionyl chloride was synthesized. These polymerization proceeds both in bulk and solution with a quantitative initiation efficiency, leading to A-B-A triblock copolymers. The macroinitiators and their block copolymers were characterized by FT-IR, FT-NMR and GPC analyses. In bulk polymerization, the kinetic study showed that the relationship between ln[M]₀/[M] vs time was linear showing that there is a constant concentration of active species throughout the polymerization and follow the first order kinetics with respect to monomer. Moreover, the experimental molecular weight of the block copolymers increased linearly with the monomer conversion and the polydispersity index remained between 1.3 and 1.5 throughout the polymerization. No formation of homo poly(methyl methacrylate) could also be detected, and all this confirms that the bulk polymerization proceeds in a controlled/“living” manner.     

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br₂-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br₂-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB₂-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.