聚丙烯酸-b-聚丙烯酸丁酯的RAFT水溶液聚合及其性能

该研究首先以2-{[(十二烷基硫基)硫代甲酰基]硫烷基}琥珀酸为链转移剂(CTA)在水溶液中调控丙烯酸(AA)进行可逆加成-断裂链转移自由基聚合(RAFT),再以得到的聚丙烯酸为大分子RAFT试剂,丙烯酸正丁酯(BA)为单体,进行扩链反应,得到聚丙烯酸-b-聚丙烯酸正丁酯。用红外光谱对产物结构进行了表征。考察了合成条件n(V501)/n(CTA)、n(AA)/n(CTA)、n(V501)/n(PAA-RAFT)、n(BA)/n(PAA-RAFT)对聚合物的表面张力、乳化性、起泡性和泡沫稳定性的影响。结果表明,当n(V501)/n(CTA)=0.2、n(AA)/n(CTA)=20、n(V501)/n(PAA-RAFT)=0.1、n(BA)/n(PAA-RAFT)=20时,得到的聚丙烯酸-b-聚丙烯酸正丁酯的水溶液表面活性最大,表面张力最低为30.89 N/m,乳化性最强,乳状液稳定时间达到1 082 s,起泡性和泡沫稳定性最弱,泡沫高度为17.01 mm,稳定时间为210 s。     

甲基丙烯酸甲酯的RAFT聚合研究

在链转移剂(CTA)二硫代苯甲酸异丙苯酯(CDB)、二硫代苯甲酸异丁氰酯(CPDB)和S,S′-二(α,α′-二甲基-α″-乙酸)-三硫代碳酸酯(CMP)的存在下,以甲基丙烯酸甲酯(MMA)为单体,采用可逆加成-断裂链转移(RAFT)聚合法合成聚甲基丙烯酸甲酯(PMMA)。研究了引发剂的用量、链转移剂与引发剂的物质的量比以及链转移剂的性质对聚合过程的影响。结果表明,对于三种CTA而言,偶氮二异丁腈(AIBN)用量为0.2%时聚合效果均最好;CTA的用量决定了聚合物的聚合度,减小CTA与AIBN的物质的量比可以得到相对分子质量较大的聚合物;在m(AIBN)∶m(MMA)=0.2%,n(CTA)∶n(AIBN)=4∶1时,三种CTA中CDB对此聚合过程的可控性最佳(相对分子质量分布指数为1.16),CPDB聚合得到的产物产率最高(86.5%),CMP聚合得到的产物数均相对分子质量最大(Mn=14 767g/mol)。     

通过RAFT聚合合成星型聚合物

采用先臂法合成(tBA/HDDA)星型聚合物。由丙烯酸正丁酯(tBA)的可逆加成-断裂链转移自由基聚合(RAFT),得到线型PtBA大分子链转移剂;PtBA与双官能团的偶联剂1,6-己二醇二丙烯酸酯(HDDA)反应得到星型聚合物。研究了偶联剂HDDA与线型PtBA大分子链转移剂的摩尔比对合成星型聚合物的影响。采用GPC法测定了线型大分子链转移剂PtBA及星型聚合物的分子量和分子量分布。结果表明,HDDA与PtBA的比例越高,星型聚合物的产率越大;超过一定值,则产生凝胶。GPC结果表示,所得星型聚合物的分子量大,分子量分布窄(PD I<1.19)。     

用MADIX/RAFT聚合合成聚(N-乙烯基己内酰胺)

MADIX/RAFT聚合是黄原酸酯调控的可逆加成-断裂链转移自由基聚合,它可用于调控非共轭单体的活性/可控自由基聚合。以乙二醇为原料,将乙二醇的两个羟基转化为O-乙基黄原酸酯,得到黄原酸酯双官能团链转移剂(CTA)。用这个CTA调控N-乙烯基己内酰胺(NVCL)的MADIX/RAFT聚合,合成了聚(N-乙烯基己内酰胺)。用1H NMR谱证明了所得聚合物和中间产物的结构。     

自由基活性聚合法制备聚苯乙烯及不同反应条件的影响

文章采用十二烷基三硫代碳酸酯为链转移剂,通过可逆加成-裂解-链转移自由基聚合(RAFT)的方法,合成了结构均一的侧链带有偶氮苯基团的聚苯乙烯。对生成的聚合物的结构用核磁共振氢谱进行表征,结果表明已成功地合成出目标产物。聚合物分子量用凝胶渗透色谱(GPC)进行测试,结果表明合成出的聚合物的分子量分布(PDI)区间在1.01-1.1。讨论了反应时间及反应物浓度对聚合的影响。结果表明,聚合物的分子量与反应时间呈正相关,呈现出"活性-可控"聚合特征。聚合物的分散度(PDI)受反应物浓度的影响很小,但转换率随着单体浓度的不断增加呈现出增大的趋势。     

丙烯酰胺在聚乙二醇水溶液中可逆加成-断裂链转移聚合

结合双水相聚合和可逆加成-断裂链转移(RAFT)聚合,提出在聚乙二醇(PEG)水溶液中进行丙烯酰胺(AM)的RAFT双水相聚合,考察反应条件对聚合反应速率和产物分子量及分布的影响。结果表明:高引发剂浓度、单体浓度和聚合温度可以提高初始聚合速率和最终转化率,PEG和RAFT试剂浓度的增加会导致聚合速率减慢和最终转化率降低;峰值聚合速率随引发剂浓度、单体浓度和聚合温度的增加而增大,同时峰值聚合速率对应的时间提前;RAFT试剂浓度增加会推迟峰值聚合速率对应的时间,但可制得分子量分布较窄的产物;PEG浓度的增加会导致产物的分子量分布变宽。     

P2VP-b-PS-b-PI三嵌段共聚物的RAFT合成及表征

以S-十二烷基-S’-(α,α’-二甲基-α’’-乙酸)-三硫代碳酸酯(DDMAT)为链转移剂,通过可逆加成-断裂链转移自由基聚合(RAFT)方法制备了窄分布的聚2-乙烯基吡啶。再以该聚合物为大分子链转移剂,引发苯乙烯的RAFT聚合,得到聚2-乙烯基吡啶-b-聚苯乙烯(P2VP-b-PS)的两嵌段共聚物。以P2VP-b-PS为RAFT试剂,合成聚2-乙烯基吡啶-b-聚苯乙烯-b-聚异戊二烯(P2VP-b-PS-b-PI)的三嵌段共聚物。运用1H NMR、IR和凝胶渗透色谱(GPC)等技术对产物的结构和分子量及分子量分布进行表征,采用原子力显微镜(AFM)观察三嵌段共聚物薄膜的微相分离结构。结果表明,所得三嵌段共聚物P2VP72-b-PS136-b-PI300分子量分布较窄(PDI=1.69),合成过程具有活性/可控聚合特征,聚合物薄膜经溶剂退火处理后出现了明显的微观相分离结构。     

水溶性丙烯酸钠和丙烯酸甲酯共聚物的合成及其分散性能研究

采用丙烯酸(AA)和丙烯酸甲酯(MA)为主体单体,次亚磷酸钠为链转移剂,过硫酸铵(APS)为引发剂,通过水相自由基聚合,并用30%浓度NaOH溶液中和,获得水溶性丙烯酸钠和丙烯酸甲酯聚合物(PAANa-co-PMA),其分子量可通过链转移剂的用量控制。这种共聚物在结构上引入亲油性单体丙烯酸甲酯,对Mg(OH)2粉体球磨分散效果有很大的改善。与聚丙烯酸钠外加剂相比,当助磨剂添加量为粉体质量的0.3%时,相同球磨时间下,粒径分布变小了1/3,比表面积增加近1倍。     

RAFT法合成超分散剂PS-b-PAA及其分散性能研究

以苯乙烯(St)和丙烯酸(AA)为单体,二硫代苯甲酸苄酯为链转移剂,偶氮二异丁腈(AIBN)作为引发剂,采用可逆加成-断裂链转移(RAFT)活性自由基聚合方法合成了两亲性嵌段共聚物分散剂聚苯乙烯-b-聚丙烯酸(PS-b-PAA),探讨了影响聚合反应的主要因素,用GPC、IR、1H NMR对其结构进行了表征.结果表明,用RAFT法制得的共聚物分子量分布为1.1～1.3,聚合反应在80℃下24h内转化率达95%.进一步的分散性能研究表明,超分散剂PS-b-PAA对SiO2粉体在水中有着较好的分散效果.     

等离子体及过氧化物引发DT聚合动力学

等离子体引发聚合具有经典自由基聚合不同的特征。文章以碘仿为链转移剂,比较了等离子体及过氧化物引发丙烯酸(AAc)的衰减链转移(DT)聚合动力学。结果表明:碘仿对过氧化物引发体系聚合速率的抑制较等离子体体系明显,同时过氧化物引发DT聚合的分子量更接近于理论值,也更容易在单体转化率较低时得到窄分子量分布(PDI)的聚合物。两种方法引发DT聚合的分子量均与单体转化率呈正比关系,其PDI分别低至1.48、1.64,符合可控/活性聚合的特征。     

Kinetics of RAFT emulsion polymerization of styrene mediated by oligo(acrylic acid‐b‐styrene) trithiocarbonate

The kinetics of ab initio reversible addition‐fragmentation chain transfer (RAFT) emulsion polymerization of styrene using oligo(acrylic acid‐b‐styrene) trithiocarbonate as both polymerization mediator and surfactant were systematically investigated. The initiator concentration was set much lower than that in the conventional emulsion polymerization to significantly suppress the irreversible termination reaction. It was found that decreased rapidly but the nucleation efficiency of micelles increased with the decrease of the initiator concentrations due to the significant radical exit. The particle number ( ) did not follow the classic Smith–Eward equation but was proportional to [I]^?0.4[S]^0.7. It was suggested that RAFT emulsion polymerization could be fast enough for commercial use even at extremely low initiator concentrations and low macro‐RAFT agent concentrations due to the higher particle nucleation efficiency at lower initiator concentration. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2126–2134, 2016     

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.     

甲基丙烯酸甲酯的RAFT微乳液聚合

该文合成了一种双官能团的RAFT试剂——S,S'-二(α,α'-二甲基-α″-乙酸)三硫代碳酸酯(BDAT)。以其为链转移剂,在微乳液体系中进行了甲基丙烯酸甲酯的RAFT聚合。分别讨论了聚合反应温度和链转移剂浓度对聚合反应的影响,并对相关的聚合反应动力学常数进行了计算。研究结果表明,在微乳液中进行的RAFT聚合具有显著的活性聚合的特征。聚合产物的相对分子质量(简称分子量,下同)随着转化率的提高而线性增加,同时聚合产物具有较窄的分子量分布,聚合过程随着链转移剂浓度的增加而逐渐可控。另外,利用透射电子显微镜对链转移剂浓度对微乳液粒子尺寸的影响也进行了考察,扫描电镜照片表明,微乳液聚合所得乳液粒子呈现单分散性状态,并且粒子尺寸随着链转移剂浓度的增加而逐渐增加。     

沉淀聚合制备低分子量聚丙烯酸及残液循环利用

以偶氮二异丁腈(AIBN)为自由基引发剂,石油醚为溶剂,异丙醇为链转移剂,通过沉淀聚合制备了低相对分子质量(简称分子量,下同)的聚丙烯酸。考察了引发剂用量、链转移剂用量、单体质量浓度对聚合收率的影响,确定最佳聚合条件为:AIBN用量为单体质量的10%,链转移剂用量为单体质量的100%,单体质量浓度100g/L,反应温度80℃,反应时间4 h。反应结束后产品在底部沉淀析出,溶剂可循环利用,在最佳聚合条件下,残液循环利用5次,单体的累计转化率达到92.6%。凝胶渗透色谱(GPC)分析表明,通过残液循环制备的产品重均分子量(Mw)变化不大,保持在1 000～1 300,多分散性(PDI)为1.92～3.38。     

Controlled synthesis of vinyl-functionalized homopolymers and block copolymers by RAFT polymerization of vinyl methacrylate

Reversible addition-fragmentation chain transfer (RAFT) polymerization of an asymmetrical divinyl monomer, vinyl methacrylate (VMA), was investigated under various conditions. RAFT polymerization of VMA using a dithioester-type chain transfer agent (CTA) under suitable conditions afforded soluble polymers with a high content of pendant vinyl ester side chains in sufficient yields (>70%). The monomer concentration, the nature of the CTA, and the CTA/initiator ratio were found to affect the polymerization reaction and the structure of the resulting polymers; this behavior is attributed to the relative propensities for intermolecular propagating/cross-linking reactions and intramolecular cyclization. A kinetic study of the RAFT polymerization of VMA with the dithioester-type CTA 1 suggested that the propagation reaction of the methacryloyl group proceeded predominantly with a certain level of intramolecular cyclization during the early stage of the polymerization and intermolecular cross-linking during the final stage of the polymerization. Block copolymers with one segment featuring pendant vinyl functionality were synthesized by RAFT polymerization of VMA using poly(methyl methacrylate) as a macro-chain transfer agent (macro-CTA).     

Poly(dimethylsiloxane‐b‐styrene) diblock copolymers prepared by reversible addition‐fragmentation chain transfer polymerization: Kinetic model

Well‐defined polydimethylsiloxane‐block‐polystyrene (PDMS‐b‐PS) diblock copolymers were prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization using a functional PDMS‐macro RAFT agent. The RAFT polymerization kinetics was simulated by a mathematical model for the RAFT polymerization in a batch reactor based on the method of moments. The model described molecular weight, monomer conversion, and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the developed model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration, and monomer concentration on the RAFT polymerization kinetics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Controlled synthesis of thermoresponsive polymer via RAFT polymerization of an acrylamide containing l-proline moiety

Reversible addition–fragmentation chain transfer (RAFT) polymerization of N-acryloyl-l-proline methyl ester (A-Pro-OMe) was investigated in order to find suitable conditions to achieve controlled synthesis of amino acid-based polymers with pre-determined molecular weight, narrow polydispersity, well-defined chain end structure, and characteristic thermoresponsive property. The effect of various parameters, such as chain transfer agent (CTA)/initiator ratio, solvent, and temperature, on RAFT polymerization of A-Pro-OMe was examined using benzyl dithiobenzoate as a CTA. Chain-end structure of the resulting poly(A-Pro-OMe) was confirmed by ¹H NMR analysis, MALDI-TOF mass spectroscopy, and chain extension experiment. Thermally induced phase separation behaviors of poly(A-Pro-OMe)s prepared by RAFT and conventional free radical polymerizations were also studied in aqueous solution.     

Synthesis and Characterization of 2-(Dimethylamino)ethyl Methacrylate Homopolymers via aqueous RAFT Polymerization and Their Application in Miniemulsion Polymerization

Summary Homopolymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) have been synthesized directly in aqueous media by reversible addition-fragmentation chain transfer polymerization (RAFT) using 4,4-azobis(4-cyanopentanoic acid) (V501) as a water-soluble azo initiator and 4-cyanopentanoic acid dithiobenzoate (CPADB) as a chain transfer agent. The resulting polymers were controlled in the range of narrow molecular weight distributions, with lower than 1.3. Using the produced dithioester-capped DMAEMA homopolymer as a macro chain transfer agent, miniemulsion RAFT polymerization of methyl methacrylate and styrene were carried out, respectively. ¹H NMR analysis showed that the diblock copolymer PDMAEMA-b-PMMA in the form of stable latices was obtained as expected. This revised version was published online at the end of November 2004. Unfortunately, the received date was incorrect due to a technical problem.     

双亲嵌段共聚物PSt-b-P(St-alt-MA)-b-PAA的自组装行为

以三硫代碳酸二(α, α'-二甲基-α-乙酸)酯(BDATC)为链转移剂, 以苯乙烯、马来酸酐、丙烯酸为原料, 通过可逆加成-断裂链转移(RAFT)合成了双亲嵌段共聚物PSt-b-P(St-alt-MA)-b-PAA。通过选择性溶剂N, N-二甲基甲酰胺(DMF)诱导聚合物进行自组装, 利用紫外-可见光光度仪、纳米激光粒度仪详细研究了共聚物中亲疏水嵌段长度、初始浓度、体系pH值对聚合物自组装行为的影响。通过化学交联的方法制备得到了聚合物交联胶束, 利用透射电镜表征了形貌与尺寸, 研究明确了其形状和尺寸的稳定性。结果表明, 上述因素均会影响共聚物的自组装行为和自组装胶束的形态, 经乙二胺交联得到的交联自组装胶束平均粒径为145.4nm, 并具有良好的形状和尺寸稳定性。