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含氟丙烯酸酯共聚物的原子转移自由基聚合与分析

时间:2011-04-14 22:40来源:未知 点击:

兼有较低表面能与优良耐候等特性的含氟丙烯酸酯共聚物最近在高档户外涂料或油漆等方面的应用中越来越多。但迄今为止,这类无规共聚物皆系通过传统自由基聚合合成的,其分子量及其分布指数(PDI)或共聚物组成与链结构及有关性能一直难以有效控制。本文通过电子转移再生活化原子转移自由基聚合(ARGET-ATRP)新技术,在水基乳液中合成了甲基丙烯酸甲酯(MMA)、丙烯酸六氟丁酯(HFBA)和丙烯酸羟丙酯(HPA)三元无规共聚物。采用凝胶渗透色谱法(GPC)测定了共聚物的分子量及其PDI ,并用红外与拉曼光谱、核磁共振氢谱和碳谱(1H-NMR、13C-NMR)以及差示扫描量热仪(DSC)分析表征了共聚物的结构组成和热性能。通过测定不同共聚配方或反应条件下的共聚物产率或单体转化率,研究了该新型ATRP乳液共聚反应的动力学与反应条件的影响特征或规律。实验结果表明,采用总用量为3.2wt%的吐温-80/十二烷基磺酸钠(2:1)复合乳化剂,反应单体乳液的静置稳定性较好。当共聚反应温度从65℃提高到85℃,ln([M]0/[M])和反应时间之间呈较好的线性关系,在75℃时线性拟合相关系数为R2=0.9963,这与ATRP等活性自由基聚合的一级反应特征相符;同时表观增长速率常数(kpapp)并未随其间温度升高而成倍增大,在75℃时为7.8×10-5s-1,表明改变温度对该聚合反应速率的影响并非很大。数均分子量随转化率升高而线性增大。相比溴苄,采用溴代异丁酸乙酯作引发剂所合成聚合物的GPC实测分子量更接近于理论预期值,且其PDI较易低于1.5,表明在本聚合体系中后者作引发剂更有利于控制合成预期分子量和更均匀或更窄分布的共聚物。这种聚合反应的可控性在分别增大催化剂溴化铜和配体的用量时也有提高,且油溶性较好而水溶性较差的配体邻二氮菲比联二吡啶及五甲基二乙烯三胺更适合水基ATRP乳液聚合。实验结果还表明,少量添加一种环状多糖化合物作助剂,有利于提高转化率和减小乳胶粒径分布,并改进聚合反应的可控性。红外与拉曼光谱表征证实聚合产物具有目标三元共聚物的羟基和含氟基团的结构特征。核磁共振氢谱计算表明,产物组成为MMA:HFBA:HPA=60:10.69:0.27,与其原料配比60:11.3:3.8接近,碳谱证实氟碳结构(-CF3等基团)的存在。DSC分析结果表明共聚产物仅在58.7℃有一个玻璃化温度,另仅出现一个熔融峰,表明制备的共聚物为无规共聚物;GPC分析结果亦表明该共聚物中无均聚物混杂。 
 

【Abstract】 Acrylic-fluoropolymers with low surface free energy and good weather resistantance are more and more used in advanced exterior coatings or paints recently. However, the random copolymers were prepared so far by typical radical polymerization;the molecular weights, their distributions or polydispersitivity index (PDI), the chain structure and compositions, and then the related properties have been not effectively controlled. In this paper the random terpolymers of methyl methacrylate (MMA) with hexafluorobutyl acrylate (HFBA) and hydroxylpropyl acrylate (HPA) were synthesized by atom transfer radical polymerization with activators regenerated by electron transfer (ARGET-ATRP) in aqueous emulsion system. Their molecular weights and PDI were measured by gel permeation chromatography (GPC), the structure and compositions as well as thermal behavior of the terpolymers have been characterized by infra-red (IR) and Raman spectroscopy, nuclear magnetic resonance spectroscopy (both 1H-NMR and 13C-NMR), as well as differential scanning calorimetry (DSC).The experimental results show that the monomer emulsion was more stable when Tween-80 and sodium dodecylsulphate in the mole ratio of 2 to 1 as the formulated emulsifying agent with the total amount used in 3.2wt%. The ln ([M]0/[M]) value versus the reaction time shows authentic linear realtionship when the reaction temperature rising from 65 to 85 centigrade degree, and the linear fitting constant R2 appears to 0.9963 at 75℃that corresponds with the first order reaction characteristic of living radical polymerization including ATRP. Meanwhile, the apparent growing rate (kpapp) does not arise along with the reaction temperature for times, and appears to 7.8×10-5s-1 at 75℃, which indicates that temperature change does not influence much on the polymerization reaction rate. The number average molecular weght rises in a linear trend with the monomer conversion augment. Compared with benzyl bromide, ethyl-2-bromoisobutanoate is employed better in the controllability of the molecular weight, and the PDI value occurring low than 1.5 more ofen than not. It is informed that the latter used as an initiator could be more available to control the synthsis of the copolymer with molecular weight designed and low in PDI value in the polymerization system associated. The controllability of such polymerization reaction would be more preferable on condition that increasing the dosage of copper (Ⅱ) bromide used as catalyst and ligand respectively. Withal, ligand available poor in water solubility and oil-soluble like orthophenanthroline is better than 2, 2`-biphenyl and pentamethyl diethylenetriamine for aqueous ATRP emulsion polymerization. In addition, the employment of a cyclic polyase compound used as aid is beneficial to elevate monomer conversion and to narrow the particle size distribution, as well as the improvement in the polymerzation reaction controllability.Structure characteristic of terpolymer designed such as hydroxyl group and fluorocarbon group are identified by infra-red absorption spectroscopy (IR) and Raman spectroscopy. According to the individual peaks area of nuclear magnetic resonance spectroscopy (1H-NMR), the composition of copolymer calculated as MMA: HFBA: HPA = 60: 10.69: 0.27, which is identical with the ratio of raw materials about 60: 11.3: 3.8, and fluoro-carbon structure (-CF3 group and so on) is evident in the 13C-NMR spectroscopy again. DSC curve shows that there is only one glass state temperature of copolymer occurring about 58.7℃, besides, the purity of copolymer is verified well with the evidence of only one fusion peak in the picture. There is none of homopolymer mixed in the copolymer supported also by the GPC curve with the unique peak. 

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