磺化木质素基链转移剂的合成及其在水相RAFT聚合中的应用

Synthesis of Sulfonated Lignin Based Chain Transfer Agent and Its Application in Aqueous RAFT Polymerization

以玉米秸秆木质素为原料,将木质素磺化改性,再利用二硫化碳、溴乙酸甲酯对磺化木质素(SL)进行黄原酸酯功能化改性,合成了磺化木质素基链转移剂(SL-CTA),之后将其用于丙烯酰胺的水相RAFT聚合反应制备磺化木质素-丙烯酰胺共聚物(SL-g-PAM),并采用多种方法对链转移剂及共聚物进行表征。研究结果表明:相比于磺甲基化改性,芳基磺化改性的效果更好,当1 g木质素与2 g氯磺酸在25℃下反应4 h时,改性效果最佳,此时磺化木质素含S量为1.83%,M_(w)/M_(n)为1.19,含总羟基量为4.86 mmol/g,且水溶性良好。FT-IR、^(13)C NMR对磺化木质素基链转移剂的结构表征结果发现:红外谱图显示900 cm^(-1)处出现C—S伸缩振动吸收峰及1738 cm^(-1)处出现C O特征峰,^(13)C NMR谱图中δ172处出现了C S的碳原子峰,共同证明了SL-CTA的成功合成。探究丙烯酰胺的水相RAFT聚合体系中单体/链转移剂/引发剂比例、pH值及反应温度对单体转化率的影响,结果表明:单体/链转移剂/引发剂物质的量之比为500∶4∶1、pH值5、70℃下反应4 h时转化率高达98.5%。该实验条件下,聚合反应一级动力学曲线呈现了较好的线性关系,所得聚合物的相对分子质量与转化率也基本呈现一次线性关系,同时其多分散系数较低且分布相对较窄(1.13~1.43),证明了反应具有较高的可控性。

The sulfonated lignin-based chain transfer agent(SL-CTA)was synthesized using pre-sulfonated corn stover lignin,followed by the functional modification of xanthate carbon disulfide and methyl bromoacetate.The SL-CTA was used in the aqueous RAFT polymerization of acrylamide to prepare sulfonated lignin-acrylamide copolymer(SL-g-PAM).Various methods were used to characterize the chain transfer agents and copolymers.The results showed that the arylsulfonation modification was more effective than the sulfomethylation modification.The best modification effect was achieved when 1g of lignin was reacted with 2 g of chlorosulfonic acid at 25℃for 4 h,where the S concentration in sulfonated lignin was 1.83%,the ratio of M_(w)/M_(n) was 1.19,the amount of total hydroxyl groups was 4.86 mmol/g,and the water solubility was good.The chemical structure of the SL-CTA was then investigated by FT-IR and ^(13)C NMR.The results showed that the stretching vibration absorption peak of C—S bond at 900 cm^(-1) and the characteristic peak at 1738 cm^(-1) relating to C O group were found in the FT-IR spectrum,and the peak atδ172 corresponding to carbon atom of the C S appeared in the ^(13)C NMR spectrum,proving the successful synthesis of the chain transfer agent.In addition,the effects of the ratios of monomer/chain transfer agent/initiator,pH value and reaction temperature on the monomer conversion in the aqueous RAFT polymerization system of acrylamide were investigated.The results showed that the conversion rate was as high as 98.5%when the ratio of monomer/chain transfer agent/initiator was 500∶4∶1,pH value was 5,reaction temperature was 70℃and reaction time was 4 h.Under the experimental conditions,the first-order kinetic curve of the polymerization reaction showed a good linear relationship,and the relative molecular mass of the obtained polymer also presented a linear relationship with the monomer conversion rate.At the same time,its polydispersity index was low and the distribution was relatively narrow(1.13-1.43),which all indicated that the reaction had high controllability.