胶束催化作用下实现聚苯乙烯的氯甲基化

用紫外分光光度法测定了离子型表面活性剂胶束溶液对聚苯乙烯四氯化碳溶液的增溶性能; 用胶束催化法实现了聚苯乙烯的氯甲基化, 用红外光谱法和佛尔哈德法表征了氯甲基化聚苯乙烯的化学结构与组成; 通过比较阴、 阳离子表面活性剂及结构不同的阳离子表面活性剂的催化效果, 探索了胶束催化的作用机理, 考察了表面活性剂结构对催化作用的影响规律. 结果表明, 表面活性剂胶束溶液可增溶聚苯乙烯的四氯化碳溶液, 随着四氯化碳在胶束中的增溶, 聚苯乙烯可转移至表面活性剂的胶束中; 胶束催化是实现聚苯乙烯的氯甲基化的有效途经, 仅用3.35 g/L的十六甲基三甲基溴化铵(CTAB),  于65 ℃， 5 h内即可使聚苯乙烯大分子链中的苯环氯甲基化程度达到37%; 聚苯乙烯与甲醛、 氯化氢的反应过程由亲电取代和亲核取代串联而成, 阳离子表面活性剂比阴离子表面活性剂的催化作用更加有效, 说明亲核取代是慢步骤; 阳离子表面活性剂疏水链越长, 对聚苯乙烯的增溶效果越好, 催化作用越强.

Cloromethylation for Polystyrene under Micellar Catalysis

The solubilization properties of ionic surfactants for polystyrene that was dissolved in carbon tetrachloride were determined by using a UV  method. The chloromethylation reaction of polystyrene was carried out in a micellar catalysis system, and the structure of chloromethylated polystyrene(CMPS) was characterized  by means of  FTIR and its composition was measured via  the  Volhard method. The catalysis effects of two types of anionic and cationic surfactants were compared; the catalysis effects of different cationic surfactants with different structures were examined; and the mechanism of micellar catalysis for chloromethylation reaction of polystyrene was explored. The experiment results show that a micellar solution of the surfactant can solubilize polystyrenes dissolved in CCl4, namely, polystyrene can be transferred  into a micellar solution of surfactant along with solubilization of CCl4 in the micellar solution of the surfactant. Micellar catalysis is an effective way to realize the  chloromethylation for polystyrene, and only 3.35 g/L  CTAB is needed for the  chloromethylation of  polystyrene with a 37%  chloromethylation degree at 65 ℃ within 5 h. The reaction mechanism of the reaction among polystyrene, formaldehyde and hydrochloric acid consists of two steps:  electrophilic substitution and nucleophilic substitution. The cationic surfactants are more effective than anionic surfactants, and the nucleophilic substitution step is a rate-controlling step. So it is appropriate to use cationic surfactants for realizing the chloromethylation of polystyrene. For cationic surfactants, the longer the hydrophobic carbon chain is, the better the solubilization property of surfactant is, so that its catalysis effect is better.