RAFT分散聚合用于聚苯乙烯微球的可控制备

Synthesis of Polystyrene Microspheres via RAFT Dispersion Polymerization

大分子RAFT 试剂存在下的分散聚合结合了非均相条件下的可控/活性自由基聚合和嵌段共聚物的自组装的优点,已成为高分子合成领域中的研究热点.本文利用RAFT 聚合方法制备出聚N,N-二甲基丙烯酰胺（PDMA）,再将PDMA 进一步用作大分子RAFT 试剂,研究其用于分散聚合可控制备聚苯乙烯（PSt）微球.结果表明,增大PDMA 相对分子质量和降低PDMA 用量,可导致粒径增大.在乙醇与水混合溶剂中水含量低于50%时,可通过调控PDMA 获得单分散性良好的稳定的聚合物颗粒,其粒径能够在200～500,nm 之间进行选择.对分散聚合过程中粒子粒径、单体苯乙烯转化率以及聚合物分子质量的变化的研究表明,大分子RAFT 试剂PDMA 存在下的苯乙烯分散聚合存在均相反应、成核和颗粒增长3 个不同的聚合阶段,反应过程中嵌段聚合物PDMA-PSt 中苯乙烯链段不断增长,最后得到的产物是PDMA-PSt 嵌段聚合物颗粒.

The reversible addition-fragmentation chain transfer(RAFT)dispersion polymerization in the presence of macro-RAFT agent combined the advantages of heterogeneous controlled/living radical polymerization and self-assembly of block copolymers,which has been paid considerable attention. In this study,the macro-RAFT agent poly N,N-dimethyl acrylamide(PDMA)prepared by RAFT polymerization was used as stabilizer in the dispersion polymerization of styrene. The effect of PDMA on particle size was studied in detail. The results indicate that PDMA with higher molecular masswill produce larger particles but the particle size will decrease with the increase of the content of PDMA. Monodisperse polymer particles with size in the range of 200-500 nm can be obtained when the mass fraction of water in the mixture of ethanol and water was lower than 50%. The changes of particle size, conversion of styrene and molecular mass of resultant polymers in the process of styrene dispersion polymerization were investigated. The results suggest that the styrene dispersion polymerization in the presence of macro-RAFT agent PDMA has three stages,including homogeneous polymerization,nucleation and particle growth. With the chain propagation of polystyrene(PSt)chain in block copolymer,the PDMA-PSt particles were obtained.