Synthesis of CO_2-philic Xanthate?Oligo(vinyl acetate)-Based Hydrocarbon Surfactants by RAFT Polymerization and Their Applications on Preparation of Emulsion-Templated Materials

摘要

Amphiphilic block copolymers poly(ethylene glycol)-block-oligo(vinyl acetate) (PEG-b-OVAc) and OVAc-b-PEG-b-OVAc have been demonstrated to be effective surfactants for CO_2-in-water (C/W) emulsions. However, the high cost and difficulty of synthesis process can render the economics of CO_2 process unfavorable. In this work, by reversible addition?fragmentation chain transfer (RAFT) polymerization, a series of well-defined CO_2-philic triblock copolymers X?OVAc-b-PEG-b-OVAc?X (where X stands for xanthate group) were synthesized. The structures and molecular weights of these copolymers were characterized by ~1H NMR and GPC. The results of GPC analysis exhibited relatively narrow polydispersity (PDI < 1.35). The process of preparation of X?OVAc-based surfactants was much more simple, inexpensive and also easy to control, which could promote industrial-scale applications. The X?OVAc-based surfactants were found effectively to produce highly concentrated stable C/W emulsions. Porous emulsion-templated materials were prepared by the polymerization of the continuous phase of C/W emulsions. The open-cell morphology of the emulsion-templated materials was evidenced by scanning electron microscope. To tune the morphology of the porous structures, the influence of the surfactant concentration and molecular weight of OVAc block were also investigated. It was shown that X?OVAc-based surfactants can outperform perfluorinated surfactants and approach OVAc-based surfactants for such applications.