Synthesis Of Poly(Vinylacetate) Based Co 2 -philic Hydrocarbon Polymers By RAFT Polymerization And Their Applications

Supercritical carbon dioxide (scCO2) has been recognized as a versatile solvent to replace the traditional organic solvents. However, CO2 is relatively a poor solvent and the majority of materials, such as polar biomolecules, pharmaceutical actives, and high molecular weight polymers, tend to exhibit low solubility in CO2. A technical barrier to the use of scCO2 is the lack of an equivalent range of inexpensive CO2-soluble surfactants, ligands, and phase transfer agents. So far, only fluorinated polymers and silicones show high solubility in CO2. However, the associated costs and low biodegradability may prohibit their industrial-scale applications. A great challenge for application of CO2 is the discovery of inexpensive CO2-philic materials or CO2-philes, which can preferably be easily biodegradable. Until now, oligo(vinyl acetate) (OVAc) has been exhibited anomalously high solubility in CO2 with respect to other vinyl hydrocarbon polymers. However, the high cost and difficulty of synthesis process can render the economics of CO2 process unfavorable.In this work, a series of well-defined CO2-philic OVAc with different topological structure and triblock copolymers X-OVAc-b-PEG-b-OVAc-X (where X stands for xanthate group) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The main contents are listed as follows.1. Synthesis of three kinds of RAFT agents (RAFT-2, RAFT-3, RAFT-4), which were used to mediate the polymerization of vinyl acetate (VAc) to prepare various OVAc with targeted molecular weight and topological structure. The polymerization proceeded with pseudo-first-order kinetics consistent with a constant radical concentration. A progressive and nearly linear increase in the molecular weight as a function of conversion is observed, which is consistent with a living process. Investigated the effect of molecular weight and topological structure on the phase behavior of OVAc in CO2. The results shown that with the increaseing of the amout of chains, reducing of molecular weight, the cloud point pressure decreased.2. Xanthate end-functional PEGs acting as macroCTAs were exploited to mediate the polymerization of VAc. A series of well-defined CO2-philic X-OVAc based triblock copolymers were synthesized by RAFT polymerization. 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. 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 out-perform perfluorinated surfactants.