Dispersion Polymerization of N-Vinyl-2-Pyrrolidone in Supercritical Carbon Dioxide in the Presence of Thiol-Terminated Poly(vinyl acetate-co-vinyl propionate)

Liquid carbon dioxide (LCO₂) or supercritical carbon dioxide (ScCO₂) can be used as an important solvent medium for preparing polymer particles through dispersion polymerization. However, based on the weak solvent characteristics of CO₂, the development of stabilizers used in dispersion polymerization has always been an important challenge. These stabilizers are progressing toward the low-cost, pollution-free, and simple synthesis routes, et al. In this research, pentaerythritol tetra (3-mercaptopropionate) (PTMP) is used to control the homopolymerization or copolymerization of vinyl acetate (VAc)/vinyl propionate (VPr), the homopolymers or copolymers with thiol group are synthesized by the one-pot method. These homopolymers or copolymers are used as the stabilizers to stabilize the dispersion polymerization of N-vinyl-2-pyrrolidone (NVP) in ScCO₂. The results show that the structural unit proportion of the stabilizers, the concentration of stabilizers or 2, 2´-azobis(isobutyronitrile) (AIBN), and the time interval for dispersion polymerization have significant impacts on the conversion percentage of NVP and the molecular weight of polymers. The maximum conversion percentage of NVP can get to 95%, and the molecular weight of poly(N-vinyl-2-pyrrolidone)(PNVP) can reach 22.3 kPa. SEM analysis indicates that the PNVP obtained has regular spherical characteristics.