Effect of molecular weight on CO2-philicity of poly(vinyl acetate) with different molecular chain structure

Abstract

The low molecular weight, topological structure and end group removal are expected to enhance the CO2-philicity of poly(vinyl acetate) (PVAc), which is of great interest for expanding CO2 applications as a green solvent. This work aims at investigating the effect of molecular weight (Mn) of PVAc with different molecular chain structure on the CO2-philicity through dissolution behavior measurement and molecular modeling. Well-defined 3-armed and 4-armed R-core PVAc was synthesized by RAFT polymerization, and then the corresponding xanthate groups were removed. The CO2-philicity of multi-armed PVAc was found to be inferior to that of linear one at low Mn. With increasing the Mn from 1000 to 7000g/mol, the cloud point pressures (Pc) of multi-armed PVAc first decreased, reached a minimum at a given Mn, and then increased, which was different from the variation trend of the Pc of linear PVAc versus Mn. In addition, removal of the xanthate groups could effectively enhance the CO2-philicity of PVAc, especially at low Mn. Moreover, the molecular dynamics (MD) simulations on the interactions in polymer/CO2 systems indicated that the multi-armed structure had different effects on the compatibility with CO2 at different Mn. At low Mn, the polymer⿿polymer interaction was the main driving force deciding the CO2-philicity due to the significant difference in different molecular chain structures. At high Mn, multi-armed structure enhanced the CO2-philicity due to the synergistic effect of moderate polymer⿿polymer interaction and large polymer⿿CO2 interaction. The appropriate molecular chain structure could be selected to enhance the CO2-philicity of PVAc at a certain Mn.