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

The low molecular weight, topological structure and end group removal are expected to enhance the CO 2 -philicity of poly(vinyl acetate) (PVAc), which is of great interest for expanding CO 2 applications as a green solvent. This work aims at investigating the effect of molecular weight ( M n ) of PVAc with different molecular chain structure on the CO 2 -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 CO 2 -philicity of multi-armed PVAc was found to be inferior to that of linear one at low M n . With increasing the M n from 1000 to 7000   g/mol, the cloud point pressures ( P c ) of multi-armed PVAc first decreased, reached a minimum at a given M n , and then increased, which was different from the variation trend of the P c of linear PVAc versus M n . In addition, removal of the xanthate groups could effectively enhance the CO 2 -philicity of PVAc, especially at low M n . Moreover, the molecular dynamics (MD) simulations on the interactions in polymer/CO 2 systems indicated that the multi-armed structure had different effects on the compatibility with CO 2 at different M n . At low M n , the polymer⿿polymer interaction was the main driving force deciding the CO 2 -philicity due to the significant difference in different molecular chain structures. At high M n , multi-armed structure enhanced the CO 2 -philicity due to the synergistic effect of moderate polymer⿿polymer interaction and large polymer⿿CO 2 interaction. The appropriate molecular chain structure could be selected to enhance the CO 2 -philicity of PVAc at a certain M n .