Dongdong Hu,Yingna Zhang,Mei Su,Lei Bao,Ling Zhao,Tao Liu
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 .
Dongdong Hu,Shaojun Sun,Pei-Qing Yuan,Ling Zhao,Tao Liu
Hydrocarbon CO2-philes are of great interest for use in expanding CO2 applications as a green solvent. In this work, multiscale molecular modeling and dissolution behavior measurement were both applied to explore CO2-philicity of the poly(vinyl acetate) (PVAc)-based copolymer. Introduction of a favorable comonomer, i.e., vinyl ethyl ether (VEE), could significantly reduce the polymer–polymer interaction on the premise that the polymer–CO2 interaction was not weakened but enhanced. The ab initio calculated interaction of the model molecules with CO2 demonstrated that the ether group in VEE or VBE was the suitable CO2-philic segment. From the molecular dynamics (MD) simulations of polymer/CO2 systems, the interaction energy and Flory–Huggins parameter (χ12) of poly(VAc-alt-VEE)/CO2 supported that poly(VAc-alt-VEE) possessed better CO2-philicity than PVAc. The dissolution behaviors of the synthesized poly(VAc-co-alkyl vinyl ether) copolymers in CO2 showed the best CO2-phile had the VEE content of about 34 mol %. The MD simulations also indicated that the interaction of random poly(VAc-co-VEE) containing about 30 mol % VEE with CO2 was the strongest and the χ12 was the smallest in these polymer/CO2 systems. Not only could the VEE monomer reduce the polymer–polymer interaction, but it could also enhance the polymer–CO2 interaction with an optimized composition. Introducing a suitable comonomer with a certain composition might be a promising strategy to form the synergistic effect of polymer–polymer interaction and polymer–CO2 interaction for screening the hydrocarbon CO2-philes.
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