Interaction Between Supercritial CO2+Cosolvent and Poly(vinyl acetate)

Interaction between Supercritial CO₂+Cosolvent and Poly(vinyl acetate)

Dong-dong Hu, Lei Bao, Ling Zhao, Tao Liu*

 (Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China)

hudd@ecust.edu.cn; liutao@ecust.edu.cn;

Phone: (+86) 21 64253470; Fax: (+86) 21 64253528

Supercritical carbon dioxide (scCO₂) is of interest as a potential alternative to conventional organic solvents. Unfortunately, the low solvating power of scCO₂ restricts its compatibility with polymers. Poly(vinyl acetate) (PVAc) was reported as one of the most CO₂-philic hydrocarbon homopolymers, which was a significant step forward. But even so, the solubility of PVAc is very low, making them unsuitable to apply on a large scale.

The cosolvents (ethanol, acetone, n-heptane, denoted by ET, AC and C7) were introduced to form CO₂+cosolvent systems for improving the solvent-solvent and solvent-solute interactions and enhancing the the compatibility with PVAc. Comparing the interaction of CO₂ with acetone, and n-heptane, it could be seen that ethanol and CO₂ provided stronger interaction energy from the ab initio calculation due to the shortest distance between the C atom of CO₂ and the O atom of ethanol (Fig. 1). The molecular dynamic modeling showed that the interaction between ethanol and CO₂ was strongest due to the bigger solubility parameter of ethanol (Fig. 2) and the obvious hydrogen bond bewteen ethanol and CO₂ (Fig. 3), which increased significantly the solubility parameter of solvent and improved the dissolution of polymers in CO₂. The dissolution behavior measurement (Fig. 4) confirmed that the addition of cosolvent could enhance the compatibility between CO₂ and PVAc to a certain extent, and the solubility of PVAc in scCO₂+cosolvent increased with the mole fraction of cosolvent, which has a good agreement with the simulated results of the solvent-solvent, solvent-solute interactions and the solubility parameter analysis.

        

Fig. 1 Most stable mode in ET/CO₂, AC/CO₂ and C7/CO₂systems.

(a) ET/CO₂/CO₂; (b) AC/CO₂; (c) C7/CO₂

Fig. 2  Solubility parameter of CO₂-ethanol binary systems with different compositions

(a) ET/CO₂/CO₂; (b) AC/CO₂; (c) C7/CO₂

          

Fig. 3  Comparison of rational correlation functions    Fig.4  Cloud point pressures of PVAc in

   between CO₂-ethanol and CO₂-acetone systems.          CO₂+solvent at different temperatures

 

Acknowledgement:

The authors are grateful to the National Key Research and Development Program of China(2016YFB0302201) and the National Science Foundation of China (21376087) and Plan for Shanghai excellent technical leaders (14xd425500) for support.

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