Interaction between supercritical carbon dioxide-cosolvent and poly(vinyl acetate)
(2.School of Materials Science and Engineering, East China University of Science and Technology, Shanghai, China 200237)
【Abstract】The effect of cosolvents (ethanol, acetone, n-heptane) on the supercritical CO2 system were evaluated through the multi-scale molecular modeling and dissolution behavior measurement, which might improve the solvent-solvent and solvent-solute interactions and enhance the compatibility with polymer. The ab initio calculation showed that the interaction between ethanol and CO2 was the strongest one, followed by those of CO2 with acetone and n-heptane. The molecular dynamics simulations indicated that ethanol significantly increased the solubility parameter of solvent, and the interaction of supercritical CO2–ethanol with PVAc chain was stronger than those of the other two at the same cosolvent content, which was helpful to improve the compatibility between PVAc and the solvent. The interaction between ethanol and CO2 was the strongest due to the bigger solubility parameter of ethanol and the obvious hydrogen bond between ethanol and CO2. The cloud point experiments confirmed that ethanol was the most effective to reduce the cloud point pressure of PVAc. The addition of cosolvent enhanced the compatibility of supercritical CO2 system with PVAc, and the solubility of PVAc in supercritical CO2–cosolvent increased with the mole fraction of cosolvent.
【Keywords】 carbon dioxide; cosolvent; poly(vinyl acetate) ; solubility; molecular simulation;
(Translated by MA XQ)
 TOMASKO D L, LI H, LIU D, et al. A review of CO2 applications in the processing of polymers [J]. Ind. Eng. Chem. Res., 2003, 42 (25): 6431–6456.
 NALAWADE S P, PICCHIONI F, JANSSEN L P. Supercritical carbon dioxide as a green solvent for processing polymer melts: Processing aspects and applications [J]. Prog. Polym. Sci., 2006, 31 (1): 19–43.
 WANG Y M, WANG Y J, LU X B. “Grafting-from” polymerization for uniformly bulk modification of pre-existing polymer materials via a supercritical-fluid route [J]. Polymer, 2008, 49 (2): 474–480.
 LI D C, LIU T, ZHAO L, et al. Controlling sandwich-structure of PET microcellular foams using coupling of CO2 diffusion and induced crystallization [J]. AICh E Journal, 2012, 58 (8): 2512–2523.
 LI L, LIU T, ZHAO L, et al. CO2-induced phase transition of isotactic poly-1-butene with form iii upon heating [J]. Macromolecules, 2011, 44 (12): 4836–4844.
 CUMMINGS S, XING D, ENICK R, et al. Design principles for supercritical CO2 viscosifiers [J]. Soft Matter, 2012, 8 (26): 7044–7055.
 BECKMAN E J. A challenge for green chemistry: designing molecules that readily dissolve in carbon dioxide [J]. Chem. Commun., 2004, 17: 1885–1888.
 BIRKIN N A, WILDIG O J, HOWDLE S M. Effects of poly (vinyl pivalate)-based stabiliser architecture on CO2-solubility and stabilising ability in dispersion polymerisation of n-vinyl pyrrolidone[J [J]. Polym. Chem., 2013, 4 (13): 3791–3799.
 ENICK R M, OLSEN D K, AMMER J, et al. Mobility and conformance control for CO2via thickeners, foams, and gels—a literature review of 40 years of research and pilot tests [C] //SPE Improved Oil Recovery Symposium. Tulsa, USA: Society of Petroleum Engineers, 2012.
 DUAN D, SU B G, ZHANG Z, et al. Synthesis, characterization and structure effects of polyethylene glycol bis (2-isopro poxyethyl) dimethyl diphosphates on lanthanides xtraction with supercritical carbon dioxide [J]. J. Supercrit. Fluid., 2013, 81: 103–111.
 GIRARD E, TASSAING T, CAMY S, et al. Enhancement of poly (vinyl ester) solubility in supercritical CO2 by partial fluorination: the key role of polymer–polymer interactions [J]. J. Am. Chem. Soc., 2012, 134 (29): 11920–11923.
 SHEN Z, MCHUGH M A, XU J, et al. CO2-solubility of oligomers and polymers that contain the carbonyl group [J]. Polymer, 2003, 44 (5): 1491–1498.
 DOBBS J, WONG J, LAHIERE R, et al. Modification of supercritical fluid phase behavior using polar cosolvents [J]. Ind. Eng. Chem. Res., 1987, 26 (1): 56–65.
 GUPTA R B, COMBES J R, JOHNSTON K P. Solvent effect on hydrogen bonding in supercritical fluids [J]. J. Phys. Chem., 1993, 97 (3): 707–715.
 STUBBS J M, SIEPMANN J I. Binary phase behavior and aggregation of dilute methanol in supercritical carbon dioxide: a Monte Carlo simulation study [J]. J. Chem. Phys., 2004, 121 (3): 1525–1534.
 CHATZIS G, SAMIOS J. Binary mixtures of supercritical carbon dioxide with methanol: a molecular dynamics simulation study [J]. Chem. Phys. Lett., 2003, 374 (1): 187–193.
 ZHANG Y. Molecular simulation for pure supercritical fluids and their binary mixtures [D]. Beijing: Tsinghua University, 2005 (in Chinese).
 WANG M Y. Study on solubility parameters of supercritical carbon dioxide by molecular dynamics simulation [D]. Tianjin: Tianjin University, 2007 (in Chinese).
 FELLER D, JORDAN K D. Estimating the strength of the water/single-layer graphite interaction [J]. J. Phys. Chem. A, 2000, 104 (44): 9971–9975.
 WANG Y, HONG L, TAPRIYAL D, et al. Design and evaluation of nonfluorous CO2-soluble oligomers and polymers [J]. J. Phys. Chem. B, 2009, 113 (45): 14971–14980.
 HU D, SUN S, YUAN P Q, et al. Evaluation of CO2 philicity of poly (vinyl acetate) and poly (vinyl acetate-alt-maleate) copolymers through molecular modeling and dissolution behavior measurement [J]. J. Phys. Chem. B, 2015, 119 (7): 3194–3204.
 SUN H. Compass: an ab initio force-field optimized for condensed-phase applications overview with details on alkane and benzene compounds [J]. J. Phys. Chem. B, 1998, 102 (38): 7338–7364.
 HU D, SUN S, YUAN P Q, et al. Exploration of CO2-philicity of poly (vinyl acetate-co-alkyl vinyl ether) through molecular modeling and dissolution behavior measurement [J]. J. Phys. Chem. B, 2015, 119 (38): 12490–12501.
 LEE H, PACK J W, WANG W, et al. Synthesis and phase behavior of CO2-soluble hydrocarbon copolymer: poly (vinyl acetate-alt-dibutyl maleate) [J]. Macromolecules, 2010, 43 (5): 2276–2282.
 GIRARD E, TASSAING T, LADAVIÈRE C, et al. Distinctive features of solubility of RAFT/madix-derived partially trifluoromethylated poly (vinyl acetate) in supercritical CO2 [J]. Macromolecules, 2012, 45 (24): 9674–9681.
 INGROSSO F, RUIZLÓPEZ M F. Modeling solvation in supercritical CO2 [J]. Chem Phys Chem, 2017, DOI: 10.1002/cphc.201700434.
 FU Y, LIAO L, YANG L, et al. Molecular dynamics and dissipative particle dynamics simulations for prediction of miscibility in polyethylene terephthalate/polylactide blends [J]. Mol. Simulat., 2013, 39 (5): 415–422.
 FU Y Z, LIAO L Q, LIANG X Y, et al. Molecular simulations of microstructures and phase morphologies of polypropylene/polyamide-11 blends [J]. CIESC Journal, 2012, 63 (6): 1951–1956 (in Chinese).
 CLANCY T C, MATTICE W L. Miscibility of poly (vinyl chloride) melts composed of mixtures of chains with differing stereochemical composition and stereochemical sequence [J]. Macromolecules, 2001, 34 (18): 6482–6486.
 RAVEENDRAN P, WALLEN S L. Cooperative C–H···O hydrogen bonding in CO2–Lewis base complexes: implications for solvation in supercritical CO2 [J]. J. Am. Chem. Soc., 2002, 124 (42): 12590–12599.