Synthesis of ionic liquids copolymerize styrene and their nucleation, carbon dioxide sorption effect on supercritical carbon dioxide microcellular foaming

Aiming to prepare polystyrene microcellular foam with improved foam morphology and high thermal stability, ionic liquids which have been well demonstrated to possess high carbon dioxide (CO 2 ) absorption capacity were introduced into polystyrene by copolymerization of styrene and polymerizable ionic liquids, i.e., vinylbenzyl trimethyl ammonium fluoroborate ([VBTMA][BF 4 ]) and vinylbenzyl trimethyl ammonium hexafluorophosphate ([VBTMA][PF 6 ]), Abbr. ILs). These copolymers showed higher glass transition temperature (T g ) and high supercritical carbon dioxide (scCO 2 ) solubility, based on which foams with smaller cell size, higher cell density, and higher thermal stability were prepared by the microcellular foaming using scCO 2 as blowing agent. The morphology of the resultant foams highly depended on the foaming temperature, ionic liquid type and content. Compared to [VBTMA][BF 4 ]-St foam, [VBTMA][PF 6 ]-St have higher CO 2 absorption and glass-transition temperature, making it exhibit superior cell morphology. This work demonstrates that the introduction of ionic liquids can benefit the morphology control and thermal stability of polymeric foams and hopefully provides a promising method for the design and preparation of polymeric foams with high performance.