Preparation Of Poly (Ionic Liquid)and Its Application In Polystyrene Supercritical Dioxide Carbon Foaming

Compared with the traditional blowing agents, supercritical carbon dioxide (CO₂) has some drawbacks, such as poor solubility in the polymer and low nucleation efficiency, which limit its application in polymer microcellular foaming. In this paper, poly[2-(methacryloyloxy) ethyl] trimethylammonium tetrafluoroborate (P[MATMA][BF₄]), as a novel poly(ionic liquid) with strong absorption of CO₂, was introduced into the polystyrene (PS) supercritical CO₂ foaming to increase CO₂ solubility and improve the cell structure. This paper used the following three methods:Firstly, P[MATMA][BF4] was introduced by simply blending with GPPS in a sovent to prepared composites. The compopsites were then foamed by a batch foaming process using supercritical CO₂ as the blowing agent. The influence of gas pressure and the concentration of P[MATMA][BF₄] on the foam morphology was studied. The results showed that foaming at high gas pressure resulted in a decreased cell size and an increased cell density. The added P[MATMA][BF4] by blending method could not significantly improve the cell morphology. Secondly, P[MATMA][BF₄] was introduced into PS matrix by the copolymerization between [MATMA][BF4] and styrene. The resultant copolymers were also foamed by a batch foaming process. Herein, the influences of [MATMA][BF₄] segment content on the glass transition temperature (Tg) of copolymer and foam morphology were systematically investigated. The results showed that with the increased content of ionic liquid, the Tg of copolymer gradually increased, the cell density and cell size were dramatically increased and decreased, respectively. However, part of unfoamed area existed in some copolymer foam samples.In order to uniformly disperse P[MATMA][BF4] into PS, P[MATMA][BF4] was grafted to silica nanoparticles (SiO₂) by using a surface-initiated atom transfer radical polymerization (ATRP), and then blended with GPPS. We investigated the heterogeneous nucleation effect of the modified SiO₂, and the amino-modified SiO₂ (SiO₂-NH2) was also applied as nucleation agent for comparison. The results showed that P[MATMA][BF4] could be grafted to silica particles by using the surface-initiated ATRP. And introducing SiO₂-P[MATMA][BF4] could improve the CO₂ solubility of GPPS. The introduction of SiO₂-NH2 only slightly reduced the cell size, but cell density declined. However, SiO₂-P[MATMA][BF4] exhibited much higher heterogeneous nucleation efficiency in the foaming process. The morphology characterization indicated that GPPS/SiO₂-P[MATMA][BF4] composite foams, which were microcellula foams, had higher cell density (more than 109 cells/cm3) and smaller cell size (less than 10 ?m) than those of pure GPPS and PS/SiO₂-NH₂ composite foams. The relationships between the size of silica particles and the amount of grafted P[MATMA][BF4], the dispersion of SiO₂ in PS matrix, the CO₂ solubility in the composites and the cell structure of foam were investigated.