Aerogels and polymorphism of isotactic poly(4-methyl-pentene-1).

Monolithic and highly crystalline aerogels of isotactic poly(4-methyl-pentene-1) (i-P4MP1) have been prepared by sudden solvent extraction with supercritical carbon dioxide from thermoreversible gels. The cross-link junctions of i-P4MP1 gels, depending on the solvent, can be constituted by pure polymer crystalline phases (I or III or IV) or by polymer-solvent cocrystalline phases (for cyclohexane and carbon tetrachloride gels). Gels with cocrystalline phases lead to aerogels exhibiting the denser crystalline form II, whereas all the other considered gels lead to aerogels exhibiting the thermodynamically stable form I. Aerogels obtained from form I gels, which do not undergo a crystalline phase transition during the CO(2) extraction process present the high structural stability most suitable for the preparation of porous membranes. The effect of solvents on the aerogel pore structure and morphology has been also investigated by scanning electron microscopy and N(2) sorption measurements. In all cases, the aerogels present highly porous interconnected structures with macropores and mesopores presenting a large size distribution and a vanishing presence of micropores.