Polystyrene Based Foam Materials for Cryogenic Targets of Fast Ignition Realization Experiment (FIREX)

This paper deals with the development of materials without volume change in the formation of uniform low density foam capsules with fine structures. Two monomers, i.e., 5-(4-vinylbenzyl)oxymethyl-5-methyl-1,3-dioxane-2-thione (M1) and 4-vinylphenyloxirane (M2), were prepared as the comonomers polymerized with styrene. Polystyrene-based copolymers using styrene and M1 or M2 were prepared by free radical copolymerization using azobis(isobutyronitrile) (AIBN) as an initiator. The solutions of the obtained polystyrene-based copolymers in benzene/dichloromethane mixture or 4-chlorotoluene were gelated by the addition of a cationic initiator, which caused cross-linking via ring-opening polymerization of the pendant cyclic moieties. The gel was transformed into an aerogel by exchanging solvent to 2-propanol, and removal of 2-propanol using supercritical CO₂. SEM images of a cross sectional view of the aerogel indicated that sub-micrometer voids were distributed randomly, and most of parts look filled bulk morphology. The density of the gel obtained from the present polystyrene-based copolymers was estimated to be 200 mg/cm , which implies existence of vacancies without observation in the SEM image, suggesting the extremely fine cell structure.