MICROPOROUS POLYCYANURATE NETWORKS

A general means of generating nanofoams from thermosetting materials w as investigated. Foams were prepared from a thermosetting monomer copo lymerized with a thermally labile material, such that the thermally la bile coblock is the dispersed phase. Upon thermal treatment, the therm ally unstable block undergoes thermolysis, leaving pores where the siz e and shape are dictated by the initial morphology. For this investiga tion the thermosetting resin was prepared from a cyanate monomer (4,4' -(hexafluoroisopropylidene) diphenyl-cyanate), with either poly(propyl ene oxide) or a propylene oxide-urethane copolymer as the thermally la bile block. The propylene oxide-based oligomers were molecularly misci ble with the cyanate resin over the entire range of compositions, and molecular weights investigated, but developed a two-phase structure up on reaction to form the polycyanurate thermoset. The molecular weight and composition of propylene oxide chemically incorporated into the po lycyanurate was varied along with the curing condition, solvents, and catalyst. Dynamic mechanical and small-angle x-ray scattering measurem ents demonstrated a two-phase morphology in the cured networks wherein the propylene oxide domains are dispersed in the polycyanurate matrix . Upon decomposition of the propylene oxide component, however, the fo am was found to collapse. Samples with the larger void size retained, to a large extent, their void composition upon the thermolysis of the propylene oxide component. (C) 1996 John Wiley & Sons, Inc.