Jeffrey C. Hedrick

Microporous polycyanurate networks

A general means of generating nanofoams from thermosetting materials was investigated. Foams were prepared from a thermosetting monomer copolymerized with a thermally labile material, such that the thermally labile coblock is the dispersed phase. Upon thermal treatment, the thermally unstable block undergoes thermolysis, leaving pores where the size and shape are dictated by the initial morphology. For this investigation the thermosetting resin was prepared from a cyanate monomer (4,4′-(hexafluoroisopropylidene) diphenyl-cyanate), with either poly(propylene oxide) or a propylene oxide–urethane copolymer as the thermally labile block. The propylene oxide-based oligomers were molecularly miscible with the cyanate resin over the entire range of compositions, and molecular weights investigated, but developed a two-phase structure upon reaction to form the polycyanurate thermoset. The molecular weight and composition of propylene oxide chemically incorporated into the polycyanurate was varied along with the curing condition, solvents, and catalyst. Dynamic mechanical and small-angle x-ray scattering measurements 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 foam 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.

A method for rubber toughening powder coatings

This paper describes a new method for rubber toughening brittle powder coatings. The design involves the use of toughening agents with specific physical and chemical properties. The modifiers are low-to-medium molecular weight polymers with polymerizable end groups (macromonomers). To achieve the physical properties required for fabrication into fine powders for subsequent deposition using conventional powder coating equipment, semi-crystalline polymers with Tgs well below room temperature and melting points above ≈70°C were required. Upon copolymerization with a thermosetting resin, crystallization of the modifier was precluded provided that low ethylene oxide compositions were employed. This scheme, in principle, yields an amorphous low Tg modifier chemically bound to the cured network. Poly(ethylene oxide), PEO, was found to be an excellent candidate, since it has a Tg of -68°C and a Tm of 70°C, sufficient crystallinity for friability and functional end groups for copolymerization. Free radical polymerization of 2,2-bis[4-vinylbenzoyloxyphenyl] hexafluoropropane and step-growth polymerization of 4,4′-(hexafluoroisopropylidene)diphenyl cyanate were utilized to demonstrate the feasibility of this approach. An electrostatic powder coater was used to co-deposit the PEO macromonomers with either of the thermosetting precursor monomers, followed by thermal curing to produce the modified networks. The resulting networks showed multiphase morphologies with improved toughness.