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 speci fic physical and chemical properties. The modifiers arc low-to-medium molecular weight polymers with polymerizable end groups (macromonomers ), To achieve the physical properties required for fabrication into fi ne powders for subsequent deposition using conventional powder coating equipment, semi-crystalline polymers with T(g)'s well below room temp erature and melting points above approximately 70-degrees-C were requi red. Upon copolymerization with a thermosetting resin, crystallization of the modifier was precluded provided that low ethylene oxide compos itions were employed. This scheme, in principle, yields an amorphous l ow T(g) modifier chemically bound to the cured network. Poly(ethylene oxide), PEO, was found to be an excellent candidate, since it has a T( g) of -68-degrees-C and a T(m) of 70-degrees-C, sufficient crystallini ty for friability and functional end groups for copolymerization. Free radical polymerization of 2,2-bis[4-vinylbenzoyloxyphenyl] hexanuorop ropane and step-growth polymerization of 4,4'-(hexafluoroisopropyliden e)diphenyl cyanate were utilized to demonstrate the feasibility of thi s 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 resu lting networks showed multiphase morphologies with improved toughness.