Use of Graded Rubber Latexes with Surface Functionality in Thermosets

USE OF GRADED RUBBER LATEXES WITH SURFACE FUNCTIONALITY IN THERMOSETS 

In 1974, Dickie and Newman obtained three related patents on the synthesis of graded rubber latexes. The latexes contained surface functionality, and their use was in toughening thermoset plastics and coatings. The materials are applicable to the production of structural plastics such as automotive body panels, electrical appliance housings, boat construction, and conduits for the transmission of heated fluids. 

The latexes themselves are basically semi-I IPNs or IPNs, prepared in a two-stage process. An acrylic, crosslinked seed latex serves as the core, while a plastic monomer mix II containing methacrylic or styrene monomers and monomers with reactive sites (epoxy, carboxy, hydroxy) is polymerized to form the shell of the latex. The graded composition is brought about by beginning to add the monomer II mix before the first monomer mix is completely polymerized. 

This latex is dispersed in a thermoset prepolymer capable of reacting both with the reactive shell and a curing agent. The fully reacted thermoset may have three or four distinct polymers, variously crosslinked and/or grafted to form a series of complex IPNs. Besides their practical importance, the spatial topology of the several compositions is unique. 

Example 1 of Reference 34 describes a four-polymer IPN. A seed latex of butyl acrylate and 1,3-butylene dimethacrylate forms Cn. Onto this seed latex core, a shell of methyl methacrylate and glycidyl methacrylate are polymerized, forming P2. After coagulation, filtration, and washing, the resulting powder is dispersed in styrene and a stoichiometric amount of methacrylic acid. The dispersion is heated until the reaction between the methacrylic acid and the epoxy groups on the graded elastomeric particles is at least 50% complete. 

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