Evaluation of dimethyl meta-isopropenyl benzyl isocyanate (TMI(RTM)) in emulsion polymerization

TMI{dollar}spcircler{dollar} is a novel bifunctional monomer possessing an unsaturation and an isocyanate group. It can be incorporated into a polymer chain via copolymerization with conventional unsaturated monomers such as styrene, methyl methacrylate (MMA), and n-butyl acrylate (BA), in order to obtain polymers with pendant isocyanate groups. Crosslinking of these polymers can then be carried out through the isocyanate groups.; The performance of TMI as a comonomer in the emulsion terpolymerization with MMA and BA was studied. The isocyanate group of TMI was quite stable towards hydrolysis when the polymerization was carried out at 40{dollar}spcirc{dollar}C using redox initiators. High concentrations of TMI were found to retard the polymerization kinetics, and lower the particle size. Several polymerization processes were developed to obtain high conversions at appreciable rates. The locus of the NCO groups in the latex particles could be controlled via seeded polymerization. NCO groups were concentrated at the particle surface by adding all the TMI during the second stage.; The mechanical properties of the TMI latex polymer films were investigated. External catalysts such as triethyl amine, when added prior to film formation, resulted in poor tensile properties as a result of premature crosslinking. When the films were cured after the completion of the film formation process, a significant improvement in the mechanical properties was observed. Tensile strength and modulus of the cured latex films were found to increase with TMI concentration. Latexes with NCO groups at the surface of the polymer particles exhibited the highest tensile strength and modulus. This was attributed to the development of a crosslinked network at the inter-particle boundaries as a result of interfacial crosslinking.; Single-pack latex systems which could be cured at room temperature were obtained by incorporating small amounts of methacrylic acid (MAA) in the TMI latex polymer. MAA acted as a catalyst to accelerate the moisture-curing reaction of the NCO groups at room temperature. These latexes exhibited excellent shelf-stability of more than one year at room temperature.