A series of polyurethane-acrylic hybrid dispersions were prepared with varying ratios of polyurethane to acrylic content.The hybrids were prepared by first producing a polyurethane comprising isophorone diisocyanate(IPDI),propylene glycol(PPG)and dimethylol propionic acid(DMPA)in N-methyl pyrrolidone(NMP).The reaction was continued until the desired free isocyanate content was achieved and then hydroxyethyl methacrylate was added.The polyurethane was neutralised with triethylamine,dispersed in water and chain extended using hydrazine monohydrate.The PU-acrylic mixtures were polymerised using a free radical initiator with n-butyl acrylate(19.6%),methyl methacrylate(78.4%)and methacrylic acid(2%).Waterborne paints were prepared at three PVC values(10,15 and 20%)using rutile titanium dioxide and were applied to SAE 1010 steel panels over one coat of an alkyd anticorrosive primer.
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