Film formation from reactive latexes

Model reactive latexes were prepared by emulsion copolymerization of n-butyl methacrylate (nBMA) and either acetoacetoxyethyl methacrylate or dimethylaminoethyl methacrylate. Batch and semi-continuous emulsion polymerization were used to prepare latex particles with different functional group distributions. Conductometric titration and 1H NMR showed that the majority of the functional groups ended up near the surface of the latex particles when batch polymerization was used and that semi-continuous emulsion polymerization resulted in a uniform distribution of the functional groups throughout the latex particles.; The acetoacetoxy and amino-functional latexes were blended in equal amounts and films were cast from the resulting latex blends, cured at temperatures ranging from 50--90°C, and characterized via swelling measurements to determine the crosslink density. At temperatures below 70°C, the films cast from blends of latexes prepared using semi-continuous polymerization consistently showed higher crosslink densities than those prepared using batch polymerization. At temperatures above 70°C, the opposite trend was observed. The reversal in trends was attributed to existence of reaction and diffusion controlled regimes. The shrinking-core model was used to model crosslinking in the films. The model was able to predict the diffusion coefficient for nBMA below 70°C. In addition, the model predicted the activation energy of the crosslinking reaction and the apparent activation energy of diffusion at all temperatures that were investigated.; The influence of blend composition was studied by varying the fraction of acetoacetoxy-functional polymer in the blends before casting the films. The crosslink density was found to increase with increasing acetoacetoxy functionality. A subsequent investigation of the crosslinking mechanism using 1H NMR showed that the mechanism was an amine catalyzed aldol condensation reaction of the acetoacetoxy functional groups. The blend composition study also showed relative maxima around the 30/70 and 70/30 (by weight) blend fractions due to optimal packing.; Analysis of the mechanical properties showed that low amounts crosslinking caused a decrease in mechanical properties due to the lack of the significant entanglement contribution of nBMA. When the fraction of acetoacetoxy-functional polymer was increased above 50% by weight, the resulting films showed improved mechanical properties over nBMA homopolymer.