Model reactive latices were synthesized by semicontinuous emulsion copolymerization of n-butyl methacrylate and acetoacetoxyethyl methacrylate or dimethylaminoethyl methacrylate. The two functional latices were then blended in various ratios to study the influence of blend composition on crosslinking and mechanical properties of the resulting films. Crosslinking was quantified through swelling measurements. It was found that the crosslink density increased with increasing amounts of acetoacetoxy-functional polymer. In addition, the crosslink density exhibited two maxima, at 30/70 and 70/30 (acetoacetoxy-functional latex/ amino-functional latex) blend compositions. The mechanical properties of the films were quantified by dynamic mechanical analysis (DMA). It was shown that optimal mechanical properties occurred when the particles packed most efficiently at the 30/70 and 70/30 blend compositions.

ABSTRACT:We prepared reactive latex blends from two copolymer latices comprised of n-butyl methacrylate (n-BMA) with acetoacetoxyethyl methacrylate and n-BMA/ dimethylaminoethyl methacrylate to study the kinetics of film formation. We generated thin films by blending equal weights of the two latices. The films were then cured at temperatures ranging from 50 to 90°C. The extent of the crosslinking reaction was calculated from the crosslink density, which was determined from swelling measurements of the films in toluene. The shrinking-core model, a diffusion/ reaction model, which was originally derived for combustion reactions of coal particles, was adopted to calculate the diffusion coefficient (D e ) and reaction rate constants from the extent of the reaction with time data. This model system exhibited a diffusion-controlled regime above 70°C and a reaction-controlled regime at temperatures below 70°C. In the reaction-controlled regime, the shrinking-core model predicted D e for the system, which was in agreement with literature values for n-BMA. In the diffusion-controlled regime, the model predicted a lower apparent value for D e but with an activation energy that was close to that obtained for n-BMA. The model was also used to examine the kinetics of the crosslinking reaction. The kinetic rate constants for the crosslinking reaction were also determined. The activation energy for the crosslinking reaction was 18.8 kcal/mol, which compared reasonably with the activation energy of 22.8 kcal/mol determined for the reaction between the functional monomers as small molecules.