Results of our recent research on crosslinked latexes and polymer nanoparticles will be reported. Goals of this long-term program have been: · Comparing precoalescence and postcoalescence crosslinking. · Synthesizing polymer nanoparticle latexes (~20 - 25 nm) from a variety of acrylic monomers, including crosslinking and crosslinkable monomers. · Blending nanoparticle latexes with compatible conventional (~120 - 130 nm) latexes and understanding their effects on film formation and on fundamental and empirical film properties. As reported in 2008, blending conventional and nanolatexes in an 85/15 ratio (w/w of polymer solids) effects substantial changes of fundamental film properties. Best results included reducing minimum filming temperatures (MFT) while increasing Young's moduli by factors of two to 17. Substantial improvements in empirical film properties such as gloss (up to 97 at 60o), hardness (increased by 2 - 5 pencils), block resistance, and adhesion to aluminum were also found. The 2008 report covered only a single blend ratio. Here we report studies of blends with ratios of conventional to nanoparticle latexes ranging from 92.5/7.5 to 30/70 (w/w). As before, the latexes and nanolatexes are BMA/BA copolymers with 0 - 4 wt. % of 1,3- butylene glycol dimethacrylate (precoalescence crosslinker) and 0 - 5 wt. % of diacetone acrylamide (for postcoalescence crosslinking with adipic dihydrazide). Films cast from these blends are subjected to everyday empirical coatings tests and are characterized using instrumental tests including Dynamic Mechanical Analysis (DMA) and Modulated Differential Scanning Calorimetry (MDSC). Film formation and film morphology are studied using Atomic Force Microscopy (AFM). The results confirm that blending nanoparticles at ratios up to 50/50 (w/w of polymer solids) can substantially improve certain properties of conventional latex films. For many properties the optimum ratio somewhere around 85/15 conventional/nano; a 92.5/7.5 ratio affords substantial improvements. As coatings, the blends have near-zero VOC.^
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