A Soft–Soft Nanocomposite Approach for Design of Water-Borne Acrylic Surface Coatings

Poly[(n-butyl methacrylate)-co-(n-butyl acrylate)]-based core-shell latexes are prepared by emulsion polymerization with a shell copolymer glass transition temperature (T_g) of 5 °C, but differences in core copolymer wt.% (4–90) and T_g (5–25 °C), and in wt.% of diacetone acrylamide (DAAM) in the shell copolymer, which facilitates crosslinking in the percolating phase of films through addition of adipic acid dihydrazide. Analysis of samples removed from reactions, together with analysis of film cross-sections by atomic force microscopy (AFM), confirms the core-shell particle structures and honeycomb morphologies in films, with simultaneous AFM and infrared spectroscopy showing the distribution of hydrazone crosslinks. Increasing wt.% DAAM (i.e., degree of crosslinking) in the percolating phase shifts film tensile stress–strain curves towards higher stresses and lower extensions at break. For core and shell copolymer T_gs of 5 °C there is a small effect of core wt.%. At 70 and 80 wt.% core, increasing core copolymer T_g also shifts the curves towards higher stresses and lower extensions at break. Thus by combining effects of core copolymer wt.% and T_g with effects of wt.% DAAM in the shell through the soft–soft nanocomposite approach, it is possible to achieve a wide range of tensile deformation behavior in films that have quite similar overall copolymer compositions.