Designing of desired nanocomposite pressure-sensitive adhesives through tailoring the structural characteristics of polysilsesquioxane-acrylic core-shell nanoparticles

Abstract

A series of novel nanocomposite pressure-sensitive adhesives (PSAs) made of core-shell nanoparticles has been designed with a diverse range of adhesion properties from general-purpose to high-shear adhesives. The PSAs were prepared by synthesis of polymethacryloxypropylsilsesquioxane (PSQ) nanoparticles and their encapsulation with an acrylic shell via semi-continuous emulsion polymerization. The effects of structural characteristics of the core-shell nanoparticles, i.e. composition of acrylic comonomers in the shell, shell thickness, and grafting density, on peel and shear strengths of the PSAs were scrutinized. Grafting of acrylic chains on the surface of PSQ nanoparticles led to an improvement in the peel and shear strengths due to enhancement in the dynamic mechanical moduli. Increase in the cohesive energy density of the PSAs through raising the methyl methacrylate content in the shell enabled designing of high peel and shear PSAs. Increasing the number of segments of the grafted chains present in the semi-dilute polymer brush (SDPB) region through 40% enlargement in the shell thickness of the nanoparticles decreased the peel and shear strengths. However, increasing the grafting density through a 4.5-fold rise in the core size and thus extension of the concentrated polymer brush region and elimination of SDPB region led to an extraordinary 1400-fold improvement in the shear strength. • Grafting of acrylic chains on PSQ enhanced peel and shear strengths simultaneously. • Optimization of cohesive energy density of shell enhanced peel and shear strengths. • Extension of semi-dilute polymer brush region deteriorated the shear strength. • Increase in grafting density led to an extraordinary improvement in shear strength.