Water-based polymer colloids with a branched chain architecture as low-gel pressure-sensitive adhesives

Abstract

The performance of water-based acrylic pressure-sensitive adhesives, in which the latex particles had minimal gel content of typically less than a few percent and the polymer chains had a branched architecture, were investigated. A series of semi-batch emulsion copolymerizations of 2-octyl acrylate, isobornyl acrylate and acrylic acid was carried out in the presence of ethylene glycol dimethacrylate as crosslinker. The molecular weight distributions and branched chain topology were regulated by using 2-ethylhexyl thioglycolate as a chain-transfer agent. The monomers and chain-transfer agent were selected as these were already available as bio-based feedstocks, or had a realistic potential to become available from non-petrochemical resources. Adhesive films cast from the polymer dispersions demonstrated good peel, shear strength and tack adhesion energies. This is attributed to polymer chain branching, which unlocks a broader window for the design rules for pressure-sensitive adhesives. Detailed rheological studies of the viscoelastic materials were conducted to support the adhesive test results.