Thermoplastic polyurethane pressure sensitive adhesives made with mixtures of polypropylene glycols of different molecular weights

Abstract

New more simple and easier strategy for synthesizing thermoplastic polyurethane pressure sensitive adhesives (TPU PSAs) has been proposed. Thus, the properties of the TPU PSAs were adjusted by fixing the NCO/OH ratio to 1.1 and varying the content of the hard segments by mixing high molecular weight and low molecular weight polyether polyols during TPU synthesis. The thermoplastic polyurethanes have been synthesized with methylene diisocyanate (MDI), 1,4 butanediol chain extender and different mixtures of two polypropylene glycols (PPGs) polyols with different molecular weights (450 and 2000 Da). TPUs with different hard segments content (12.5–38.7%) were synthesized and their pressure sensitive adhesive properties depended on their hard segments contents and degree of phase separation. In general, the TPU PSAs with higher hard segments content exhibited low probe tack and low loop tack regardless of the nature of the metallic and polymeric substrate. In contrast, the 180° peel strength depended noticeably on the nature of the polymeric substrate and on the hard segments content of the TPU. TPU PSAs with hard segments content lower than 20.9% were general purpose or removable PSAs and the ones with higher hard segments content were high shear PSAs.