Thermoplastic polyurethane coatings made with mixtures of polyethers of different molecular weights with pressure sensitive adhesion property

Thermoplastic polyurethane (PU) coatings with pressure sensitive adhesion property were synthetized by reacting 4,4'-diphenylmethane diisocyanate (MDI) with 1,4-butanediol and mixtures of polypropylene glycols (PPGs) of different molecular weights (1000 and 2000 Da). Good tack at 10-37 degrees C was obtained in PU coatings prepared with PPG2000 + PPG1000 mixtures containing 50 wt% or more PPG2000. The pressure sensitive adhesion properties of the PU coatings were related to their minor content of bonded urethane groups and important degree of phase separation. Furthermore, these PU coatings followed Dahlquist criterion, they showed low glass transition temperatures, high tack, and low 180 peel strength. Therefore, the PU coatings had potential as pressure sensitive adhesives. Finally, PU coating made with PPG of molecular weight 1000 Da did not show pressure sensitive adhesion property.