Influence of the hard segments content on the structure, viscoelastic and adhesion properties of thermoplastic polyurethane pressure sensitive adhesives

New thermoplastic poly(ether-urethane)s (PUs) with different hard segments (HS) contents (13.9–24.4% by weight) intended for pressure-sensitive adhesives (PSAs) have been synthesized by reacting different blends of polyether diols of different molecular weights – poly(propyleneglycol) (PPG) of molecular weight 2000 Da and poly(tetrahydrofuran) (PTHF) of molecular weight 1000 Da – 4,4′-diphenylmethane diisocyanate, and 1,4-butanediol, the prepolymer method was used. The increase of the HS content increased the contribution of the associated by hydrogen bond urethane groups and decreased the degree of micro-phase separation in the PUs synthetized with PPG + PTHF blends, an increase of the thermal stability was also obtained. On the other hand, the PU made with NCO/OH ratio of 1.10 showed unexpected properties because the contribution of the free urethane groups, the storage modulus and the temperature at the cross-over between the storage and loss moduli were higher than in the rest of the PUs synthesized with different NCO/OH ratios. The PUs with HS contents of 14.0–16.7% by weight were typical general-purpose pressure-sensitive adhesives (PSAs), whereas the PUs with HS content of 19–22% by weight were typical high shear PSAs. All PU PSAs followed the Dahlquist criterion and the one synthesized with 50 wt% PPG + 50 wt% PTHF and an NCO/OH ratio of 1.10 showed an optimal balance between tack, shear resistance and 180° peel strength values.