Impact of macrodiols on the adhesion strength of polyurethane pressure-sensitive adhesives

In this study, we evaluated the influence of stiff and flexible contents on the adhesive characteristics of polyurethane (PU). This was achieved through the optimization of macrodiol contents in the PU composition, which developed soft segments. The composition of the polymer comprises of two different macrodiols: poly(propylene glycol) and hydroxyl-terminated polybutadiene with various molecular weights. 4,4′-Methylene bis(cyclohexyl isocyanate) was used to maximize the adhesion strength of the final product, which was evaluated with a texture analyzer. The hard-segment content (30%) positively affected the adhesive properties. The probe–tack showed a maximum adhesion energy of 147 J/cm², and the 180° peel test showed a 15.67 N/25 mm peel force. The glass-transition temperature values obtained through differential scanning calorimetry were in good agreement with the theoretically calculated Flory temperature. The proportion of the loss tangent to the storage modulus showed an optimum value of 2.54 MPa⁻¹. The accurate selection criteria of the macrodiol composition resulted in good PU pressure-sensitive adhesives.