Solvent-Borne Polyurethane Adhesives with High Molecular Weight, High OH Content and Low Solution Viscosity

A method of manufacturing an adhesive composition comprising dissolving a polyurethane polymer in a solvent and a co-solvent,

• wherein
• the polyurethane polymer is an internally and/or externally hydrophilized thermoplastic polyurethane having a mass average molecular weight Mw, as determined by gel permeation chromatography against polystyrene standards using N,N-dimethyl acetamide as the eluent, of ≥50000 g/mol,
• the solvent is a polar-aprotic solvent,
• the co-solvent is selected from water, a primary alcohol having ≤10 carbon atoms, a vicinal diol or a mixture thereof,
• the solvent and the co-solvent are present in such amounts that they form a homogenous mixture without formation of a second phase when combined together at 20° C.,
• a hydroxyl group content is ≥1 weight-%, based on total weight of the composition,
• a polyurethane polymer content is ≥10 weight-%, based on the total weight of the composition and
• the composition forms a single continuous liquid phase.

A method of dissolving a thermoplastic polyurethane polymer in a mixture of a solvent and a co-solvent,

• wherein
• the polyurethane polymer is an internally and/or externally hydrophilized thermoplastic polyurethane having a mass average molecular weight Mw, as determined by gel permeation chromatography against polystyrene standards using N,N-dimethyl acetamide as eluent, of ≥50000 g/mol,
• the solvent is a polar-aprotic solvent,
• the co-solvent is selected from water, a primary alcohol having ≤10 carbon atoms, a vicinal diol or a mixture thereof,
• the solvent and the co-solvent are present in such amounts that they form a homogenous mixture without formation of a second phase when combined together at 20° C. and
• the mixture and the thermoplastic polyurethane polymer form a single continuous liquid phase.