Methods of preparing polyurethane adhesives, and pressure sensitive adhesives produced thereby

A method of preparing a polyurethane adhesive composition comprising: a) reacting a polyol component selected from the group consisting of polyether polyol, a polyester polyol, and combinations thereof having at least 1.75 hydroxyl groups per molecule with a diisocyanate compound selected from the group consisting of aliphatic, cycloaliphatic, and araliphatic diisocyanate compounds and mixtures thereof in the presence of a non-cytotoxic catalyst to form an intermediate product having a viscosity of at least 5,000 cps when measured at a temperature of from about 25 to 35 °C; and b) reacting greater than a stoichiometric amount of said intermediate product with an isocyanate compound having a functionality of at least 2.0 in the presence of a non-cytotoxic catalyst. Also described is a polyurethane adhesive composition produced by the above method. Also described is a polyurethane adhesive composition comprising a matrix of polyurethane having a molar excess of from 10% to 40% of hydroxy groups over fully reacted isocyanate groups, a cytotoxicity grade level of no more than 2 and an isocyanate index level of from about 50 to 90.