Abstract

This invention relates to silicone pressure-sensitive adhesives having improved viscosity stability and film physical property stability upon aging by a method comprising the condensation of a benzene-soluble resin copolymer of 0.6 to 0.9 triorganoxiloxy units per SiO4/2 unit which contains silicon-bonded hydroxyl radicals and a polydiorganosiloxane preferably containing silicon-bonded hydroxyl or other hydrolyzable endblocking radicals with a sufficient amount of an endblocking agent containing endblocking triorganosilyl units such as hexamethyldisilazane or trimethylmethoxysilane to result in a 1:0.8 to 1:3 mole ratio of silicon-bonded hydroxyl radicals and hydrolyzable endblocking radicals to total moles of triorganosilyl units provided by the endblocking agent. The condensation is conducted, when desirable, in the presence of a catalytic amount of a mild silanol condensation catalyst if one is not provided by endblocking agent and when, necessary, in the presence of an effective amount of an organic solvent such as xylene. Condensation is preferably conducted with heating under solvent reflux conditions.