Abstract

This invention relates to silicone pressure-sensitive adhesives having improved viscosity stability, film physical property stability upon aging and lap shear stability made by a method comprising the condensation of a benzene-soluble resin copolymer of 0.6 to 0.9 triorganosiloxy 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 ammonia releasing endblocking agent containing endblocking triorganosilyl units such as hexamethyldisilazane 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 with heating at 80° C.-160° C. in the presence of 0.1 to 10 moles of water per mole of =NH present in the endblocking agent, 0.001 to 10 parts by weight per 100 parts by weight of total resin copolymer and polydiorganosiloxane and when necessary, in the presence of an effective amount of an organic solvent such as xylene. Condensation is preferably conducted under solvent reflux conditions. When the condensation reaction is substantially complete, the remaining endblocking agent, water, ammonia scavenger compound and ammonia released by the endblocking agent is stripped from the composition.