disclosed herein are novel polyorganosiloxanes , both linear and cyclic , havingpendant thereon isocyanate groups derived from specific α , α - dimethyl isopropenyl benzyl isocyanates . also disclosed is a method for production of said polyorganosiloxanes . the disclosed polyorganosiloxanes are useful as crosslinking agents and as intermediates in the production of star polymers , starburst dendrimers , urethanes and ureas .