Telechelic Aryl Cyanate Ester Oligosiloxanes: Impact Modifiers for Cyanate Ester Resins

We describe the synthesis of monomers and characterization of polymers and blends derived from telechelic siloxanes terminated with dimethyl(4-cyanatophenyl)silyl units. These are synthesized by base-catalyzed equilibration of THP-protected 1,1,4,4-tetramethyl-1,4-bis(4-hydroxyphenyl)disiloxane with octamethylcyclotretrasiloxane (D 4 ) and octaphenylcyclotetrasiloxane (D 4 ") followed by deprotection and reaction with cyanogen bromide. Homopolymerization of the telechelic siloxane cyanate esters produce cross-linked materials whose glass transition temperatures range from 277°C(disiloxane) to -120°C(dimethyl-10-mer). Blending with commercial novolac based-cyanate ester resins (Primaset PT-30) produces a single phase material for the disiloxane and two-phased materials for the higher oligomers. The completely dispersed rubber phase has an average domain size of 20 microns.