Oligodimethylsiloxane linked cyanate ester resins

A series of dimethylsiloxane linked cyanate ester monomers (NCOC6H4(CH2)(3)(Si(CH3)(2)O)(n)Si(CH2)(3)C6H4OCN, n = 1, 2, 3) have been synthesized and characterized. Monomer melting points range from 5 to - 12 degreesC, and characterization includes H-1, C-13 NMR, and IR spectroscopies and DSC. Thermoset formation occurs by a cyclotrimerization of the cyanate group to a cyanurate structure. Cured resins are homogeneous rubbery castings with T-g ranging from 15 to -43 degreesC. Dielectric constants display little dependence on siloxane chain length but a strong dependence on frequency (2.5/15 GHz; 2.85/1 GHz). The corresponding loss tangent increases with siloxane chain length and displays a small frequency dependence.