Abstract
New polymers with tuneable dielectric properties were prepared by modifying trimethylsilyl end-terminated poly(methylhydro) siloxane with polar gamma-cyanopropyl groups. The amount of polar groups was tuned by adjusting the allyl cyanide/n-hexene ratio in poly(methylhydro) siloxane co-hydrosilylation. The copolymers were characterized by FTIR and NMR spectroscopy. The distribution of the polar groups along the chain was evaluated based on H-1 NMR spectroscopy. The influence of the amount of polar gamma-cyanopropyl on the glass transition temperature (T-g) and on the dielectric properties was investigated by DSC and impedance spectrometry. All polymers showed T(g)s well below room temperature. A linear increase in permittivity (epsilon') with increasing amount of gamma-cyanopropyl groups was observed. A maximum epsilon' value of 15.9 for the copolymer containing 89 mol% polar groups was achieved, which is 6-fold higher than polydimethylsiloxane. The incomplete conversion of Si-H groups observed in all hydrosilylation reactions with allyl cyanide opened up the possibility of using the prepared copolymers as cross-linkers.