AN EXAMINATION OF A STYRENIC THERMOSET FORMED BY AN ALPHA,OMEGA-4-VINYLPHENYL FUNCTIONAL DIPHENYLSILOXANE OLIGOMER

To overcome the difficulties associated with processing polydiphenylsi loxane, a method for generating a regular three-dimensional network fr om easily processable and curable diphenylsiloxane oligomers has been examined. This has involved the successful tethering of various groups at the terminal positions of the three unit oligomer, hexaphenyltrisi loxanediol. A curable composition was obtained by end functionalizatio n with 4-vinylphenyldimethylsilyl units. The derived material can be c ured thermally at temperatures above 200 degrees C or at lower tempera tures by adding a radical initiator. The composition, cured under nitr ogen as films or monoliths, was transparent, hard, and amorphous. The thermal stability of the cured composition was good but failed to reac h the stability observed for pure polydiphenylsiloxane. Mechanical ana lysis has revealed a slight reduction in the modulus of the cured mate rial below 100 degrees C that might be attributable to the onset of di phenylsiloxane segmental motion; otherwise, the material is rigid to a temperature above 300 degrees C. The thermal expansion coefficient of 168 ppm/degrees C was rather high compared to other highly crosslinke d thermosetting resins. The electrical properties of the cured materia l were good and similar to those of polydiphenylsiloxane, with a low d ielectric constant, good resistivity, and moisture resistance.