Development of cyanate ester-oligosiloxane copolymers for deployable satellite applications.

Binary blends of an alpha,omega-hydroxyoligosiloxane (with degree of polymerization, n = 39) with an oligomeric cyanate ester (PrimasetTM PT-30, 1) are prepared as microphase separated, monolithic samples. The uncured blends display complex viscosities of 21-97 Pa.s at 30°C depending on composition, rendering them suitable for infusion processes at 70°C. This alpha,omega-hydroxyoligosiloxane undergoes co-reaction with (1) to yield network structures. Initiation using copper(II) acetylacetonate/nonylphenol reduces the onset of polymerization of the 1(90)2(10) binary blend by some 99°C and a value of 61-62 kJ/mol. cyanate groups is obtained for the ucatalyzed polymerization of the homopolymer (1) and the binary blend 1(95)2(5), while there was little difference in the enthalpy when catalyzed with copper (64 kJ/mol. OCN), cobalt (66 kJ/mol. OCN), and iron (60 kJ/mol. OCN), although the shape of the exotherm and thus the mechanism were changed significantly. A short initial cure cycle (170°C, 1 hour) effects a high initial conversion of > 80%, while a second post cure step (200°C 1 hour) yields an ultimate conversion of at least 93%. The cured binary 1(90)2(10) binary blend displays good thermal stability (Tdec5% = 429°C and char yield = 62.4% at 800°C, compared with (Tdec5% = 433°C and char yield = 68.0% at 800°C).