Studies of polycyanurates based on phenoxy-substituted cyclic phosphazenes: Synthesis of the monomer and a preliminary study of its thermal properties in binary blends

The four-step preparation of a new monomer, 1,2,3-tris(4-cyanatophenoxy)-, 3′,5,5-tris-phenoxy-2λ ⁵,4λ ⁵, 6λ ⁵-[1,3,5,2,4,6]-triazatriphosphinine, is reported. Characterization of the monomer is undertaken using spectroscopic and chromatographic methods and elemental analysis and the data are in agreement with the proposed structure (as a mixture of isomers). The thermal polymerization of the monomer and its behaviour within selected blends containing 2,2-bis(4-cyanatophenyl)propane (AroCy B10) are studied using differential scanning calorimetry. The blends appear to melt sharply at ca. 80 °C onset of polymerization (corresponding to the melting point of the commercial dicyanate) before commencing polymerization directly thereafter. Typical exothermic peak maxima at ca. 135°C are observed, whilst the cure is apparently concluded by 200°C under the scanning conditions. On rescan, the cured samples display glass transition values in the region of 160-190°C, depending on composition with the higher values reflecting increasing amounts of the new material. The cured polycyanurate of the tricyclophosphazene is also analysed using thermogravimetric analysis and displays a mass loss of 5% at approximately 381°C in air and 366°C in nitrogen. When 1,2,3-tris(4-cyanatophenoxy)-,3′,5,5-tris-phenoxy-2λ ⁵, 4λ ⁵,6λ ⁵-[1,3,5,2,4,6]-triazatriphosphinine is combined with AroCy B10, the cured copolymers (containing between 10 and 30 wt% of the tricyclophosphazene) show disappointing thermal stability with a progressive reduction in the onset of degradation with increasing phosphazine content; this may be a result of incomplete cure.