Effect of chemical structure and network formation on physical properties of di(cyanate ester) thermosets

Key physical properties of three dicyanate ester monomers, bisphenol A dicyanate (BADCy), bisphenol E dicyanate (LECy), and the dicyanate of a silicon-containing analogue of bisphenol A (SiMCy) were investigated as a function of cyanurate conversion at conversions ranging from approximately 70% to greater than 90% in order to assess the range of applicability of both traditional and more unusual structure-property-process relationships known for cyanate ester resins. A more complete understanding of these relationships is essential for the continued development of cyanate ester resins and their composites for a wide variety of aerospace applications. The degree of cure in each system was determined by differential scanning calorimetry (DSC). The degree of conversion achieved at a given temperature was dependent on the structure of the repeat unit, with SiMCy displaying the highest relative ease of cure. The density at room temperature was found to decrease monotonically with increasing conversion for all monomer types studied. In contrast, the water uptake decreased with increasing cure for all three materials over most or all of the conversion range studied, but leveled off or began to increase with increasing conversion at conversions of approximately 90%. The T(g) decreased after exposure to hot water in resins with greater than 85% conversion, but unexpectedly increased in samples with lower conversions. An investigation of the effect of hot water exposure on network chemistry via infrared spectroscopy indicated that carbamate formation varied with both monomer chemistry and extent of cure, but was greatest for the BADCy polycyanurates. On the other hand, the unreacted cyanate ester band tended to disappear uniformly, suggesting that reactions other than carbamate formation (such as cyclotrimerization) may also take place during exposure to hot water, possibly giving rise to the observed unusual increases in T(g) upon exposure.

Synthesis, Characterization and Applications of Polyurethane Aryl Cyanate Ester Resin

Polyurethane-based aryl cyanate ester resin (PU-CER) with a biphenyl backbone obtained from polymeric 4,4‘-diphenylmethanediisocyanate, bisphenol A and cyanogen bromide was synthesized to get a polymer with better functional properties such as better adhesion and impact resistance. Synthesis of polyurethane based 4,4‘-(oxy biphenyl propane) cyanate ester involved two steps of polyurethane hydroxyl-terminated prepolymer (PU-PP) formation and esterification (PU-CER). PU-CER was cyclotrimerized to yield a triazine ring-containing polymer that possesses better adhesion at high temperature and has greater impact strength. PU-PP and PU-CER were characterized by wet chemical analysis, spectral methods and thermal methods. PU-CER showed better thermal stability and adhesion with single part polyurethane lamination adhesive and also functioned as a better toughening agent in two-part epoxy laminate system..