Examination of the Thermal and Thermomechanical Behavior of Novel Cyanate Ester Homopolymers and Blends with Low Coefficients of Thermal Expansion

A new four-step synthetic method is presented and applied to the preparation in high purity of three novel dicyanate monomers that comprise aryl/alkylene ether backbones with high molecular flexibility. The multistep route involves four individually high-yielding steps (each ≥70% thus giving overall reaction yields for total synthesis of 42—50 % depending on the length of the backbone. All products are characterized using FT-IR and 1 H NMR spectroscopy, elemental analysis, and melting point determination. DSC analysis of "uncatalyzed" samples displays relatively sharp melting endotherms ranging from 66 to 125 °C depending on the length (i.e., flexibility) of the backbone. All monomers display broad polymerization exothe rms (87 ± 2 kJ/mol cyanate), although the polymerizations occur in different temperature regimes. When catalyzed (aluminum(III) acetylacetonate/dodecylphenol), the exothermic polymerization peaks occur at significantly lower temperatures than the uncatalyzed analogues and have much narrower profiles but tend to occur in a similar temperature regime (i.e., peak maxima 205-216 °C). The polymerization enthalpies for the catalyzed monomers are ca. 93 ± 9.9 kJ/mol cyanate. TGA shows that the polymers typically lose 5% of their masses by ca. 346-366 °C, which is comparable to AroCy B10. DMTA analysis of cured AroCy B10 yields results that are consistent with published data, and T g values (tan δ max ) of the homopolymers are 221 (4a), 139 (4b), and 121 °C (4c) and fall with increasing backbone length/flexibility. The storage moduli at 25 °C for the binary blends are significantly lower than the respective homopolymers, but the reduction in E' (25-200 °C) is significantly improved compared with AroCy B10. When combined with AroCy B10 in binary blends, the new monomers showed a reduction in CTE of up to 12 ppm/°C while maintaining the same value of Tg.