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 dicy anate monomers that comprise ary l/alky lene 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 ¹H NMR spectroscopy, elemental analysis, and melting point determination. DSC analysis of "uncatalyzed" samples displays relatively sharp melting endotherms ranging from 66 to 125 0C 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 BlO. DMTA analysis of cured AroCy BlO yields results that are consistent with published data, and Tg values (tan ámax) of the homopolymers are 221 (4a), 139 (4b), and 121 °C (4c) and fall with increasing backbone length/flexibility. The storage moduli at 25 0C 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 BlO. When combined with AroCy BlO in binary blends, the new monomers showed a reduction in CTE of up to 12 ppm/°C while maintaining the same value of Tg.