Fluoromethylene Cyanate Ester Resins. Synthesis, Characterization, and Fluoromethylene Chain Length Effects

Fluoromethylene cyanate ester resins derived from the monomer series N⋮CO−CH 2 (CF 2 ) n CH 2 −OC⋮N (where n = 3, 4, 6, 8, and 10) have been synthesized and characterized. Monomer melting points range from −8 to 181 °C, and characterization includes 1 H, 13 C, and 19 F NMR and IR spectroscopy and DSC. Purification is a critical requirement for melt processing. The thermal curing reaction is a cyclotrimerization reaction of the cyanate functional group to the cyanurate heterocycle. Physical properties of resin castings and their variation with an increase in fluoromethylene sequence length from 3 to 10 CF 2 units include density, 1.77−1.91 g/cm 3; critical surface tension, 40−23 dyn/cm; refractive index, 1.447−1.382; dielectric constant, 2.7−2.3; 100 °C immersion water absorption, 1.67−0.68%; T g, 84−101 °C; glass/rubber thermal expansion coefficient, (109/238−152/275 ppm/ °C; and gravimetric thermal stability, 0.0196−0.0064% weight loss/min at 300 °C). Compared with aromatic cyanate ester resins, the fluoromethylene cyanate esters have significantly lower T g, dielectric constant, critical surface tension, and water absorption. For low-dielectric applications, the optimum trade-off between properties and processing occurs at a fluoromethylene chain length of 6.