⁴He permeation and H₂O uptake of cyanate ester resins-an alternative to commonly used epoxy resins at low temperature

Cyanate ester (CE) thermoset is a polymer with a high glass-Transition temperature of ≈ 300 °C. CE is expected to be an alternative to Stycast 1266 as a sealing and casting glue for low temperature experiments, especially for adsorption experiments where baking of the substrate at T > 100 °C before cooling is required to eliminate surface contaminations. We experimentally confirmed that thermosets of CE monomers are non-porous and absorbs/desorbs water very little from measurements of (1) ⁴He permeation properties at temperatures from room temperature (RT) to 77 K and of (2) weight gains (δW) after storage for days in water and in air at RT. The ⁴He permeation is rather large at RT but negligibly small at T 130 K where the diffusion constant of ⁴He in CE is vanishingly small. δW in water and air are 0.3-0.5% and 0.5-1.0%, respectively, which are much smaller than those of Stycast 1266. Therefore, cyanate ester is an excellent alternative to commonly used epoxy resins especially in surface-sensitive experiments at low temperature.