The internal stress of epoxide resin coatings cured with aliphatic α, ω-dicarboxylic acids, HOOC(CH2)pCOOH (p=2, 4, 7, 8, 10) in the presence or absence of tertiary amine accelerator and those cured catalytically has been investigated by measuring the changes of sample size and internal stress in the curing and cooling processes. Three types of network structures based on ester bonds, ether bonds or ester-and-ether bonds were formed in these cured systems.
The internal stress was caused by shrinkage occurring in the cooling process from the glass-transition temperature to room temperature in all systems. This stress increased with elevating glass-transition temperature in the cured systems, and with decreasing methylene chain length of the curing agents.
From the above observations, it was suggested that the lowering of glass-transition temperature was necessary to reduce the internal stress and shrinkage caused by curing.
