Abstract: Acomparison of the effects of acetoxy and hydroxy groups on the water uptake into the cured epoxy resin was made using the gravimetric method, DSCand corrosion test. The experimental results show that the replacing of the hydroxy groups with acetoxy groups in the resin causes less water uptake, but increases the diffusibility of water in the resin. For example, at 30℃, the equilibrium water sorption of the o-cresol novolac epoxy resin cured with phenol novolac acetate resin (EPA ) is 0.84% (mass fraction), while the epoxy resin cured with phenol novolac resin(EP) is 1. 97 %; the activation energies for diffusion of water in EPAand EPare 40 and 48 kJ. mol^-1 respectively. The effects may be mainly due to the hydrophobic methyl group of the acetoxy groups. The methyl group prevents the uptake of water, but makes the acetoxy group more flexible, which causes water diffusion less difficult. Moreover, the results show that the unique structure of the interphase of the EPAcoating/Al substrate even causes further less water uptake, and improves the effectiveness of corrosion protection for the coating accordingly.

Key words: Epoxy resin, Epoxy coating, Water absorption