Diffusion and permeation of water through unsaturated polyester resins - influence of resin curing

The diffusion and permeation properties of liquid water through an isophtha lic-maleic acid-propanediol-based copolyester resin were studied with a hig hly sensitive permeameter. The value of the parameters of the exponential d ependence of the diffusion coefficient on the water concentration decreases with the curing extent, except that of the plasticization coefficient, whi ch decreases after a post-curing at 120 degrees C, Infrared-spectrophotomet ric and calorimetric data show that the curing involves mainly a polymeriza tion of styrene during the curing at 25 degrees C, and a crosslinking by th e opening of the double bonds on the polyester chains in the subsequent cur ing step at 80 degrees C. The water sorption by the resin results in a 20 d egrees C-decrease in the glass transition temperature of the water saturate d resin. lending to the diffusivity enhancement by the plasticization effec t. (C) 2000 Elsevier Science Ltd. All rights reserved.