Endgroup modification of unsaturated polyesters. Effect on chemical resistance

Abstract

synopsisEndgroups of unsaturated polyesters formulated with mole ratios of 2/1/3 and 11112 isophthalic acid/maleic anhydridejpropylene glycol were modified. Carboxylic acid content was effectively reduced by esterification with alcohols or epoxides, amidation with phenyl isocyanate, or neutralization with amines. Hydroxyl content was reduced by esterification with acids or anhydrides and urethane formation with phenyl isocyanate. Chemical resistance was determined by measuring the decrease in flexural strength and modulus with exposure to 10% solutions of sodium hydroxide and sulfuric acid a t 82°C. A %week test using the medium chemical-resistant 21113 polyester indicated that any modification which decreased the carboxylic acid content improved chemical resistance. Modifications which increased or decreased the hydroxyl content had no significant effect in the %week tests; however, decrease of hydroxyl content appeared important in &month exposure tests. The 11112 resins which have high initial chemical resistance had poorer chemical resistance. after endgroup modification than the unmodified 1/1/2 resin, with the exception of the phenyl isocyanate-modified product which was equal to the unmodified resin. Water (0.8%) and xylene (O.lyo) had no effect on chemical resistance. However, larger amounts of residual solvent were disadvantageous.