Blocked isocyanates and isocyanated soybean oil as new chain extenders for unsaturated polyesters

Two different blocked isocyanates, diphenylmethane–bis‐4,4′‐ethyleneurea and diphenylmethane–bis‐4,4′‐carbamoil–ϵ‐caprolactam, and isocyanated soybean oil were used as chain extenders for low‐molecular‐weight unsaturated polyesters. Oligomeric polyesters (molecular weight = 600–700), taken from a manufacturing process in the sixth hour of a 16‐h polyesterification reaction, were reacted with these chain extenders, and the desired chain lengths (molecular weight = 1000–1500) were obtained in a very short time through the reaction of the chain extenders with the polyester end groups. The increase in the molecular weight was monitored with gel permeation chromatography. The obtained polymers were characterized with Fourier transform infrared and ¹H‐NMR and with styrene solubility and gel time measurements. After dilution with styrene, the polyesters were cured with a radical initiator. The thermal and mechanical properties of the cured polyesters were examined with dynamic mechanical analysis and thermogravimetric analysis tests and then compared to those of a commercially available reference unsaturated polyester. The results show that unsaturated polyesters can be chain‐extended with these compounds to shorten the polyesterification time substantially without alterations of the styrene solubility or gel time of the polyesters. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011