Synthesis of a tung oil–rosin adduct via the diels–alder reaction: Its reaction mechanism and properties in an ultraviolet‐curable adhesive

ABSTRACT A Diels–Alder adduct of rosin with tung oil was effectively prepared for use as a filler and adhesion promoter in UV‐curable adhesives. The characteristics of the adduct were analyzed by Fourier transform infrared (FTIR) spectroscopy and ultraviolet–visible (UV–vis) absorption spectra. The reaction mechanism was studied with gel permeation chromatography, thermogravimetric analysis, 1 H‐NMR, and the density functional theoretical method. The FTIR and 1 H‐NMR results showed that the Diels–Alder addition occurred between the rosin and tung oil. The still‐existing characteristic peaks of the conjugated diene in the adduct, as shown in the FTIR and UV–vis absorption spectra, indicated that the most favorable reaction between the rosin and tung oil was when the rosin was used as the conjugated diene and the tung oil was used as the dienophile. The molecular weights of the adduct with different molar ratios showed that the most possible addition molar ratio between the rosin and tung oil was 3:1. The favorable addition mechanism was further proved by a comparison of the relative energies of different isomers of the adduct with theoretical calculation, and the most stable structure of adduct showed that the addition position of tung oil was the terminal CC double bond. The properties analysis indicated that the adduct could improve the adhesion of UV‐curable adhesives and reduce the curing shrinkage rate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4201–4208, 2013