A structural study of epoxidized natural rubber (ENR-50) ring opening under mild acidic condition

A structural study of ring opening reaction of purified epoxidized natural rubber (ENR) with acetic acid was conducted using the NMR techniques and its thermal characteristic was evaluated with Thermal gravimetry/Differential Thermal Gravimetry (TG/DTG) and Differential Scanning Calorimetry (DSC) analyses. H-1-NMR revealed that 19.56% of epoxide was ring-opened from the total amount of the epoxide unit in ENR-50 and this was supported by Fourier Transform Infrared (FTIR) spectroscopy. C-13-NMR suggests the fixation of alkyl (R) i.e., acetate group to the epoxide carbon via ester linkage and formation of hydroxyl groups in the polymer chains. The attachment location of R occurred at both most () and least () hindered carbons of the epoxide. The TG/DTG results of acid treated ENR-50 showed three decomposition steps at 235-338, 338-523, 523-627 degrees C due to the presence of the polymer chains mixture, i.e., ring-opened and intact epoxide of ENR-50. This increases the T-g value of acid treated ENR-50 at 24.6 degrees C as compared to purified ENR-50 at -17.7 degrees C. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44123.