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

Abstract

ABSTRACT 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. 1 H‐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. 13 C‐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 °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 °C as compared to purified ENR‐50 at −17.7 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 44123.