A thermally-stimulated-current study of ethylene-methyl-methacrylate copolymers

Abstract

Two ethylene-methyl methacrylate (EMMA) copolymers were studied by infrared (i.r.) spectroscopy, Differential Scanning Calorimetry (DSC) and Thermally Stimulated Currents (TSCs). The critical temperature, T _c, relaxation time, τ_c (measured in seconds), and Degree of Disorder (DOD) of the polymers were also measured by Relaxation Map Analysis (RMA). The i.r. and DSC results showed that these two copolymers are random copolymers with a melting point, T _m, at 82.6 °C for a sample containing 18 wt % methyl methacrylate (EMMA18), and at 53.0 °C for a sample having a MMA content of 38 wt % (EMMA38). From TSC spectra analysis, EMMA18 showed a glass-transition point, T _g, at − 41.0 °C, whereas EMMA38 had a T _g at − 36.0 °C together with a γ-relaxation at − 120 °C. Both samples have their space charges in the range 5–30 °C. The RMA showed that EMMA18 has T _c = − 5.74 °C, log τ_c = − 2.90 (τ in seconds) and DOD = 54.65. EMMA38, however, has T _c = − 1 5.71 °C, log τ_c = − 1.59 and DOD = 48.69. The absence of γ-relaxation in EMMA18 was explained by evidence that it has a higher DOD. While the low mechanical properties of EMMA38 were mainly attributed to the contribution from the short chain segments, demonstrated by its low T _c.