Thermal behaviour of acrylonitrile copolymers having methacrylic and itaconic acid comonomers

Abstract The effect of comonomers, methacrylic (MAA 3–6 mol%) and itaconic acid (IA 2–3 mol%) on the glass transition temperature, T g , hydration melting and thermo-oxidative stabilization of acrylonitrile copolymers has been studied by differential scanning calorimetry (DSC). While, two T g ‘s were observed, near 70 and 140°C, for PAN homopolymer, copolymers showed another baseline shift below 70°C. The melting point, T m , of PAN and copolymer, P(AN/IA) containing 3.2 mol% of IA, has been reduced to 186 and 158°C, respectively, in high-pressure DSC. The copolymers showed two distinct melting peaks in the first heating cycle, but the melt on subsequent cooling exhibited a single exotherm due to crystallization. The melting point of IA copolymer (158°C) was found to be lower than that of MAA copolymer (164°C) and PAN homopolymer (186°C). T m further decreases with increase in the comonomer content. In the second heating cycle, observed T m is higher than that noted in the first heating run, indicating some amount of physical transformations. The enthalpy of fusion, Δ H f decreases with the incorporation of comonomers, e.g. it is maximum for PAN homopolymer (57.8 J g −1 ) and minimum for P(AN/IA) copolymer (26 J g −1 ) having 3.2 mol% of IA content. The lower entropy of fusion (Δ S f ) of copolymers indicates that they are less mobile in the molten state. DSC of copolymers run in air atmosphere, at a heating rate of 10°C min −1 , shows a broader exotherm compared to homopolymer. But, the broadening of exotherm seems to be more in P(AN/IA) polymers than P(AN/MAA) and the onset of cyclization shifts to a lower temperature as compared to PAN. The activation energy of nitrile cyclization, E a , for PAN is found to be 30 kcal mol −1 . For copolymer P(AN/IA), IA=3.2 mol%, E a is 18 kcal mol −1 .