Thermal behaviour of acrylonitrile copolymers having methacrylic and itaconic acid comonomers

The effect of comonomers, methacrylic (MAA 3-6 mol%) and itaconic acid (LA 2-3 mol%) on the glass transition temperature, T-g, hydration melting and t hermo-oxidative stabilization of acrylonitrile copolymers has been studied by differential scanning calorimetry (DSC). While, two T-g's were observed, near 70 and 140 degreesC, for PAN homopolymer, copolymers showed another b aseline shift below 70 degreesC. The melting point, T-m, of PAN and copolym er, P(AN/IA) containing 3.2 mol% of IA, has been reduced to 186 and 158 deg reesC, respectively, in high-pressure DSC. The copolymers showed two distin ct melting peaks in the first heating cycle, but the melt on subsequent coo ling exhibited a single exotherm due to crystallization. The melting point of LA copolymer (158 degreesC) was found to be lower than that of MAA copol ymer (164 degreesC) and PAN homopolymer (186 degreesC). T-m further decreas es with increase in the comonomer content. In the second heating cycle, obs erved T-m is higher than that noted in the first heating run, indicating so me amount of physical transformations. The enthalpy of fusion, DeltaH(f) de creases with the incorporation of comonomers, e.g. it is maximum for PAN ho mopolymer (57.8 J g(-1)) and minimum for P(AN/IA) copolymer (26 J g(-1)) ha ving 3.2 mol% of LA content. The lower entropy of fusion (DeltaS(f)) of cop olymers indicates that they are less mobile in the molten state. DSC of cop olymers run in air atmosphere, at a heating rate of 10 degreesC min(-1), sh ows a broader exotherm compared to homopolymer. But, the broadening of exot herm 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 activatio n energy of nitrile cyclization, E-a, for PAN is found to be 30 kcalmol.For copolymer P(AN/IA), IA = 3.2 mol%, E-a is 18 kcal mol(-1). (C) 2000 Elsevi er Science Ltd. All rights reserved.