Various Comonomers in Acrylonitrile BasedCopolymers: Effects on Thermal Behaviour

Identification of suitable comonomers and achieving their optimum molar contentsare the main objectives of this investigation, in which, a series of acrylonitrile (AN)copolymers were synthesized with comonomers (AN/M), such as methyl acrylate(MA), vinyl acetate (VAc) and acrylamide (AM) by aqueous precipitationcopolymerization. The molar feed contents of the comonomers were 5-25 mol%. Thecopolymers were characterized by using Fourier transform infrared spectroscopy,nuclear magnetic resonance (1H NMR), differential scanning calorimetry, thermogravimetry(TG) and X-ray diffraction (XRD) analyses. 1H NMR studies revealed thatthe compositions of AN/MA agreed best with the feed molar ratios. Differential scanningcalorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) results showedthat the effect on delaying cyclization reactions, depression of melting points andcrystallinities, all ranged in the order MA VAc AM for various types of comonomers.With comonomer contents increasing, it was interesting to note that the decompositiontemperature of AN/MA shifts continuously to higher temperatures. With increasedcomonomer content, the decomposition temperature of AN/VAc is initially increasedand then decreased. For AN/AM, it shows an opposite trend to that of AN/VAc.Incorporating 15 mol% of MA, melting peak value (Tm) and crystallinity of the AN/MAdrop to the lowest values of 174°C and 18.5%, respectively. The decomposition peakvalue (Td) of AN/MA with the feed molar ratio of 85/15 increases to 321°C. There is awider window of 147°C for melt processing of AN/MA. It is concluded that MA is themost suitable comonomer for enhancing the melt processing of PAN basedcopolymers.