Thermal behavior of acrylonitrile carboxylic acid copolymers

Polyacrylonitrile (PAN) and copolymer of acrylonitrile-vinyl acids prepared by solution polymerization technique have been characterized by Differential Scanning Calorimetry (DSC) (under dynamic as well as isothermal conditions), themograviemetric analysis (TGA), and on-line DSC-FTIR spectroscopy. The DSC of copolymers was carried out at 5degreesC/min in nitrogen and air. In nitrogen atmosphere the DSC exotherm show a very sharp peak, whereas, in air atmosphere DSC exotherm is broad, and starts at a much lower temperature compared to what is observed in nitrogen atmosphere. The initiation temperature of PAN homopolymer is higher than that for the copolymers. For instance, the initiation temperature of PAN in air is 244degreesC, whereas, the onset of exothermic reaction is in the range of 172 to 218degreesC for acrylonitrile-vinyl acid copolymers. As the vinyl acid content increases the DeltaH value reduces. The DeltaH value of PAN in air was 7025 J/g, whereas, for P(AN-AA) with 5.51 mol % of acid it was 3798 J/g. As the content of acrylic acid comonomer is increased to 17.51 mol % the value of DeltaH decreases further to 1636 J/g. The same trend was observed with MAA and IA as well. DSC-FTIR studies depict various chemical changes taking place during heat treatment of these copolymers. (C) 2003 Wiley Periodicals, Inc.