Thermal degradation studies of methacrylonitrile polymers and copolymers—3. Polymers capable of chain end-initiated colouration

Polymethacrylonitrile (PMAN) prepared by free-radical polymerisation with the initiator 4,4′-azo-bis(4-cyanovaleric acid) (ACVA) has chain ends from the initiator fragment which incorporate carboxyl groups. These ends are found to act as reactive sites for initiation of colouration in the polymer at temperatures from 140 °C. Several polymers, with different chain-end concentrations, have been made and the thermal degradation behaviour has been studied under programmed heating in the absence of air to 500 °C, with full product characterisation. In contrast with pure PMAN prepared with 2,2′-azo-bis(isobutyronitrile) (AIBN) as initiator, which degrades quantitatively to monomer, these ACVA-initiated polymers give very much reduced monomer yields, an important tar/wax fraction and a substantial amount of residue, amounting to 32–48% of the sample weight, dependent on the initial molecular weight of the polymer. The infrared spectral changes at the onset of the colouration reaction have been examined at 160 °C. Mechanisms are suggested to account for the observed products.