Thermal degradation of polystyrene—5. Effects of initiator residues

The thermal degradation at sub-volatilisation temperatures of polystyrenes prepared with the radical initiators benzoyl peroxide and azoisobutyronitrile was studied. The plots of degree of degradation vs heating time show marked curvature in contrast to those of anionically and thermally polymerised polystyrenes. These plots were well simulated by a four-parameter equation which indicates that chain-scission occurs by at least three concurrent processess of markedly differing rates—rapid “weak link” scission, slow normal bond scission and scission at an intermediate rate. The last-mentioned appears to occur at ca one bond per polymer molecule. Neither these bonds nor the “weak links” have been identified but neither appears to be associated with end-groups.