Thermal degradation of poly(α‐methyl styrene) in a closed system

Poly(α‐methyl styrene), produced in various ways, was degraded in a closed system over a range of temperatures from 260 to 320°C. in the absence of air. Except for the initial parts of the degradation reaction (up to about 20% conversion to monomer), all samples had a random initiation reaction, followed by a depropagation step with a number‐average kinetic chain length larger than the number‐average polymer chain length. The energies of activation, after the initial part of the degradation, were all of similar magnitude (ca. 63 kcal./mole) and agreed with values found by previous workers. A few samples showed distinct maxima during the first 20% conversion in their curves of rate of monomer versus conversion, whereas others showed only constant rates or slowly decreasing rates during the initial periods of the reaction. The latter rates can be accounted for by chain‐end initiation (kinetic chain length ≫ polymer chains) or by a random initiation process followed by depropagation and disproportionation as termination reaction. The initial maxima found in some samples could be accounted for by a theory of random initiation in conjunction with a number‐average kinetic chain length larger than the polymer chains, which is inhibited by a reaction of polymer radicals with catalyst fragments. The inhibitor is consumed during the reaction.