Thermal degradation intramolecular cyclization

All of tl products l,3 triphenylbenzene, 1,3-diphenylpropane, 1,3,5-triphenylpen-tane, ethylbenzMie, methylben2 ne, and styrene are volatile products of thermal degradation of polystyrene This kind of intramolecular cyclization is not likely to be important in thermal degradation of poly(methyl methacrylate) and poly(a-methylstyrene), because the reactive site is linked to two bulky substituents which restrict the rotation of the terminal carbon atom containing the unpaired electron and thus prevent it from coming into proper orientation to attack the other carbon atoms in the chain. 

It may, therefore, be concluded that such parameters as intramolecular cyclization, intramolecular hydrogen abstraction, steric effects, and resonance effect can most satisfactorily explain the yields of monomers in thermal degradation of polyolefins. Unfortunately, excq)t for hydrogen abstraction, three otiier parameters have not been taken into consideration in deducing expressions of rate constants for diermal d adation of polyolefins. The resonance effect should influence the activation energy of the degradation reaction and the steric effects are more prominent in the frequency factors of the rate constants ... 

It is shown in this article that such parameters as intramolecular cyclization, steric effects, and resonance stabilization can most satisfactorily explain the yields of monomers in thermal degradation of addition polymers. 

PAN homopolymer fibers are also used to produce carbon fibers utilized in composite materials. The process involves a controlled thermal degradation that begins with an intramolecular cyclization... 

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