Intramolecular back-biting mechanism

Probabilities of configurations conducive to the intramolecular back-biting abstraction of a hydrogen atom are evaluated for growing unperturbed PVAc chains. A realistic RIS model is used for the chain statistics, Probabilities are found to be smaller than those seen in an earlier treatment of the polyethylene chain. The smaller probabilities of PVAc contribute to the virtual absence of short branches. The present study therefore provides support for the validity of the Roedel mechanism for the formation of short branches in the free radical initiated polymerization of ethylene. 

Polystyrene represents a case in which monomer is only one of several spedes formed by thermal degradation at 350°C as monomer, dimer, trimer, and tetramer are formed in the relative proportions of 40 10 8 1. The thermal breakdown process is beheved to begin at unsaturated linkages which constitute the weak points along the chain. A cleavage at these sites initiates a fi-ee-radical mechanism leading to liberation of monomer and to an intramolecular back-biting process. The process Kberates dimer, trimer, and so on, by a transfer mechanism such as the shown in Equation 1.60... 

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