Kinetic chain length scission

The primary photolytic reactions postulated are not themselves self-propagating, but provide the variety of radical species involved in subsequent oxidation and chain scission reactions characteristic of PET. The extent of oxidation reaction will depend in part on the balance of scission reactions in the initial process. Once established, the autoxidation cycle has a very long kinetic chain length, and will result in a rapid build-up of hydroperoxide in the polyester. 

If the reaction is initiated by random scission and the kinetic chain length is long, long chains have a greater probability of scission and are removed completely as monomer. In this case, the mass of polymer falls, and the average molecular weight decreases. Also, the molecular weight distribution narrows. 

The reduced molecular weight of the irradiated sample is less than the average kinetic chain length for the non-irradiated sample, hence for a given scission, less product is evolved and the stability is increased. 

The amplified tension caused by adsorption of side chains can lead to the scission of covalent bonds in the backbone once it exceeds their strength. We have shown that the C-C bonds in poly(2-hydroxyethyl methacrylate) backbone with long poly(n-butyl acrylate) (PBA) side chains mptured spontaneously uprm adsorption onto an aqueous substrate (Fig. 9) [126]. The kinetics of backbone scission was followed by monitoring the average contour length by AFM as a... 

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