Chain depolymerization 1064 / Subject

PBS (Figure 30) is an alternating copolymer of sulfur dioxide and 1-butene. It undergoes efficient main chain scission upon exposure to electron beam radiation to produce, as major scission products, sulfur dioxide and the olefin monomer. Exposure results first in scission of the main chain carbon-sulfur bond, followed by depolymerization of the radical (and cationic) fragments to an extent that is temperature dependent and results in evolution of the volatile monomers species. The mechanism of the radiochemical degradation of polyolefin sulfones has been the subject of detailed studies by O Donnell et. al. (.41). 

Since the equilibrium constants for the addition of monomer onto the sequence of length 1 or to longer sequences are so different, the following situation must be considered. The living sequences with two monomer units cannot split off a monomer unit, but higher sequences are subject to polymerization-depolymerization equilibria with an equilibrium constant which no longer depends on chain length. We consider the special case in which the equilibrium constant K2 and the constants... 

Organic insulating materials are generally subject to temperature dependent deterioration during their operational lifetime. The relevant chemical processes are complicated and may be described (with a certain simplification) as slow oxidation which introduces acid groups into the polymeric insulation, the loss of plasticizer, oxygen cross-linking of polymer chains and internally catalysed depolymerization of plastic insulation. 

There has been a slight increase in activity in this area compared with that in the previous two year period. For the polymeric esters of acrylic, methacrylic acids, and related polymers the simplest reaction, apart from thermal depolymerization, is hydrolysis, and one or two papers on this subject have appeared. One of these concerns a comparison of the kinetics of hydrolysis of a number of methacrylate esters and a further two deal with the formation of copolymers containing carboxylic acid functions. Methyl trifluoroacrylate forms alternating copolymers with cE-olefins (ethylene, propylene, isobutylene) and these are readily hydrolysed in boiling aqueous methanolic sodium hydroxide to yield hydrophilic fluoropolymers. Hydrolysis is reported to be nearly quantitative with no chain scission. An alternating copolymer is also formed by radical polymerization of maleic anhydride with A-vinyl succinimide. On hydrolysis this copolymer is... 

Polyolefin melts under excessive loads are subject to mechanically and oxidatively activated chain cleavage. Polyolefins do not depolymerize. Polyethylene and polypropylene are relatively insensitive to purely thermal degradation, but react easily with oxygen and radicals. Under mild conditions and the presence of oxygen, oxidation is preferred to thermal degradation due its lower level of activation energy (oxidation PE approx. 96 kj/mol vs. thermal degradation PE approx. 264 kj/mol) [20]. 

---