Degradation of addition polymers

It is shown in Ms article that such parameters as intramolecular cycHzation, sterk effects, and resonance stabilizalim can most satisfactorily explmn the yields of monomers in thermal degradation of addition polymers. 

Scheme 4.1 General mechanism for the thermal degradation of addition polymers.

Scheme 4.1 shows a general mechanism proposed by Stivala et al.15 for the thermal degradation of addition polymers with the following steps ... 

Mostafa, M. A. The degradation of addition polymers by ultrasonic waves. 2. J. Polym. 

All known eight-stranded a/p-barrel domains have enzymatic functions that include isomerization of small sugar molecules, oxidation by flavin coenzymes, phosphate transfer, and degradation of sugar polymers. In some of these enzymes the barrel domain comprises the whole subunit of the protein in others the polypeptide chain is longer and forms several additional domains. An enzymatic function in these multidomain subunits, however, is always associated with the barrel domain. 

Copper alloys are particularly prone to attack by long-chain fatty acids which are often present in sealing compositions, temporary protectives and as trace additives in many plastics under acid conditions ester plasticisers may saponify in the presence of copper giving rapid corrosion of the copper and accelerating degradation of the polymer. 

Bhuiyan, A. L. Some Problems Encountered with Degradation Mechanisms of Addition Polymers. Vol. 47, pp. 1 —65. 

Organotin compounds are important industrial chemicals. One major use is as stabilizers for poly(vinyl chloride) (PVC) plastics. These additives, one example of which is dioctyltinmaleate, inhibit degradation of the polymer by heat, light, and oxygen. In the absence of these tin compounds, PVC yellows and becomes brittle. 

When similar photolysis of 11 in the presence of MeOD was carried out, again the product whose NMR reveals the resonance due to the Si-H proton was observed. The relative ratio of the Si-H and CH3-0 protons was identical with those of the products obtained in the presence of non-deuterated methanol. The formation of the methoxysilyl group can be understood by the addition of methanol across the silicon-carbon double bonds. H NMR spectra of all photoproducts obtained from the photolyses of 11 in the presence of methanol reveal no resonances attributed to the cyclohexadienyl ring protons. This indicates that the photochemical degradation of the polymer 11 gives no rearranged silene intermediates, but produces... 

As discussed in Chapter 10, a wide variety of additives is used in the polymer industry. Stabilizers, waxes, and processing aids reduce degradation of the polymer during processing and use. Dyes and pigments provide the many hues that we observe in synthetic fabrics and molded articles, such as household containers and toys. Functional additives, such as glass fibers, carbon black, and metakaolins can improve dimensional stability, modulus, conductivity, or electrical resistivity of the polymer. Fillers can reduce the cost of the final part by replacing expensive resins with inexpensive materials such as wood flour and calcium carbonate. The additives chosen will depend on the properties desired. 

To resolve this dilema, we propose that the polymer is interacting with the additive in the excited state, (27) perhaps via electron transfer, and that this interaction leads to the irreversible degradation of the polymer. The direct interaction of photoexcited monomeric polysilanes with halogen derivatives resulting in the cleavage of Si-Si bonds had been reported (28). In a similar fashion, we must conclude either that this interaction does not occur with the alkyl silane polymers or that it does not result in rapid polymer degradation. 

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