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Mechanism of the initiation of changes by peroxides in polymers

R. Rado

Forschungsinstitut für Kabel und Isolierstoffe, Bratislava

 

Abstract: The 'cage effect' of the solvent mols. (Noyes, CA 48, 13372e) can account for changes in the rate of decompn. of (BzO)2 only in the gaseous state or in soln. In order to account for the decrease of its spontaneous and induction decompn. (CA 55, 20494i) in a medium of steadily increasing viscosity, it is necessary to consider the increased activation energy (20 kcal./mole BzO radical) which is needed for the effect of activated diffusion to come into play (CA 58, 7805c). This effect will permit the BzO radicals to dissoc. by overcoming the resistance of the surrounding segments of the polymer, and also (as a prerequisite for effective dissocn.) the escape of at least one BzO through the areas of amorphous polymer, that are limited by the ordered cryst. structures through which no diffusion at all can take place. The 2nd-order inductive decompn. of (BzO)2, by reaction with BzO radicals, goes on throughout all the stages of the polymerization in progress until its completion, because more and more free BzO radicals become available as the chain process of the polymerization comes to its end. On the other hand, the calcd. rate const. of the inductive reaction is 103 kg./mole. sec. and, when compared to the rate const. of the collisions through activated diffusion (105 kg./mole sec. even in highly viscous solns.), which control the progress of the polymerization, indicates that induction cannot be severely influenced by increasing viscosity. The same picture holds true for the chain formation in the mass of the solid polymer, in view of the much smaller rate of the effective collisions of the radicals with the hydrocarbon chains as compared to those of the addn. reaction. The phenomena assocd. with the peroxide-initiated polymerization are explained by assuming the diffusion of free (partly stabilized) radicals which also carry out the inductive decompn. of the peroxide. The suggestion that BzO radicals are formed only in the stage of the spontaneous decompn. of (BzO)2 and that they carry out their function without being liberated from the 'cage' (Haas, CA 56, 2558d) does not seem to be well founded, in view of the great probability of recombination of the radicals before collision to occur between them and the walls of the polymer cage. If any radical has to collide with the walls, it must lose its features as a member of the 'cage pair' and move through diffusion.

Full paper in Portable Document Format: 179a648.pdf (in Slovak)

 

Chemical Papers 17 (9) 648–655 (1963)

Tuesday, June 18, 2024

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