Benzoxazolone Derivatives for PVC

Derivatives of benzoxazolone may provide useful heat stabilizers for PVC. During the thermal breakdown of PVC, the stabilizing effect of benzoxazolone can be observed in a reduction in an overall concentration of polyenes in the macromolecules, an increase in the induction period of formation of hydrogen chloride, and a reduction in the dehydrochlorination rate of the PVC. 

When /V-methacryloylbenzoxazoIone is introduced, the temperature at which thermal breakdown commences is raised by about 3()-40°C from the unstabilized compound. This compares with an increase of only about 1()°C when calcium stearate is used as the stabilizer. 

Experiments with other derivatives indicate that salts of benzoxazolone derivatives raise the thermo-oxidative decomposition temperature by about 15°C, depending on the nature of the metal of the salt and the presence of substituents in their molecules. Sodium and cobalt salts raise the level by about 2()°C. The stabilizing action of sodium and cobalt salts seems to be due to inhibition of free radical breakdown of the PVC by acceptance of the HCl formed, and replacement of the labile chlorine atom of PVC by benzoxazolone groups. 

Copolymerization of vinyl chloride with unsaturated benzoxazolone derivatives produces a copolymer belonging to the class of self-stabilized polymers. In comparison with PVC, these copolymers have increased thermo-oxidative stability. The maximum effect of stabilization is gained at a content of up to 2 mol%. 

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