City Research Online

Abstract

Free-radical polymerization processes are used in the surface coatings industries.

One of the main problems with the free-radical as opposed to the ionic process is the oxygen inhibition of cure. The latter can be attributed to oxygen scavenging the growing polymeric radicals, scavenging the radicals derived from the photoinitiator or quenching an excited state of the initiator.

Oxygen inhibition can be minimised by incorporating amines into the formulation.

These materials yield radicals which rapidly and efficiently scavenge oxygen, thus depleting the oxygen in the curing layer.

If cure is sufficiently fast, the amine may be able to deplete oxygen at a rate which is greater than the diffusion into the film. A more recent way of overcoming oxygen inhibition, as yet unproved in thin films, is that of the use of sulphur-containing compounds.

Sulphides will transform peroxy radicals into alkoxy radicals (which can initiate polymerization) and reduce hydroperoxides to alcohols. This leads on to the next piece of work which involves regeneratable photosensitisers. Previous work carried out at City University has shown that 2,3 - diphenylquinoxaline, when used in conjunction with a amine is quite a remarkable, if not unique photosensitiser. Through careful work of Moran, as yet unpublished, it was shown that the use of this sensitiser leads to surface cure and hence may find application in 3D - imaging. Current thinking on the mechanism of reaction involves its continuous regeneration by reaction with oxygen.

Various u.v./visible range photoinitiators were prepared:

(i) cyanine borates (ii) cyclopentadienyliron (II) alkylborates and (iii) diazonium salts to show the effect of oxygen on the rate of polymerization.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QD Chemistry
Departments:	School of Science & Technology School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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