Organic sulphur compounds are widely used in rubber industries as accelerator as well as curing agents. Not only do they influence the course of these reactions, but the presence of accelerator fragments in the finished product is important for its ultimate properties and in particular, the weathering property of the material.
In vinyl polymerization organic sulphur compounds are well known chain transfer agents and are often used for controlling mol. Wt. of the polymers. However their participation in polymerization reactions as initiators especially under irradiation has also been reported in the literature, though the detailed mechanism is not well understood in many cases.
Some of the important sulphur–containing photoinitiators includes alkyl and aryl disulphides, thiocarbamates, thiurams, mercaptans and thiols, sulfenates, chloro- sulfonamodes, etc. Of all these compounds, thiurams and disulphides have got relatively wider attention as photoinitiators in vinyl polymerization.
The lower electron affinity of the sulphur atom should lead to a higher energy, loose–bond, non–bonding electron pair in the sulphur atom. As a consequence transitions involving these electrons n -> ï°*, n -> ï³* etc. occur at higher wavelength than with oxygen containing analogs. It is thus possible to generate free radicals when irradiated with actinic radiation in the wavelength range 280–400 nm.
The prime objective of the present work is concerned with the photoinitiation of vinyl monomers using organic sulphur compounds containing mercaptobenzothiozole moiety. We have observed that these compounds are not only effective photoinitiators but they also incorporate the benzothiazole moieties in the polymer chains as end groups. In an attempt to explore this possibility of attaching end group in the polymer chain, to increase their antioxidant activity, a detailed kinetic and mechanistic study has been undertaken and selecting 2–mercaptobenzothiazole as photoinitiator. Experiments have also been carried out in presence of some additives such as benzoyl peroxide and solvents. The effect of some substitution has also been investigated using dicyclohexyl benzothiazole sulfenamide as photoinitiator.
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