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It is evident from the titles of the two previous papers and from papers given at recent conferences 1] that there is renewed interest in the thiol-ene reaction. Whilst the chemistry of acrylates and methacrylates still serves the coatings industry well there is as search for other polymerisable systems that may offer some advantages. Undoubted attractions of the thiol-ene reaction include its apparent insensitivity to the presence of oxygen and relative humidity as well as he speed of the reaction. Other useful aspects include the facility to cure thick sections and to carry out cure in the absence of photoinitiator. When one considers this list of positive aspects one is led to ask 'Why isn't the use of the thiol-ene reactiom more widespread?" 2]. The thiol-ene reaction was introduced in the 1970's 3] and at that time the thiols available were characterised by a strong unpleasant odour which created problems for handling the materials in the workplace. This problem has been addressed and a number of multifunctional low-odour thiols are now commercially available 4]. Cost is clearly an issue but the properties of the thiol-ene reaction would suggest that it should find application in those areas where problems are encountered with
the classical (meth)acrylate systems such as adhesion to metals plastics and glass. The main issue appears to be the stability of formulations with shelf lives varying enormously form a few seconds to months.