GB639918A - The production of articles of synthetic resinous materials - Google Patents

Abstract

Articles such as optical elements, rods and sheets are made by photopolymerizing in a mould a previously prepared partially polymerized syrup, the syrup containing a light activated polymerization catalyst but substantially no heat activated polymerization catalyst which is effective at any temperature reached during the polymerization of the syrup to the solid state and the syrup being prepared by partially polymerizing by heat one or more polymerizable liquids containing one or more CH2=C< groups in the presence of an aliphatic thiol or a compound obtained by oxidizing it to any state below the maximum normal valency state of sulphur but in the absence of any substance which is an active heat polymerization catalyst at any temperature reached during the light polymerization of the syrup to the solid stage. In a modification the syrup is prepared in the presence of a heat polymerization catalyst, the nature and amount of which is such that its activity is destroyed during the preparation of the syrup. Catalysts specified for use in the modification are alpha, alpha1-azodiisobutyronitrile; dimethyl and diethyl alpha, alpha1-azodiisobutyrates; alpha, alpha1-azodicyclohexane-carbonitrile; alpha, alpha1-azobis (alpha-ethyl butyronitrile) and alpha, alpha1 - azodiisobutyrocarbonamide. Specified monomers are methyl and cyclohexyl methacrylates. Suitable aliphatic thiols are monothioglycol, lauryl mercaptan, octyl mercaptan and 2-ethyl hexyl mercaptan. Suitable photopolymerization catalysts are benzoin, acetoin, butyroin, benzoin ethyl ether and diacetyl. The solid obtained by photo-polymerization may be subjected a heat treatment. Specifications 579,353 and 626,155 are referred to. The Provisional Specification also specifies as suitable monomers esters of methacrylic acid with fluorinated alcohols.