s and aryloxyaralkylketones ; - any of the above groups comprising at least one hydrocarbyl group or a divalent hydrocarbon group R 1 , wherein said hydrocarbyl group or said R 1 is itself substituted by at least one of the above listed monovalent substituting groups, e.g. an arylketone -C(=O)-R, where R is an aryl group substituted by one hydroxyl group ; where : - the hydrocarbyl groups contain