Patent GB-636323-A (GB)
Title: Polymerization of alpha-haloacrylic compounds
IPC: C08F20/22
Filed: 1946-07-01
Abstract: Colourless polymers suitable for use as optical media are produced by polymerization of an a -haloacrylic acid ester which has been prepared by dehydrohalogenating the corresponding ester of a dihalopropionic acid, containing at least one a -halogen atom, in the presence of 0.1-6.0 per cent of a polyhydric alcohol or a partial ester or ether thereof.  Specified polyhydric alcohols and their derivatives are glycol, glycerine, diethylene and trimethylene glycols, glycol monoacetate, monoacetin, diacetin, ethyl glycol monomethyl ether and glycol monomethyl ether.  Listed esters from which polymers of a -haloacrylic esters are prepared include the methyl, ethyl, propyl, butyl, amyl, p  isoamyl, n-hexyl, cyclohexyl, allyl, benzyl and furfuryl esters. Preferably dehydrohalogenation is effected by refluxing in an aqueous alkali or aqueous solution of a carboxylic acid salt, and the monomeric a -haloacrylic acid ester obtained from the reaction mixture by distillation.  If a polyhydric alcohol or derivative thereof with a high vapour pressure has been used the a -haloacrylic ester distilled contains a proportion of polyhydric alcohol and may be polymerized without rigorous exclusion of air.  Where the polyhydric alcohol has a low vapour pressure, e.g. glycerine, diethylene and trimethylene glycols, insufficient is present in the monomer distilled and polymerization is effected either under anaerobic conditions or a small amount, preferably 1-3 per cent of the monomer, of a monohydric alcohol, e.g. methyl, ethyl, propyl alcohols, is added to the distilled a -haloacrylic acid ester to react with any oxalyl halide formed subsequently, either before, during or after polymerization.  Specifications 527,494, 618,965, 636,318, 636,319, 636,321 and 636,322 are referred to.ALSO:Esters of a -haloacrylic acid from which colourless polymers suitable for use as optical media may be prepared are obtained by dehydrohalogenating the corresponding ester of a dihalopropionic acid, containing at least one a -halogen atom, in the presence of 0.1-6.0 per cent of a polyhydric alcohol or a partial ester or ether thereof.  Listed dihalopropionic acid esters are the methyl, ethyl, propyl, butyl, amyl, isoamyl, n-hexyl, cyclohexyl, allyl, benzyl and furfuryl esters of a ,a - or a ,b -dichloropropionic acids.  Specified polyhydric alcohols or their partial esters or ethers are glycol, glycerine, diethylene and trimethylene glycols, glycol monoacetate, monoacetin, diacetin, ethyl glycol monomethyl ether and glycol monomethyl ether. Preferably dehydrohalogenation is effected by refluxing the dihalopropionate and polyhydric alcohol or its derivative in presence of an aqueous alkali or solution of a carboxylic acid salt, e.g. sodium or potassium hydroxides, carbonates or bicarbonates, sodium or potassium acetates, alkali or alkaline earth metal salts of tartaric, lactic, citric, benzoic, salicylic, naphthalic, malonic and maleic acids.  The monomeric a -haloacrylic ester is obtained from the reaction mixture by distillation.  If a polyhydric alcohol or derivative thereof with a high vapour pressure has been used the a -haloacrylic ester distilled contains a proportion of polyhydric alcohol and may be polymerized without rigorous exclusion of air. Specifications 527,494; 618,965, 636,318, 636,319, 636,321 and 636,322, [all in Group IV (a)], are referred to.