GB779291A - Process for the production of polyesters of high molecular weight - Google Patents

Abstract

Polyesters are made by polymerizing optically active lactic acid or a polylactide-forming derivative thereof (e.g. lactide or an ester of lactic acid with a monohydric alcohol) which contains not more than 20 per cent of the oppositely rotating component. The resulting polylactides are optically active and have a higher molecular weight (e.g. greater than 5000) and a higher melting point (e.g. 90-140 DEG C. or higher) than previously known polylactides. Polymerization is effected at 100-250 DEG C., preferably in the absence of oxygen and may be effected in presence of a solvent or entraining agent, e.g. benzene or toluene. When polymerizing lactic acid, catalysts which may be used are sodium bicarbonate, magnesium oxide, zinc oxide, lead oxide, zinc, lead, lead acetate, p-toluene sulphonic acid, sulphuric acid or boric acid. When polymerizing lactide, catalysts which may be used are metals of the 2nd sub-group or the 4th main group of the periodic system or their oxides, hydroxides, acetates, lactates or carbonates; also magnesium, magnesium oxide, titanium dioxide, lanthanum oxide, antimony oxide, bismuth acetate, uranyl acetate, manganese lactate, p-toluene sulphonic acid, halides of metals of the 2nd sub-group of the periodic system or bicarbonates of metals of the 1st main group of the periodic system. When polymerizing lactides, small amounts of free acids (e.g. lactic acid) or trivalent or higher valent metals (e.g. aluminium, chromium or manganese) or their salts (e.g. aluminium lactate) may be added in addition to the catalyst (e.g. lead oxide). Polymerization of the lactic acid or polylactide-forming derivative may also be effected in presence of other polyester forming components (e.g. glycollic acid, glycollide or adipic acid and ethylene glycol) or chain-breaking agents (e.g. benzoic acid, cyclohexylamine or glycerine). The crude polylactide may be purified or separated from low molecular weight material by an extraction method or by dissolving it in a solvent, e.g. chloroform and precipitating the pure polylactide by adding cold methanol. Some of the polylactides are soluble in chloroform, methylene chloride, acetone, toluene or benzene. They may be used in the manufacture of coating materials, moulded articles and foils and may be modified with drying oils, furfural or trivalent or higher-valent metal salts. Specification 755,447 is referred to.