Cellulose derivative compositions

A cellulose derivative composition comprises a cellulose carboxylic-acid ester or cellulose ether plasticized with the sole aid of a liquid condensation polymer of ethylene glycol and phthalic acid, said polymer cotaining a predominating molar proportion of the glycol residue and having an average molecular weight (as determined chemically) between 500 and 1,500. The polymer may be made by reaction between ethylene glycol and phthalic anhydride or phthalyl chloride, or by ester exchange polycondensation between ethylene glycol and an ester of phthalic acid, e.g. dimethyl phthalate. Preferably phthalic anhydride and glycol are heated together at a temperature not exceeding 260 DEG C. at atmospheric pressure for a period not exceeding 8 hours. The proportion of glycol to anhydride may be in the molar ratio range of 1.5 : 1 to 2.5 : 1. Provision is made for distilling off excess of glycol. The average molecular weight of the polymer is determined chemically from the acid-equivalent and the ester-equivalent. According to a modification, the composition may comprise, as sole plasticizer of the cellulose ester or ether, a liquid condensation polymer of 1, 2, 5, 6- tetrahydrophthalic acid and ethylene glycol, this polymer also having a predominating molar proportion of the glycol residue and having an average molecular weight between 500 and 1500. In an example of the production of the polymer, ethylene glycol and phthalic anhydride in molar proportions of 2:1 are heated at atmospheric pressure to 260 DEG C. for 8 hours. The product is boiled with water until the washings are neutral and then dried. It is purified by dissolving in chloroform, filtering, and then evaporating the chloroform from the solution. The product has a viscosity characteristic of 1.56 centistokes for a 20 per cent. solution in chloroform at 20 DEG C. In another example, ethylene glycol and dimethyl phthalate in molar proportions of 2:1 are heated at 190 DEG C. for 9 hours at atmospheric pressure, and then for 3 hours at 250 DEG C. under a pressure of 2 mm. Alternatively the reaction mixture is heated at 190 DEG C. under a pressure of 100 mm. in an atmosphere of nitrogen and in presence of 0.5 grams per mole of potassium carbonate until methanol ceases to distil. an example of making the composition, cellulose acetate of acetyl value, calculated as acetic acid, of 52-54 per cent. and 30 per cent. of its weight of an ethylene glycol-phthalic anyhdride condensation polymer are dissolved in ace