Carbon Dioxide → Terephthalic Acid

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4.8 g of isophthalic acid and 33.6 g of trimellitic acid are added at room temperature to 419 g of a solution of N,N'-bis-[methoxy carbonyl propyl-(2)-]-4,4'-diaminodiphenyl methane in a mixture of 36% by weight of γ-butyrolactone and 64% by weight of toluene (29.2% N), followed by the addition at 50° C. of 204 g of 4,4'-diisocyanatodiphenylmethane. After stirring for 2 hours at 50° C., another 87.4 g of 4,4'-diisocyanatodiphenyl methane and 0.6 g of endoethylene piperazine are added at 50° C., followed by homogenisation for 1 hour at 50° C. Then another 201.2 g of trimellitic acid anhydride and 120 g of terephthalic acid dimethyl ester are added to this solution in portions at 50° C., followed by homogenisation for 30 minutes at 50° C. The suspension obtained is left standing overnight at room temperature and, on the following day, is heated to 205° C. with elimination of carbon dioxide, methanol and toluene, maintained for 3 hours at 205° C. and, then, for 1 hour at 215° C. 218.8 g of terephthalic acid dimethyl ester are then added at from 170° to 180° C., followed by the addition at from 150° to 160° C. of 318 g of N,N',N"-tris-hydroxyethyl triazolidine-3,5-dione, 1.8 g of lead acetate and 0.6 g of titanium tetrabutylate. The mixture is then heated for 2 hours to 170° C. Then 30 g of xylene and 160 g of a polyester produced from 4 moles of terephthalic acid, 1.5 moles of glycerol and 3 moles of glycol (OH-content 4.53%, acid number 4.8 mg KOH) are added at from 160° to 170° C., after which the mixture is again subjected to condensation for 3 hours at from 200° to 220° C. first directly and, finally, in vacuo until a sample diluted to 50% by weight with γ-butyrolactone has a viscosity of approximately 10,000 mPa.s at 25° C. 1501 g of a brittle, approximately 80% by weight resin are obtained, of which a 15% by weight solution in γ-butyrolactone has a viscosity of 156 mPa.s at 25° C.

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