ANALYSIS OF POLYESTERS STRUCTURE BASED ON MALIC ACID AND ITS ESTER

Abstract

Four polyesters based on malic acid and its dibutyl ester were obtained. Ethylene glycol and 1,4-butanediol were used as comonomers. The reaction of polycondensation was carried out without a catalyst, and the transesterification of glycol esters was carried out in the presence of tetrobutoxytitanium in an amount of 1wt%. The malic acid during polycondensation we melted and dissolved in glycols at a temperature of 100 °C to prevent the reaction of intramolecular dehydration. The reactions were carried out for 3 hours with stirring and gradual heating of the reaction mass. The processes were carried out in a flow of nitrogen to remove the formed low-molecular products. These products were condensed and analyzed by gas-liquid chromatography. The control of the polycondensation reaction was carried out by the molecular weight determined by the viscometric method. The structure of the obtained polyesters was determined using IR and (1H, 13C) NMR spectroscopy. The obtained polymer samples represent a resinous mass from light yellow to light brown with average molecular weights from 2000 to 4000 g/mol. Analysis of IR spectra showed that in the samples obtained by ester transesterification, the intensity of the hydroxyl group band is more than that of acid and diol based polymers. This difference can be explained by the presence of polymer chain branches obtained as result of the reaction of self-condensation. Analysis of (1H, 13C) NMR spectra confirms that in the process of polycondensation of malic acid with diols, a side reaction of self-condensation of the acid occurs with the formation of branched polymer units. In the case of the use of an ester as a monomer, polyester of a linear structure is obtained. In all obtained samples of polyesters, the presence of unsaturated bonds in the structure was also observed. This confirms that a side reaction of internal malic acid dehydration took place under the synthesis conditions. To reduce the unsaturation of polyesters, the polycondensation process must be carried out at a lower temperature.