Densities and viscosities were measured as a function of temperature for 12 esters of glycolic, dl-lactic, and dl-malic acids and linear chain alcohols C1–C5. The density and kinematic viscosity were obtained using a pycnometer and a Pinkevitch capillary viscometer in a temperature range of 293.15–363.15 K with accuracies of 0.1 and 0.35%, respectively. The obtained data were used for dynamic viscosity calculation. It was demonstrated that the viscosity–temperature dependence of esters was described by the ASTM D341 model with an average absolute relative deviation of 1%. The temperature dependence of dynamic viscosity was fitted using the Arrhenius-like equation and Vogel–Fulcher–Tammann (VFT) model. It was found that the adjustable parameters A and B have the similar value for compounds in one homologous series. These parameters were taken as constant for each series of esters of the corresponding acids. The dynamic viscosity–temperature dependence of esters was better described by the VFT model than the Arrhenius-like equation. The capabilities of some group-additivity methods for predicting density have been reviewed and compared with experimental results.

Objectives. The study aims to identify the optimal choice of an effective catalyst for the esterification of malic acid to produce esters of high purity. Methods. To determine the qualitative and quantitative composition of reaction masses, the following analysis methods were used: mass-spectroscopy (using FinniganTrace DSQ device with NIST 2002, Xcalibur 1.31 Sp 5 database) and gas–liquid chromatography (using the Kristall 2000M software and hardware complex). Results. Esters of malic acid and butyl alcohol of normal structure were synthesized using the following catalysts: sulfuric, orthophosphoric, p-toluenesulfonic acid, Amberlyst 36 Dry, Amberlyst 36 Wet, KU-2-FPP, and KIF-T. The obtained products were analyzed by gas–liquid chromatography. The structure of the products was confirmed by mass spectrometry. Schemes for the formation of byproducts are proposed. The yields and purity of the malic acid butyl esters obtained using different catalysts were evaluated. The results show that the heterogeneous catalyst Amberlyst 36 Dry is optimal for obtaining a pure malic acid ester with a maximum yield. Conclusions. The results show that during the esterification of malic acid with butyl alcohol of normal structure, byproducts, such as esters of fumaric and maleic acids, are formed using different catalysts. An accumulation of byproducts occurs as a result of reactions of dehydration of malic acid or its ester. The results also show that the number of byproducts is almost independent of the catalyst, with the exception of sulfuric acid. The Amberlyst 36 Dry catalyst provides an optimal ratio between conversion and selectivity for malic acid dibutyl ester production.

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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.