The method of determining the content of hydroxyl groups in the epoxy resin

 

(57) Abstract:

The invention relates to the analysis of epoxy resins, namely the determination of hydroxyl groups in the epoxy resins. The method includes processing the resin in the 0.1-0.2 M solution of maleic anhydride in ethyl ketone in the presence of a catalyst in the form of 0.5-1 M solution of triethylamine in ethyl ketone at elevated temperatures, hydrolysis of unreacted anhydride and potentiometric titration with alkali. Improved accuracy and reproducibility of the determination, the reduction of energy consumption and acceleration analysis. table 2.

The invention relates to the analysis of epoxy resins, namely the determination of hydroxyl groups in the epoxy resin, and can be used to assess the quality epoxy resins.

Known methods for determining the hydroxyl groups spectrophotometric methods [Kalinina L. S. , Motorina M. A., Nikitina N. And., Khachapuridze N. A. The analysis of the condensation polymers. - M.: Chemistry. 1984. 296 C.]. Methods a long, laborious and give poorly reproducible results.

The closest technical solution definition hydroxyl groups in the epoxy resins that are selected in the anhydride in pyridine, catalyzed by sulfuric acid, followed by hydrolysis of unreacted parts of acetic anhydride with water and determining the formed acetic acid by titration with alkali indicator check the equivalence point [Plastic. Methods of determining the content of hydroxyl groups in the epoxy resins and epoxydecane connections. GOST 17555-72].

Known prototype method has the following disadvantages:

1. Along with the hydroxyl groups in the process of acetylation in response enter an epoxy group, thus to calculate the required values, you first need to determine the content of epoxy groups in the resin, which significantly reduces the accuracy and reproducibility of the analysis results, and for low molecular weight resin (the content of hydroxyl groups is less than 1%) method is not applicable due to the high ratio of epoxy and hydroxyl equivalents.

2. The volatility of acetic anhydride in the acetylation process necessitates the careful sealing of the reactor space in order to avoid losses, which complicates the course of analysis.

3. The reaction is carried out for a long time at a temperature of 100oC, which leads to a large saving is shown by the solvent.

Object of the invention is to provide a method for determining the content of hydroxyl groups in the epoxy resins, which will improve the accuracy and reproducibility of the determination, including low molecular weight resins, due to elimination reaction of the epoxy groups in the process of interaction anhydride with hydroxyl groups, to ensure the safety of work due to the substitution of pyridine to a less toxic solvent, and allow to reduce energy consumption and analysis time.

The solution of this problem is achieved by the proposed method of determining the content of hydroxyl groups in the epoxy resins, including the processing of resin solution by the excess of the anhydride of the organic acid in the presence of a catalyst at elevated temperature, the hydrolysis of unreacted anhydride and definition formed from acid by titration with alkali, in which the processing of the resin is carried out in the 0.1-0.2 M solution of maleic anhydride in ethyl ketone, as catalysis torus using 0.5-1.0 M solution of triethylamine in ethyl ketone and titration with alkali carried out potentiometrically.

Experimentally set the I for the esterification of hydroxyl groups of the epoxy resin is selected by minimizing the consumption of titrant during the titration of the control sample and the excess anhydride after the reaction with hydroxyl groups, as well as taking into account the neutralization of part of the resulting maleic acid catalyst with triethylamine. To minimize the consumption of titrant provides high accuracy and reproducibility of the determination by automatic potentiometric titration. The molar ratio of the catalyst to maleic anhydride of 1:2 provides complete binding of 0.1-0.4 equivalents of hydroxyl groups of 1 mol of maleic anhydride. The reaction is carried out for 20 min at 70oC. Hydrolysis of maleic anhydride in its mixing 0.2 M solution in methylethylketone with water 1:3 by volume at 20oC runs completely within 2 minutes In the determination of hydroxyl groups in the epoxy resin with a mass fraction of epoxy groups is less than 15% to avoid the formation of gel-like sludge treatment of the sample with a solution of maleic anhydride is carried out in the presence of dimethyl sulfoxide (volume 1 to 5 volumes of a solution of maleic anhydride in ethyl ketone).

Based on the results of potentiometric titration in the determination of hydroxyl groups in the epoxy resins with different content of epoxy groups found that epoxy groups do not react in the process of interaction anhydride with My standard methods, and also the comparison of the results of determination of the linear dependence of the concentrations of hydroxyl and epoxy groups with mass fraction last 8-24,5 % in epoxy resins [Li X. K. Neville reference guide for epoxy resins.- M: Energy. 1973, 416 S.].

This dependence is calculated by the method of least squares [Bulatov, M. I. , Kalinkin I. P. a Practical guide photocolorimetric and spectrophotometric methods of analysis.- L., Chemistry. 1968. 384 C.], is:

COH=(-3,730,21)Cepoxy+(25,650,55);

SrOH=0,19,

where COHand Cepoxy- mass fraction, respectively, hydroxyl and epoxy groups in the epoxy, %,

SrOH- the standard deviation in the determination of hydroxyl groups.

Table. 1 illustrates a satisfactory convergence results define two independent methods. Titration of alkali can be accomplished with the use of indicator bromophenol blue, but in this case, the detection error is higher than the potentiometric titration, and comparable to those of the method of acetylation (prototype).

Examples of carrying out the invention

Example 1. Determination of hydroxyl GRU is g dissolve in a conical flask with a capacity of 250 ml in 10 ml of 0.1 M solution of maleic anhydride in ethyl ketone, add 1 ml of 0.5 M solution of triethylamine in ethyl ketone, covered with aluminium foil and incubated in a heating Cabinet 20 min at the temperature (702)oC. the Solution is cooled to room temperature, add 30 ml of water, stirred for 2 min and titrate with 0.1 M solution of KOH in water potentiometric method on autotitrator with glass and calomel electrodes in the mode that provides the maximum precision of the titration results: the feed rate of the titrant 5 ml/min; increment 0.1 ml; offset (threshold value changes the feed rate of the titrant) 0 mV/ml; factor deceleration (dimensionless quantity, controlling the feed rate of the titrant depending on the magnitude of the signal changes) of 0.5. The determination results are presented in table. 2.

Example 2. Determination of hydroxyl groups in the epoxy resin with a mass fraction of epoxy groups of 16.7%.

To determine the charge of 0.2-0.3 g of a sample resin and carry out the determination in accordance with the description in example 1. The concentration of maleic anhydride and 0.2 M, the concentration of triethylamine and 1.0 M. the Results of determination are shown in table. 2.

Example 3. Determination of hydroxyl groups in the epoxy resin with a mass fraction of epoxy GRU is ore 1. The concentration of raspberry anhydride 0.2 M, the concentration of triethylamine and 1.0 M. the Results of determination are shown in table.2.

The method of determining the content of hydroxyl groups in the epoxy resins, including the processing of resin solution by the excess of the anhydride of the organic acid in the presence of a catalyst at elevated temperature, the hydrolysis of unreacted anhydride and definition formed from acid by titration with alkali, wherein the processing of the resin is carried out in the 0.1 - 0.2 M solution of maleic anhydride in ethyl ketone, as a catalyst using 0.5 - 1 M solution of triethylamine in ethyl ketone and titration with alkali carried out potentiometrically.

 

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FIELD: analytical methods.

SUBSTANCE: invention concerns analytical determination of acids, acid salts, and other substances having acid reaction and reacting with alkalis, in particular titration method for use both in educational process and in industry. Method comprises weighing and dissolving in water sample of a substance, or taking measured volume of a substance followed by titration thereof using alkali titrants and pH-meter-mediated determination of equivalence point, said titrants being electrochemically activated alkaline water with pH 11.9-12.1 thereto 0.1% NaCl was added before activation.

EFFECT: reduced expenses on preparation of alkali solutions.

7 dwg, 12 ex

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