RU2318005C1 - Polytriester of phenol and boric acid and method for its preparing - Google Patents

Abstract

FIELD: chemistry of high-molecular compounds, chemical technology.

SUBSTANCE: invention relates to a method for synthesis of polytriesters of boric acid and phenol. Proposed polytriesters of boric acid and phenol are synthesized by the complete esterification reaction of boric acid with phenol resulting to formation of a mixture containing triphenylborate followed by distillation of mixture under vacuum. Hydrocarbon forming azeotropic mixtures with water - benzene, toluene and xylene are used as solvents. Then isolated triphenylborate is polymerized with trioxymethylene or paraformaldehyde using boron trifluoride etherate as a catalyst. Also, invention claims polytriester of phenol and boric acid synthesized by a method above said. Synthesized polymers represent thermostable boron-containing phenolformaldehyde resins that are easily soluble in polar solvents. Synthesized compounds can be used in industry instead phenolic resins for conferring thermostable properties for articles.

EFFECT: improved method of synthesis, valuable properties of ester.

2 cl, 1 tbl, 2 ex

Description

The invention relates to the field of polymer chemistry, in particular to synthesis, the establishment of a chemical structure and the study of the properties of polymethylene-n-triphenyl ester of boric acid, which can be used in industry instead of phenolic resins to give products heat-resistant properties.

The heat resistance of phenolic polymers increases dramatically with the introduction of inorganic fillers and can be significantly improved due to chemical modification. It is known that in the structure of phenolic resins there are two elements that are particularly susceptible to oxidation - methylene bond and phenolic hydroxyl group. Moreover, if we compare the heat resistance of methylene derivatives of phenol with the heat resistance of methylene derivatives of benzene (for example, poly-n-xylene), then the latter, which do not have a phenolic hydroxyl group, are much higher [1].

Currently, for the modification of phenolic resins, the esterification of the phenolic hydroxyl group is widely used in order to increase their resistance to thermo-oxidative effects. The presented technical solution is devoted to the synthesis of phenolic resins esterified with boric acid to give the latter heat-resistant properties, while these resins retain the properties of ordinary phenolic resins.

A number of stoichiometric and non-stoichiometric organoboron polymers are already known that are obtained by esterification of boric acid and phenol with the separation of water and condensed in the presence of formaldehyde (α-trioxymethylene, paraformaldehyde), however, the study of the structure of such resins is very difficult due to the preparation of several polymer mixtures, since along with triphenyl and phenyl ethers of boric acid at the stage of phenol and boric acid esterification also form phenyl ether. A mixture of these esters is very difficult to separate, since the latter are hydrolyzed by air moisture.

An analogue of this type of polymers can be the polymers described in German patent DT 2436358 A1 [2]. According to the patent, heat-resistant polymers of the general formula are formed from phenol and substituted phenols at a certain molar ratio:

R ₁ , R ₂ , R ₃ - hydrogen, halogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl or aralkyl radicals.

The disadvantages of the presented polymers include:

- the possibility of the formation of triester structures of boric acid and, as a consequence, a change in the structure and properties of the polymer are not taken into account;

- the addition of the -CH ₂ -OH group during polycondensation of boric acid diesters can also occur in the o- and p-position of adjacent molecules of the formed borates, which leads to a significant complication of the structure and makes it impossible to study the structure of the compound and obtain it individually ;

- instead of the “bridges” —CH ₂ —O — CH ₂ —addition can take place through the —CH ₂ group observed when the phenol resins “Resol” and “Novolak” are obtained, insofar as the polymerization reaction is carried out in an acidic environment (as phenyl boric acid esters are weak acids and decompose in an alkaline environment [3]), in addition, the reaction occurs at temperatures no higher than 150 ° C.

Such conditions make possible the existence of both methylene and methylene bridges [1].

Studies conducted by the authors of the proposed technical solution showed that with the complete esterification of boric acid (the formation of a boric acid ester of 3 moles of phenol and 1 mole of boric acid) and further polycondensation of the aforementioned ether in the presence of boron trifluoride etherate, a polymer structure is formed:

n≥1.

The polymer has a color from bright yellow to dark green, depending on the conditions of the polycondensation reaction of triphenylborate and on the amount of catalyst. The resulting polymer does not have a clear melting range.

On diffractograms of the polymer obtained in the "on the light" mode, two diffuse reflections (halo) with interplanar approximate distances d1 = 0.48 nm and d2 = 1.18 nm are observed. This indicates its amorphous structure.

The structure of the polymer as a product of n-substitution follows from NMR ¹ H-spectroscopy of the polymer, polymer hydrolyzate (water, 100 ° C, 24 hours) and elemental analysis of the polymer. Found,%: C 78.00; H 4.95. Calculated,%: C 76.00; H 4.92. ¹ H NMR spectrum of the polymer (CO ₃ OD), δ, ppm: 3.84 s (6H, CH ₂ ), 6.71 d (6H, H ^3.5 , J _3-2.5-6 8.4 Hz, J _{3 -5} , 2.8 Hz), 6.81 d (6H, H ^2.6 , J _2-3.6-5 8.4 Hz, J _2-6 1.7 Hz). ¹ H NMR spectrum of hydrolyzate (CD ₃ OD), δ, ppm: 3.98 s (6H, CH ₂ ), 6.91 d (12H, H ^3.5 , J _3-2.5-6 8.4 Hz, J _{3 -5} 2.8 Hz), 7.11 d (12H, H ^2.6 , J _2-3 , _6-5 8.4 Hz, J _2-6 1.7 Hz).

A significant difference between this polymer and analogues is the presence of a boron atom in the polymer molecule exclusively in the form of a triether, which is confirmed by ¹¹ B NMR spectroscopy. ¹¹ V NMR spectrum of the polymer (CD ₃ OD), δ, ppm: 18.45 s (BO ₃ R ₃ ). In this regard, the formation of non-stoichiometric compounds (mixtures of various polymers) does not occur.

The intrinsic viscosity of the obtained polymer, determined by the viscometric method at 25 ° C in acetone, is 0.045 ... 0.098 dl / g.

The mass-average molecular weight of the polymer, determined from gel permeation chromatography data, is 419 ... 514 amu, which corresponds to n≥1.

The approximate thermal stability of the polyether ester of boric acid and phenol can be determined by the results of differential thermal analysis. The results of the differential thermal analysis of the polymer are presented in table 1.

Table 1: DTA results of polytriphenyl boric acid ester No. decomposition stage on the DTA curve The temperature of the onset of intense decomposition T _NIR , ° C Maximum temperature T _MAX , ° С The degree of decomposition of the sample, η,% I one hundred - 2,52 II 180 - 8.77 III 280 320 11.59 IV 370 420 23.84 V 440 - 37.65 VI 560 630 95.34

According to the results, it can be seen that at the first stage of decomposition, the polymer begins to lose the available moisture, at the second stage, part of the phenol contained in it is removed from the polymer, and the decomposition of the product itself begins at 280 ° C. The beginning of the intensive decomposition of the main part of the polytriphenyl ester of boric acid (namely 57.69%) occurs at a temperature of 560 ° C.

In addition, when the polymer samples are heated to 800 ° C, up to 5% of the unburned residue, boric anhydride, which is formed during the combustion of organic boron compounds, remains. This is confirmed by the presence of a glass-like solid transparent mass on the walls of the platinum crucible.

It is known that phenolic resins (PS) were the first polymers created more than 100 years ago.

Currently, the most important areas of FS use are the woodworking industry, the production of press compositions, heat and sound insulating materials, laminated plastics and impregnated paper, various kinds of coatings, binders for foundry molds, abrasive and friction materials, phenolic antioxidants, etc.

PS is obtained by the interaction of phenols with aldehydes, mainly with formaldehyde, however, the heat resistance of such resins is relatively low, which complicates their use where it is necessary to maintain physical and mechanical characteristics at elevated temperatures.

The properties of PS are largely determined by the conditions for their preparation, therefore, in order to satisfy the diverse, sometimes contradictory requirements of modern technology for these products, the reaction conditions for the preparation of PS are varied: molar ratio of formaldehyde and phenol, type and amount of catalyst, reaction temperature and duration, content water and free phenol in the reaction product (drying conditions). In addition, to alter the properties of PS, they are modified with other aldehydes and phenols, and esterification and / or dissolution of resins in organic solvents is used [1].

The solution proposed by the authors of this application is devoted to the synthesis of heat-resistant triesters of boric acid, phenol and / or substituted phenols, and is one of the methods for modifying PS by boric acid.

Patent DT 1816241 can be considered as a prototype for the proposed method for the synthesis of polyesters. According to this patent, triphenylborate is obtained from 3 moles of phenol and 1 mole of boric acid, which is then polymerized with trioxane in xylene in a stream of nitrogen without using a catalyst. The molar ratio of phenol to trioxane is 1: 0.83.

The prototype has significant disadvantages that impede the synthesis of the polymer in its pure form and its further use in industry.

So at the first stage of the synthesis, according to the patent, after the esterification reaction, the solvent is distilled off, and the obtained triphenyl borate is used for polymerization without purification. However, it was found that in the reaction of phenol and boric acid, along with triphenyl borate, various compounds are formed, for example, phenyl borate, diphenyl borate, phenyl orthoborates, etc. [4]. In this regard, without purification of triphenylborate after the reaction, it is impossible to obtain the polyester in its pure form, and therefore, curing is difficult. The prototype does not present the thermal characteristics of the obtained resin. In addition, it is impossible to develop requirements for this polymer because of its highly variable quality due to the changing amount of impurities after esterification.

No catalyst is used at the polymerization stage, which complicates the polycondensation of triphenylborate with trioxane. However, when using catalysts, the polycondensation reaction of phenols and formaldehyde proceeds faster, and the fraction of free phenol in the obtained PS decreases significantly, which indicates the depth of the reaction and facilitates subsequent drying of the resin. This disadvantage significantly complicates the synthesis. Moreover, drying the resin significantly complicates the process of obtaining the polymer.

The synthesis method proposed by us is characterized in that the mixture of boric acid esters obtained after esterification was purified by vacuum distillation in order to obtain pure triphenylborate. As a solvent in the first and second stages, various hydrocarbons can be used that form azeotropic mixtures with water, for example benzene, toluene and xylene. The polycondensation reaction of triphenylborate and trioxymethylene is catalyzed by boron trifluoride etherate.

According to the proposed method, 3.1 mol of phenol, 1 mol of boric acid and 3 mol of solvent are placed in a round-bottomed three-necked flask equipped with a stirrer, thermometer and Dean-Stark nozzle with a reflux ball cooler. The mixture is heated to a boil and boiled for 3 hours until the evolution of water stops. The resulting yellowish liquid mixture was cooled and distilled in vacuo. All solvent is completely distilled off from the reaction mass. The yield of triphenylborate after distillation is 92% of theoretically possible.

After distillation of the main part of the solvent, triphenyl borate was distilled under vacuum. It was previously noted that at temperatures above 180 ° C triphenyl borate decomposes [5]. Triphenylborate is a high boiling point compound; its boiling point is 150 ° C / 0.01 mmHg. However, the authors of the application found that triphenylborate can be distilled at higher temperatures using air cooling. In this case, it is necessary to increase the distillation rate to 2-3 drops per second. So, triphenylborate is distilled at 220-245 ° С / 1 mmHg. There is no need to create a deep vacuum. The melting point of freshly distilled triphenylborate is 97-98 ° C by the capillary method.

Triphenylborate is poorly stored in air and in vacuum. Already after 1 hour after distillation, its melting temperature drops to 55-57 ° C. At the same time, phenol needles with a characteristic odor are formed on the walls of the vessel in which triphenylborate was stored. In a vacuum, triphenylborate decomposes on the surface in 12 hours, forming white needle crystals.

After purification, liquid triphenyl borate was immediately used for polycondensation.

To do this, triphenyl borate and 1 mol of solvent with vigorous stirring were placed in a five-necked flask equipped with an electric stirrer, a thermometer, a gas supply tube, a Dean-Stark nozzle, and a return ball cooler. The mixture was heated to 80 ° C, boron trifluoride etherate was added as a catalyst at the rate of 5% of the etherate by weight of triphenylborate and kept at this temperature for about 15 minutes. Then, trioxane was added in small pieces at the rate of 0.28 mol of trioxane per 1 mol of phenol. In this case, the temperature was observed, which should not be higher than 110 ° C. After adding the last portion of trioxane, the reaction mass was kept for another 1 hour at 90 ° C.

The resulting polymer solution was dried under vacuum. After removing all of the solvent and part of the unreacted trioxane, the resulting viscous mass was dissolved in a polar solvent, for example, alcohol, dimethylformamide, acetone, etc., and then filtered. Then the solvent was distilled off, and the obtained polymer was dried under vacuum in a cabinet at 150 ° C.

Obtained by this method, the polyester of phenol and boric acid cures more easily than the resin presented in the prototype. The polymer cures in 10 minutes at 150-160 ° C with urotropine (5% wt.), While the resin presented in the prototype cures under the same conditions in 10 minutes.

Example 1. 115 g of phenol, 22.89 g of boric acid and 147 ml of o-xylene were heated to boiling. M- or p-xylene, or 107 ml of benzene, or 127 ml of toluene can also be used as a solvent. At 129.5 ° C, the reaction mass began to boil. Boiling was continued until water ceased to stand out. The reaction temperature should not exceed 145 ° C, since above this temperature boric anhydride is formed from boric acid. The reaction lasts approximately 3-5 hours, depending on the solvent. After that, the reaction mass was cooled and distilled under vacuum. Received 98.75 g of triphenylborate with a melting point of 95-97 ° C by the capillary method.

Triphenyl borate was mixed with o-xylene and heated to 80 ° C in a stream of dry nitrogen. M- or p-xylene, or benzene, or toluene can also be used as a solvent. 4.9 g of freshly prepared boron trifluoride etherate was added to the mixture as a catalyst, and the mixture was kept for 15 minutes. Then, trioxane was added in portions. In this case, when a new portion of trioxane is added, the temperature of the reaction mixture increases. After adding 25.7 g of trioxane, the reaction mass was kept for another 1 hour at 90 ° C. Then the reaction mixture was cooled, the solvent and part of the unreacted trioxysmethylene were distilled off under the vacuum of a water-jet pump. The thick portion was dissolved in a five-fold volume of ethyl alcohol and filtered through a pleated filter. After that, the alcohol was distilled off, and the polymer was dried for 30 minutes in a vacuum oven at 150 ° C.

Example 2. Act as in example 1, only instead of trioxane use paraformaldehyde. At the same time, 1.2-1.5 times more boron trifluoride etherate is used for the above amount of triphenylborate and paraformaldehyde. The yield in the reaction does not change; the polymer properties remain the same as during polycondensation with trioxane.

Bibliography

1. A.Knop, V.Sheyb. Phenolic resins and materials based on them. - Per. from English under the editorship of F.A. Shutova. - M .: Chemistry, 1983. - 280 p., Ill.

2. Hoechst AG .: DE-OS 2436358.

3. Nord-Aviation Societe Nationale de Constructions Aeronautiques: DE-AS 1816241.

4. V.V. Korshak, V.A. Zamyatina, N.I. Bekasova. Organoboron polymers. - M .: Nauka, 1975 .-- 255 p., Ill.

5. A.N. Nesmeyanov, R.A. Sokolik. Methods of Organoelemental Chemistry. Boron, aluminum, gallium, indium, waist. Under. ed. K.A. Kocheshkova. - M .: Nauka, 1964 .-- 499 p., Ill.

Claims (2)

1. A method of obtaining a heat-resistant polymethylene-n-triphenyl ester of boric acid by esterification of boric acid and phenol followed by polycondensation of the obtained triphenylborate with trioxane (paraformaldehyde), characterized in that the boric acid is fully esterified with phenol to form a mixture containing triphenylborate, followed by distillation of the mixture under vacuum, using as solvents hydrocarbons forming azeotropic mixtures with water, benzene, toluene and xylene, then isolated triphenyl borate polymerized with trioxymethylene or paraformaldehyde using boron trifluoride ether as a catalyst. 2. The polyether of phenol and boric acid obtained by the method according to claim 1.