PL249253B1 - Method for producing polyols - Google Patents

Abstract

The subject of the application is a method for producing polyols, which is carried out by introducing polyvinyl alcohol and ethylene carbonate in an amount of 20 to 25 moles per mole of polyvinyl alcohol units into a reactor. The reactor contents are heated to a temperature in the range of 120°C to 140°C and simultaneously stirred at a speed of 500-2000 rpm. Heating is continued until the polyvinyl alcohol is completely dissolved. The reaction mixture is cooled to a temperature of at most 80°C, and then potassium carbonate is added in an amount of 0.6% to 1.5% by weight, based on the weight of the remaining ingredients. The reactor contents are heated to a temperature in the range of 170°C to 190°C and stirred at a speed of 400-600 rpm until the reaction is complete.

Description

The subject of the invention is a method for producing multifunctional polyols for use in the production of polyurethanes, especially biodegradable, flexible polyurethane foams.

Polyvinyl alcohol is widely used as a component of adhesives, textile finishes, varnishes, and as a stabilizer for emulsion paints. It is also used as a component of eye drops and artificial tears, and is used in the production of dental floss, protective gloves, foils, sheets, and pipes resistant to hydrocarbons and oils. Polyvinyl alcohol is a non-toxic, environmentally friendly, and partially biodegradable compound. It is obtained by hydrolysis of polyvinyl acetate, which results in a small amount of polyvinyl acetate-derived units remaining in the polyvinyl alcohol macromolecules. Polyvinyl alcohol is commercially available in three forms: high-hydrolysis, in which the hydroxyl group content exceeds 98%; medium-hydrolysis, in which the hydroxyl group content ranges from 86 to 92%; and low-hydrolysis, in which the hydroxyl group content ranges from 70 to 80%. The presence of hydroxyl groups in polyvinyl alcohol (PVA) units allows it to be used in the production of polyurethane foams, provided it is converted into a liquid resin that still contains hydroxyl groups in its structure. However, the reactions for obtaining polyols from PVA are not known.

The oxyalkylation reactions of poly(vinyl alcohol) are known from the publications by Cohen S. G., Haas H. C., Slotnick H.: Studies on Hydroxyethyl polyvinyl alcohol, J. Polymer Sci, 11(3), 193-201, 1953, in which oxiranes, especially ethylene oxide, propylene oxide, and epichlorohydrin, are used. Attempts to graft ethylene oxide onto poly(vinyl alcohol) were carried out in a pressure reactor using powdered poly(vinyl alcohol) and a two-fold excess of ethylene oxide by weight relative to the weight of poly(vinyl alcohol) and conducting the reaction at 80°C for 12, 17, or 30 hours. The reaction resulted in a series of products in the form of white powders containing approximately 12, 19, or 35% of attached ethylene oxide. The above-mentioned publication also describes a reaction in which a polyalcohol is used as a solvent, and as a result a product is obtained in the form of a transparent, gelatinous mass.

Patent application US2990398A describes an ethoxylation reaction of polyvinyl alcohol in which 100 g of powdered polyvinyl alcohol reacts with 200 g of ethylene oxide in a pressure reactor at an initial temperature of 100°C, during which an exothermic effect was observed causing the temperature to increase to 200°C. This known reaction produces a dark brown, viscous tar product. In turn, the reaction conducted in ethyl acetate at 90°C for 6.6 hours produces a cream-colored powder containing 10% of attached ethylene oxide.

In the patent application description US3099646A, a method of ethoxylation of polyvinyl alcohol was disclosed, in which the reactions of dried polyvinyl alcohol are carried out in a pressure reactor at a temperature of 92 to 97°C for 6 hours with continuous dosing of ethylene oxide, as a result of which a product in the form of a light yellow powder is obtained.

Other oxiranes, particularly propylene oxide and butylene oxide, are also used for the oxyalkylation of poly(ethylene alcohol). An example of such a reaction, carried out in a heptane environment at a temperature of 85 to 100°C, is disclosed in patent application US3052652A. This known method also includes the reaction of ethoxylated poly(vinyl alcohol) with 2,4-toluylene diisocyanate and water, which produces a rubbery product that resembles a sponge when wet.

Patent application US3106543A describes polyvinyl alcohol oxyalkylation reactions (primarily with ethylene oxide) conducted in an aqueous medium. The film cast from the resulting solution is flexible and well plasticized. Epichlorohydrin is also used for the oxyalkylation reaction.

The patent application EP0021131 discloses a method for obtaining expanding, cross-linked poly(vinyl alcohol) ethers, in which epichlorohydrin is used as a cross-linking agent.

Patent description EP0189375B1 describes a hydrogel contact lens in which cross-linking of poly(vinyl alcohol) with polyoxirane is used.

A method for obtaining polymers is known from the publication by Carlotti S. J., Giani-Beaune O., Schue F.: Water-Soluble Poly(vinyl alcohol) Grafted with Propylene Oxide and Epichlorohydrin: Characterization, Mechanical Properties, and Model Reactions, J. Appl. Polymer Sci, 81, 2868-2874, 2001. In this method, poly(vinyl alcohol) was oxyalkylenated with propylene oxide and epichlorohydrin in an aqueous medium using sodium hydroxide or sulfuric acid as a catalyst. The obtained polymers exhibit very good water solubility and a low glass transition temperature, while films with good elastic properties and good tensile strength are obtained from aqueous solutions. The use of epichlorohydrin for epoxidation of poly(vinyl alcohol) in order to use their reaction product for adhesives is described in the publication by Shui T., Chae M., Bressler D. C.: CrossLinking of Thermally Hydrolyzed Specified Risk Materials with Epoxidized Poly(Vinyl Alcohol) for Tackifier Applications, Coating, 10, 630, 1-17 (2020).

Alkylene carbonates are also known from the literature as oxyalkylating agents, especially ethylene carbonate and propylene carbonate. However, the use of these carbonates for the oxyalkylation of poly(vinyl alcohol) is not known. The publication by Wang X.L., Du F.G., Meng Y.Z., Li R.K.Y.: Novel in situ crosslinking reaction of ethylene-vinyl alcohol copolymers by propylene carbonate, Mater. Lett., 60, 509-513, 2006 discloses only that propylene carbonate can be used in amounts of at most 5% as a crosslinking agent for ethylene-vinyl alcohol copolymer.

However, prior art methods for the oxyalkylation of poly(vinyl alcohol) have limitations. Oxiranes are low-boiling, toxic, and flammable compounds that form explosive mixtures with air. They also exhibit carcinogenic properties, and their low boiling point requires the use of pressurized reactors. The reaction of poly(vinyl alcohol) with oxiranes is sometimes conducted in an aqueous medium in the presence of sodium hydroxide or sulfuric acid as a catalyst, thus producing glycols and polyglycols as byproducts of the oxirane-water reaction. These byproducts must be removed from the reaction medium to obtain pure poly(vinyl alcohol) oxyalkylation products. The use of other solvents or reaction mediums, such as ethyl acetate or saturated hydrocarbons, requires their removal after the reaction is complete by distillation from the reaction mixture. Moreover, the prior art alkoxylation reactions of poly(vinyl alcohol) lead to the production of powdery or gel-like rubber products that are incompatible with liquid isocyanates used to produce polyurethane foams.

The aim of the invention is to develop a new method for producing polyols from polyvinyl alcohol, which can be mixed with liquid isocyanates, thanks to which they can be used in the production of flexible, biodegradable polyurethane foams.

The method for producing polyols according to the invention is characterized in that polyvinyl alcohol and ethylene carbonate are introduced into the reactor in an amount of 20 to 25 moles per 1 mole of polyvinyl alcohol units, then the reactor content is heated to a temperature in the range of 120 to 160°C and simultaneously stirred at a speed of 500-2000 rpm, heating is carried out until the polyvinyl alcohol is completely dissolved, then the reaction mixture is cooled to a temperature of at most 80°C, and then potassium carbonate is added to it in an amount of 0.6 to 1.5% by weight relative to the weight of the remaining components, then the reactor content is heated to a temperature in the range of 170 to 190°C and stirred at a speed of 400-600 rpm until the reaction is completed.

Preferably, polyvinyl alcohol with a degree of hydrolysis of 86% is introduced into the reactor, wherein the content of the reactor, during dissolution of the polyvinyl alcohol, is heated to a temperature of 160°C, and in addition potassium carbonate, in relation to the weight of the other components, is used in an amount of 1.3% by weight.

Further advantages are obtained if the reaction with potassium carbonate is carried out at a temperature of 190°C, the end of the reaction being determined by determining the ethylene carbonate content.

The new method for producing polyols, according to the invention, enables the production of polyols from polyvinyl alcohol that can be mixed with liquid isocyanates, and thus find application in the production of polyurethane foams. Using a large excess of the oxyalkylenating agent relative to the polyvinyl alcohol allows for the grafting of long oxyalkylene chains onto its hydroxyl groups, giving the product a liquid character. Another advantage of this new method is the use of ethylene carbonate for the oxyalkylenation of polyvinyl alcohol. The polyvinyl alcohol dissolves completely in it at an elevated temperature and then reacts with it in the presence of a potassium carbonate catalyst. An additional advantage is the ability to conduct the reaction in a single step, without the use of low-boiling and toxic oxiranes or the use of pressurized reactors, as ethylene carbonate has a high boiling point and can be conducted under reflux. Another advantage of using ethylene carbonate is its non-flammability and non-toxicity, as well as its very high polarity, which allows it to dissolve poly(vinyl alcohol). This makes it both a reagent and a solvent, which does not need to be removed after the reaction is complete, as it reacts completely with poly(vinyl alcohol). To produce flexible foams, a polyol based on poly(vinyl alcohol) grafted with ethylene carbonate is required to obtain long, flexible oxyalkylene chains terminated with hydroxyl groups. Another advantage of the new polyol production method is that, depending on the polyol's intended use for producing more or less flexible foams, the production process can be easily modified by using an appropriate excess of ethylene carbonate relative to poly(vinyl alcohol).

The subject of the invention is presented in the embodiment examples and in the drawing, in which Fig. 1 shows the infrared spectrum of poly(vinyl alcohol), Fig. 2 - the infrared spectrum of polyol, Fig. 3 - the H-NMR spectrum of poly(vinyl alcohol), Fig. 4 - the H-NMR spectrum of poly(vinyl alcohol) after adding D2O, Fig. 5 - the H-NMR spectrum of polyol in the full range, Fig. 6 - the H-NMR spectrum of polyol in the area where signals occur, and Fig. 7 - the H-NMR spectrum of polyol after adding D2O.

Example 1

The method for producing polyols according to the invention, in the first embodiment, was carried out by introducing 4.4 g, i.e. 0.1 mol, of polyvinyl alcohol with a degree of hydrolysis of 86% and 176 g, i.e. 2.0 mol, of ethylene carbonate into a 250 cm3 round-bottomed, ^three -necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirrer. The contents of the flask were vigorously stirred at 700 rpm and heated to 160°C. The contents of the flask were maintained in this state until the polyvinyl alcohol was completely dissolved. The reaction mixture in the flask was then cooled to 80°C and 1.5 g of potassium carbonate as a catalyst was added. The whole was heated at 190°C with continuous stirring at a speed of 500 rpm until the reaction was complete, which was determined based on the determination of the ethylene carbonate content, and the reaction was considered complete when the ethylene carbonate content was at most 2%.

As a result of the reaction, the final product was obtained in the form of a dark brown resin with a density of 1.198 g/ ^cm3 , a viscosity of 1255 mPa-s at 20°C and a hydroxyl number of 215 mg KOH.

Example 2

The method for producing polyols, according to the invention, in the second embodiment was carried out by introducing 4.4 g, i.e. 0.1 mol, of polyvinyl alcohol with a degree of hydrolysis of 86% and 220 g, i.e. 2.5 mol, of ethylene carbonate into a 250 cm3 round-bottomed, ^three -necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirrer. The flask contents were vigorously stirred at 1500 rpm and heated to 160°C. The flask contents were maintained in this state until the polyvinyl alcohol was completely dissolved. The reaction mixture in the flask was then cooled to 80°C and 1.5 g of potassium carbonate as a catalyst was added. The whole was heated at 190°C with continuous stirring at a speed of 600 rpm until the reaction was complete, which was determined based on the determination of the ethylene carbonate content, and the reaction was considered complete when the ethylene carbonate content was at most 2%.

As a result of the reaction, the final product was obtained in the form of a dark brown resin with a density of 1.196 g/ ^cm3 , a viscosity of 323 mPa-s at 20°C and a hydroxyl number of 177 mg KOH.

Example 3

The third embodiment of the method for producing polyols according to the invention was carried out by introducing 4.4 g, i.e. 0.1 mol, of polyvinyl alcohol with a degree of hydrolysis of 86% and 220 g, i.e. 2.5 mol, of ethylene carbonate into a 250 cm3 round-bottomed, ^three -necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirrer. The contents of the flask were vigorously stirred at 1000 rpm and heated to 160°C. The contents of the flask were maintained in this state until the polyvinyl alcohol was completely dissolved. The reaction mixture in the flask was then cooled to 80°C and 3.0 g of potassium carbonate as a catalyst was added. The whole was heated at 180°C with continuous stirring at a speed of 500 rpm until the reaction was completed, which was determined based on the determination of the ethylene carbonate content, and the reaction was considered complete when the ethylene carbonate content was at most 2%.

As a result of the reaction, the final product was obtained in the form of a dark brown resin with a density of 1.138 g/ ^cm3 , a viscosity of 619 mPa-s at 20°C and a hydroxyl number of 171 mg KOH.

The formation of polyols as a result of oxyalkylenation of poly(vinyl alcohol) with ethylene carbonate is confirmed by the IR and H-NMR spectra of the resulting products in comparison with the corresponding spectra of poly(vinyl alcohol) - PAV.

In the IR spectrum of PAV, shown in Fig. 1, a broad band at 3289 cm ^-1 arising from the stretching vibrations of the hydroxyl groups is observed, as well as bands due to deformation vibrations of these groups, at 1427 and 601 cm ^-1 , respectively. At about 1086 cm ^-1 , a band due to valence vibrations of the CO- bonds in the secondary hydroxyl group is present. The presence of unhydrolyzed acetate groups CH3COO- of PAV is indicated by the presence of a band of the carbonyl group at 1725 cm ^-1 and a band at 1240 cm ^-1 originating from the CO ester residue. Figure 2 shows the IR spectrum of the polyol obtained in Example 1. Compared to the PAV spectrum, a very strong band appears at 1095 cm ^-1 , originating from new COC bonds formed as a result of the reaction of the hydroxyl groups of PAV with ethylene carbonate. This indicates the oxyalkylation of PAV and the introduction of structural fragments into the polyol resulting from the opening of ethylene carbonate rings during the reaction. The intensity of the valence vibration band of the OH groups at 3460 cm ^-1 decreases due to their decreasing share in the polyol structure in relation to the methylene groups at 2866 cm ^-1 formed as a result of the cleavage of the ethylene carbonate ring during the reaction.

In the 1H-NMR spectrum of the mentioned PAV, shown in Figure 3, the protons of the hydroxyl groups give several signals with chemical shifts of 4.22, 4.45 and 4.62 and further in the range of 4.7 to 5.1 ppm. Evidence that they originate from the protons of the hydroxyl groups is their disappearance after the addition of heavy water - the lower line shown in Figure 4. At 3.90 ppm, there is a signal from the methine proton at the carbon atom connected to the hydroxyl group, and in the range of 1.3-1.7 ppm, signals from the protons of the methylene groups in the PAV unit are observed. The signal of the protons of the methyl group at 1.95 ppm indicates that the product structure retains the residues of the acetate groups CH3COO from the incompletely hydrolyzed poly(vinyl acetate), from which PAV is obtained. From the integration curves assigned to the methyl groups of 1.95 ppm and the methylene groups of CH2 of 1.3-1.7 ppm in the PAV structure, it can be calculated that the degree of hydrolysis of PAV is 86%.

In the 1H-NMR spectrum, shown in Fig. 5 and Fig. 6, of the polyol obtained in the first example, practically no signals of methylene groups are observed at 1.3-1.7 ppm, because their share decreased significantly due to the appearance of signals from a large number of methylene groups in the range of 3.0-3.6 ppm, indicating the decomposition of ethylene carbonate rings in PAV oxyalkylenation reactions. The signals of PAV hydroxyl groups in the range of 4.22-5.10 ppm disappear, and at 4.6 ppm, signals appear from hydroxyl groups formed as a result of the decomposition of the mentioned ring, which disappear after adding D2O to the system - the lower line shown in Fig. 7.

Analogous dependencies are observed in the IR and H-NMR spectra of polyols obtained from PAV in Example 2 and Example 3. Furthermore, the simplest and most convincing evidence that PAV undergoes oxyalkylenation under the influence of ethylene carbonate is the transformation of solid PAV into a liquid polyol.

Claims (6)

1. A method for producing polyols, characterized in that polyvinyl alcohol and ethylene carbonate are introduced into the reactor in an amount of 20 to 25 moles per 1 mole of polyvinyl alcohol units, then the reactor content is heated to a temperature in the range of 120 to 160°C and simultaneously stirred at a speed of 500-2000 rpm, heating is carried out until the polyvinyl alcohol is completely dissolved, then the reaction mixture is cooled to a temperature of at most 80°C, and then potassium carbonate is added thereto in an amount of 0.6 to 1.5% by weight relative to the weight of the remaining components, then the reactor content is heated to a temperature in the range of 170 to 190°C and stirred at a speed of 400-600 rpm until the reaction is completed. PL 249253 Β1 2. A method according to claim 1, characterized in that polyvinyl alcohol with a degree of hydrolysis of 86% is introduced into the reactor. 3. A method according to claim 1 or 2, characterized in that the contents of the reactor are heated to a temperature of 160°C during dissolution of the polyvinyl alcohol. 4. The method according to one of claims 1 to 3, characterized in that potassium carbonate, relative to the weight of the other components, is used in an amount of 1.3% by weight. 5. The method according to any one of claims 1 to 4, characterized in that the reaction with potassium carbonate is carried out at a temperature of 190°C. 6. The method according to any one of claims 1 to 5, characterized in that the end of the reaction is determined by determining the ethylene carbonate content.