DE10121806A1 - Hydroxy-functional oligomeric copolymers used as polyol components for the production of polyurethane, comprises vinyl alcohol and vinyl ester with a low degree of polymerization - Google Patents

Abstract

Copolymers (I) of vinyl alcohol with vinyl esters (and optionally monomers which copolymerize with vinyl esters), with a degree of polymerization (DP) of less than 30 and an OH-functionality of 1-10. Independent claims are also included for (a) a method for the production of (I) by polymerization of vinyl esters (and optionally comonomers) in presence of initiators and chain-transfer agents to give polymers with a DP of less than 30, followed by base-catalysed partial hydrolysis in inert solvent with the addition of definite amounts of a solvolysis agent; and (b) polyurethanes containing reaction products of (I).

Description

The invention relates to oligomeric copolymers of vinyl alcohol, vinyl esters and monomers copolymerizable with vinyl esters, if appropriate, process for their Production and their use for the production of polyurethanes.

Liquid oligomers with hydroxyl groups are interesting polyols or polyol Intermediate stages for polyurethane formulations. Polyols based on vinyl mono Mers, especially of vinyl acetate, have so far only become known to a limited extent.

Macromol. Symp. 102 (1996) 91 goes about the production of α, ω-functional based oligomeric methyl methacrylate diols by radical polymerization in Presence of 2-thioethanol as a chain transfer agent. The Polymeri obtained simply functionalized oligo-methyl methacrylates are obtained by selective transesterification of the terminal ester group converted into diols.

The known synthetic routes are for the preparation of liquid, hydroxy functionalized oligo vinyl acetate unsuitable. Studies on radical Polymerization of vinyl acetate in the presence of various chain transfer agents such as Carbon tetrachloride (Kogyo Kagaku Zahsshi 64 (1961) 1691), alcohols (Kobunshi Kagaku 17 (1960) 120), alkyl halides (Kobunshi Kagaku 7 (1950) 269), Aldehydes (Kobunshi Kagaku 12 (1955) 453) and thiols (Kogyo Kagaku Zahsshi 62 (1959) 1274) often show poor control of molecular weight associated with a sharp reduction in the rate of polymerization and of monomer sales. Products have been included in all previous studies get a degree of polymerization greater than 30, the glass transition temperature does not differ from that of high molecular weight polyvinyl acetate.

The partial hydrolysis of high molecular weight polyvinyl acetate, e.g. B. by bases Catalyzed hydrolysis or transesterification with methanol is known. The received  high molecular weight polyvinyl acetate / polyvinyl alcohol copolymers show very high Viscosities and poor miscibility with other polyols. Furthermore they have a vinyl alcohol content of over 70%.

It has now been found that by radical polymerization under Use of 2-propanol as chain transfer agent and subsequent polymer Analogous implementation of oligomeric copolymers of vinyl alcohol with vinyl esters and optionally have monomers copolymerizable with vinyl esters prepared, which has a low viscosity at room temperature, a precisely adjustable OH radio functionality, a low glass transition temperature and good miscibility with others Show polyols. These oligomers can be used in polyol components for polyurethane formulations are used.

The invention relates to oligomeric copolymers of vinyl alcohol Vinyl esters and optionally monomers copolymerizable with vinyl esters with a degree of polymerization <30, preferably 2 to 15, particularly preferably 6 to 12 and an OH functionality of 1 to 10, preferably 2 to 8, particularly preferred 2 to 6.

Carboxylic acid esters of vinyl alcohol are used as vinyl esters. Next to the vinyl acetate or vinyl propionate are preferably used Vinyl esters of long chain carboxylic acids, e.g. B. vinyl stearate, vinyl laurate or vinyl ester branched fatty acids, but also vinyl esters of maleic acid or fumaric acid used. Vinyl esters of acrylic acid or methacrylic acid can also be used find. As a rule, vinyl esters become long-chain or unsaturated Use carboxylic acids in a mixture with vinyl acetate or vinyl propionate, since mostly even small proportions of monomer units, which differ from man vinyl esters deriving long-chain or unsaturated carboxylic acids suffice to own the to modify the copolymer in the desired manner. Become OH-functional copolymers according to the invention, those of vinyl esters long-chain Containing fatty acid derived monomer units in polyurethane formulations  used, they can be used in polyurethane as internal plasticizers or Release agents act.

Examples of monomers copolymerizable with vinyl esters are ethylene and vinyl chloride, crotonic acid, maleic anhydride, maleic esters such as dibutyl maleate and Dioctyl maleate and acrylates such as butyl acrylate or 2-ethylhexyl acrylate.

The invention also relates to processes for producing the invention copolymers according to. In a first step, vinyl esters, e.g. B. Vinyl acetate, and optionally monomers copolymerizable with vinyl esters in Presence of an initiator and a chain transfer agent oligomerized to a To obtain polymer of the desired degree of polymerization. For example oligomeric polyvinyl acetates colorless, highly viscous liquids.

The degree of polymerization of the polymer obtained is determined by the ratio determined from monomer to chain transfer agent. When hiring a large one Excess chain transfer, the polymer chain grows only a few monomers units long before it returns to the transfer reaction to the chain transmitter comes and a new chain begins to grow. The one for the one you want The excess of chain transfer agent required for the degree of polymerization can be easily obtained determine experimentally.

All common initiators for radical polymerizations are initiators principally suitable, e.g. B. dibenzoyl peroxide or 2,2'-azo-bis-isobutyronitrile (AIBN). However, di-tert.-butyl peroxide (DTBP) is preferably used, since this is the case with the initiation of tert-butanol is easily distilled from the reaction can remove mixture. The required concentration of the initiator depends on the reaction temperature and the rate of decomposition of the initiator used. In the As a rule, concentrations of 0.5 to 4 mol%, based on the amount used on vinyl monomers. The degree of polymerization of the oligomer is determined by affects the initiator concentration little.  

Isopropanol is preferably used as the chain transfer agent, but there are also others Chain transfer agents can be used, for example alcohols such as isobutanol, aldehydes or ketones. The chain transfer agent also acts as a solvent in the reaction. Excess chain transfer agent or excess solvent can the reaction can be easily removed by distillation.

A reaction temperature is to be chosen at which the decomposition rate of the initiator is high enough to produce an adequate radical concentration. Frequently as the reaction temperature the boiling point of the chain transfer agent used or solvent selected.

In a second step, the polymer obtained is specifically converted into a vinyl alcohol Saponified copolymer with the desired number of OH groups. The saponification takes place in an inert solvent base catalyzed with the addition of defined Amounts of a solvolysis agent, e.g. B. of water or primary alcohols.

The saponification of polyvinyl acetate is usually under according to the prior art basic conditions with the help of an excess of water or Alcohol is carried out, with control of the degree of saponification via the reac tion time. A major problem with this method is that it becomes block copolymer structures made of polyvinyl acetate and polyvinyl alcohol. This is at the opaque end see the materials recognizable, which is caused by phase separation.

To prevent this effect, and only a few OH groups in the polymer introduce the solvolysis reaction of the polymer obtained in the first step carried out according to the invention under controlled conditions.

The reaction is carried out in an inert solvent. Inert solutions medium are those that are not or not significantly under the reaction conditions edge react with the polymer and by the catalyst used  Base cannot be deprotonated. Examples are aprotic solvents such as tetra hydrofuran (THF), but also protic solvents, e.g. B. isopropanol, are ge suitable if they have a much lower acidity than solvolysis agent.

As a solvolysis agent are all compounds that are capable of Cleave the ester bond of the vinyl ester units. Water or are preferred primary alcohols used, especially methanol. The amount of solvolysis agent, which is added depends on the number of OH groups that make up the final product should have. It has been found in determining the functionality of the Vinyl alcohol copolymers demonstrated by end group titration that when added stoichiometric amounts of solvolysis agent about 70% of the theoretically expected OH groups are formed, d. H. for example when adding 2 moles Solvolysis agent per mole of polymer becomes a vinyl alcohol copolymer on average Obtained 1.4 OH groups per molecule.

The reaction is carried out in the presence of catalytic amounts of base. suitable Bases are, for example, alcoholates such as potassium methylate.

Should a uniform distribution of the OH groups in the vinyl alcohol obtained Copolymers are achieved, it is advantageous to saponify at low Carry out reaction temperatures. The reaction temperature is not preferred higher than room temperature, particularly preferably not higher than 0 ° C. An equal moderate distribution of the introduced OH groups along the polymer chain leads to transparent products.

In a preferred embodiment of the invention, both steps of Ver driving carried out as a one-pot reaction in 2-propanol as a solvent, which in first step also acts as a chain transfer agent. On the isolation of the first The polymers formed in this step are dispensed with, since the first step by-products formed do not interfere with the subsequent saponification.  

If the base is to be removed from the product after the saponification, this is done Neutralized reaction mixture. This is advantageously done by the reaction mixture is passed over an acidic cation exchange resin.

The solvent can be added after the reaction or after, if appropriate neutralization can be removed by distillation.

The polyether polyols obtained are with commercially available polyols, for. B. Polyoxy alkylene polyols, miscible and can be used for the production of polyurethanes (e.g. Elastomers, foams, coatings) are used. The mechanical Properties of the polyurethanes made from vinyl alcohol copolymers are comparable to that of commercial polyurethanes.

Examples

Vinyl acetate (VAc) was distilled just before use. THF was dried over sodium, 2-propanol ( ⁱ PrOH) was used without further purification. The potassium methylate solution used was prepared by the reaction of 2.45 g of potassium with 250 ml of methanol. Baygal® K55 (Bayer AG), a trifunctional propylene oxide / ethylene oxide block copolymer, was dried in a vacuum mixer at 80 ° C. for 5 hours.

Characterization of the samples

¹ H-NMR spectra were used to determine the molecular weight and the end groups of the PVAc samples. The spectrum shows three different proton signals of the PVAc: between 1.6-2.0 ppm the signals of the methylene H-2 and the methyl group H-3 and between 5.0-5.2 ppm the signals of the methine group H-4. The two methyl groups of the 2-propanol-2-yl initiator H-1 give a signal at 1.2 ppm. Provided that the reaction is initiated by 2-propanol-2-yl radicals, all PVAc chains have the isopropanol unit as the start of the chain. Under this condition, the number-average degree of polymerization DP _n can be calculated from the ratios of the intensities of the signals of the monomer units (H-2, H-3, H-4; 6 H) and the intensities of the signals of the initiator (H-1, 6 H) become. In order to confirm the degrees of polymerization or molecular weights calculated from the ¹ H-NMR spectra, the molecular weight was also determined by means of vapor pressure osmosis (VPO).

¹ H-NMR spectra were recorded with a Bruker ARX300 spectrometer in d ₅ -pyridine. GPC measurements were carried out in DMF at 45 ° C. VPO (vapor pressure osmosis) was measured with a Knauer vapor pressure osmometer in CHCl ₃ . DSC measurements were carried out on a Perkin Elmer DSC-7. The glass transition temperatures (T _g ) were measured from the 2nd heating cycle at a heating rate of 10 K / min. The measurements were carried out in a temperature range from -100 ° C to 120 ° C. Dynamic mechanical analysis (DMA) was measured on a Rheometrics Solids Analyzer RSAII at 1 Hz and a heating rate of 2 k / min with "dual cantilever" geometry (50 × 4 × 2.5 mm) and an elongation of 0.2%. The storage modulus (E '), the loss modulus (E ") and the loss tangent (tan δ) were measured in the temperature range from 30 ° C. to 100 ° C. For the precise determination of the glass temperature by DMA, each sample was measured 5 times, the maximum of Loss tangent was evaluated as T _g in each case.

The number of OH groups was determined by titration and ¹ H-NMR. A mixture consisting of 0.45 L dry pyridine, 64.25 g phthalic anhydride and 10 mL N-methylimidazole was used as the esterification reagent for the titration. Tertiary OH groups are not esterified in this reaction and are therefore not detected. These groups also show negligible reactivity to isocyanates.

To determine the blank value V _blind , 25 mL of this reagent were stirred for 15 min with 25 mL pyridine and 50 mL water and then titrated with 1 N NaOH.

A polymer _sample with the mass m _sample g was heated under reflux with 25 ml of the esterification reagent for 15 min. 25 ml of pyridine and 50 ml of water were then added in order to hydrolyze the excess anhydride. V _sample is obtained from the titration of this solution with 1 N NaOH. Each polymer was measured twice. The number of OH groups per polymer (OHF) then results from the following formula: OHF = ((V _blind - V _sample ) .M _n ) / (1000.m _sample ) where M _{n is} the molecular weight of the polymer (determined by VPO or ¹ H-NMR).

The number of OH groups per polymer chain (OHF) can be determined by comparing the ¹ H-NMR spectra of the saponified sample with that of the PVAc used. Since the methyl group is removed with the acetate during the methanolysis, the signal of the methyl group also decreases between 1.7 and 2.3 ppm (H-2, H-3). By comparing the ratios of the signal intensities (H-2 + H-3) / H-1 of the saponified sample with that of the PVAc used, the OHF can be according to the formula

OHF = 2. ([(H-2 + H-3) / H-1] _substrate - [(H-2 + H-3) / H-1] _product )

be calculated.

example 1 PVAc6

A solution of 100 ml (1.08 mol) VAc in 1900 ml ⁱ PrOH, corresponding to a monomer concentration of 4.2 mol%, was placed in a 4 l three-necked flask with a KPG stirrer and reflux condenser and degassed with nitrogen for 60 min. 2 ml (10.9 mmol) of di-tert-butyl peroxide (DTBP) were added and the mixture was stirred under reflux for 18 h. The solvent was removed in vacuo and the polymer was dried in vacuo on a rotary evaporator at 100 ° C. for 60 min. 65 g of PVAc6 were obtained as a colorless, highly viscous oil.

Example 2 PVAc10

Example 1 was repeated with a monomer concentration of 8.3 mol%.

Example 3 PVAc11

Example 1 was repeated with a monomer concentration of 12.5 mol%.

The samples produced in Examples 1 to 3 were examined by means of ¹ H-NMR spectroscopy, vapor pressure osmosis (VPO), GPC and DSC. Table 1 summarizes the results obtained.

Table 1

Molecular weights between 600 and 1000 g / mol were achieved for VAc concentrations of 4 to 12 mol% in 2-propanol. The molecular weights calculated from the ¹ H-NMR spectra agree very well with the values obtained from the vapor pressure osmosis, which indicates that all chains have a 2-propanol-2-yl group on one end and a hydrogen atom on the other end of the chain. The apparent molecular weights M _n from the GPC correlate well with the absolute values of the VPO. From the slope of the plot M _n (GPC) against M _n (VPO) it follows that the molecular weight of the oligomeric PVAc in the GPC is overestimated by a factor of 30.

Example 4 PVAc6 / 3

0.39 ml (9.6 mmol) 2% potassium methoxide solution became a solution of Put 2.0 g (3.2 mmol) of PVAc6 in 40 ml of dry THF. The approach was Stirred at 0 ° C. for 60 min and at RT for a further 60 min. 3 g acidic ion exchanger Amberlite® IR 120 (Fluka) were added to neutralize the reaction mixture and filter after 15 min. The solvent was reduced Distilled off pressure and the polymer dried for 18 h at 60 ° C in a vacuum. PVAc6 / 3 was obtained as a highly viscous, colorless oil.  

Example 6 PVAc6 / 1

Example 4 was repeated, but only 0.13 ml (3.2 mmol) of potassium methanolate solution used.

Example 7 PVAc6 / 2

Example 4 was repeated, but only 0.26 ml (6.4 mmol) of potassium methanolate solution used.

Example 8 PVAc10 / 2

Analogous to Example 4, PVAc10 was twice the molar amount of potassium implemented methanolate solution.

Example 9 PVAc10 / 4

Analogous to Example 4, PVAc10 with four times the molar amount of potassium implemented methanolate solution.

Example 10 PVAc10 / 6

Analogous to Example 4 was PVAc10 with six times the molar amount of potassium implemented methanolate solution.

Example 11 PVAc11 / 2

Analogous to Example 4, PVAc11 was twice the molar amount of potassium implemented methanolate solution.  

Example 12 PVAc11 / 4

Analogous to Example 4 was PVAc11 with four times the molar amount of potassium implemented methanolate solution.

Example 13 PVAc11 / 6

Analogous to Example 4 was PVAc11 with six times the molar amount of potassium implemented methanolate solution.

Example 14 PVAc6 / 3

0.39 ml (9.6 mmol) 2% potassium methoxide solution was added to a solution of 2.0 g (3.2 mmol) PVAc6 in 40 ml ⁱ PrOH. The mixture was stirred at 0 ° C. for 60 min and at RT for a further 60 min. 3 g of acidic ion exchanger Amberlite® IR 120 (Fluka) were added to neutralize the reaction mixture and filtered off after 15 min. The solvent was distilled off under reduced pressure and the polymer was dried under vacuum at 60 ° C. for 18 h.

Example 15 PVAc6 / 1

Example 14 was repeated, but only 0.13 ml (3.2 mmol) of potassium methanolate solution used.

Example 16 PVAc6 / 2

Example 14 was repeated, but only 0.26 ml (6.4 mmol) of potassium methanolate solution used.

In all cases, the samples obtained were transparent, which indicates an even distribution of the introduced OH groups along the polymer chain. The experimental data obtained on the products produced in Examples 4-16 are summarized in Table 2; the samples are designated as PVAc x / y, where x refers to the degree of polymerization DP _{n of} the PVAc used and y to the number of OH groups introduced per chain (without the tertiary OH group at the beginning of the chain).

Table 2

In Table 2 it is clear that in all cases the experimentally observed number of OH groups per molecule (OHF) is smaller than the value expected from the stoichiometry. However, it can be seen that the degree of saponification is only controlled by the amount of methanol used. In all samples, the difference between the theoretically expected and actually introduced number of OH groups increases with increasing degree of saponification, e.g. B. are expected for the sample PVAc 10/6, 6 OH groups but found only 3.6 OH groups in the NMR spectrum. However, the deviations in the degree of saponification determined do not depend on the degree of polymerization of the samples used. It is therefore possible to predict the number of OH groups actually introduced using a certain amount of methanol. The methanolysis is not affected when using ⁱ PrOH instead of THF as an inert solvent. The different pK _a values of methanol and ⁱ PrOH cause only the methanolysis is observed.

In Fig. 1, the experimentally observed number of OH groups (ordinate) was plotted against the theoretically expected value (abscissa). Fig. 1a shows the NMR spectra obtained and Fig. 1b shows the experimental data obtained from the titration. The diagonal corresponds to the values expected for complete sales.

Example 17 Synthesis of a polyurethane elastomer

50 g (82 mmol) PVAc6 / 3 and 50 g (114 mmol) of a trifunctional propylene oxide Ethylene oxide block copolymer with a number average molecular weight of 440 g / mol (Baygal® K55, Bayer AG) was in a vacuum mixer for 2 hours at 120 ° C dried in an oil vacuum. The homogeneous mixture was cooled to 30 ° C and 68.4 g (274 mmol) methylene diphenylene diisocyanate (MDI, Baymidur® KL 3-500, Bayer AG) were dispersed in the polyol mixture. After stirring for 10 min the transparent mixture is poured into a mold (200 mm × 200 mm × 4 mm) and hardened for 12 h at 30 ° C and for a further 24 h at 80 ° C.  

Example 18 comparison

Example 17 was repeated, but PVAc6 / 3 was replaced by an equimolar amount of a trifunctional propylene oxide / ethylene oxide block copolymer with a number average molecular weight of 440 g / mol (Baygal® K55, Bayer AG) replaced.

The polyurethane sheets obtained were yellow and transparent. The mechanical Properties of the samples from Examples 17 and 18 are summarized in Table 3.

Table 3

The Young's modulus, a measure of the stiffness of the polymer, is larger in the polyurethane sample made with PVAc. The glass transition temperature, determined using dynamic mechanical analysis (DMA), increases only slightly from 79.2 to 81.5 ° C. The DMA curves in FIG. 2 show that there is no phase separation in the polyurethane (Ex. 17: solid squares, Ex. 18: circles).

Claims (4)

1. Copolymers of vinyl alcohol and vinyl esters and optionally with Vinyl ester copolymerizable monomers that have a degree of polymerization <30 and have an OH functionality of 1 to 10. 2. A method for producing a copolymer according to claim 1, wherein Vinyl ester monomers and optionally copolymerizable with vinyl esters Monomers in the presence of an initiator and a chain transfer agent polymerized with a degree of polymerization <30 and then base this polymer in an inert solvent partially catalyzes with the addition of defined amounts of a solvolysis agent is saponified. 3. Use of copolymers according to claim 1 for the production of Polyurethanes. 4. Polyurethane containing reaction products of copolymers according to Claim 1.