GB2076416A

GB2076416A - Polyurethanes of enhanced hydrolytic stability

Info

Publication number: GB2076416A
Application number: GB8115610A
Authority: GB
Original assignee: Instytut Chemii Przemyslowej
Current assignee: Instytut Chemii Przemyslowej
Priority date: 1980-05-24
Filing date: 1981-05-21
Publication date: 1981-12-02
Also published as: PL224461A1; JPS5755960A; BE888945A; PL127309B1

Abstract

The invention relates to a method for manufacturing of polyurethanes of an enhanced hydrolytic stability by an addition of a stabilizer to the polyurethane resin or to one of the initial reagents. Stabilizers used are organic compounds containing in the molecule at least one epithio group or mixtures of these compounds, optionally containing epoxy groups. The stabilizer is added to a solution of polyurethane in an organic solvent or to an aqueous dispersion of polyurethane, or else to the initial reagents at a concentration of 0.01 to 10 pbw per 100 pbw of polyurethane or the initial reagents.

Description

SPECIFICATION A method for manufacturing of polyurethanes having an enhanced hydrolytic stability The invention relates to the method for manufacturing of polyurethanes having an enhanced hydrolytic stability by use of suitably chosen additives.

Polyurethanes and, particularly, polyurethanes derived from polyester poloyols, are not sufficiently resistant to hydrolysis, especially when applied at elevated temperature and humidity or in an aqueous medium.

Methods for increasing of the hydrolytic stability of polyurethanes by use of suitably chosen initial reagents or by an addition of stabilizers are known.

The stabilizers added to polyurethanes contain functional groups, which are reactive towards acidic groups formed during hydrolysis of polyurethanes and enhance the rate of hydrolytic degradation by an autocatalytic mechanism. According to US 3193 522, US 3711 439 and US 3716 502 patent specifications, polycarbodiimides with an active -N C =N- group, which can react with acidic groups, are effective stabilizers for polyurethanes. An addition of colloidal silica, according to the US 3716502 patent specification, and of N - (trichloromethyl thio) phthalimide, according to the US 3711 439 patent specification, results in an enhancement of the effectivity of the carbodiimide stabilizers.

Polycarbodiimides are, however, insoluble in polyurethanes and in organic solvents used for preparation of polyurethanes, such as dimethylformamide and dimethylsulfoxide, and therefore - in spite of the high reactivity of-N =C=N- group -they are not sufficiently effective as stabilizers.

The other known group of stabilizers are epoxy compounds, which - according to (West) German 99 808, Belgian 816688 and Japanese 74 012 354 patent specifications - are more effective stabilizers than polycarbodiimides. Generally, aliphatic or aromatic glycidyl ethers and esters are added to the polyurethane solution after the synthesis is completed, but prior to polyurethane processing. Epoxy stabilizers claimed in the Japanese 74912354 patent specifications can be added either to the solution of polyurethane or the reaction medium at the moment of achieving intrinsic viscosity of the polymer higher than 0.4 and the process is continued in the presence of stabilizers until the required properties of polyurethane are obtained.

Epoxy compounds are, however, also not sufficiently effective probably because of the rather low reactivity of the epoxy group (even of an epoxy group in cycloaliphatic compounds), which reacts too slowly with acidic groups formed during degradation of polyurethanes.

An object of the present invention is to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided a method for the manufacture of polyurethanes having an enhanced hydrolytic stability due to the presence of stabilizers comprising introducing a stabilizer selected from organic compounds containing at least one epithio group per molecule into a polyurethane or into one of the initi cal reagents used to prepare the polyurethane at a concentration of from 0.01 to 10 parts by weight per 100 parts by weight of polyurethane or reagent.

Preferably the organic compound contains at least two epithio groups per molecule and may optionally contain at least one epoxy group.

The epithio compound may be added to the solution of polyurethane in an organic solvent, especially in dimethylformamide, dimethylsulfoxide ortet rahydrofuran or to the aqueous dispersion of polyurethane. In the last case, the stabilizer is prefer ably added as a solution in an organic solvent used for preparation of polyurethane, particularly in toluene.

The stabilizer, according to the present invention, can also be added to the initial reagents: either to the polyol reagent, particularly to polyether or polyester containing mainly hydroxyl end-groups, or else to the isocyanate reagent.

Preferred stabilizers comprise compounds, con taining 2,3 - epithiopropyl groups, particularly 2,3 epithiopropyl phenyl ether, 2, 3 - epithiopropyl cresyl ether, 2, 3 - epithiopropyl 2 - ethylhexyl ether or 2,3 epithiopropyl benzoate, or compounds containing groups derived from epithiocyclopentane or epithiocyclohexane particularly di - cyclopentadiene monosulfide or epithiocyclohexane.

According to the present invention, besides com pounds containing one epithio groups, organic compounds containing at least two epithio groups can be used. The reaction of functional groups of the stab i lizer with the acidic end-groups of polyurethane makes possible, in the case of stabilizers containing at least two epithio groups, a partial restoration of hydrolytically degraded macromolecules of polyurethane.

Preferred organic compounds containing at least two epithio groups comprise compounds with two epithiocyclohexyl groups, particularly 2 - (7 thiabicyclo - [4.1.0] heptyl- 3)-spiro-S1,3- dioxane- 5,3' - (7 - thiabicyclo - [4.1.0] heptane)or3,7 thiabicyclo - [4.1.0] heptyl - 3 - methyl 7 - thiabicyclo - [4.1.0] heptane carboxylate or a compound of the formula 1:

wherein R is hydrogen or methyl and n is zero to 6 or di - (2,3 - epithiopropyl) phthalate, di - (2,3 epithiopropyl) hexahydrophthalate, di - (2, 3 - epithiopropyl) adipate our a compound of the general formula 2:

or3::

wherein A is an alkylene group particularly -CH2CH2-,-CH2CH(CH3 > or-(CH2)4- group or -CH2CH2OCH2CH2- group, R is the same as in formula 1 and k and p have a value from zero to 6.

The present invention also provides stabilizers selected from epithionovolac resins of the formula 4;

wherein R is as previously defined for formulae 1, and m has a value of from zero to 6, esters of Cl-c8 alcohol, C1-C4 glycol or glycerol with unsaturated fatty acid in which double bonds are partly or completely replaced with epithio groups.

Equally preferable stabilizers to the above mentioned epithio compounds comprise compounds or mixtures, containing besides epithio groups also epoxy groups, e.g. the product obtained by chemical transformations of triglyceride of a mainly unsaturated fatty acid, in which the majority of double bonds has been replaced by epithio groups and the rest or part of the residual double bonds have been replaced with epoxy groups, or compounds of the formulae 1,2,3 or 4, wherein R, km, n and pare as defined previously and at the most half of sulphur atoms in epithio groups are replaced with oxygen atoms in eopxy groups.

Epithio compounds which are utilized in the present invention, can be advantageously obtained in the reaction of corresponding epoxy compounds with thiocyanates or with thiourea.

Organic compounds containing epithio groups, according to the invention, can be used as stabilizers suppressing hydrolysis of polyurethanes in a wide range of polyurethane applications, as for instance for fibres, synthetic leather, elastomers, expanded polyurethanes, adhesives and coatings.

The present invention will now be described by way of the following Examples.

Example I To a solution of 100 pbw of polyester based polyurethane in dimethylformamide were added 2 pbw of the product of chemical modification of rape-seed oil, in which double bonds have been partly replaced with epithio groups and containing 0.27 gram equivalents of epithio groups per 100 g of the modified oil. The resulting solution was thoroughly mixed, de-aerated, poured onto glass plate and placed in a drying box at 80"C to obtain a film. The film was cut into strips, half of which have been subjected to mechanical testing directly and the other half, after hydrolysis in a bath containing aqueous urea (1.20 gull) at 100 Cfor 12 hours, rinsing in distilled water and drying. Tensile strength, elongation at break and 100% modulus of polyurethane films stabilized with the epithio compound are compared with corresponding data for nonstabilized polyurethane film and for polyurethane film containing 3 pbw of the known stabilizer-polycarbodiimide Stabaxol P per 100 pbw of polyurethane (Table 1).

Table 1

Prior to hydrolysis After hydrolysis Elonga- Elonga- Composition of Tensile tion at 100% Tensile tion at 100% the polyurethane strength break modulus strength break modulus film MPa % MPa MPa % MPa Polyurethane stabilized with the epithio compound (modified rapeseed oil) 28.1 725 4.8 17.9 565 4.5 Nonstabilized polyurethane 25.5 680 4.1 3.2 225 1.6 Polyurethane stabilized with polycarbodiimide StabaxolP 22.8 I 712 3.9 6.5 430 1.6 Example II To a solution of 100 pbw of polyester based polyurethane in dimethylsulfoxide were added 5 pbw of 2 - (7 - thiabicyclo - [4.1.0] heptyl - 3) - spire {1, 3 - dioxane - 5, 3' - (7 - thiabicyclo [4.1.0] - heptane)}.

The resulting solution was thoroughly mixed, deareated and poured onto a glass plate to form a layer 1.5 mm thick.

The plate was placed in a drying box at 60"C. The film obtained this way was cut into strips. Half of the strips were immersed in the hydrolyzing bath having the composition described in Example I. After 12 hours the strips were taken away, rinsed in distilled water, dried and subjected to mechanical testing. In Table 2 are listed data concerning tensile strength, elongation at break and 100% modulus for the astabilized film, prior to and after hydrolysis, as well as corresponding results for nonstabilized film and forthe film containing 5 pbwofcarbodiimide Stabaxol 1 per 100 pbw of polyurethane and for the film containing 5pbw of colloidal silica and 3 pbw of the Stabaxol P stabilizer per 100 pbw of polyurethane, correspondingly.

Table2

Prior to hydrolysis Afterhydrolysis Elonga- Elonga Composition of Tensile tion at 100% Tensile tion at 100% the polyurethane strength break modulus strength break modulus film MPa % MPa MPa % MPa Polyurethane stabilized with cycloaliphatic epithio compound 28.1 685 4.0 22.1 594 4.2 Nonstabilized polyurethane 27.3 715 4.3 4.6 220 1.3 Polyurethane stabilized with carbodiimide Stabaxol 1 28.2 712 4.7 4.9 290 2.4 Polyurethane stabilized with Stabaxol P and colloidal silica 27.8 750 4.3 9.3 435 3.3 Example III To the solution of 100 pbw of polyester based polyurethane in dimethylformamide were added 3 pbw of a solution of the organic compound of the general formula 1, wherein R is hydrogen and n = 6, in dimethylformamide. After thorough mixing and de-aeration the solution was used for coating of a microporous synthetic leather substrate, comprising non-woven fabric impregnated with polyurethane and doubled to a thickness of 1 mm. The coated substrate was immersed in a coagulating bath, containing a water- dimethylformamide 75/25 mixture.

Then the coating was washed a number of times with water and squeezed to wash out dimethylformamide and dried. Samples of 4 x 7 cm were cut of the resulting material and tested in a Bally flexome ter, half of them - directly and the other half after hydrolysis, respectively. The samples were subjected to hydrolysis under conditions described in Example I. Data concerning flexural strength of microporous coatings are tabulated in Table 3 and compared with corresponding data for nonstabilized polyurethane coating and for polyurethane coating stabilized with 3 pbw of the Stabaxol P stabilizer per 100 pbw of polyurethane.

Table 3

Flexural strength, thousands of bends Composition of the sample Prior to hydrolysis After hydrolysis Polyurethane stabilized with the epithio compound 1000 750 Nonstabilized polyurethane 1000 200 Polyurethane stabilized with Stabaxol P polycarbodiimide X000 470 Organic compounds containing at least one, and preferably at least two epithio-groups, and, optionally, epoxy groups are highly effective in suppressing hydrolysis of polyurethanes. High solubility in organic solvents used for preparation of polyurethanes, such as dimethyl formamide and dimethylsulfoxide, as well as in initial reagents, such as polyester and polyether polyols and in isocyanates, and no effect on the course of isocyanatepolyol addition make for the other advantages of this group of stabilizers.

Claims

1. A method for the manufacture of polyurethanes having an enhanced hydrolytic stability due to the presence of stabilizers comprising introducing a stabilizer selected from organic compounds containing at least one epithio group per molecule into a polyurethane or into one of the initial reagents used to prepare the polyurethane at a concentration of from 0.01 to 10 parts by weight per 100 parts by weight of polyurethane or reagent.

2. A method according to claim 1 wherein the organic compound contains at least two epithio groups per molecule.

3. A method according to either claim 1 or claim 2 wherein the organic compound further contains at least one epoxy group in the molecule.

4. A method according to any one of claims 1,2 or 3 wherein the stabilizer comprises a mixture of the organic compounds.

5. A method according to any one of the preceding claims wherein the stabilizer is added before synthesis of the polyol reagent used for preparation of the polyurethane.

6. A method according to claim 5 wherein the polyol reagent is a polyester or polyether with mainly hydroxyl end-groups.

7. A method according to any one of claims 1 to 4 wherein the stabilizer is added to the isocyanate reagent used for preparation of the polyurethane.

8. A method according to any one of claims 1 to 4 wherein the stabilizer is introduced to the reaction mixture during the preparation of the polyurethane.

9. A method according to any one of claims 1 to 4 wherein the stabilizer is added to a solution of polyurethane in a polar solvent.

10. A method according to claim 9 wherein the polar solvent is selected from dimethylformamide, dimethylsulphoxide and tetrahydrofuran.

11. A method according to any one of claims 1 to 4wherein the stabilizer is added to an aqueous dispersion of polyurethane in the form of a solution in an organic solvent used for the preparation of polyurethane.

12. A method according to claim 11 wherein the organic solvent is toluene.

13. A method according to any preceding claim wherein the stabilizer comprises an organic compound having a 2,3 - epithiopropyl group in its molecule.

14. A method according to claim 13 wherein the organic compoundlis selected from 2,3 - epithiopropyl phenyl ether,-,2,3- epithiopropyl cresyl ether, 2,3 - epithiopropyl!2 - ethylhexyl ether and 2,3 epithiopropyl benzoate.

15. A method according to any one of claims 1 to 12 wherein the stabilizer comprises an organic compound selected finom those containing epithiocyclopentane derived groups and epithiocyclohexane derived groups..

16. A method according to claim 15 wherein the stabilizer comprises an organic compound selected from dicyclopentadiene, monosulphide and epithiocyclohexane.

17. Ametrhod accordingto anyoneof claims2to 12 wherein the stabilizer comprises an organic compound containing at least two epithiocyclohexyt groups per molecule

18. A method according to claim 17 wherein the stabilizer comprises an organic compound selected from 2 - (7 - thiabicyclo - [4.1.0] heptyl - 3) - spiro -(1, 3 - dioxane - 5, 3' - (7 - thiabicyclo - p4.1.0] heptane); 3,7 - thiabicyclo - [4.1.0] heptyl - 3- methyl 7 - thiabicyclo [4.1.ûl heptane carboxylate; a compound of the general formula

wherein R is hydrogen or a methyl group and n has a value of from zero to 6; di - (2,3 - epithiopropyl phthalate); di - (2,3 - epithiopropyl) hexahydroph thalate; di - (2,3 - - epithiopropyl adipate); a com- pound of the general formula 2;

and a compound of the general formula 3;

in each of which A is an alkylene group, R is hydrogen or a methyl group and k and p respectively have a value of from zero to 6.

19. A method according to claim 18 wherein the alkyiene group represented byA in the general for mulae 2 and 3 is selected from -CH2CH2-, -CH2CH(CH3t, CH2)4- and -CH2CH20CH2CH2- groups.

20. A method according to any one of claims 2 to 12 wherein the stabilizer is selected from an epithionovolak resin of the general formula 4:

wherein R is hydrogen or a methyl group and m has a value of from zero to 6; an ester of a C1-C8 alcohol, an ester of a C1-C4 diol, and an ester of a C1-C4 triol wherein each ester is formed with a mainly unsatu rated fatty acid in which the double bonds are partly or completely replaced with epithio groups.