Process for the preparation of a polythioethersulfide

Abstract

Process for the production of a mercapto-terminated liquid polymer with the formula HS—R—(Sy —R)t —SH, wherein each R is independently selected from branched alkanediyl or branched arenediyi groups and groups with the structure —(CH2)p—O—(CH2)q—O—(CH2)r- and wherein 0-20% of the number of R-groups in the polymer are branched alkanediyl or branched arenediyl groups and 80-100% of the number of R-groups in the polymer have the structure —(CH2)p—O—(CH2)r—, wherein t has a value in the range 1-60, y is an average value in the range 1.0-1.5, q is an integer the range 1 to 8, and p and r are integers the range 1-10. The resulting polymer has an improved ability of recovering its original shape after release from deforming compression forces and improved tendency to recover during the application of those forces.

Claims

1. A process for the production of a mercapto-terminated liquid polymer with the formula
HS—R—(S.sub.y—R).sub.t—SH   (I) wherein each R is independently selected from: branched alkanediyl or branched arenediyl groups of the formula —R.sup.1(—X).sub.n—, wherein R.sup.1 is a hydrocarbon group, n=1 or 2, and X is a branching point that connects to another polythioether chain, and groups with the structure —(CH.sub.2).sub.p—O—(CH.sub.2).sub.q—O—(CH.sub.2).sub.r— and wherein 0-20% of the number or R-groups in the polymer are said branched alkanediyl or branched arenediyl groups and 80-100% of the number or R-groups in the polymer have the structure —(CH.sub.2).sub.p—O—(CH.sub.2).sub.q—O—(CH.sub.2).sub.r—, wherein t has a value in the range 1-60, y is an average value in the range 1.0-1.5, q is an integer the range 1 to 8, and p and r are integers the range 1-10, said process comprising the following steps: a) forming a polymer by reacting a bis(haloalkyl)formal with alkali polysulfide of the average formula M.sub.2S.sub.x, wherein M is an alkali metal and x is an average value in the range from 1.04 to 1.8, optionally in the presence of an amount of branching agent of the formula —R.sup.1(—X).sub.n—, wherein R.sup.1 is a hydrocarbon group, n =1 or 2, and X is a branching point that connects to another polythioether chain, b) reacting said polymer with a reducing agent in an aqueous reaction mixture, thereby reductively splitting polysulfide linkages, and c) lowering the pH of the mixture resulting from step b) to below 6.0 by adding an acid.

2. The process according to claim 1 wherein the polymer has the structure
HS—(CH.sub.2).sub.p—O—(CH.sub.2).sub.q—O—(CH.sub.2).sub.r—[S.sub.y—(CH.sub.2).sub.p—O—(CH.sub.2).sub.q—O—(CH.sub.2).sub.r].sub.t—SH wherein p, q, r, y, and t have the same meaning as in claim 1.

3. The process according to claim 1 wherein 9-20% of the number of R-groups in the polymer are branched alkanediyl or branched arenediyl groups and 80-91% of the number or R-groups in the polymer have the structure —(CH.sub.2).sub.p—O—(CH.sub.2).sub.q—O—(CH.sub.2).sub.r—.

4. The process according to claim 1 wherein the bis(haloalkyl)formal has the structure (II):
Cl—(CH.sub.2).sub.p—O—(CH.sub.2).sub.q—O—(CH.sub.2).sub.r—Cl   (II) wherein p and r are integers, independently chosen from the range 1-10 and q is an integer in the range 1-8.

5. The process according to claim 1 wherein q is in the range 1-4.

6. The process according to claim 4 wherein the bis(haloalkyl)formal is bis(2-dichloroethyl)formal.

7. The process according to claim 1 wherein y is in the range from 1.01 to 1.50.

8. The process according to claim 1 wherein the reducing agent is Na.sub.2S.sub.2O.sub.4 or a mixture comprising NaSH and Na.sub.2SO.sub.3.

9. The process according to claim 1 wherein the alkali polysulfide is sodium polysulfide and wherein the molar ratio of sodium polysulfide (calculated as Na.sub.2S.sub.x), relative to bis(haloalkyl)formal, is in the range 0.8-2.4.

10. The process according to claim 1 wherein said branching agent is present in step a).

11. The process according to claim 10 wherein the branching agent is a trihalide or a tetrahalide.

12. The process according to claim 11 wherein the branching agent is selected from 1,2,3-trichloropropane, 1,2,3-tribromopropane, 1,3-dichloro-2-(chloromethyl)-2-methylpropane, pentaerythritol tetrabromide, tetrabromoethane, 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene, and 1,2,4,5-tetrakis(bromomethyl)-benzene.

13. The process according to claim 12 wherein the branching agent is 1,2,3-trichloropropane.

14. The process according to claim 10 wherein the branching agent is present in an amount of 0.1 to 25 mol %, relative to the amount of bis(haloalkyl)formal.

15. The process according to claim 14 wherein the branching agent is present in an amount of 10 to 25 mol %, relative to the amount of bis(haloalkyl)formal.

16. The process according to claim 4, wherein p and r are integers, independently chosen from the range 1-6.

17. The process according to claim 16, wherein p and r are each equal to 2.

18. The process according to claim 5 wherein q is equal to 1 or 2.

Description

FIGURES

(1) FIG. 1 shows cured samples of a reference polysulfide and of the polymers of Example 1 and 2.

(2) FIG. 2 shows the same samples after annealing at 80° C. under load (2.6 kg) for 4 hours. On the left, the reference polysulfide before annealing, i.e. the sample of FIG. 1, is shown as a comparison.

EXAMPLES

Example 1

(3) A 1.5-liter round-bottomed flask was fitted with a heating mantle, reflux condenser, thermometer and mechanical stirrer. The flask was charged with 362 ml water, 196 ml of a sodium hydrogen sulfide solution (8.9 mol/I, 1.74 mol) and 87.4 ml sodium polysulfide-liquor (3.29 mol/l, 0.29 mol, sulfur content 2.45). The x-value at this stage was 1.21. Further, 11.9 ml of a 30 wt % solution of C6-alkylglucoside (65 wt % solution in water; AG6206, supplied by AkzoNobel), 1.4 g tetra-butylammonium hydrogensulfate, 18.1 g of a magnesium chloride solution (45 wt % in water) and 155.5 g sodium hydroxide (50 wt % solution in water) were added to the flask.

(4) The suspension was stirred at approximately 350 rpm and heated to 76° C. After reaching 76° C., a solution containing 327.8 g bis(2-chloroethyl)formal (1.81 mol) and 5.3 g 1,2,3-trichloropropane (3.6 mmol) was added dropwise within 1.5 hours. During the addition and the following 4.5 hours, the temperature was kept constant in the range of 76 to 84° C., during which an additional 84 ml of a sodium hydrogen sulfide solution (8.9 mol/L, 0.7 mol) were added, reducing the x-value to 1.15.

(5) The suspension was cooled down to ambient temperature. After sedimentation of the polymer, the mother liquor was decanted off. The polymer was washed with 1 liter of water. The washed polymer was charged to a 1.5-liter round-bottomed flask fitted with a heating mantle, reflux condenser, thermometer and mechanical stirrer. 417 ml water, 40.3 g sodium dithionite (90 wt %), 39.4 ml sodium hydrogen sulfite-solution (41 wt %) and 26.4 g sodium hydroxide (50 wt % solution in water) were added to the stirred (350 rpm) suspension. It was heated to 80±4° C. and was kept at that temperature for 2 hours. The mother liquor was decanted off and the polymer was washed with 1 liter of water. The polymer was suspended in 1 liter of water and acidified with acetic acid to a pH-value of 4.8. The mother liquor was decanted off and the polymer was washed three times with 1 liter of water. The washed polymer was stripped in a rotary evaporator at 85° C. under vacuum to obtain 230 g (yield: 95%) of a pale yellow liquid polymer with a viscosity of 5.3 Pa.Math.s and a number average molecular weight of 2,300 g/mol, determined by GPC (polystyrene standards).

(6) Attenuated total reflectance fourier transformation infrared spectroscopy of the samples was performed between 600 cm.sup.−1 and 4,000 cm.sup.−1 with 30 scans. The non-detection of an absorbance in the wavelength region between 3,200 cm.sup.−1 and 3,700 cm.sup.−1 confirmed the absence of any hydroxyl-functional end-groups.

(7) In order to determine the number of mercapto-terminal groups of the resulting polymer, the polymer was dissolved in toluene, water was added, and the resulting mixture was titrated with an iodine solution. After that, a starch solution containing mercury(II)-iodine was added and the excess of iodine was back-titrated with a sodium thiosulfate solution.

(8) ICP-OES indicated that the y value of the polymer was 1.3.

Example 2

(9) A 2.5-liter reactor was fitted with a heating mantle, reflux condenser, thermometer and mechanical stirrer. The reactor was charged with 600 ml water, 490 ml of a sodium hydrogen sulfide solution (8.8 mol/liter, 4.3 mol) and 212 ml sodium polysulfide-liquor (3.35 mol/l, 0.7 mol, sulfur content 2.41). The x-value at this stage was 1.2. Further, 37.7 ml of a 30 wt % solution of C6-alkylglucoside in water (AG6206; supplied by AkzoNobel; 65 wt % solution in water), 2.4 g tetra-butylammonium hydrogensulfate, 32.6 g of a magnesium chloride solution (45 wt % in water) and 270 g sodium hydroxide (50 wt % solution in water) were added to the flask.

(10) The suspension was stirred at approximately 350 rpm and heated to 76° C. After reaching 76° C., a solution containing 498 g bis(2-chloroethyl)formal (2.76 mol) and 48 g 1,2,3-trichloropropane (0.3 mmol) was added dropwise within 1.5 hours. During the addition and the following 4.5 hours, the temperature was kept constant in the range of 76 to 84° C., during which an additional 84 ml of a sodium hydrogen sulfide solution (8.9 mol/L) were added.

(11) The resulting highly branched polymer was a rubbery substance which could not be processed to a curable state. A subsequent splitting step was therefore required.

(12) The suspension was cooled down to ambient temperature. After sedimentation of the polymer, the mother liquor was decanted off. The polymer was washed with 1.2 liter of water. The washed polymer was charged to a 2.5-liter reactor fitted with a heating mantle, reflux condenser, thermometer and mechanical stirrer. 750 mL water, 109 g sodium dithionite (90 wt %), 106 ml sodium hydrogen sulfite-solution (41 wt %) and 71 g sodium hydroxide (50 wt % solution in water) were added to the stirred (350 rpm) suspension. It was heated to 80±4° C. and was kept at that temperature for 2 hours. The mother liquor was decanted off and the polymer was washed with 1.2 liter of water. The polymer was suspended in 1.2 liter of water and acidified with acetic acid to a pH-value of 4.8. The mother liquor was decanted off and the polymer was washed three times with 1 liter of water. The washed polymer was stripped in a rotary evaporator at 85° C. under vacuum to obtain 389 g (yield: 89%) of a pale yellow liquid polymer with a viscosity of 3.2 Pa*s and a number average molecular weight of 1,700 g/mol.

(13) ICP-OES indicated that the y value of the polymer was 1.3.

(14) Compression Set Tests

(15) In order to determine the Compression Set of the cured polymers of Examples 1 and 2 and to compare it with the commercial polysulfide polymer with an y-value of 2.0 (Thioplast® G21; ex-AkzoNobel), material was cured using a curing paste having the ingredients listed in Table I. The curing paste was finely grounded on a triple-roll mill and stored at low temperature before use.

(16) TABLE-US-00001 TABLE 1 Composition of the curing-paste. Component pbw Manganese(IV)oxide 100 Benzyl phthalate 100 Diphenyl guanidine 6.0 Deaerator (Airex 900) 7.4 Sodium hydroxide (50 wt. %) 3.6

(17) Polymer was mixed with the paste, poured in a mold, stored at ambient temperature for 30 minutes to enable the release of enclosed air-bubbles, and cured at 60° C. for 18 hours. The amount of curing paste used depended on the thiol content of the polymer.

(18) TABLE-US-00002 TABLE 2 Curable compositions Sample Polysulfide G21 Example 1 Example 2 Quantity polymer (g) 30 30 30 Quantity curing paste (g) 6.3 6.9 15 Water (μL) 0.5 0.5 0.5

(19) The Compression Set test was performed according to ISO 815. This test determines the ability of elastomeric materials to return to their original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber material is compressed over time, it loses its ability to return to its original thickness. Compression Set data are expressed as a percentage. The lower the percentage, the better the material resists permanent deformation under a given deflection and temperature range.

(20) In this example, specimen B was used, which was compressed to 25% of its original height, and the compression device was placed in an oven at specified temperatures (23 and 80° C.) for a period of 24 hours. After removing the sample from the oven, the specimen was allowed to cool for 30 minutes before measuring the final thickness.

(21) TABLE-US-00003 TABLE 3 Compression sets measurements Compression set (%) Temperature (° C.) Polysulfide G21 Example 1 Example 2 23 68.2 9.4 8.7 80 96.6 94.6 92.4

(22) Table 3 shows that the compression set of the cured polysulfide polymer G21 is with 68.2% at ambient temperature quite high. This indicates a high level of cold flow. In comparison to that, the compression set of the cured polymers of Examples 1 and 2 depict levels as low as 9.4% and 8.7% at ambient temperature. This clearly shows the beneficial effect of the reduced disulfide-content on the creep-resistance.

(23) To further support the above finding and to depict the phenomenological improvement related to the reduced disulfide-content of the polymer, samples were cured in the same manner as the compression set test specimen. The cured samples were removed from the mold and stored while loaded with 2.6 kg each for 4 hours at 80° C. The relation between the original and the retained height was used as indicator for the pressure-induced flow of the material.

(24) The cured polysulfide G21 sample reduced in height to 71% of the original value, which indicates a considerable extent of flow under pressure. The reduction in height is clearly seen in FIG. 2.

(25) The polymer of Example 1 retained 95% of its original height, while the polymer of Example 2 retained 99% of its original height (see also FIG. 2). These results clearly indicate a reduced flow of the material and high mechanical strength at high temperature.