Process for the Preparation of a Mercapto-terminated Liquid Polymer

Abstract

Process for the preparation of a mercapto-terminated liquid polymer comprising the steps of: a) reacting (para)formaldehyde with a halo-alcohol to form a reaction mixture comprising bis(2-dihaloalkyl)formal and b) reacting the reaction mixture of step a) with either (i) sodium polysulfide or (ii) a combination of sodium hydrosulfide and sulfur, wherein the process is performed in the presence of a branching agent selected from the group consisting of di-aldehydes and their corresponding actetals and hemi-acetals.

Claims

1. Process for the preparation of a mercapto-terminated liquid polymer comprising the steps of: a) reacting (para)formaldehyde with a halo-alcohol to form a reaction mixture comprising bis(2-dihaloalkyl)formal and b) reacting the reaction mixture of step a) with either (i) sodium polysulfide or (ii) a combination of sodium hydrosulfide and sulfur, wherein the process is performed in the presence of a branching agent selected from the group consisting of di-aldehydes and their corresponding actetals and hemiacetals.

2. Process according to claim 1 wherein the branching agent is a di-aldehyde with the formula (O)(H)C(CH.sub.2).sub.nC(H)(O), where n is in the range 0-8.

3. Process according to claim 1 wherein the branching agent is a hemi-acetal with the formula (O)(H)C(CH.sub.2).sub.nC(H)(OR.sup.1)(OH) or (OH)(OR.sup.1)(H)C(CH.sub.2).sub.nC(H)(OR.sup.1)(OH), in which n is in the range 0-8 and each R.sup.1 is independently selected from alkyl groups with 1-10 carbon atoms.

4. Process according to claim 1 wherein the branching agent is an acetal with the formula (O)(H)C(CH.sub.2).sub.nC(H)(OR.sup.1)(OR.sup.2) or (OR.sup.1)(OR.sup.2)(H)C(CH.sub.2).sub.nC(H)(OR.sup.1)(OR.sup.2), in which n is in the range 0-8 and each R.sup.1 and R.sup.2 is independently selected from alkyl groups with 1-10 carbon atoms.

5. Process according to claim 2 wherein n is in the range 0-3.

6. Process according to claim 3 wherein each R.sup.1 and/or R.sup.2 is independently selected from alkyl groups with 1 or 2 carbon atoms.

7. Process according to claim 4 wherein the acetal is selected from the group consisting of glyoxal dimethyl acetal, glyoxal bis(dimethyl acetal), malonic aldehyde bis(diethyl acetal), and glutaric aldehyde bis(dimethyl acetal).

8. Process according to claim 1 wherein the branching agent is present in step a).

9. Process according to claim 8 wherein branching agent is added during step b).

10. Process according to claim 1 wherein the branching agent is used in an amount of 0.01 to 10 mol %, relative to (para)formaldehyde (calculated as CH.sub.2O).

11. Process according to claim 1 wherein the halo-alcohol is a chloroalcohol.

12. Process according to claim 1 wherein step b) is conducted in the presence of a dihaloalkane.

13. Process according to claim 1 wherein step a) is conducted in the presence of a polyol.

14. Process according to claim 1 wherein step b) is conducted in the presence of a pre-polymer with the structure
X(R.sup.2O).sub.n-CH.sub.2O(R.sup.1O).sub.m-CH.sub.2(OR.sup.2).sub.p-X wherein R.sup.1 and R.sup.2 can be the same or different and are selected from alkane chains containing 2-10 carbon atoms, X is a halogen atom, and n, m, and p are integers that can be the same or different and have a value in the range 1-6.

15. Process according to claim 14 wherein X is Cl, R.sup.1 is CH.sub.2CH.sub.2, and R.sup.2 is CH.sub.2CH.sub.2, CH.sub.2CH.sub.2CH.sub.2, or CH.sub.2CH.sub.2CH.sub.2CH.sub.2.

16. Mercapto-terminated liquid polymer obtainable by the process of claim 1.

17. Process according to claim 3 wherein n is in the range 0-3.

18. Process according to claim 4 wherein n is in the range 0-3.

19. Process according to claim 4 wherein each R.sup.1 and/or R.sup.2 is independently selected from alkyl groups with 1 or 2 carbon atoms.

20. Process according to claim 5 wherein each R.sup.1 and/or R.sup.2 is independently selected from alkyl groups with 1 or 2 carbon atoms.

Description

EXAMPLES

Comparative Example A

Step a)

[0067] A mixture of 4 moles paraformaldehyde, 10 moles ethylenchlorohydrin (ECH), and 5.4 g 37% HCl was heated to 60 C. while stirring, until the solubilization of the paraformaldehyde occurred. The reaction mixture was then subjected to two azeotropic distillation steps under reduced pressure (120 mbar/54 C. head temperature and 20 mbar/94 C.) in order to remove the reaction water with excess ECH. 680 g bis(2-chloroethyl)formal was formed.

Step b)

[0068] 2.2 moles of Na.sub.2S.sub.x (x=2.4) in an aqueous 2.1 mol/l solution were mixed with 25.1 g of a 30 wt % aqueous MgCl.sub.2 solution and 12.6 g of a 50% NaOH solution (to form in situ Mg(OH).sub.2) and 10 mL of sodium butyl naphthalene sulfonate (a wetting agent). The resulting mixture was heated to 96-98 C. A mixture of 2.2 moles of the bis(2-chloroethyl)formal formed in step a) with 0.04 mol trichloropropane was added dropwise within 1 hour while keeping the temperature between 96 and 98 C. After a post reaction of 30 minutes at 98 C., the reaction mixture was treated with 0.5 mol Na.sub.2S (which was prepared by addition of 0.5 moles NaOH to 0.5 moles NaSH). Finally, the reaction mixture was stirred for 2 hours at 100 C. The formed latex was washed with water several times to remove any soluble salts.

[0069] The washed latex was treated with 0.18 moles sodium dithionite (34 g Na.sub.2S.sub.2O.sub.4, 90 wt %), 0.6 moles NaOH (50 wt % solution) and 0.2 moles sodium bisulfite (50 mL; 39 wt % solution), while stirring for 30 minutes at 98 C. The resulting product was washed free of soluble salts and coagulated by acidification with acetic acid to a pH in the range 4-5. After coagulation, the polymer is washed free of acetate ions and dewatered under reduced pressure (90 C., 20 mbar). The reaction yielded 350 g of mercapto-terminated polysulfide.

[0070] The obtained mercapto-terminated polysulfide was cured with an MnO.sub.2-based curing paste, according to a generally known procedure. MnO.sub.2 cures the polysulfide resin by oxidation of the SH-terminal groups to disulfide linkages. The prepared test pieces were evaluated regarding their Shore A hardness (SAH)following the method of DIN 53505as a measure of the extent of crosslinking.

Result:

[0071] After 5 secs: SAH=40

[0072] After 3 min: SAH=38

[0073] The Shore A hardness before crosslinking was:

[0074] After 5 s: SAH=28

[0075] After 3 min: SAH=25

Example 1

[0076] Comparative Example 1 was repeated, except that 0.05 moles glyoxal (added as 40 wt % water solution) was additionally present in step a) and no trichloropropane was present in step b).

[0077] The process yielded 358 g mercapto-terminated polysulfide.

[0078] The Shore A hardness of the product was:

[0079] After 5 s: SAH=41

[0080] After 3 min: SAH=39

Example 2

[0081] Example 1 was repeated using 0.05 moles malonic aldehyde bis(diethylacetal) instead of 0.05 moles glyoxal

[0082] The process yielded 355 g mercapto-terminated polysulfide.

[0083] The Shore A hardness of the product was:

[0084] After 5 s: SAH=40

[0085] After 3 min: SAH=38

Example 3

[0086] Example 1 was repeated using 0.05 moles glutaric dialdehyde (add as 50 wt % aqueous solution) instead of 0.05 moles glyoxal.

[0087] The process yielded 352 g mercapto-terminated polysulfide.

[0088] The Shore A hardness of the product was:

[0089] After 5 s: SAH=41

[0090] After 3 min: SAH=38

Comparative Example B

Step a)

[0091] A mixture of 4 moles paraformaldehyde, 7.5 moles ethylenchlorohydrin (ECH), 1 mol triethylene glycol (TEG) and 5.4 g 37% HCl was heated to 60 C. while stirring until solubilization of the paraformaldehyde. The reaction mixture was then subjected to two azeotropic distillation steps under reduced pressure (120 mbar/54 C. head temperature and 20 mbar/94 C.) in order to remove the reaction water with excess ECH.

[0092] This step resulted in the formation of a mixture comprising 680 g pre-polymer with an average molecular weight of 233 g/mol.

Step b)

[0093] 2.2 moles of Na.sub.2S.sub.x (x=2.4) in an aqueous 2.1 mol/l solution were mixed with 25.1 g of a 30 wt % aqueous MgCl.sub.2 solution and 12 g of a 50% NaOH solution (to form in situ Mg(OH).sub.2) and 10 mL of sodium butyl naphthalene sulfonate. The resulting mixture was heated to 88 C.

[0094] To this mixture was addeddropwise within 1 hour while keeping the temperature between 88 and 92 C.a pre-polymer containing mixture consisting of 0.71 mol dichloroethan, 1.07 mol prepolymer of step a and 0.42 mol diformal together with 0.04 mol trichloropropane.

[0095] After a post reaction of 30 minutes at 98 C., the reaction mixture was treated with 0.5 mol Na.sub.2S (which was prepared by addition of 0.5 moles NaOH to 0.5 moles NaSH). Finally, the reaction mixture was stirred for 2 hours at 100 C. The formed latex was finally washed with water several times to remove any soluble salts.

[0096] The washed latex was treated with 0.18 moles sodium dithionite (34 g Na.sub.2S.sub.2O.sub.4, 90 wt %), 0.6 moles NaOH (50 wt % solution) and 0.2 moles sodium bisulfite (50 mL; 39% solution), while stirring for 30 minutes at 98 C. The resulting product was washed free of soluble salts and coagulated by acidification with acetic acid to a pH in the range 4-5. After coagulation, the polymer is washed free of acetate ions and dewatered under reduced pressure (90 C., 20 mbar). The reaction yielded 352 g of mercapto-terminated polysulfide.

[0097] The obtained polysulfide was cured with MnO.sub.2 as described in Comparative Example A. The prepared test pieces were evaluated regarding their Shore A hardness (SAH) as a measure of the extent of crosslinking.

Result:

[0098] After 5 secs: SAH=40

[0099] After 3 min: SAH=37

[0100] The Shore A hardness before crosslinking was:

[0101] After 5 s: SAH=26

[0102] After 3 min: SAH=23

Example 4

[0103] Comparative Example B was repeated, except that in step a) 0.05 moles glyoxal (added as 40 wt % aqueous solution) was additionally present and no trichloropropane was present in step b).

[0104] The Shore A hardness of the product was:

[0105] After 5 s: SAH=42

[0106] After 3 min: SAH=39