LOW-SALT PROCESS FOR THE PREPARATION OF A POLYSULFIDE

Abstract

Process for the preparation of a polysulfide comprising the step of reacting in the absence of a dihaloalkane a bis(2-dihaloalkyl)formal in the presence of (i) a pre-polymer (I) according to structure (I)

X(R2O)nCH2O(R1O)mCH2(OR2)pX(I),

wherein R1 and R2 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, with either (i) sodium polysulfide or (ii) a combination of sodium hydrosulfide and sulfur.

Claims

1. Process for the preparation of a polysulfide comprising the step of reacting a bis(2-dihaloalkyl)formal with either (i) sodium polysulfide or (ii) a combination of sodium hydrosulfide and sulfur, the reaction being performed in the absence of a dihaloalkane and in the presence of a pre-polymer (I) according to structure (I)
X(R.sup.2O).sub.nCH.sub.2O(R.sup.1O).sub.mCH.sub.2(OR.sup.2).sub.pX(I), 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.

2. Process according to claim 1, wherein the bis(2-dihaloalkyl)formal is bis(2-dichloroalkyl)formal.

3. Process according to claim 1 wherein the X is a halogen selected from Cl, Br, and I.

4. Process according to claim 3 wherein the X is Cl.

5. Process according to claim 1, wherein the R.sup.1 of the pre-polymer (I) is CH.sub.2CH.sub.2.

6. Process according to claim 1, wherein the R.sup.2 of the pre-polymer (I) is CH.sub.2CH.sub.2, CH.sub.2CH.sub.2CH.sub.2, or CH.sub.2CH.sub.2CH.sub.2CH.sub.2.

7. Process according to claim 1, wherein the product resulting from the reaction of the bis(2-dihaloalkyl)formal with sodium polysulfide in the presence of the pre-polymer (I) is treated with a reduction agent to obtain a liquid polysulfide.

8. Process according to claim 1, wherein the molar ratio of sodium polysulfide (calculated as Na.sub.2S.sub.x) relative to the bis(2-dihaloalkyl)formal is in the range 0.8-1.4.

9. Process according to claim 1, wherein a mixture comprising bis(2-dihaloalkyl)formal and the pre-polymer (I) is added to an aqueous solution of sodium hydrosulfide and sulfur.

10. Process according to claim 9, wherein the aqueous solution has a temperature in the range of 60 to 100? C.

11. Process according to claim 1, wherein the weight ratio of the bis(2-dihaloalkyl)formal to the pre-polymer (I) is in the range of 90:10 to 10:90.

12. Product obtained by the process according to claim 1.

13. A composition comprising a product obtained by the process according to claim 1, said composition selected from sealants, adhesives and coating compositions.

Description

[0033] In one embodiment, the process of the invention is performed by first preparing a mixture comprising the bis(2-dihaloalkyl)formal, the pre-polymer, and optionally the branching agent, and adding this mixture to an aqueous solution of sodium polysulfide and alkali metal hydroxide whereby the process is performed in the absence of a dihaloalkane. Optionally, a dispersing agent, such as magnesium hydroxide, and/or a wetting agent (e.g. sodium butylnaphthalenesulfonate) may be present in the solution.

[0034] The mixture is preferably added slowly, e.g. dropwise, to the solution. The temperature of the solution is preferably in the range 60 to 100? C., more preferably from 80 to 95? C. and most preferably from 85 to 90? C.

[0035] In a second embodiment, the process of the invention is performed by first preparing a mixture comprising bis(2-dihaloalkyl)formal and the pre-polymer (I), and optionally the branching agent, and adding this mixture to an aqueous solution of NaHS and sulfur. This embodiment has the additional advantage of a simple process design. The bis(2-dihaloalkyl)formal-containing mixture is preferably added slowly, e.g. dropwise, to the NaHS and sulfur solution. The temperature of the NaHS and sulfur solution is preferably in the range 60 to 100? C., more preferably from 80 to 100? C. and most preferably from 90 to 100? C. Preferably, a phase transfer catalyst (PTC), such as a quaternary ammonium compound, is added to the mixture. A PTC according to the invention is a catalyst which facilitates the migration of a reactant from a first phase into a second phase, wherein the reaction occurs in the second phase. The polymer obtained in this embodiment is a liquid polysulfide.

[0036] In a further embodiment, the process according to the invention is performed by adding the reactants to one reactor, preferably sequentially.

[0037] As a subsequent step, the resulting reaction mixture is preferably treated with a desulfurization agent (e.g. sodium hydroxide and sodium hydrogen sulfide) to eliminate any labile sulfur atoms. This desulfurization step can be conducted at a preferred temperature of 80-110? C., more preferably 85-105? C., and most preferably 90-100? C. The reaction time is preferably 1-4 hours, more preferably 1-3 hours, and most preferably 1-2 hours.

[0038] In case of reacting the bis(2-dihaloalkyl)formal in the presence of the pre-polymer (I) with sodium polysulfide according to the invention, the macromolecules in the resulting polysulfide polymer need to be reduced to the required chain length by reductive splitting of the disulfide bonds to obtain a liquid polysulfide. The most common reduction agents are sodium dithionite (Na.sub.2S.sub.2O.sub.4) and a combination of NaSH and Na.sub.2SO.sub.3. The amount of reduction agent to be used depends on the desired molecular weight, as commonly known in the art.

[0039] The preferred reduction agent in the process according to the invention is sodium dithionite. Reductive splitting using sodium dithionite is preferably performed for 20-40 minutes. The temperature preferably ranges from 80 to 110? C., more preferably from 85 to 105? C. and most preferably from 90 to 100? C. The reaction time is preferably 1-4 hours, more preferably 1-3 hours, and most preferably 1-2 hours.

[0040] If desired, the splitted disulfide bonds can then be converted into reactive terminal thiol groups by acidification at pH 4-5. Acetic acid is preferably used as acidifier.

[0041] As a last step, the polysulfide can be washed and dewatered under reduced pressure.

[0042] The polysulfide resulting from the process of the present invention has various applications, including the use as binder in sealants, adhesives, and coating compositions, in isocyanate cure, in epoxy-resin cure, and in acrylate resin cure.