METHOD FOR PRODUCING BROMINATED AND HALOHYDRATED POLYMERS

Abstract

Conjugated diene polymers such as a styrene-butadiene copolymer are sequentially brominated by reaction with a quaternary ammonium tribromide or quaternary phosphonium tribromide and halohydrated by reaction with an N-haloimide compound. This produces a brominated and halohydrated polymer with very good thermal stability. The product is useful as a flame retardant in a variety of polymer systems.

Claims

1. A process for preparing a brominated and halohydrated polymer of at least one conjugated diene, comprising (a) reacting a starting polymer of at least one conjugated diene with a quaternary ammonium tribromide, quaternary phosphonium tribromide compound or both a quaternary ammonium tribromide and a quaternary phosphonium tribromide to brominate 50% to 98% of the conjugated diene repeating units in the starting polymer to form a partially brominated polymer and then (b) reacting the partially brominated polymer with an N-haloimide compound in the presence of water and a water-miscible solvent system for the partially brominated polymer to halohydrate at least a portion of the remaining conjugated diene repeating units and produce a brominated and halohydrated polymer.

2. The process of claim 1 wherein the N-haloimide is an N-halosuccinimide.

3. The process of claim 1 wherein the N-haloimide is an N-bromoimide.

4. The process of wherein 65 to 95% of the conjugated diene units are brominated in step (a), 5 to 35% of the conjugated diene units are halohydrated in step (b), and 0 to 5% of the conjugated diene units are unreacted.

5. The process of claim 1 wherein 75 to 98% of the conjugated diene units are brominated in step (a), 2 to 25% of the conjugated diene units are halohydrated in step (b) and 0 to 5% of the conjugated diene units are unreacted.

6. (canceled)

7. The process of claim 1, wherein in step (b) the concentration of the partially brominated polymer in the water-miscible solvent system is 2 to 25 weight percent based on the combined weight of partially brominated polymer and solvent system.

8. The process of claim 1 wherein in step (b), water is present in an amount from 0.25 to 1 parts by weight per part by weight of the solvent system.

9. The process of claim 1 wherein the starting polymer is a copolymer of styrene and butadiene having a weight average molecular weight of at least 20,000 by gel permeation chromatography against a polystyrene standard.

10. The process of claim 1 wherein the brominated and halohydrated polymer obtained from the process is a thermoplastic material that contains no more than 3 weight percent of gel material.

11. The process of claim 1 wherein the brominated and halohydrated is crosslinked in step (b) or in a subsequent step.

12. The process of any preceding claim wherein the brominated and halohydrated polymer is formed into particles.

13. A brominated and halohydrated polymer made according to the process of claim 1.

14. A brominated and halohydrated polymer of at least one conjugated diene, wherein 2 to 50% of the conjugated diene units of the polymer are halohydrated, 50 to 98% of the conjugated diene units are brominated and 0 to 10% of the conjugated diene units are unreacted, which brominated and halohydrated polymer has a 5% weight loss temperature of at least 250° C.

15-20. (canceled)

21. A polyol composition comprising at least one polyol and the brominated and halohydrated polymer of claim 14.

22. An isocyanate-based polymer containing the brominated and halohydrated polymer of claim 14.

23. An extruded polymer foam containing a bulk polymer and the brominated and halohydrated polymer of claim 14.

24. A process for making the extruded polymer foam of claim 23 comprising forming a pressurized melt that contains the bulk polymer, the brominated and halohydrated polymer and a blowing agent that contains at least one of carbon dioxide, water and an alcohol, and forcing the melt through an opening into a zone of lower pressure where the blowing agent expands and the bulk polymer solidifies to form a foam.

25. A polymer blend comprising a bulk polymer which is one or more polymers or copolymers of styrene, a polyacrylate or polymethacrylate polymer or a mixture of any two or more thereof, and the brominated and halohydrated polymer of claim 14.

Description

EXAMPLE 1

[0059] A styrene-butadiene-styrene triblock copolymer containing 46% polymerized styrene and 54% polymerized butadiene is partially brominated by reaction with tetraethylammonium tribromide according the general method described in WO 2007/021418 such that approximately 82% of the butadiene units are brominated. The polymer is recovered from the reaction solvent and dried. 6.13 g of the partially brominated polymer is dissolved in 200 mL tetrahydrofuran. With stirring, 16.35 g of deionized water is added, at which point the solution becomes cloudy. Another 50 mL of tetrahydrofuran are stirred in to produce a clear solution. 3.54 g of N-bromosuccinimide are added and stirred in, followed by another 80 mL of tetrahydrofuran. Another 6.1 g of deionized water are then added to produce a clear solution. The clear solution is stirred for 4 hours at room temperature. During this time, the solution gradually turns orange in color.

[0060] 375 mL of 2-propanol is added to the reaction solution over a period of 20 minutes. The brominated and halohydrated polymer precipitates from solution, is filtered, washed with 2-propanol, and re-dissolved into dichloromethane and again precipitated by addition of 2-propanol. The re-precipitated product is dried at 60° C. to a constant weight of 6.45 g.

[0061] An infrared spectrum of the dried product is taken. A strong band associated with an OH stretch is found at 3572 cm.sup.−1. This band is missing from the partially brominated polymer prior to the halohydration step. Carbonyl groups are essentially absent. Proton NMR indicates the absence of carbon-carbon double bonds and the presence of hydroxylated carbon atoms. The 5% weight loss temperature of this product is about 264° C.

EXAMPLE 2

[0062] The same styrene-butadiene-styrene triblock copolymer described in Example 1 is partially brominated by reaction with tetraethylammonium tribromide according the general method described in WO 2007/021418 such that approximately 91% of the butadiene units are brominated. The partially brominated polymer is recovered from the reaction solvent and dried. 40 g of the partially brominated polymer is dissolved into a mixture of 1250 mL tetrahydrofuran, 103.7 g of deionized water and 20 g of N-bromosuccinimide to form a clear reaction solution that turns orange over time. The solution is stirred for 24 hours at room temperature. The brominated and halohydrated polymer is recovered in the same manner as described in Example 1.

[0063] Proton NMR indicates the presence of hydroxylated carbons at about 3.5 ppm and that approximately 2% of the aliphatic carbon-carbon double bonds of the starting material remain unreacted. The 5% weight loss temperature of this product is about 256° C.

[0064] A portion of the brominated and halohydrated polymer is compression molded at 180° C. under 25 tons pressure for 5 minutes on a platen press, and cooled to 20° C. on the press. A rectangular sample having dimensions of about 7.5×7.5×1.5 mm is cut from the compression molded material. The sample is heated to 125° C. in a sealed 50 mL batch foamer. Carbon dioxide is injected into the chamber to a pressure of 1000 psi, and the sample is maintained at that temperature and pressure for 3.5 hours to allow the carbon dioxide to dissolve into it. The pressure is then released within the heated chamber to rapidly depressurize the sample and cause it to expand and cool to produce a foam structure. The sample is immediately removed.

[0065] The foam structure is cut to expose the cell structure. The exposed surface is darkened with black ink to enhance contrast, and then examined under an optical microscope. The diameter of each cell in an image is measured along its longest axis. The average cell size and standard deviation are calculated.

[0066] For comparison, a sample of the partially brominated polymer is taken prior to the halohydration step, and formed into a foam in the same manner. The cell size of the foamed brominated and halohydrated polymer is significantly larger than that of the foamed partially brominated (but not halohydrated) material. This indicates a significant increase in the solubility of carbon dioxide due to the presence of the hydroxyl groups. The increased cell size is beneficial, as the formation of larger cells (instead of more, smaller cells) correlates to more efficient foam expansion, resulting in lower foam densities and improved ease of producing larger cross-sections at a given amount of blowing agent.

[0067] A portion of the brominated and halohydrated polymer is dissolved in toluene to form a 10% by weight solution. The interfacial energy of this solution against water is measured using the Du Nouy ring method. The force maximum is measured using a tensiometer equipped with an electronic force sensor, and the interfacial tension σ calculated as σ=F/(L−cos θ), where F is the measured force, L is the wetted length of the ring (calculated as the sum of the inner and outer circumference) and θ is the contact angle. Cos θ=1 for the platinum-iridium ring material.

[0068] The interfacial tension for the brominated and halohydrated material produced in Example 2 is about 27 mN/m. For comparison, the interfacial system of the brominated but not halohydrated polymer is measured in the same manner, and found to be over 29 mN/m. These results indicate that the presence of hydroxyl groups on the brominated and halohydrated polymer affects the hydrophilicity of the material.