PROCESS FOR THE PREPARATION OF BROMINATED COPOLYMERS OF CONJUGATED DIENES AND STYRENIC MONOMERS

Abstract

A brominated copolymer of at least one conjugated diene and at least one styrenic monomer is prepared such that at least 45 percent, but no more than 70 percent, of the non-aromatic double bonds In the copolymer are brominated. The produced brominated copolymer is useful as a flame retardant and exhibits surprisingly small domain sizes after dissolution in styrenic monomer which is subsequently polymerized.

Claims

1. A process for producing a brominated copolymer flame retardant of at least one conjugated diene and at least one styrenic monomer, comprising reacting a copolymer of at least one conjugated diene and at least one styrenic monomer with a brominating agent in the presence of a solvent for the copolymer under conditions sufficient to brominate at least 45 percent, but no more than 70 percent, of the non-aromatic double bonds in the copolymer, wherein the copolymer prior to bromination contains from 20 to 50 percent by weight of polymerized styrenic monomer units and from 50 to 80 percent by weight of polymerized conjugated diene units, and has a weight average molecular weight of at least 1000 g/mol.

2. The process according to claim 1, wherein the copolymer of at least one conjugated diene and at least one styrenic monomer following the bromination has a bromine content by weight of from 47 to 60 percent.

3. The process according to claim 1, wherein the copolymer of at least one conjugated diene and at least one styrenic monomer is reacted with the brominating agent under conditions sufficient to brominate at least 50 percent, but no more than 68 percent, of the non-aromatic double bonds in the copolymer.

4. The process according to claim 1, wherein the copolymer of at least one conjugated diene and at least one styrenic monomer following the bromination has a bromine content by weight of from 50 to 58 percent.

5. The process according to claim 1, wherein the copolymer of at least one conjugated diene and at least one styrenic monomer prior to the bromination contains from 60 to 75 percent by weight of polymerized butadiene units and from 25 to 40 percent by weight of polymerized styrenic monomer units.

6. The process according to claim 1, wherein the weight average molecular weight of the copolymer of at least one conjugated diene and at least one styrenic monomer prior to the bromination is in a range of from 1,000 to 400,000 g/mol.

7. The process according claim 1, wherein the at least one conjugated diene is butadiene.

8. The process according to claim 1, wherein the at least one styrenic monomer is styrene.

9. The process according to claim 1, wherein the copolymer of at least one conjugated diene and at least one styrenic monomer is a block copolymer containing one or more polybutadiene blocks and one or more polymerized styrenic monomer blocks.

10. The process according to claim 9, wherein the one or more polymerized styrenic monomer blocks are one or more polystyrene blocks.

11. The process according to claim 10, wherein the copolymer is a styrene-butadiene-styrene triblock copolymer.

12. The process according to claim 1, wherein the at least one conjugated diene is butadiene and from 50 to 95 percent of the polymerized butadiene units in the copolymer prior to the bromination are 1,2-butadiene units.

13. The process according to claim 1, wherein the brominating agent comprises a tribromide chosen from pyridinium tribromide, a phenyltrialkylammonium tribromide, a benzyltrialkylammonium tribromide and a tetra-alkylammonium tribromide.

14. A brominated copolymer flame retardant of at least one conjugated diene and at least one styrenic monomer produced according to the process of claim 1, wherein at least 45 percent, but no more than 70 percent, of the non-aromatic double bonds are brominated.

15. The brominated copolymer flame retardant of claim 14, wherein average domain size after dissolution in subsequently polymerized styrenic monomer is 5 microns or less when measured using scanning electron microscopy (SEM) imaging on cross-sectioned samples.

Description

EXAMPLES

Example 1

[0029] To a 250-mL round-bottom flask equipped with overhead stirring, addition funnel, and a nitrogen inlet were added 95 g of dichloromethane and 5.0 g of a styrene-butadiene-styrene triblock copolymer having 32 wt. % polymerized styrene units and 68 wt. % polymerized butadiene units (0.0623 mol eq., of which 82 wt. % were 1,2-butadiene units and 18 wt. % were 1,4-butadiene units) and a total weight average molecular weight (M.sub.w) of 93,000 g/mol measured by GPC relative to a polystyrene standard. The mixture was allowed to dissolve fully. To the 100-mL addition funnel was added 21 mL (0.0378 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide. The solution was added via drop wise addition to the polymer solution over 5 minutes. After 2 hours at reflux the reaction was allowed to cool to room temperature and a reaction aliquot was taken and precipitated into methanol. The resulting precipitate was filtered, and the solids were washed with methanol. .sup.1H-NMR indicated that 60% of the non-aromatic double bonds in the copolymer were brominated (i.e., 60% conversion of butadiene units). The bromine content by weight in the resulting copolymer was 55%, measured by potentiometric titration after treatment with sodium biphenyl reagent.

Example 2a (Comparative)

[0030] To a 250-mL round-bottom flask equipped with overhead stirring, addition funnel, and a nitrogen inlet were added 95 g of dichloromethane and 5.0 g of a styrene-butadiene-styrene triblock copolymer having 32 wt. % polymerized styrene units and 68 wt. % polymerized butadiene units (0.0623 mol eq., of which 82 wt. % were 1,2-butadiene units and 18 wt. % were 1,4-butadiene units) and a total weight average molecular weight (Me) of 93,000 g/mol measured by GPC relative to a polystyrene standard. The mixture was allowed to dissolve fully. To the 100-mL addition funnel was added 37 mL (0.0661 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide. The solution was added via drop wise addition to the polymer solution over 5 minutes. After 2 hours at reflux the reaction was allowed to cool to room temperature and a reaction aliquot was taken and precipitated into methanol. The resulting precipitate was filtered, and the solids were washed with methanol. .sup.1H-NMR indicated that 96% of the non-aromatic double bonds in the copolymer were brominated (i.e., 96% conversion of butadiene units). The bromine content by weight in the resulting copolymer was 66%, measured by potentiometric titration after treatment with sodium biphenyl reagent.

Example 2B (Comparative)

[0031] To a 250-mL round-bottom flask equipped with overhead stirring, addition funnel, and a nitrogen inlet were added 95 g of dichloromethane and 5.0 g of a styrene-butadiene-styrene triblock copolymer having 32 wt. % polymerized styrene units and 68 wt. % polymerized butadiene units (0.0623 mol eq., of which 82 wt. % were 1,2-butadiene units and 18 wt. % were 1,4-butadiene units) and a total weight average molecular weight (M.sub.w) of 93,000 g/mol measured by GPC relative to a polystyrene standard. The mixture was allowed to dissolve fully. To the 100-mL addition funnel was added 30 mL (0.0541 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide. The solution was added via drop wise addition to the polymer solution over 5 minutes. After 2 hours at reflux the reaction was allowed to cool to room temperature and a reaction aliquot was taken and precipitated into methanol. The resulting precipitate was filtered, and the solids were washed with methanol. .sup.1H-NMR indicated that 86% of the non-aromatic double bonds in the copolymer were brominated (i.e., 86% conversion of butadiene units). The bromine content by weight in the resulting copolymer was 63%, measured by potentiometric titration after treatment with sodium biphenyl reagent.

Example 2C (Comparative)

[0032] To a 250-mL round-bottom flask equipped with overhead stirring, addition funnel, and a nitrogen inlet were added 95 g of dichloromethane and 5.0 g of a styrene-butadiene-styrene triblock copolymer having 32 wt. % polymerized styrene units and 68 wt. % polymerized butadiene units (0.0623 mol eq., of which 82 wt. % were 1,2-butadiene units and 18 wt. % were 1.4-butadiene units) and a total weight average molecular weight (M.sub.w) of 93,000 g/mol measured by GPC relative to a polystyrene standard. The mixture was allowed to dissolve fully. To the 100-mL addition funnel was added 27.3 mL (0.0491 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide. The entire solution was added via drop wise addition to the polymer solution over 5 minutes. After 2 hours at reflux the reaction was allowed to cool to room temperature and a reaction aliquot was taken and precipitated into methanol. The resulting precipitate was filtered, and the solids were washed with methanol. .sup.1H-NMR indicated that 78% of the non-aromatic double bonds in the copolymer were brominated (i.e., 78% conversion of butadiene units). The bromine content by weight in the resulting copolymer was 61%, measured by potentiometric titration after treatment with sodium biphenyl reagent.

Example 3—Domain Size Testing

[0033] Sample Preparation.

[0034] For each of the brominated block copolymers (Br-SBS) synthesized in the above Examples, 0.02 g of the brominated block copolymer and 2 g of styrene monomer were added to a 20 mL glass vial. The mixture was sealed and placed on an orbital shaker for 2 hours to allow complete dissolution. The samples were then polymerized under standard conditions (temperature of 100° C. for a minimum of 18 hours) to allow complete conversion to polymer. Sample discs were then cross sectioned and scanning electron microscope (SEM) imaging performed.

[0035] Domain sizes of the brominated copolymers were evaluated through a series of images (typically 5 images per sample) at various locations of the cross sectioned disc, representing areas at the top, middle, and bottom of the disc. FIG. 1 shows an exemplary SEM image for each of the four evaluated samples. Imaging software was used to determine the diameter of a minimum of 10 domains from each image to calculate the average domain size per sample. The results are shown in the table below. The Br-SBS copolymers of Comparative Examples 2A, 2B and 2C, which had degrees of bromination of 78% or higher (and bromine contents by weight of 61% or higher), led to higher domain sizes after dissolution in subsequently polymerized styrene monomer as compared with the Br-SBS of Example 1.

TABLE-US-00001 Percent Bromination Bromine content Average Domain Size Br-SBS of Butadiene Units (wt %) (μm) (SEM imaging) Ex. 1 60% 55% 4.5 Ex. 2A 96% 66% 9.9 Ex. 2B 86% 63% 7.4 Ex. 2C 78% 61% 6.6

[0036] Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure that various modifications and variations can be made without departing from the scope of the invention, as claimed. Thus, it is intended that the specification and examples be considered as exemplary only, with a true scope of the present invention being indicated by the following claims and their equivalents.