Process for preparing brominated copolymers of conjugated dienes and styrene monomers

Abstract

Brominated copolymers of at least one conjugated diene and at least one styrene monomer are prepared such that at least 45% but not more than 70% of the non-aromatic double bonds in the copolymer are brominated. The brominated copolymers prepared are useful as flame retardants and exhibit unexpectedly small domain sizes upon dissolution in subsequently polymerized styrene monomer.

Description

Technical Field

[0001] The present invention relates to brominated copolymers of at least one conjugated diene and at least one styrene monomer as flame retardants, prepared such that at least 45% and not more than 70% of the non-aromatic double bonds in the copolymer are brominated. Background Art

[0002] US 7851558 and US 8202945 disclose the preparation of thermally stable brominated butadiene / vinyl aromatic copolymers as flame retardant additives for vinyl aromatic polymer compositions. It is disclosed that residual (unbrominated) butadiene double bonds in the brominated copolymer can lead to undesirable crosslinking reactions, particularly when the brominated copolymer is blended with a vinyl aromatic polymer. Preferred brominated butadiene / vinyl aromatic copolymers are fully brominated or nearly fully brominated, meaning that all or nearly all (e.g., up to 95%, up to 99%, or 100%) of the double bonds or unsaturations present in the butadiene portion prior to bromination are brominated.

[0003] However, the flame retardants, upon dissolution in subsequently polymerized styrene monomer, may exhibit domain sizes that are too large and may, for example, interfere with foam cell formation and cell size when making expanded styrene polymer foams. Summary of the invention

[0004] In accordance with the present invention, it has been discovered that brominating a copolymer of at least one conjugated diene and at least one styrene monomer under conditions sufficient to brominate at least 45% and not more than 70% of the non-aromatic double bonds in said copolymer produces a brominated copolymer of conjugated diene / styrene monomers that exhibits surprisingly small domain sizes upon dissolution in subsequently polymerized styrene monomer.

[0005] Disclosed herein is a method for producing a brominated copolymer flame retardant of at least one conjugated diene and at least one styrene monomer, comprising reacting a copolymer of at least one conjugated diene and at least one styrene monomer with a brominating agent in the presence of a solvent for the copolymer under conditions sufficient to brominate at least 45% and not more than 70% of the non-aromatic double bonds in the copolymer, wherein prior to bromination, the copolymer comprises 20 wt% to 50 wt% of polymerized styrene monomer units and 50 wt% to 80 wt% of polymerized conjugated diene units and has a weight average molecular weight of at least 1000 g / mol.

[0006] In a further aspect, a brominated copolymer flame retardant of at least one conjugated diene and at least one styrene monomer is produced according to the method disclosed herein. In another aspect, a brominated copolymer flame retardant of at least one conjugated diene and at least one styrene monomer is disclosed, the copolymer having 20 wt%-50 wt% of polymerized styrene monomer units and 50 wt%-80% of polymerized conjugated diene units before bromination, and having a weight average molecular weight of at least 1000 g / mol, and wherein at least 45% and no more than 70% of the non-aromatic double bonds in the brominated copolymer are brominated.

[0007] Unless otherwise specified, the word "a" or "an" in this application means "one or more".

[0008] The copolymer starting material is a copolymer of at least one conjugated diene and at least one styrene monomer. As used herein, "styrene monomer" refers to a copolymer having one or more (usually one) directly bonded to an unsubstituted or alkyl-substituted (e.g., C1-C 12 Compounds of vinyl (CH2=CR-, wherein R is hydrogen or methyl) of a ring carbon of an aromatic ring (substituted with C1-C6 alkyl) such as a benzene ring. Preferred styrene monomers include styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, dimethylstyrene, 2-ethylstyrene, 4-ethylstyrene, diethylstyrene, tert-butylstyrene, 2-isopropylstyrene, 4-isopropylstyrene, vinyltoluene, divinylbenzene and mixtures thereof. It is preferred that, for example, styrene is used as the sole styrene monomer, or, if more than one styrene monomer is used, styrene is used as the majority weight component within the styrene monomer. Preferred conjugated dienes have 4-8 carbon atoms, such as butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadiene and mixtures thereof. It is preferred that, for example, butadiene is used as the sole conjugated diene, or, if more than one conjugated diene is used, butadiene is used as the majority weight component of the conjugated diene.

[0009] As used herein, "polymerized styrene monomer units" refers to repeating units in the copolymer starting material formed when at least one styrene monomer is polymerized. Similarly, as used herein, "polymerized conjugated diene units" refers to repeating units in the copolymer starting material formed when at least one conjugated diene is polymerized. The starting copolymer contains 50 wt% to 80 wt% of polymerized conjugated diene units and 20 wt% to 50 wt% of polymerized styrene monomer units, such as 60 wt% to 75 wt% of polymerized butadiene units and 25 wt% to 40 wt% of polymerized polystyrene monomer units.

[0010] Butadiene is polymerized to form two types of repeating units. The "1,2-butadiene unit" referred to here takes the form

[0011]

[0012] And thus, pendant (pendant, side chain) unsaturated groups are introduced into the polymer. The second type, referred to herein as "1,4-butadiene units", adopts -CH2-CH=CH-CH2-, and introduces unsaturation into the polymer backbone. Generally speaking, at least 10% of the butadiene units in the starting copolymer of butadiene and styrene monomers are 1,2-butadiene units, such as at least 15%, at least 20% or at least 25% butadiene units. In many embodiments, at least 50% of the butadiene units are 1,2-butadiene units, such as at least 60%, at least 70%, at least 80% or at least 90% butadiene units. In many embodiments, 50%-95% of the butadiene units in the copolymer are 1,2-butadiene units.

[0013] The copolymer starting material of the conjugated diene / styrene monomer may have a weight average molecular weight (M) of 1000 to 400000 g / mol, for example 2000 to 300000 g / mol, 5000 to 200000 g / mol, or 10000 to 180000 g / mol. w As used herein, weight average molecular weight is the apparent molecular weight as determined by gel permeation chromatography (GPC) relative to a polystyrene standard.

[0014] The copolymer of conjugated diene / styrene monomer can be random, block or graft copolymer. In many embodiments, the copolymer is a block copolymer comprising one or more polymerized conjugated diene blocks and one or more polymerized styrene monomer blocks. The copolymer of conjugated diene / styrene monomer can be any of diblock, triblock, tetrablock or other multiblock copolymers. Preferably, the copolymer of at least one conjugated diene and at least one styrene monomer comprises one or more polystyrene blocks and one or more polybutadiene blocks. In many embodiments, the block copolymer starting material is a triblock copolymer, such as a triblock polymer with a central polybutadiene block and a terminal polystyrene block (styrene-butadiene-styrene).

[0015] The brominating agent can be elemental bromine or other brominating agents, such as brominating agents known in the art. For example, the brominating agent can comprise a combination of elemental bromine and a solvent, such as a chlorinated hydrocarbon (e.g., methylene chloride or carbon tetrachloride) or a solvent blend, such as a blend of a chlorinated hydrocarbon and / or a cyclic ether (e.g., tetrahydrofuran).

[0016] In many embodiments, the brominating agent comprises a tribromide selected from pyridinium tribromide, phenyltrialkylammonium tribromide, benzyltrialkylammonium tribromide and tetraalkylammonium tribromide. Examples include benzyltrimethylammonium tribromide, benzyltrimethylammonium tribromide, tetramethylammonium tribromide, tetraethylammonium tribromide, tetrapropylammonium tribromide and tetra-n-butylammonium tribromide, etc. The brominating agent may comprise a solvent for the tribromide, such as to facilitate mixing with the copolymer of the conjugated diene / styrene monomer and the solvent of the copolymer.

[0017] The tribromide can be prepared by mixing the corresponding quaternary ammonium monobromide salt with elemental bromine, such as by adding elemental bromine to an aqueous solution of the monobromide salt. The tribromide tends to precipitate from the aqueous phase and can therefore be recovered from the liquid phase by any convenient solid-liquid separation method.

[0018] In addition, by adding elemental bromine and corresponding quaternary ammonium monobromide salt respectively, tribromide brominating agent can be formed in situ in the presence of a copolymer of a solvent and / or a conjugated diene / styrene monomer. It is believed that once bromine and monobromide salt mix, tribromide is formed, and the tribromide generated reacts with the copolymer of a conjugated diene / styrene monomer subsequently, and bromination and regeneration of the monobromide salt are made in the copolymer. Because elemental bromine is consumed in this reaction sequence, more bromine can be added to the reaction mixture continuously or intermittently, and tribromide is reproduced and reaction is maintained. This area discloses the continuous and semi-continuous process of adding elemental bromine and / or a newly started copolymer and forming quaternary ammonium tribromide, bromination of this copolymer and regeneration of this monobromide salt in situ, such as US 8202945.

[0019] Suitable solvents for copolymers of conjugated diene / styrene monomers include ethers such as tetrahydrofuran, halogenated alkanes such as carbon tetrachloride, chloroform, dichloromethane, bromochloromethane and 1,2-dichloroethane; hydrocarbons such as cyclohexane, cyclopentane, cyclooctane and toluene, and halogenated aromatic compounds such as bromobenzene, chlorobenzene and dichlorobenzene. Generally speaking, the solvent has a boiling point (at atmospheric pressure) below 100°C, such as below 80°C, is substantially immiscible in water, is aprotic, and does not contain oxygen or hydrogen atoms bonded to tertiary carbons. In many embodiments, the solvent is a halogenated or hydrocarbon solvent. For example, halogenated hydrocarbons, halogenated aromatic compounds, and cycloalkanes that do not contain hydrogen atoms bonded to tertiary carbon atoms are often used.

[0020] The amount of solvent used is sufficient to dissolve the copolymer of conjugated diene / styrene monomers under the reaction conditions. The concentration of the copolymer in the solvent may be, for example, in the range of 1 wt% to 35 wt%, such as 5 wt% to 25 wt%.

[0021] Typically, the brominating agent is added to a solution of the copolymer starting material and a solvent.

[0022] According to the present disclosure, a copolymer of at least one conjugated diene and at least one styrene monomer is brominated by reacting the copolymer with a brominating agent in the presence of a solvent under conditions sufficient to brominate at least 45% and no more than 70% of the non-aromatic double bonds in the copolymer. For example, in many embodiments, the degree of bromination of the non-aromatic double bonds is in the range of 50%-68%, 50%-65%, or 55%-65%.

[0023] For example, by controlling the ratio of the brominating agent to the polymerized conjugated diene units in the copolymer in the reaction mixture and / or the amount of time for the brominating agent and the copolymer to react, the desired bromination range of the non-aromatic double bonds can be achieved. Generally speaking, the bromination reaction involves 0.45-about 0.70 moles of brominating agent / mole of conjugated diene units in the copolymer. A higher molar ratio can be used, such as up to about 1 mole or up to about 2 moles of brominating agent / mole of conjugated diene units, while controlling the reaction kinetics to achieve no more than 70% (for example, in some embodiments, no more than 68% or no more than 65%) of the bromination of non-aromatic double bonds. For example, the reaction time and temperature can be controlled to achieve bromination within the required range. Therefore, in some embodiments, each mole of conjugated diene unit in the copolymer will react 0.45 moles up to about 2 moles, 0.48 moles up to about 1.5 moles, or 0.50 moles up to about 1 mole of brominating agent, wherein the degree of bromination of the non-aromatic double bonds in the copolymer does not exceed 70% (for example, in some embodiments, no more than 68% or no more than 65%). In some embodiments, at least 0.45 moles but less than 1 mole of brominating agent reacts per mole of conjugated diene unit in the copolymer, such as about 0.50 moles to about 0.68 moles, or about 0.55 moles to about 0.65 moles of brominating agent per mole of conjugated diene unit.

[0024] Generally, only mild conditions are required to carry out the bromination. The bromination temperature ranges from -20 to 100°C, such as 0-85°C or 0-40°C. In some embodiments, the reaction temperature ranges from 10-40°C.

[0025] In the case where the brominated copolymer is insoluble in the reaction mixture, the product can be recovered using any convenient solid / liquid separation method (e.g., filtration, decantation, etc.). If the brominated copolymer is still soluble in the reaction mixture, it can be conveniently separated from the mixture by suitable methods, such as distillation of the solvent, or addition of an anti-solvent (which renders the brominated copolymer insoluble and precipitates it). Examples of such anti-solvents include lower alcohols, such as methanol, ethanol, and 1-propanol, 2-propanol, n-butanol, and tert-butanol. The separated brominated copolymer can be purified (as known in the art) to remove residual bromine, brominating agent, solvent, and by-products as desired or required for a particular application.

[0026] Using proton nuclear magnetic resonance spectroscopy ( 1 H-NMR) can be used to determine the degree of bromination of non-aromatic double bonds. Specifically, the residual double bond percentage, the polymerized monomer content, and the 1,2-butadiene isomer content can all be determined by comparing the integrated areas of the signals due to the relevant protons.

[0027] The copolymer of conjugated diene / styrene monomer is preferably selectively brominated so that the brominated copolymer contains no more than 2% by weight of aromatically bound bromine, such as no more than 1% or less than 1%. Typically, the brominated copolymer of conjugated diene / styrene monomer produced according to the present invention has a bromine content of 47 wt% to 60 wt%, such as 50 wt% to 58 wt% or 50 wt% to 56 wt%. The bromine content of the brominated copolymer is determined by potentiometric titration after treatment with sodium biphenyl reagent, as is known in the art for organohalogens.

[0028] A degree of bromination of at least 45% but no more than 70% of the non-aromatic double bonds in the conjugated diene / styrene monomer copolymer results in the copolymer exhibiting surprisingly small domain sizes after dissolution in subsequently polymerized styrene monomer. In some embodiments, the resulting domain size after dissolution of the brominated copolymer in subsequently polymerized styrene monomer is less than 10 microns, such as 8 microns or less, such as 1 micron or less, or 2 microns or less to 8 microns. In some embodiments, the average domain size of the brominated copolymer after dissolution in subsequently polymerized styrene monomer is less than 6 microns, such as 5 microns or less, such as 1 micron to 5 microns, or 2 microns or less, or 3 microns or less, to 5 microns. In many embodiments, the styrene monomer is styrene. The domain size of the brominated copolymer in the styrene polymer matrix is ​​measured using scanning electron microscopy (SEM) imaging on cross-sectional samples.

[0029] The brominated copolymers described herein exhibit good compatibility (and minimal impact) in the polymerization of styrene monomers and are provided in an effective amount to provide flame retardancy to the resulting styrene polymers. Generally speaking, the amount used to provide effective flame retardancy is an amount sufficient to provide a bromine content of 0.5 wt%-10 wt%, based on the weight of the mixture. The styrene polymer composition may include other additives, for example, other flame retardant additives, flame retardant aids, heat stabilizers, ultraviolet light stabilizers, nucleating agents, antioxidants, foaming agents, acid scavengers and colorants.

[0030] The following examples are used to further illustrate the present invention; they do not limit the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Exemplary SEM images of each of the samples evaluated in Example 3 of the present application are shown. DETAILED DESCRIPTION

[0032] Example 1

[0033] To a 250 mL round bottom flask equipped with overhead stirring, an addition funnel, and a nitrogen inlet was 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 equivalents, 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 w ) was 93000 g / mol, which was determined by GPC relative to polystyrene standards. The mixture was completely dissolved. 21 mL (0.0378 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide was added to a 100 mL addition funnel. The solution was added dropwise to the polymer solution over 5 min. After refluxing for 2 hours, the reaction was cooled to room temperature, an aliquot of the reaction was taken, and precipitated in methanol. The resulting precipitate was filtered out and the solid was washed with methanol. 1 H-NMR showed that 60% of the non-aromatic double bonds in the copolymer were brominated (ie, the conversion of butadiene units was 60%). After treatment with sodium biphenyl reagent, the weight content of bromine in the copolymer was determined by potentiometric titration to be 55 wt%.

[0034] Example 2A (Comparative Example)

[0035] To a 250 mL round bottom flask equipped with overhead stirring, an addition funnel, and a nitrogen inlet was 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 equivalents, of which 82 wt% were 1,2-butadiene units and 18 wt% were 1,4-butadiene units) with a total weight average molecular weight (M w ) was 93000 g / mol as measured by GPC relative to a polystyrene standard. The mixture was allowed to dissolve completely. 37 mL (0.0661 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide was added to a 100 mL addition funnel. The solution was added dropwise to the polymer solution over 5 min. After refluxing for 2 hours, the reaction was cooled to room temperature and an aliquot of the reaction was taken and precipitated in methanol. The resulting precipitate was filtered out and the solid was washed with methanol. 1 H-NMR showed that 96% of the non-aromatic double bonds in the copolymer were brominated (ie, the butadiene unit conversion was 96%). After treatment with sodium biphenyl reagent, the bromine weight content of the copolymer was determined by potentiometric titration to be 66 wt%.

[0036] Example 2B (Comparative Example)

[0037] To a 250 mL round bottom flask equipped with overhead stirring, an addition funnel, and a nitrogen inlet was 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 equivalents, of which 82 wt% were 1,2-butadiene units and 18 wt.% were 1,4-butadiene units) with a total weight average molecular weight (M w ) was 93000 g / mol as measured by GPC relative to a polystyrene standard. The mixture was allowed to dissolve completely. 30 mL (0.0541 mol, 1.8 M solution in dichloromethane) of tetraethylammonium tribromide was added to a 100 mL addition funnel. The solution was added dropwise to the polymer solution over 5 min. After refluxing for 2 hours, the reaction was cooled to room temperature, an aliquot of the reaction was taken and precipitated in methanol. The resulting precipitate was filtered out and the solid was washed with methanol. 1 H-NMR showed that 86% of the non-aromatic double bonds in the copolymer were brominated (ie, the butadiene unit conversion was 86%). After treatment with sodium biphenyl reagent, the bromine weight content of the resulting copolymer was determined by potentiometric titration to be 63 wt%.

[0038] Example 2C (Comparative Example)

[0039] To a 250 mL round bottom flask equipped with overhead stirring, an addition funnel, and a nitrogen inlet was 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 equivalents, of which 82 wt% were 1,2-butadiene units and 18 wt% were 1,4-butadiene units) with a total weight average molecular weight (M w ) is 93000 g / mol, which is measured by GPC relative to polystyrene standards. The mixture is completely dissolved. 27.3 mL (0.0491 mol, 1.8 M solution, in dichloromethane) of tetraethylammonium tribromide is added to a 100 mL addition funnel. The entire solution is added to the polymer solution via dropwise addition within 5 min. After refluxing for 2 hours, the reaction is cooled to room temperature, an aliquot of the reaction is taken, and precipitated in methanol. The resulting precipitate is filtered out, and the solid is washed with methanol. 1 H-NMR showed that 78% of the non-aromatic double bonds in the copolymer were brominated (ie, the conversion of butadiene units was 78%). After treatment with sodium biphenyl reagent, the bromine weight content of the copolymer was determined by potentiometric titration to be 61 wt%.

[0040] Example 3—Domain Size Testing

[0041] Sample preparation.

[0042] For each brominated block copolymer (Br-SBS) synthesized in the above examples, 0.02 g of 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 completely dissolve. The sample was then polymerized under standard conditions (100° C. for a minimum of 18 hours) to completely convert it into a polymer. The sample disc was then cross-sectioned and imaged by a scanning electron microscope (SEM).

[0043] The domain size of the brominated copolymer was evaluated by a series of images (typically 5 images per sample) at different locations of the cross-sectioned disk representing the top, middle and bottom regions of the disk. Figure 1 An exemplary SEM image of each of the four evaluated samples is shown. Imaging software was used to determine the diameter of a minimum of 10 domains in each image to calculate the average domain size for each sample. The results are shown in the table below. Compared to the Br-SBS of Example 1, the Br-SBS-copolymers of Comparative Examples 2A, 2B and 2C, which have a degree of bromination of 78% or more (and a bromine content of 61% or more), produce larger domain sizes after dissolution in the subsequently polymerized styrene monomer.

[0044]

[0045] Although specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art, in view of the specification and practice of the present disclosure, that various modifications and changes may be made without departing from the scope of the invention as claimed. Therefore, it is contemplated that the specification and embodiments are to be considered exemplary only, with the true scope of the present invention being indicated by the appended claims and their equivalents.

Claims

1. A method for producing a brominated copolymer flame retardant of at least one conjugated diene and at least one styrene monomer, comprising reacting the copolymer with a brominating agent in the presence of a solvent for the copolymer under conditions sufficient to brominate at least 55% and not more than 65% of the non-aromatic double bonds in the copolymer, wherein prior to bromination the copolymer comprises 20 wt% to 50 wt% of polymerized styrene monomer units and 50 wt% to 80 wt% of polymerized conjugated diene units, and has a weight average molecular weight of at least 1000 g / mol, wherein from 0.50 mole to a maximum of 1 mole of the brominating agent is reacted per mole of the conjugated diene unit, and after the bromination the copolymer of at least one conjugated diene and at least one styrene monomer has a bromine content of 47 wt% to 60 wt%.

2. The method of claim 1, wherein the copolymer of at least one conjugated diene and at least one styrene monomer has a bromine content of 50 wt% to 58 wt% after the bromination.

3. The process according to claim 1 or 2, wherein the copolymer of at least one conjugated diene and at least one styrene monomer contains 60 wt% to 75 wt% of polymerized butadiene units and 25 wt% to 40 wt% of polymerized styrene monomer units prior to the bromination.

4. The process according to claim 1 or 2, wherein the weight average molecular weight of the copolymer of at least one conjugated diene and at least one styrene monomer prior to the bromination is in the range of 1,000-400,000 g / mol.

5. The method of claim 1 or 2, wherein the at least one conjugated diene is butadiene.

6. The method of claim 1 or 2, wherein the at least one styrenic monomer is styrene.

7. The method of claim 1 or 2, wherein the copolymer of at least one conjugated diene and at least one styrene monomer is a block copolymer comprising one or more polybutadiene blocks and one or more polymerized styrene monomer blocks.

8. The method of claim 7, wherein the one or more polymerized styrene monomer blocks are one or more polystyrene blocks.

9. The method of claim 8, wherein the copolymer is a styrene-butadiene-styrene triblock copolymer.

10. The method of claim 1 or 2, wherein the at least one conjugated diene is butadiene, and 50% to 95% of the polymerized butadiene units in the copolymer prior to the bromination are 1,2-butadiene units.

11. The method of claim 1 or 2, wherein the brominating agent comprises a tribromide selected from the group consisting of pyridinium tribromide, phenyltrialkylammonium tribromide, benzyltrialkylammonium tribromide, and tetraalkylammonium tribromide.

12. A brominated copolymer flame retardant of at least one conjugated diene and at least one styrene monomer produced according to the process of any one of the preceding claims.

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