GB2076831A - Compositions of a polyphenylene ether resin and a copolymer of styrene and bromostyrene - Google Patents

Abstract

Molding compositions comprise a polyphenylene ether resin and a styrene-bromostyrene copolymer, preferably having a styrene-bromostyrene weight ratio from 85:15 to 15:85. Preferred compositions comprise 20 to 90% by weight of polyphenylene ether and 80 to 10% by weight of the copolymer. Such compositions are inherently flame-retardant, and have better stability towards UV light than polyphenylene ether compositions rendered flame-retardant by low molecular weight brominated additives.

Description

SPECIFICATION Compositions of a polyphenylene ether resin and a copolymer of styrene and bromostyrene This invention relates to compositions comprising a polyphenylene ether resin and a styrene/bromostyrene copolymer.

The term "polyphenylene ether resin" is descriptive of a well known group of polymers that may be made by a variety of catalytic and non-catalytic processes, as described in, for example, U.S. Patents No. 3,306,874, 3,306,875,3,257,357, 3,257,358,3,356,761, 3,337,499,3,219,626, 3,384,619,3,440,217, 3,442,885,3,573,257, 3,455,880 and 3,382,212.

U.S. Patent 3,383,435 describes compositions of polyphenylene ether resins and styrene resins, including halogenated styrene resins. In U.S. Patent 3,887,646, compositions that include a polyphenylene ether resin and a chlorostyrene resin are disclosed. U.S. Patent 3,629,506 describes compositions of a polyphenylene ether resin that iriclude styrene resins, phosphates and halogenated flame retardants.

It has been found that the compositions of a polyphenylene ether resin and a copolymer of styrene-bromostyrene have better ultraviolet light stability as compared to compositions containing low molecular weight brominated additives, are inherently flame retardant and require little or no additional flame retardant additive to achieve acceptable levels of flame retardance. In addition, the applicants have discovered that copolymers of styrene-bromostyrene are compatible with polyphenylene ether resins as compared to 100% bromostyrene polymers which when combined with polyphenylene ether resins, exhibit phase separation.It has been found that an 85:15 bromostyrene:styrene copolymer is miscible as 75:25 composition of polyphenylene ether: bromostyrene copolymer, while a composition of 50:50 polyphenylene ether: bromostyrene copolymer of either 85:15 or bromostyrene:styrene copolymer or of the polymer of bromostyrene alone forms two phases. A 70:30 bromostyrene: styrene copolymer is compatible with polyphenylene ether resins in all proportions as are all bromostyrene copolymers containing less than 70% bromostyrene. The same degree of compatibility for the bromostyrene-styrene copolymer is expected at the lower end of the concentration range.

The compositions containing the bromostyrene copolymer can be extruded and molded without discoloration. They have higher heat distortion temperatures as well as much better resistance to burning than analogous polyphenylene ether resin compositions made with polystyrene.

The bromine when present in the styrene-bromostyrene copolymer has been found to be more efficient as a flame retardant than an equivalent amount of bromine that is added as a low molecular weight flame retardant in analogous polyphenylene ether-styrene resin compositions.

It has also been found that bromine in the form of a bromostyrene-styrene copolymer is more stable to the degradative effects of ultraviolet radiation as compared to a low molecular weight bromine containing compound such as decabromodiphenyl ether when tested in the presence of a polyphenylene either resin. In addition, it has been discovered that compositions of a polyphenylene ether resin and a copolymer of styrene-bromostyrene are more stable to ultraviolet light discoloration than are compositions of a polyphenyiene ether and a homopolystyrene.

The compositions of the invention comprise: (a) a polyphenylene ether resin; and (b) a copolymer of styrene-bromostyrene.

The polyphenylene ether resins comprise polymers of structural units of the formula:

wherein Q is selected from the group consisting of hydrogen, hydrocarbon radicals, halohydrocarbon radicals having at least two carbon atoms between the halogen atom and the phenyl nucleus, hydrocarbonoxy radicals and halohydrocarbonoxy radicals having at least two carbon atoms between the halogen atom and the phenyl nucleus, Q' and Q" are the same as 0 and in addition halogen with the proviso that 0 and 0' are both free of a tertiary carbon atom and n is an integer of at least 50.

The preferred polyphenylene ether resin is a poly(2,6-dimethyl-1,4-phenylene) ether resin having an intrinsic viscosity of from about 0.40 dl/g to about 0.60 dl/g as measured chloroform at 30"C.

The copolymers of styrene-bromostyrene may be prepared from styrene and bromostyrene. In addition isomeric mixtures of bromostyrene may be employed which include para-, meta- and ortho-bromostyrene.

Generally the weight ratio of styrene to bromostyrene in the copolymer may vary from 15:85 to 85:15 and more preferably from 30:70 to 85:15.

From 80 to 10 parts by weight of the copolymer of styrene-bromostyrene may be utilized in combination with from 20 to 90 parts by weight of thepolyphenylene ether resin. These copolymers may be prepared by various procedures that are well known to those skilled in the art including free radical polymerization, bulk polymerization, suspension polymerization and emulsion polymerization techniques. These copolymers have been obtained from Makhteshim Chemical Co. as copolymers containing 26.6 wt% bromine and 30.4 wt% bromine.

From 1 to 15 parts by weight of thermoplastic rubber such as an ABA or AB block copolymer may be utilized in the compositions of the invention. Suitable ABA block copolymers are the Kraton or Kraton-G polymers that are described in U.S. Patent 3,646,162 and U.S. Patent 3,595,942, respectively.

If desired, reinforcing amounts of reinforcing fillers may be added to the compositions in amounts of from 5 to 40% by weight of total compositions. Glass fibers or other reinforcing agents such as quartz, mica, wollastonite or carbon fibers may be used as the reinforcing fillers.

If the amount of bromine in the compositions of the invention is inadequate to attain the desired degree of flame retardance, a minor amount of a phosphorus compound, that is, 0.1 to 7.5 parts by weight of a phosphorus compound, calculated as elemental phosphorus, per 100 parts by weight of total composition, may be added.

In general, the preferred phosphorus compounds may be selected from elemental phosphorus or organic phosphonic acids, phosphonates, phosphinates, phosphonites, phosphinites, phosphine oxides, phosphines, phosphites and phosphates. Illustrative are triphenyl phosphine oxide. These can be used alone or with antimony oxide.

Typical of the preferred phosphorus compounds which may be employed in this invention would be those having the general formula:

where each Q represents the same or different radicals including hydrocarbon radicals such as alkyl, cycloalkyl, aryl, alkyl substituted aryl and aryl substituted alkyl; halogen; hydrogen and combinations thereof provided that at least one of said O's is aryl. Typical examples of suitable phosphates include, phenylbisdodecyl phosphate, phenylethyl hydrogen phosphate, ethyldiphenyl phosphate, 2-ethylhexyl di(p-tolyl) phosphate, diphenyl hydrogen phosphate, tricresyl phosphate, triphenyl phosphate, 2chloroethyldiphenyl phosphate, and diphenyl hydrogen phosphate.The preferred phosphates are those which are commercially available, such as, Kronitex-50, which is a mixture of isomers of tri-i-propylphenyl phosphate.

The compositions may be prepared by tumble blending powders, beads or extruded pellets of the components with or without suitable reinforcing agents, stabilizers, pigments, non-reinforcing fillers, e.g.

5-50% by total weight of composition of clays, talcs etc., added flame retardants, plasticizers or extrusion aids. The compositions may be prepared by extrusion of the ingredients into a continuous strand, chopping the strand into pellets and molding the pellets into any desired shape.

Description of the Preferred Embodiments EXAMPLE 1 Compositions of 65 parts of poly(2,6-dimethyl-1 ,4-phenylene) ether (I.V. = 0.47 dl/g in CHCI3 at 30DC), 35 parts of a styrene-bromostyrene copolymer containing 27% bromine, 10 parts of hydrogenated styrenebutadiene-styrene block copolymer (Kraton G 1652), 3 parts of titanium dioxide, 1.0 part diphenyldecyl phosphite 0.15 parts zinc sulfide, 0.15 parts zinc oxide and 1.5 parts of polyethylene were extruded and molded into standard ASTM test pieces. For comparison, a mixture having the same composition, but with homopolystyrene (Dylene 8G) substituted for the bromostyrene copolymer, was similarly extruded and molded. Properties of the blends are listed in Table 1. The blend containing the bromostyrene copolymer had gloss, tensile strength and impact strength about the same as the blend with the styrene homopolymer, but significantly higher heat distortion temperature and much better flammability characteristics.

TABLE 1 Blend with Blend With Polystyrene Bromostyrene Homopolymer Copolymer Elongation (%) 29 33 Tensile Yield Strength (kg/m2) 5484180 5765420 Tensile Strength (kg/m2) 5273250 5624800 Izod Impact (J/m. of notch) 272.2 250.9 Gardner Impact (m.kg) 2.59 2.48 Gloss (at 7"C) 62.0 61.3 Yellowness Index 23.2 18.7 Heat Distortion Temp. ("C) 137 146 UL-94 Rating Fails (drip) V-1 Average Burning Time (seconds) 53 5.1 EXAMPLES 2-4 Compositions of 85 parts of poly(2,6-dimethyl-1 4-phenylene) ether having intrinsic viscosity of 0.54 dl/g (in CHIC13 at 30"C), 15 parts of the styrene-bromostyrene copolymer described in Example 1,5 parts of hydrogenated block copolymer (Kraton G 1652), 3 parts of titanium dioxide, 1 part of diphenyldecyl phosphite, 0.15 parts of zinc sulfide, 0.15 parts of zinc oxide and 1.5 parts of polyethylene were extruded and molded as described in Example 1. For comparison, a blend of the same composition, but with polystyrene homopolymer Dylene 8G instead of the bromostyrene copolymer was similarly extruded and molded.

Blends of the same composition, but with the addition of 3 parts of triphenyl phosphate, were prepared in the same way, using the same lot of poly(2,6-dimethyl-1,4-phenylene ether, and one blend with low molecular weight poly(2,6-dimethyl-1, 4-phenylene) ether (I.V. = 0.37 dl/g). properties of these blends are listed in Table 2. Blends containing the styrene-bromostyrene copolymer had tensile strength, impact strength, gloss and color about the same as blends of the same composition made with polystyrene homopolymer, but higher heat distortion temperature much better flammability characteristics. The 85:15 compositions containing the bromostyrene copolymer had good resistance to burning (V-1 rating by UL-94) without any added flame retardant but was further improved (V-0 rating) by the addition of three parts of triphenyl phosphate.

Molecular weight of the poly(2,6-dimethyl-1 ,4-phenylene) ether used in the blends with the bromostyrene copolymer can be varies over a wide range without significant effect on flammability or most other properties, but Izod impact strength was reduced and Gardner impact strength greatly increased by reduction in intrinsic viscosity of the poly (2,6-dimethyl-1 ,4-phenylene) ether from 0.54 to 0.37 dl/g as measured in CHIC13 at 30"C.

TABLE 2 I.V.

Poly (2,6dimethyl -1,4phenyl- Average Comp. ene Poly- Elong T.Y. T.S. Izod Gardner Gloss HDT Burning No. ether styrene TPP (%) kg/m (psi) (J/m) m.kg. Y.I. (7 C) ( C) UL94 Time(Sec) A .54 Bromo- None 23 7593480 6116970 186.8 0.058 30.6 55.5 171 V-1 3.1 styrene Copolymer B* .54 Poly- None 23 7523170 6116970 208.2 0.173 32.4 61.1 164 Fail 24.6 styrene C .54 Bromo- 3 24 7593480 6116970 186.8 0.230 31.1 62.6 164 V-0 2.6 styrene parts Copolymer D* .54 Poly- 3 29 7452860 5624800 165.5 0.230 33.9 60.9 157 V-1 12.9 styrene parts E .37 Bromo- 3 36 7734100 4921700 101.4 1.44 31.2 62.7 158 V-0 2.5 styrene parts EXAMPLES 5-7 A blend of 75 parts of poly(2,6-dimethyl-1,4-phenylene) ether, 25 parts of the bromostyrene copolymer, 10 parts of hydrogenated styrene-butadiene copolymer (Kraton G 1652), 3 parts of titanium dioxide, 1 part of diphenyldecyl phosphite, 0.15 parts of the zinc sulfide, 0.15 parts of zinc oxide, and 1.5 parts of polyethylene was extruded and molded as described in Example 1. Another blend of the same composition, with the addition of 3 parts of triphenyl phosphate, was also prepared, and, for comparison, blends of the same composition, with the bromostryene copolymer replaced by polystyrene homopolymer (Dylene 8G).

Other blends were prepared as described above, using polystyrene (Dylene 8G) with the addition of enough decabromodiphenyl ether to make the percent bromine. based on poly(2,6-dimethyl-1,4-phenylene) ether and polystyrene only, the same as in the blends with the bromostyrene copolymer, and others with slightly more of the decabromodiphenyl ether, so that the percent bromine, based on total weight of the blend, was the same as in the blends with the bromostyrene copolymer. Properties of the blends are listed in Table 3. The blends containing the bromostyrene copolymer have high heat distortion temperature, and high Izod impact strength. Most properties are approximately equivalent to those of the control blends made with polystyrene homopolymer, with heat distortion temperature slightly higher and flammability characteristics greatly improved.The blend made with the bromostyrene copolymer has V-1 flammability rating without any added flame retarding agent; it becomes V-0, with very short burning time, on addition of only three parts of tnphenyi phosphate.

The same amount of bromine, added in the form of decabromodiphenyl ether, causes an increase in color, a decrease in heat distortion temperature, lower Izod impact strength, and is much less effective as a flame suppressant.

TABLE 3 Comp. Deca Bromo- (pts)* Tri- bromo Melt Avg.

styrene styrene phenyl diph- Gard- Visc. Burn Comp. Copoly- homo- Phos- ethyl Elong T.Y. T.S. Izod ner Gloss HDT poise UL94 Time No. mer polymer phate ether (%) (kg/m) (kg/m) (J/m) m-kg (7 C) Y.I. ( C) 287 C) Rating (sec) F 25 None None None 41 5835730 5343560 715.3 1.15 62.1 23.02 149 4500 V-1 6.2 G 25 None 3 None 42 5765420 5413870 939.5 2.30 61.4 22.68 147 4250 V-0 2.2 H** None 25 None None 32 5624800 5343560 608.5 2.59 59.1 24.60 147 Fail 27.1 I** None 25 3 None 40 5624800 5202940 960.8 2.59 59.7 24.60 140 V-1 16.5 J** None 25 None 8.1 37 5976350 5906040 314.9 2.02 59.2 26.40 143 Fail 14.8 K** None 25 None 8.8 37 5976350 5906040 282.9 2.30 37.7 28.40 146 V-1 11.0 L** None 25 3 8.1 36 5976350 5765420 256.2 1.73 58.2 27.80 140 V-1 8.6 M** None 25 3 8.8 33 5976350 5906040 331.0 2.88 58.0 28.90 142 V-1 6.9 * Each blend also contains 75 parts lopy(2,6-dimethyl-1,4-phenylene)ether, 3 parts titanium dioxide, 1 part diphenyl decyl phosphite. 0.15 parts zinc sulfide. 0.15 parts zinc oxide, 1.5 parts polyethylene, and 10 parts hydrogenated styrene butandiene bolck copolymer Kraton G 1652.

** Control.

EXAMPLE 8 The blends described in Examples 5-7 were molded into 3.2 x 63.5 x 82.5 mm. plates. The plates were placed in racks under a single thickness of ordinary window glass on a rotating platform and illuminated at a distance of three inches by a battery of fluorescent blacklight lamps. Yellowness index was measured at 24 hour intervals by the procedure of ASTM Test D1925, with the results shown in Table 4. The compositions contaning the low molecular weight bromine-containing additive yellowed rapidly (Biends J-M), whereas F and G containing the bromostyrene copolymer, actually yellowed slightly less than blends H** and l**, with no bromine in any form.

TABLE 4 Increase In Yellowness Index Composition * 24 Hours 48 Hours 72 Hours F - 0.5 1.2 2.8 G - 0.5 1.7 2.8 H** 0.0 2.1 3.7 0.1 0.1 2.1 3.6 14.2 32.1 37.8 K** 15.0 28.6 39.2 L** 13.0 29.7 36.7 M** 13.7 29.4 37.7 * Compositions of Table 3 ** Control EXAMPLE 9 A blend of 75 parts of poly (2,6-dimethyl-1 ,4-phenylene)ether, 25 parts of the bromostyrene copolymer, 10 parts of hydrogenated styrene-butadiene-styrene block copolymer (Kraton G 1651), 3 parts of titanium dioxide, 3 parts of triphenyl phosphate, 1 part of diphenyidecyl phosphite, 0.15 parts of zinc sulfide, 0.15 parts of zinc oxide, and 1.5 parts of polyethylene was extruded and molded as described in Example 1.

Properties of the composition are listed below: Elongation (%) 29 Tensile Yield Strength (kg/m2) 7593480 Tensile Strength (kg/m2) 6116970 Izod Impact Strength (J/m) 96.1 Gardner Impact (m.-kg) 2.765 Gloss (7'C) 38.9 Yellowness Index 24.3 Heat Distortion Temperature ("C) 151 UL-94 Rating V-0 Average Burning Time (seconds) 3.1 EXAMPLE 10 Molded compositions of 75 parts of poly(2,6-dimethyl-1,4-phenylene) ether; 24 parts of a bromostyrene polymer of bromostyrene-styrene copolymer; 3 parts of titanium dioxide; 1.5 parts of triphenyl phosphate and 10 parts of a styrene-butadiene-styrene block copolymer (Kraton G 1651) were prepared by extrusion and molding. The compositions had the properties shown in Table 5.

TABLE 5 % Bromo styrene Izod Gardner Avg. Burn in Impact Impact Time Polymer (J/m) (m.-kg.) UL-94 Appearance 70 325.6 3.168 1.9 Good 85 459.1 3.456 1.7 Good 100* 427.0 0.173 .9 Laminated * Control EXAMPLE 11 Molded compositions of 60 parts of poly(2,6-dimethyl-1,4-phenylene) ether resin; 40 parts of a bromostyrene polymer or a copolymer of bromostyrene-styrene; 1.5 parts of triphenyl phosphate and 10 parts of a styrene-butadiene-styrene block copolymer were prepared by extrusion and molding. The compositions had the properties shown in Table 6.

TABLE 6 % Bromo styrene Izod Gardner Avg. Burn in Impact Impact Time Polymer (J/m) (m.-kg.) UL-94 Appearance 70 299.0 2.592 2.9 Good 85 218.9 0.346 2.0 Laminated 100* 213.5 0.058 0.6 Laminated * Control COMPARATIVE EXAMPLE 1000 g of bromostyrene monomer (Makhteshim-27% ortho; 70% para; 3% meta) was stirred under nitrogen with 0.6 g of azo-bis-isobutyronitrile and 0.6 g of dicumyl peroxide at 82 C.

After six hours the product was suspended in 1500 ml of water containing 6 g of polyvinyl alcohol and 4.5 g of gelatin and polymerization was continued at 85-1 000C for 14 hours. Blends with poly(2,6-dimethyl-1,4phenylene) ether were prepared by coprecipitation from toluene into methanol and the blends were pressed into films for determination of the glass transition temperature.

% poly(2,6 dimethyl-1,4- Tg (1) Tg (2) phenylene) ether ( C) ( C) 131 25 136 208 50 137 206 75 137 209 100 --- 211 The blends show the presence of two glass transition temperatures which is a characteristic of the lack of compatability of these two materials.

Claims (11)

1. A flame retardant thermoplastic molding composition which comprises: (a) a polyphenylene ether resin; and (b) a copolymer of styrene-bromostyrene.

2. A composition as claimed in Claim 1 wherein the polyphenylene ether resin includes structural units of the formula:

wherein Q Q' and Q", which can be the same or different, are each hydrogen, halogen, hydrocarbon, halohydrocarbon having at least two carbon atoms between the halogen atom and the phenyl nucleus, hydrocarbonoxy and halohydrocarbonoxy having at least two carbon atoms between the halogen atom and the phenyl nucleus, with the proviso that Q and Q' are both free of a tertiary carbon atom, 0 is not halogen, and n is at least 50.

3. A composition as claimed in Claim 2 wherein each Q" is hydrogen.

4. A composition as claimed in Claim 2 wherein the polyphenylene ether resin is poly(2,6-dimethyl-1 ,4- phenylene) ether resin.

5. A composition as claimed in any preceding Claim wherein the styrene-bromostyrene weight ratio is 85:15 to 15:85.

6. A composition as claimed in any preceding Claim which comprises by weight from 20 parts to 90 parts of a polyphenyl ether and from 80 parts to about 10 parts of said copolymer.

7. A composition as claimed in any preceding Claim which further includes a filler.

8. A composition as claimed in any preceding Claim which further includes a phosphate flame retardant.

9. A composition as claimed in any preceding Claim which further includes a thermoplastic rubber.

10. A composition as claimed in Claim 9, wherein the thermoplastic rubber is an A-B-A block copolymer.

11. A composition as claimed in Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 11.