DE1495419B2 - Process for the production of flame-retardant, thermoplastic alkenyl aromatic polymers - Google Patents

Description

Alkenyl aromatic resins obtained by incorporating the usual halogen-containing agents Made self-extinguishing have disadvantages, including the fact that drops of molten Polymers that separate from a burning object are not self-extinguishing.

Thermoplastic foams are often obtained by expanding foamable beads, which the alkenyl aromatic resin such as polystyrene or a copolymer thereof is a volatile foaming agent and contain a flame retardant. Foamable beads or spheres of this material can by polymerizing the monomer or monomer mixtures in aqueous suspensions and in the presence of the flame retardant and the foaming agent, such as. B. pentane or petroleum ether, getting produced. The well-known flame-retardant phosphonates, as they are, for. B. in the British Patent 825 611 are described, however, have a very unfavorable effect on the bead formation and impair the dimensional stability of foamed masses in general.

The inventive method for the production of flame-retardant thermoplastic alkenylaromatic Polymers by polymerizing alkenyl aromatic monomers, optionally together with no more than 30 percent by weight of one or more other ethylenically unsaturated compounds, in the presence of 0.5 to 8 percent by weight of bromine-containing organic phosphorus compounds and optionally in the presence of foaming agents, is characterized in that one'als a bromine-containing organic phosphorus compound is a phosphonate of the general formula

flame-retardant additives are used, which are free of phosphorus.

The organic, bromine-containing phosphonates do not have high thermal stability. As a result, they should not be used in resin compositions which are subject to excessively high temperatures, as are commonly used in extrusion technology. However, the thermal stability of the phosphonates is completely and entirely sufficient for the polymerization processes customarily used, according to which the alkenyl aromatic resins are obtained from monomers by polymerization in the presence of the phosphonates.
Phosphonates of the structural formula below are preferably used

C _n H, “Br

O = P

(Π)

^ (OC _n H _2n Br) ₂

O = P-ORX

(I)

used in which R is aliphatic radicals with 2 to 4 carbon atoms and X is one or more halogen atoms means at least one of which is a bromine atom.

It has been shown that when using the above Phosphonates in the polymerization mixture favor the formation of regular pearls is, in contrast to the previously known flame-retardant additives, which the pearling very much adversely affect.

It has also been shown that when using the phosphonates according to the invention, the self-extinguishing Properties also of detaching drops and foams from the respective molding compound be improved. It is also to be rated as an advantage that the phosphonates used according to the invention do not affect the molecular weight of the polymers during the polymerization.

In addition to the phosphonate, a peroxide is preferably used as a synergistic aid. Smaller amounts of the phosphonate are then required to bring about self-extinguishing, especially in the case of foams and drips. Preferably, stable organic peroxides which (determined in benzene) a half-life of at least 2 hours at 10O ⁰ C are relatively own. The phosphonates used according to the invention can also be used together with the conventional bromine-containing.

in which η is an integer from 2 to 4. Phosphonates according to the formula © I and II can be prepared in a known manner, the latter z. B. by reacting an alkylene oxide with 2 to 4 carbon atoms in the molecule, such as ethylene oxide, 1,2-propylene oxide or 1,2-butylene oxide, with phosphorus tribromide in a solvent such as o-dichlorobenzene, toluene or xylene. After the reaction, the reaction mixture to 15O ⁰ C or higher is heated to induce the rearrangement of phosphate to phosphonate. The yields of phosphonate in this process are almost quantitative and the product is of such a purity that, after removal of the solvent, the phosphonate obtained can be used immediately in the process according to the invention.

It is preferred to use organic peroxides which are distinguished by a certain stability; refer to the relatively low volatile organic peroxy compounds include having a boiling point of 10O ⁰ C or higher at 760 mm pressure. These peroxy compounds are characterized by a half life of at least 2 hours at 100 ⁰ C (determined in benzene) and contain at least 6 carbon atoms in the molecule, at least one tertiary carbon is bonded to an oxygen atom of the peroxy group. The preferred peroxides are characterized by the formula below

R [O- O -

(III)

In this formula, R denotes an alkyl radical with 2 to 9 carbon atoms, an aryl or an aralkyl hydrocarbon radical of the benzene series, the acetoyl, phthaloyl and benzoyl radical, R 'is hydrogen, an alkyl radical of 2 to 9 carbon atoms, an aryl - or aralkyl hydrocarbon radical of the benzene series, η the numbers 1 or 2.

Preferred representatives of the possible peroxy compounds are:

tert-butyl peracetate,
tert-butyl perbenzoate,
Di-tert-butyl-di-perphthalate,
tert-butyl hydroperoxide,
Di-tert-butyl peroxide,
Cumene hydroperoxide,

Dicumyl peroxide,

Cumyl ether peroxide,

Di-tert-amyl peroxide,

Cumyl tert-butyl peroxide,

Cumyl tert-octyl peroxide,

Cumyl isopropyl peroxide,

Bis (a-methylbenzyl) peroxide,

Bis (a- ethylbenzyl) peroxide,

Bis (a-propylbenzyl) peroxide.

Among alkenyl aromatic monomers, which are at least 70 percent by weight, based on the total monomers, are used, compounds of the general formula IV are to be understood:

IO

Ar-C = CH ₂

(IV)

20th

In this formula, Ar denotes an aromatic radical or a ring-substituted aromatic halogenated hydrocarbon radical of the benzene series, R hydrogen atom or methyl group.

Examples of the alkenyl aromatic monomers are styrene, vinyl toluene, vinyl xylene, isopropyl styrene, p-tert-butyl styrene, ar-ethylvinylbenzene, ar-chlorostyrene, ar-dichlorostyrene, ar-bromostyrene. As comonomers, not more than 30 percent by weight are used: acrylonitrile, methyl methacrylate and divinylbenzene, the latter in amounts from 0.001 to 0.5%.

The volatile organic compounds that act as foaming agents in the alkenyl aromatic Resins used must dissolve in the solid polymer, but not the polymer dissolve or swell. Suitable foaming agents are: saturated aliphatic hydrocarbons with 4 to 7 carbon atoms in the molecule and perchlorofluorocarbon with a molecular weight of at least 58 and a boiling point which at 760 mm pressure is not higher than 95 ° C, e.g. B. n-pentane, Isopentane, neopentane, η-butane, isobutane, hexane, heptane, petroleum ether. Mixtures of the substances mentioned can also be used. The volatile organic compounds are generally in amounts of 0.05 to 0.4 gmol of the volatile organic compounds per 100 g of the to be polymerized Monomers used.

The foamable polymer material is made by polymerizing the starting monomer as a mixture obtained with the phosphonate and optionally with a volatile, organic foaming agent. However, the polymerization can also be carried out with advantage in such a way that the monomer and the additives, e.g. B. the volatile foaming agent and the phosphonate, in an inert, aqueous Medium, such as water or brine, are suspended. The suspension polymerization of the monomers in Mixing with the foaming agent and the phosphonates allows control in a simple manner the course of the reaction to obtain beads of the desired size. The polymerization is preferred carried out in the presence of a peroxy polymerization catalyst, e.g. B. in the presence of benzoyl peroxide, Acetyl peroxide, di-tert-butyl peroxide, dicumyl peroxide, tert-butyl peroxide, di-tert-butyl diperphthalate, tert-butyl peracetate, tert-butyl perbenzoate.

The catalysts mentioned can also be used in a mixture, namely in one Amount of about 0.1 to 5 percent by weight based on the weight of the monomer used.

As customary organic bromides to be used simultaneously with the phosphonates according to the invention may be mentioned: 1,1,2,2-tetrabromoethane, 1,2-dibromotetrachloroethane, 1,2,3,4-tetrabromobutane, monochloropentabromocyclohexane, Styrene dibromide, di (bromoethyl) benzene.

The peroxy compounds to be used as a synergistic aid in addition to the phosphonates one in amounts that the foamed product from 0.01 to 2, preferably from 0.1 to 0.5 percent by weight the peroxy compound contains.

example 1

A number of attempts were made. For each experiment, 100 parts by weight became one monomeric styrene together with 0.04 parts of divinylbenzene, 7.67 parts of n-pentane, 0.43 parts of benzoyl peroxide as a polymerization catalyst, dicumyl peroxide as a peroxygen compound and bis (2-bromoethyl) -2-bromo-ethylphosphonate as a flame retardant in the quantities as listed in the table below, put in a pressure-resistant glass flask, namely in a mixture with 125 parts by weight of water, 0.125 parts of potassium dichromate, 0.115 parts of one Ammonium salt of sulfonated polyvinyltoluene as a dispersing agent and 0.385 parts of ammonium sulfate contained. The pH of the aqueous solution was adjusted to 6.0. The mixture was stirred and heated to 90 ° C for 11 hours in a closed flask. This was followed by 5 hours heated to 103 ° C to polymerize the monomer. After cooling down and after opening the bottle the polymeric product was filtered, washed and dried at room temperature. The product had the shape of fine pearls and about 1 mm in diameter. The pearls were long through 3 minutes Pre-foamed by steam heating at 100 ° C and then brought into a closed, porous shape and taken with it Steam heated. In this way, a foam body of 254 × 254 × 16 mm thickness was produced and cut off test pieces with a cross section of 6 × 25 mm and a length of 127 mm. These test pieces were used to determine the self-extinguishing of the foamed product. To carry out the test, the foamed test piece with its 6 mm edge was in held in a horizontal position. A micro-burner with a 25.4 mm flame was moved under the test piece until the foam was ignited. Thereupon the flame was removed. The time (in seconds) from the onset of ignition to extinction was ascertained. For another test method, the foamed pieces were completely burned, by placing them in continuous contact with the flame and setting the burning time in seconds found, during which the burning polymer dripping from the test piece continued to burn. In the end the collected droplets detached from the polymer were reignited by a flame. After ignition, the flame was removed again to determine the time in seconds until the re-ignited drop itself went out. Table I shows the results of the experiments.

Table I.

Polymerization Composition Stvrol parts Divinyl benzene Additions to the Polymerization foam Burn test reignited U IV 1 VJ I IwI Iw Parts Self- removed tropres drops Experimental • r. ■ ■: Dicumyl Bromine- expiry time Self- Self- No. .10Ov ■ ..- 0.04 Peroxide phosphoniite (Sec.) extinction time deletion time 100 0.04 Parts Parts burns (Sec.) . (Sec.), •. 1 100 0.04 0.2 12th burns burns 2 idp 0.04 0.2 2 3 3 15th ■ 3 ■ 100. 0.04 0.2 3 1 0.5 8th '4 100 0.04 0.2 4th 15th 0.5 3. ^: '5 100 0.04 0.4 1 5 4th 4 ' 6th 100 0.04 0.4 2 1 5 15th 7th 100 0.04 0.4 3 0.25 0.5 3 8th 0.4 3 0.25 0.25 1 9 0.4 4th 0.25 1

Example 2

For each of two runs, foamable alkenyl aromatic resin beads were made by using a mixture of 99.924 percent by weight styrene, 0.04% divinylbenzene, 0.036% ethylvinylbenzene in mixture with 7.67 percent by weight of n-pentane (based on the sum of the weights of the monomers) and 4 or 5% of bis (2-bromobutyl) -2-bromobutylphosphonate as a flame retardant in an aqueous Medium, corresponding to Example 1, polymerized, but with the difference that the aqueous medium Contained 6 percent by weight methyl alcohol. The product was in the form of small grains of approximately gained uniform size. Parts of the product were foamed and put on the self-extinguishing Properties similar to those in Example 1 were tested. The foamed product has the in the properties shown in Table II below.

Table II

drops

Burn test

Again-

inflamed c

drops

(Sec.)

40

45

4th
5

B e i s ρ i e 1 3

For each of a series of experiments, foamable, alkenyl aromatic resin beads were prepared by polymerizing a mixture of monomers consisting of 99.924 percent by weight styrene, 0.04 percent by weight divinylbenzene, and 0.036 percent by weight ethylvinylbenzene, in aqueous suspension, in a mixture of 7.67 percent by weight n- Pentane (based on total monomers) as foaming agent, 0.43% benzoyl peroxide as polymerization catalyst, with bis- (2-bromoethyl) -2-bromoethyl-phosphonate and an organic peroxygen compound, as indicated in the table below, as an agent to improve the flame-retardant properties of the phosphonate. The procedure was similar to that in Example 1. The divinylbenzene used in this example was a distillation fraction which contained about 60 percent by weight of a mixture of m- and p-divinylbenzenes and about 40 percent by weight of a mixture of m- and p-ethylvinylbenzenes. In the last fraction, the proportion of the “meta” isomers was around 65% ^and that of the “para” isomers around 35%. Little or no “ortho” isomers were present in the mixture. The polymerization product was obtained in the form of small beads of uniform size. A foam body was produced and tested for self-extinguishing properties as in Example 1. The results are summarized in Table III.

Table III

Flame-retardant additives in the polymer (%) Bromine- foam Burn time again Experimental 0.4 phosphonate (Sec.) inflamed
drops No. Organic peroxy compounds 0.4 (%) 15th drops (Sec.) 0.2 1 1 (Sec.) 4th 1 Dicumyl peroxide 0.4 3 1 4th 2 2 Dicumyl peroxide 0.2 4th 2.5 0.5 3 3 Dicumyl peroxide 4th 3 0.5 2 4th Di-tert-butyl peroxide 4th 0.25 10 5 Di-tert-butyl diperphthalate 0.5

The following comparative experiment shows the superiority of the molding compositions obtainable according to the invention compared to molding compounds according to British Patent 825 611, which also Provides phosphorus and bromine-containing compounds as flame retardants in resins will.

Comparative experiment I

A 350 ml glass bottle was also with 139 g of water containing 0.14 g of K ₁ Cr ₂ O ₇ , 0.26 g of ammonium sulfate, 0.08 g of sulfonated polyvinyltoluene (degree of sulfonation 0.9 to 0.95) 103 g of styrene, 8 g of n-pentane, 0.44 g of benzoyl peroxide, 0.21 g of dicumyl peroxide, 0.04 g of divinylbenzene and a phosphate or phosphonate according to the following Table IV filled. The bottle was closed and hand shaken to result in a dispersion of droplets of the styrene solution in the aqueous solution. Then the bottle in a liquid bath with continued turning and circulating heated, namely for 11 hours at 90 ⁰ C and then 5 hours at 105 ° C. After cooling has been opened the bottle and its contents are poured through a sieve. The polymer which settled on the sieve was washed with water and dried at room temperature. Table IV shows that when the phosphonates according to the invention are used, bead-shaped polymers with diameters between 0.59 and 1.68 mm are obtained, while when the phosphate known from British patent 825 611 is used, bean-shaped particles with larger diameters or no discrete ones at all Particles are obtained.

For the production of foam bodies, however, it is necessary to be as spherical as possible Polymer beads with a diameter are obtained, the standard sieves with sieve openings of 1.68 to 0.59 mm correspond. This pearl size has resulted from "practical experience.

Table IV

Tris- (2,3-di-
bromopropyl) -
ohosphate (g) Bis- (bromine-
alkyl) bromine Type of
Alkyl group Size and shape (British alkane in the ver the received Patent specification phosphonate turned polymer particles 825 611) (G) Phosphonate 1 'bean-shaped Particles with much bigger outer dimensions sung as 2 mm 3 complete togetherness baking (a single Lump) 2 ethyl Pearls with Diameters between 1.68 and 0.59 mm - 4th ethyl the same - 1 Propyl the same - 2 Propyl the same

Tris- (2,3-di- Bis- (bromine-
alkyO-bromine- Type of
Aikyl group Size and shape bromopropyl) -
phosphate (g) alkane in the ver the received (British phosphonal turned polymer particles Patent specification (G) Phosphonate 825 611) 4th Propyl ': Diameters between 1.68 and 0.59 mm ■ 5 Propyl the same - 1 Butyl the same - 2 Butyl the same - 3 Butyl the same - 4th Butyl the same -

Comparative experiment II

Beads containing tris (2,3-dibromopropyl) phosphate were prepared according to Example 6 of British Patent 825,611 and foamed. In the same way, pearls were produced which contained bis (bromoethyl) bromoethane phosphonate instead of the brominated phosphate. Foam bodies were produced from both products by filling the products into a perforated, closable mold cavity with the dimensions 25 × 25 × 1.27 cm and preheating them with steam for 1 minute. The mold cavity was then closed and steam was forced into the mold cavity under a pressure of 4.55 kg / cm ² until a back pressure of 1.26 kg / cm ² resulted over 25 seconds. (The back pressure was read from a manometer connected to the interior of the perforated mold.) Then, water at a pressure of 0.35 kg / cm ^{2 was} used to cool the mold. The water was forced into the mold cavity through the same pipe connection that was used for the steam. After cooling for 6 minutes, the mold was opened. The beads which contained tris (2,3-dibromopropyl) phosphate had given a shrunken molded article, the cells of which had collapsed and the external appearance of which was very poor. The beads, which contained bis (bromoethyl) bromoethane phosphonate, produced a molded article with exactly the dimensions of the mold cavity without collapsed cells and with an excellent surface appearance.

Example 4

In the following it is shown that it is possible to obtain useful flame-retardant polymers even in the absence of foaming agents. For this purpose, styrene is mixed with a phosphonate and a catalyst according to the table below: -run ir
Table V

sample Weight percent
Bis- (bromopropyl) -
bromopropane
phosphonate Weight percent
Benzoyl peroxide Weight percent
Dicumyl peroxide 1 1 0.4 0.5 ■) 1 0.4 0.5 3 2 0.4 0 4th 3 0.4 0 5 0.5 0.4 0.5

009 529/283

The first four samples were sealed in glass bottles, which were shaken head in a glycol bath for 16 hours at 80 ⁰ C and 6 hours at 103 ⁰ C; Sample 5 was polymerized in a similar manner, but for 16 hours at 75 to 80 ° C. and 3 hours at 100 and finally at 105 ° C. The polymers obtained were processed into disks of 0.32 × 0.64 cm. The self-extinguishing time was determined by igniting the samples for 10 seconds with a pilot flame, after which the pilot flame was removed and the time taken for the flame to be extinguished. The self-extinguishing properties of drops of the molten polymer were determined by placing a cotton layer 30 cm below From 10 tests for each sample it was found that all samples had extinguished within one second (self-extinguishing time) and that in no case did the cotton layer ignite (cotton ignition).

Claims (2)

Patent claims: 1. Process for the production of flame-retardant thermoplastic alkenyl aromatic ίο see polymers through polymerization of alkenyl aromatic Monomers, optionally together with not more than 30 percent by weight of one or more other ethylenically unsaturated Compounds, in the presence of 0.5 to 8 percent by weight of bromine, organic 'Phosphorus compounds and optionally in the presence of foaming agents, thereby characterized that, as bromine-containing, organic phosphorus compound a phosphonate of the general formula , RX
O = P-ORX used in which R is aliphatic radicals with 2 to 4 carbon atoms and X is one or more halogen atoms means at least one of which is a bromine atom. 2. The method according to claim 1, characterized in that a peroxide is also used will.