CA1202330A - S-butyl bis(3-hydroxypropyl) phosphine oxide - Google Patents

Abstract

ABSTRACT

s-BUTYL BIS(3-HYDROXYPROPYL) PHOSPHINE OXIDE
s-Butyl bis(3-hydroxypropyl) phosphine oxide, useful as a flame retardant in plastic compositions, is described.

Description

~ZC~33~1 The present invention relates to thermoplastic polyphenylene oxide polymers which are rendered flame retardant by having combined therewith an effective amount of a 3-hydro~yalkyl phosphine ~xide.
The polyphenylene ethers are known and described in numerous publicatior~s .including U.S. Patents No.
3,306,874 and 3,306,875 of AJlan S. Hay and U.S. Patents Nos. 3,257i357 and 3,257,358 of ~elu 5~oeff Stamatoff.
The high molecular weight polymers are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points - that is, in excess of 275C, and are useful for many commercial applications requiring high temperature resistance including formation of film, fiber and molded articles.
The combination of polyphenylene oxide ethers with polystyrene and modified polystyrene i6 also known and described in U.S. Patent No. 3,385j435. The pre-ferred polystyrenes are the high impact polystyrenessuch as the styrene acrylonitrile copolymers and styrene-acrylonitrile-butadiene copolymers.
In general r compositions containing from 35 to 85 percent by weight polyphenylene oxide and from 65 to 15 percent by weight of a polystyrene resin exhibit the best overall combination of properties and these compositions are preferred. Such compositions are referred to in this specification and in the claims as "polyphenylene oxide compositions"O
With ~he current and future federal re~uirement~
obligating automotive manufacturers to improve the efficiency of their product and reduce fuel consumptionr there is a substantial growth in the use of engineering plastics as a replacement for metal to achieve weight reduction. The use of polyphenylene oxide compositions in the transportation, electrical/electronic and appli-ance categories accounts for a majority of its volume, ~Z33~

and polyphenylene oxide compositions are the dominant engineering thermoplastic in appliance use. Such compositions are in general, characterized as being relatively stable thermally upon lon~ exposure to processing temperatures and shear. Upon exposure to flame, however, they burn quite readily as would be anticipated from their relative high styrene content.
There is a substantial and increasing demand for flame retardant polyphenylene oxide compositions.
To improve flame retardant characteristics, poly-phenylene oxide compositions have been compounded with flame retardant additives~ i.e., aromatic haloyen com-pounds plus aromatic phosphates as described in U.S.
Patent No. 3,639l506. A preferred composition in accordance with that teaching comprises from 20 to 80 by weight of poly(2,6-dimethyl-1,4-phenylene) ether, 20 ~o 80% by weight of a high impact polystyrene (sty-rene modified with rubber) and rom 3 to 25 parts by weight per 100 parts by weight of the polyphenylene oxide composition of a flame retardant combination of 1 part triphenyl phosphate and 3 to 4 parts of a heavily chlorinated biphenyl. U.S. Patent No. 4,154,775 states that cyclic phosphates are, by themselves, an effective;
non-plasticizing flame retardant additive for poly-phenylene oxide compositions. Such additives, however, frequently degrade or cause degradation under processing conditions (extrusion at about 250~C) resulting in poor mechanical performance of the thermoplastic polyphenylene oxide compositions themselves.
The known flame retardants for polyphenylene oxid~
compositions suffer generally from one or more deficien-cies including low compatibility, low thermal stability or poor fire retardant behavior in molded polyphenylene oxide compositionsO Additionally, a serious problem posed by aromatic halogen flame retardants in polypheny-lene oxide compositions is attributable to acid forma-tion, either due to or arising from light exposure or ~ f ~

thermal degradation with the released acid then attack-ing metal components in end-use applications. Some aromatic halogen compounds are contraindicated as fire retardant additives due to toxicity problems of the co~lpound, i.e., mutagenicity~
According to the present invention, the addition of a small but effective amount of a 3-hydroxyalkyl phos-phine oxide having the formula:

(~CH2CHCH2)(3-n) ~ ~ ~

wherein Rl may be the same or different radicals selected from the group consisting of hydrogen and the methyl radical, R~ is an alkyl radical of 4 to 8 carbon atoms and n is either zero or one, to a thermoplastic polyphenylene oxide composition substantially improves the flame retardant properties of the polyphenylene oxide compo~sition. The addition of the 3-hydroxyalkyl phos~
phine oxide to the polyphenylene oxide composition in the amount required to improve flame retardant properties does not adversely modify the physical properties of the polyphenylene oxide composition to a point where its commercial use is impaired. The 3-hydroxyalkyl phosphine oxides described above are readily compatîble with the polyphenylene oxide composition and effective when added in small quantities, i.e., 4-10 parts per hundred parts of polyphenylene oxide composition. Par-ticularly preferred compositions are flame retardant polyphenylene oxide compositions to which have been added from about 4 to about 7 parts oE a 3-hydroxyalkyl phosphine oxide per hundred parts of polyphenylene oxide composition~
The flame resistant polyphenylene oxide composition and 3-hydroxyalkyl phosphine oxide blends of the present invention are particularly advantageous for use in 3~

appliances, business rnachines, terminal strips, connec-tors and blocks.
The 3-hydroxyalkyl phosphine oxides of the present invention are more soluble in water than in polar organic solvents such as chloroform. Such 3--hydroxyalkyl phos phine oxides combine high compatibility in polyphenylene oxide compositions with high thermal stability and excellent fire retardant efficierlcy either alone or in combination with organohalogen products.
The merits that may be attributed to the 3-hydroxy-alkyl phosphine oxide flame retardant (relative to con-ventional flame retardant agents in present use) include no corrosion, high ultraviolet stability, non-toxicity and minimal adverse change in the physical properties 15 of the polymer. The heat distortion temperature of the polyphenylene oxide composition is not appreciably effected by ~he addition thereto of 5-7 parts per hundred of a pho~phine oxide flame retardant. Particularly advantageous are the alkyl bis(3-hydroxyalkyl) phosphine oxides such as butyl bis(3-hydroxypropyl) phosphine -oxide which is compatible with polyphenylene oxide and polystyrene polymers and has improved mixing parameters that reduce polymer degradation by lowering the process-ing temperature. Also useful as flame retardan~ addi-tives are the tris~3-hydroxyalkyl) phosphine oxides such as tris~3-hydroxypropyl) phosphine oxide, tris(2-methyl-3-hydroxypropyl) phosphine oxide and mixtures of the same.
3-~ydroxyalkyl phosphine oxides may be prepared by first reacting a 3-hydroxy-1,~-unsaturated olefin~
such as allyl alcohol with phosphine in the presence of a free radical catalyst as described in United States Patent No. 3,489,811. The use of stoichiometric ~uan-tities of reactants (or as little as 4% excess alcohol) reduce the formation of higher molecular weight by-products. The 3-hydroxyalkyl phosphine obtained by this process is readily converted to the corresponding phos-~Z33(~

phine oxide by oxidation with hydrogen peroxide.
An example of phosphine oxide useful as fireretardant additives in polyphenylene oxide compositions is the tris(3-hydroxypropyl) phosphine oxide, derived from allyl alcohol. These compound; may be added to polyphenylene oxide compositions in amounts o~ 4 to 10 parts per hundred. Tris(3-hydroxy-2-methylpropyl) phosphine oxide, derived from m~thallyl alcohol may also be used as a fire retardant additive but is more volatile.
Phosphine oxides having different 3-hydroxyalkyl groups on the phosphorus atom such as:
C~3 O
..
(HOCH2CHcH2)nP-(c~2cH2cH2 )3-n wherein n is either 1 or 2, may be prepared by reacting phosphine with a mixture of allyl and methallyl alcohol and oxidizing the resulting product. Such mixed phos-phine oxides are more volatile than the tris(3-hydroxy-propyl) phosphine oxide. The relative volatility of this series of compounds (rate of vaporiæation by thermo-gravimetric technique) in order of increasing volatility is tris(3-hydroxypropyl) phosphine oxide, bis(3-hydroxy-propyl) 2-methyl-3-hydroxypropyl phosphine oxide, tris-(2 methyl-3-hydroxypropyl) phosphine oxide and 3-hydroxy-propyl bis(2-methyl-3-hydroxypropyl) phosphine oxide.
These mixed phosphine oxides as well as physical mix-tures of such mixed phosphine oxides with tris(3--hydroxy-propyl) phosphine oxide and/or tris~2-~ethyl-3-hydroxy-propyl) phosphine oxide are useful additives having~application in the present invention.
The following examples more fully illustrate the invention.
Example I
Preparation of Tris(3-Hydroxypropyl) Phosphine Oxide Into a one liter pressure reactor is placed 307 9 (5.3 moles) allyl alcohol and 20 ml of a solution con-~tU233~3 taining 3 9 azobisisobutyronitrile dissolved in 100 mlof allyl alcohol. The pressure reactor is closed and charged with 36 g (1.06 moles) of phosphine. The reaction mixture is agitated by rocking the reactor for two hours at 80~C. The reaction mixture is permitted to cool to room temperature and the pressure vessel is vented in a hood to release any unreacted phosphine. An additional 20 ml of the azobisisobutyronitrile solution described above is added to the reactor which is closed and the system is again heated to ~0C and rocked for one hour~ The addition of 20 ml of the azobisisobutyro-nitrile solution is repeated with intermediate agitation at 80C for one hour under pressure until all of the aæobisisobutyronitrile solution (lO0 ml) has been added.
The contents of the reactor are then heated to 80~C
under pressure and rocked for an additional five hours.
The yellow solution that results from the above reaction is vacuum distilled by heating to about 85C
at 133 Pa absolute and maintaining that temperature and pressure for about four hours to remove volatiles [mono-, and bis(3-hydroxypropylJ phosphine] and unreacted allyl alcohol. The residue remaining in the distillation pot is a clear yellow syrup weighing 184 g.
This non-volatile yellow syrup is dissolved in an e~ual volume of a 50:50 mixture of isopropanol/methanol and oxidized by stirring with the dropwise addition of a 30% aqueous hydrogen peroxide solution diluted with an e~ual volume of isopropanol. When the exothermic reac-tion subsides, the solution of phosphine oxide ls tested by adding one drop of the solution to 1 ml of carbon~
disulfide until no red coloration can be detected visually in the carbon disulfide layer. This indicates complete oxidation of the phosphine to tris~3-hydroxy propyl3 phosphine oxide.
Following oxidation with hydrogen peroxide, the solvents (water, isopropanol and methanol~ are removed from the reaction product by heating to 65C under 3~

vac~um. The viscous yellow slush which remains is fil-tered through a Buchner Funnel to collect 42.4 grams of a white solid that is insoluble in isopropanol at room temperature. ~he yield~ based on the phosphine used is 17.8%. After washing with isopropanol and air drying, the white solid analyses for tri 5 ( 3-hydroxypropyl) phosphine oxide.
Found Theory C=48.29~ C=48.21%
H-9.28~ H=9.38~
P=13.3% P=13.84%
The tris(3-hydroxypropyl) phosphine oxide is evaluated as a Eire retardant in polyphenylene oxide compositions (UL 94 Vertical Burn Test). The results are reported in Table I.
In a similar rnanner 2-methyl-3-hyc1roxypropyl bis-(3-hydroxypropyl) phosphine oxide may be prepared by reacting one mole of methallyl alcohol and two rnoles of allyl alcohol with phosphine and oxidizing with hydro-gen peroxide. Five parts of this compound with 100 parts of a polyphenylene oxide composition by weight give a UL 94 rating of V-1 (see Table I).
Example II
n-Butyl-bis(3-Hydroxypropyl) Phosphine Oxide Into a 4 liter stainless steel pressure reactor is placed 0.5 9 azobisisobutyronitrile dissolved in 600 ml of toluene. The reactor is purged with nitrogen and charged with 112 g ~2.0 moles) of butene and 102 g (3.0 moles, 50% excess) phosphine. The reaction mixture is heated and stirred at 85-90C for one hour and main-~tained at that temperature with stirring while five 20 ml portions of azobisisobutyronitrile solution (5.5 g in 350 ml of toluene) are added at 20 minute intervals over 1 hour 40 minutes. No exotherm is noted during the catalyst addition and the absolute pressure reading dropped from 1.432 MPa (at the time of the first 20 ml catalyst addition) to 1.397 MPa ~20 minutes after the last catalyst addition~.
The excess phosphine is vented from the reaction vessel and 278 g ~4.8 moles, 20% excess~ of allyl alcohol and 40 ml of the azobisisobutyronitrile catalyst solu-tion is added to the reaction vessel. No exotherm isobserved and heating is continued at 85-90C with stir-ring and addition of 20 ml of azobisisobutyroni~rile every 20 minutes until all of the catalyst solution ~350 ml) has been added. The temperature is maintained with stirring at 85-9ODC for 11 hours. A clear yellow liquid is removed from the reactor and heated to 110C
at 133 Pa absolute to distill off the volatile materials.
The residue is a clear yellow liquid weighing 290.9 grams. This residue is dissolved in an equal volume of isopropanol and oxidized with 30% hydrogen peroxide dis-solved in an equal volume of isopropanol as described above in Example I to give 308.2 9 of a viscous yellow liquid (after removal of water and isopropanol) contain-ing a small amount of a white suspended solid. The mix-ture is diluted with chlorof~rm, filtered to remove thewhite solid, and the chloroform is evaporated to give a clear yellow liquid. The analysis of this liquid product is:
Found ~%) Calculated for n-butyl bis(3-hydroxypropyl) ~hos~hlne oxide_(%) C=54.50, 5~.40 54.05 H=10~21, 10.21 10.36 P=13~28, 13.65 13096 This product, which is believed to contain both~
n-butyl bis~3-hydroxypropyl) phosphine oxide and 3-hydroxypropyl di-n-butyl phosphine oxide, is evaluated as a fire retardant in polyphenylene oxide compositions ~UL 94 Vertical Burn Test). The results are reported in Table I.

3~C~

Example III
Preparation of Tris(3-Hydroxy-2-Methylpropyl) Phosphine Oxide Tris(3-hydroxy-2-methylpropyl~ phosphine is pre-pared by the method described in Example I above.
~ nto a four liter pre~sure reactor equipped witha stirrer and thermometer is placed 690 g (9.6 moles) of methallyl alcohol and 40 ml of a solution containing 9 9 azobisisobutyronitrile dissolved in 200 ml of toluene. The pressure reactor is elosed and charged with 96 g (2.8 moles) of phosphine. The reaction mixture is heated with stirring to 60-C at which temperature the reaction becomes exothermic and the temperature rises to 107C. Stirring is continued as the temperature subsides from 107C to 90C and the absolute pressure drops from 803.2 k Pa to 349.2 k Pa. The temperature is maintained at 90C with heating and stirring for one hour at which time 5~ ml of the a~obisisobutyronitrile solution in toluene is pumped into the reactor. The reaction mixture is maintained at gonC for one hour with stirring after the second addition of catalyst. The addition of 50 ml of the a~obisisobutyronitrile solution is repeated with continuous stirring at 90C each hour until all of the azobisisobutyronitrile solu~ion t200 ml) has been added. The contents of the reactor are then stirred while maintainin~ the temperature at 90C
for an additional four hours. After the la~t adclition of catalyst solution, the pressure in the reaction vessel has dropped to atmospheric pressure.
The reaction mixture is cooled to room temperature,~
removed from the reaction vessel and heated up to 35C
at 266.6 Pa absolute to distill off the volatile compo-nents (toluener methallyl alcohol, mono and bis- addi-tion products).
The non-volatile colorless li~uid residue tris-(3-hydroxy 2-methylpropyl) phosphine weighs 614.7 g.
It is dissolved in an equal volume o~ isopropanol and ~2~2~3~

chilled on ice. The phosphine present in solution i5 oxidized by the dropwise addition with stirring of a 30% aqueous hydrogen peroxide solution diluted with an equal volume of isopropanol. Inasmuch as the oxidation reaction is exothermic, the course of the reaction may be followed by the temperature increase upon addition of hydrogen peroxide. When the exotherm subsides, a small aliquot of the reaction mixture is tested after each addition of hydrogen peroxide with hydrogen peroxide test paper and by addition of a few drops of the reac-tion mixture to 1 ml of carbon disulfide. At the end of the oxidation reaction, the observed red color of the carbon disulfide indicative of unoxidized phosphine disappears and the hydrogen peroxide test paper indicates the presence of hydrogen peroxide.
When the oxidation of the phosphine to phosphine oxide has been completed, the water and isopropanol are removed from the phosphine oxide by heating to 65C under vacuum until all volatiles have distilled off. The resi-due, a clear colorless viscous liquid, weighs ~33.5 9 and has the following analysis:
Found (~) Theory (%) C-54.59 C=54.14 H=9.35 H=10.15 P=11~1 P=11.65 The "theory" values are calculated for tris(3-hydroxy-

2-methylpropyl) phosphine oxide.
Five parts of this oompound when added to 100 parts of polyphenylene oxide composition gives a 94 UL Verti-cal Burn Test rating of V-1 (see Table I).
_ample IV
s~Butyl bis(3-Hydroxypropyl) Phosphine Oxide Into a 4 liter stainless steel pressure reactor is placed 224 g (4 moles) of mixed 2-butene, 6Q0 ml of 35 toluene, 204 g (6.0 moles, 50~ excess) of phosphine and 25 ml of a solution of 4 g azobisisobutyronitrile in 100 ml of toluene. The reaction vessel is heated and ~ 2~

stirred at 85C to 90JC for one houx and the remaining azobisisobutyronitrile solution is added in 25 ml por-tions every 30 minutes until the 100 ml of catalyst solution is used up. The reaction mixture is heated and stirred at 90~C for 4 hours after the last addition of catalyst solution and then allowed to cool overnight.
The phosphine is vented from the reaction vessel and 487 g (8.4 moles, 5~ excess) allyl alcohol is added together wi~h 50 ml of a solution of 8 g azobisisobuty-ronitrile in 20 ml of toluene. The reaction mixture isheated with stirring at gOC with the addition of 50 ml a~obisisobutyronitrile catalyst solution every 30 minutes until all 200 ml of solution has been added. Heating and stirring are continued at 90C for 4 hours and the reac-tion vessel is then allowed to cool to room temperature.The liquid from the reaction vessel is heated to 130C
at 200 Pa absolute to remove volatile components. The residual product is a greenish liquid weighing 519.3 g.
The residual product is believed to contain both s-butyl his(3-hydroxypropyl~ phosphine and 3-hydroxy-propyl di-s-butyl phosphine. It is dissolved in an equal volume of isopropanol and oxidized with 30~ hydro-gen peroxide in an equal volume of isopropanol as described above in Example I until a negative carbon disulfide reading is obtained. ~he solution of oxidized phosphine is concentrated under reduced pressure to yield a syrupy yellow liquid weighing 555.6 g ~99.2% yield on oxidation or a yield of 62.5% based on the starting butene).
This product has the following analysis.
Found (_ Calculated for s- -butyl bis(3-hydroxy-propyl) phosphine oxide (%) ________________ ___

3~ C=51.80, 52.06 5~.05 H=8.72, 8.94 10.36 P=13.79 13.96 3~

This i~ an effective flame retardant when added to polyphenylene oxide composition6 in amvunts of 4 to 10 par~s by weight per hundred parts of polyphenylene ~xide compositlons.
~xampl _ Effect of 3-Hydroxyalkyl Phosphine Oxide As A Flame Retardant For Polyphenylene Oxide Compositions The phosphine oxide6 described above in Examples 1 and 3 are added to a polyphenylene oxide composition in the amounts per hundred parts of resin ~PHR) indi-cated in Table I and dispersed throughout the resin.
Mixing of the additive and resin is accomplished in a ~aake mixer (HAAKE RHEOMIX MODEL 600 with REOCORD EU10 attachment, manufactured by Haake Inc., 244 Saddle River 15 Road, Saddle Brook, New Jersey 07662). The mixing takes place at 265C at which temperature some of the additive is volatilized. The Underwriter Laboratories rating (Vertical Burn Test) for the various combinations tested is indicated in Table I.
In testing the polyphenylene oxide compositions containing a 1ame retardant additive, the flame re-tardant properties are determined following procedures established by the Underwriter Laboratories Bulletin No. 94, STANDARD FOR TESTS FOR FL~MMABILITY OF PI~STIC
MATERIALS FOR P~RTS IN D~VICES AND APPLIANCES; Second Edition, Second Impression (as revised to February 1, 1974) dated July 30, 1976. Tests were run on 3.175 mm specimens and the Vertical Burning Test for classifying Materials 94 V-0, 94 V-1 or 94 V-2 and described in Section 3 of this publication is used. In this test, the V-0 rating indicates the best flame resistance and the V-1 rating indicates less flame resistance.

* Trade Mark 3~

TABLE I
Effect of phosphine oxide as a flame ;retardant in poly-phenylene oxide compositiQnS. All quantities are expressed in parts by wei~ht.
A B C D E F G El 10~ 5 ~ V~0 100 - 6 ~ V-0 100 - ~ 6.5 - ~ - V-0 ~ 4.~5 - - - V-0 - 1~0 - - 8 - - V-1 100 ~ - - CB*
- CB*

A = 35 P~]R polyphenylene oxide and 65 PHR polystyrene B ~ 40 PHR polyphenylene oxide and 60 PHR polystyrene C = Tris(3~hydroxypropyl) phosphine oxide D = s~butyl bis(3-hydroxypropyl) phosphine oxide E = Mixed isopropylphenyl/phenyl phosphate esters F = Tris~2-methyl-3-hydroxypropyl) phosphine oxide G = 2-methyl-3-hydroxypropyl bis(3-hydroxypropyl) phosph i ne ox ide H = UL 94 Vertical Burn Test CB* = Complete burn

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are de-fined as follows

1. s-Butyl bis(3-hydroxypropyl) phosphine oxide.