Phosphine oxide substituted polycarbonate

Novel flame retardant polycarbonates are prepared that maintain a T.sub.g and an impact strength similar to that of non-modified polycarbonates. More particular, phosphine oxide containing polycarbonates are prepared that demonstrate improved flame retardancy and the retention of impact strength and glass transition temperature.

BACKGROUND OF THE INVENTION 
This invention relates to the preparation of flame retardant polycarbonates 
and more particularly to phosphine oxide containing polycarbonates. 
Polycarbonates are well known as tough, clear, highly impact resistant 
thermoplastic resins. It is desirable to have polycarbonates possess flame 
retardancy. Several flame retardant agents are known to be effective. It 
is known to use alkali metal salts of strong sulfonic acids as flame 
retardant agents, however, the increased hydrolytic sensitivity of the 
polymer matrix presents some difficulties. When alkali metal salts of 
strong sulfonic acids are used, it is also necessary to use drip 
inhibitors and often gas phase flame retardant agents. Drip inhibitors 
such as Teflon.RTM. are used, but the resulting polymers lose clarity. Gas 
phase inhibitors such as halogenated flame retardants have also been used. 
The use of halogens presents problems with corrosion and toxicity. As an 
alternative to halogenated compounds, phosphorus containing compounds such 
as triphenylphosphate have been used. Most effective phosphorus compounds 
are soluble in polycarbonates, and the resulting polymer blends have low 
glass transition temperatures (T.sub.g) and low impact resistance compared 
to the base resin. 
The present invention is based on the discovery that certain 
dihydroxyarylphosphine oxide units can be incorporated into polycarbonates 
to form polymers, and these polymers unexpectedly retain high T.sub.g 
values similar to polycarbonates not containing these 
dihydroxyarylphosphine oxide units. In addition to retaining high T.sub.g 
values, the phosphine oxide substituted polycarbonates exhibit improved 
flame retardancy as shown by high limiting oxygen index values. 
SUMMARY OF THE INVENTION 
Accordingly, the invention is a phosphine oxide substituted polycarbonate 
comprising the structural units of the formula 
##STR1## 
wherein A.sup.1 is a trivalent substituted or unsubstituted aromatic 
radical; and A.sup.2 and A.sup.3 each are independently selected from 
aromatic radicals. Generally, 1-25 mole percent of the units of formula I 
are present in the phosphine oxide substituted polycarbonate, and 
preferably 5-10 mole percent of the total polymer. 
Additionally, the polycarbonates of the present invention can further 
comprise structural units of the formula 
##STR2## 
wherein A.sup.4 is a divalent substituted or unsubstituted aromatic 
radical.

DETAILED DESCRIPTION OF THE INVENTION 
Polycarbonates are generally formed by the reaction of a dihydroxyaromatic 
compound and a carbonate source. 
One reactant for formation of the polycarbonates of this invention is a 
dihydroxyarylphosphine oxide of the formula 
##STR3## 
wherein A.sup.1, A.sup.2 and A.sup.3 are as previously described. 
Specifically A.sup.1 can be 
##STR4## 
wherein R.sup.1, R.sup.2 and R.sup.3 are hydrogen or alkyl radicals. 
A.sup.1 is preferably C.sub.6 H.sub.3. A.sup.2 and A.sup.3 may be any 
unsubstituted aromatic radical or substituted derivatives thereof. 
Suitable substituents include alkyl, alkenyl, halo, nitro, alkoxy and the 
like. Unsubstituted phenyl radicals are preferred. The hydroxy groups of 
formula III are preferably para to each other. 
The dihydroxyarylphosphine oxide can generally be formed by the reaction of 
a quinone and a phosphine oxide or a suitable treated chlorophosphine. The 
formation of dihydroxyarylphosphine oxide compounds is disclosed in U.S. 
Pat. No. 5,003,029. Illustrative quinones include parabenzoquinone, 
1,4-naphthoquinone, 1,4-anthraquinone, methyl-p-benzoquinone and 
dimethyl-p-benzoquinone. The preferred quinone is p-benzoquinone. Suitable 
phosphine oxides or chlorophosphine include diphenyl phosphine oxide or 
diphenyl chlorophosphine. 
The preferred dihydroxyphenylphosphine oxide is 
2,5-dihydroxyphenyldiphenylphosphine oxide and can be prepared as in 
Example 1. 
EXAMPLE 1 
A 2000 mL, three-neck round bottomed flask equipped with a mechanical 
stirrer, a N.sub.2 bypass and an addition funnel was charged with 33.4 g 
(0.31 moles) of p-benzoquinone along with 900 mL of toluene and 100 mL of 
water. The addition funnel was charged with 68.0 g (0.31 moles) of 
chlorodiphenylphosphine dissolved in 80 mL of toluene. The reaction 
mixture was stirred into an emulsion and heated to 60.degree.-65.degree. 
C. The phosphine was added dropwise over a 1.5 hour period. The phosphine 
initially reacts with water to generate the phosphine oxide, which then 
reacts with the p-benzoquinone. The reaction mixture was stirred a further 
2 hours as the precipitate solidified. The crude product (84.2 g) was 
filtered, washed with toluene and recrystallized with hot filtration from 
3.8 L of acetone. The isolated white crystalline 
2,5-dihydroxyphenyldiphenylphosphine oxide weighed 44.6 g (46.6% yield). 
The melting point was 213.degree.-215.degree. C. and .sup.1 H and .sup.13 
C NMR showed the material to be the desired product. 
The polycarbonates of the present invention can include both homo- and 
copolycarbonates. The copolycarbonates preferably contain about 1.0 mole 
percent to about 25 mole percent dihydroxyarylphosphine oxide units, and 
more preferably contain about 5 mole percent to about 10 mole percent 
units. 
The non-phosphorus dihydroxyaromatic compounds useful for forming 
copolycarbonates may be any such compound known to the art. The material 
represented by formula IV 
EQU HO--A.sup.4 --OH(IV) 
is the source of the structural units of formula II above. Illustrative 
non-limiting examples of non-phosphorus dihydroxyaromatic compounds 
include: 
2,2-bis(4-hydroxyphenyl-propane (bisphenol A); 
2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane; 
2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; 
1,1-bis(4-hydroxyphenyl)cyclohexane; 
1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane; 
1,1-bis(4-hydroxyphenyl)decane; 
1,4-bis(4-hydroxyphenyl)propane; 
1,1-bis(4-hydroxyphenyl)cyclododecane; 
1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclododecane; 
4,4-dihydroxydiphenyl ether; 
4,4-thiodiphenol; 
4,4-dihydroxy-3,3-dichlorodiphenyl ether; and 
4,4-dihydroxy-3,3-dihydroxydiphenyl ether. 
Other useful non-phosphorus dihydroxyaromatic compounds which are also 
suitable for use in the preparation of the above polycarbonates are 
disclosed in U.S. Pat. Nos. 2,999,835; 3,028,365; 3,334,154; and 
4,131,575, all of which are incorporated herein by reference. The 
preferred bisphenol is 2,2-bis(4-hydroxphenyl)propane (bisphenol A). The 
amount of non-phosphorus dihydroxyaromatic generally used is from about 75 
mole percent to about 99 mole percent and preferably from 90 mole percent 
to about 95 mole percent. 
The phosphine oxide containing polycarbonates can be formed by any method 
known to the art. Examples of methods to prepare phosphine oxide 
containing polycarbonates include an interfacial process, a 
transesterification process and a bishaloformate process. 
The preferred method of forming the phosphine oxide substituted 
copolycarbonates is interfacially, that is, in a mixed aqueous-organic 
system which results in recovery of the polycarbonate in the organic 
phase. A carbonate precursor is used in the interfacial reaction and is 
preferably phosgene. When using an interfacial process it is also standard 
practice to use a catalyst system well known in the synthesis of 
polycarbonates and copolyestercarbonates. Suitable catalysts include the 
tertiary amines. Tertiary amines include aliphatic amines such as 
triethylamine, tri-n-propylamine, diethyl-n-propylamine, and 
tri-n-butylamine, and highly nucleophilic heterocyclic amines such as 
4-dimethylaminopyridine. Such amines generally contain at least about 6 
and preferably about 6-14 carbon atoms. The most useful amines are 
trialkylamines containing no branching on the carbon atoms in the 1- and 
2-positions. Triethylamine is the most preferred. 
A chain terminating agent to control the molecular weight of the polymers 
is usually present. Suitable chain termination agents are those commonly 
employed for polycarbonate formation, including monohydroxyaromatic 
compounds such as phenol, p-t-butylphenol and p-cumylphenol. Phenol is 
preferred. Quantities of chain terminating agents can range from about 0.5 
to about 7 mole percent based on the total amount of non-phosphorus 
dihydroxyaromatic compound employed. 
Another method of preparing polycarbonates is by transesterification with a 
bisphenol of a carbonate ester such as diphenyl carbonate or a 
bis-polyfluoroalkyl carbonate. U.S. Pat. Nos. 4,217,438, 4,310,656 and 
4,330,664 describe the formation of polycarbonates by a 
transesterification method and are hereby incorporated by reference. 
Still another method of polycarbonate formation is the reaction of 
bishaloformates with alkali metal hydroxides and various amines. One 
method for reacting bishaloformates with dihydroxy compounds is disclosed 
in U.S. Pat. No. 4,737,573 which is hereby incorporated by reference. 
Generally bischloroformate oligomer compositions are prepared by passing 
phosgene into a heterogeneous aqueous-organic mixture containing at least 
one dihydroxyaromativ compound. The reaction is a condensation reaction 
that typically takes place interfacially. 
The following are examples of forming the phosphine oxide substituted 
copolycarbonate. 
EXAMPLE 2 
The phosphine oxide substituted copolycarbonate was prepared by 
interfacially phosgenating a mixture of 20.5 g of BPA, 3.1 g of 
2,5-dihydroxyphenyldiphenylphosphine oxide (10 mole % compared to BPA), 
0.64 g of p-cumylphenol chainstopper and 1.0 g of triethylamine in 160 mL 
methylene chloride and 125 mL of water. To the vigorously stirred emulsion 
was added 12.9 g of phosgene over a 25 minute period. Once the reaction 
was complete, the phases were separated and the polymer solution 
(methylene chloride layer) was extracted two times with 300 mL of 0.5N HCl 
followed by five times with 300 mL of water. The polymer solution was 
precipitated into 1 L of methanol in a blender. The white polymer powder 
(20.0 g) was isolated and dried at 120.degree. C. Gel Permeation 
Chromatography (GPC) analysis of the polymer showed an Mn=18000. .sup.1 H 
and elemental analysis showed all the phosphine oxide was incorporated. 
The copolycarbonate shows a .sup.31 P resonance at 24.5 ppm in deuterated 
chloroform. The copolymer gave a strong clear colorless solvent cast film. 
The Tg of the copolymer determined by DSC was 149.degree. C. 
The glass transition temperature of the substituted polycarbonate is an 
important property which affects the amount of unwanted polymer dripping 
that occurs during flame retardancy testing. Low T.sub.g polymers are more 
prone to this undesirable dripping, therefore it is desirable to maintain 
a higher T.sub.g. A key aspect of the current invention is that the 
polycarbonate T.sub.g is maintained thus allowing the copolycarbonate to 
be flame retardant without sacrificing thermal properties. 
EXAMPLE 3 
Example 3 compares physical properties of phosphine oxide containing 
copolycarbonate with triphenylphosphine oxide polycarbonate blend and 
unsubstituted polycarbonate. 
__________________________________________________________________________ 
Limiting 
Oxygen Notched Izod.sup.2 
Index.sup.1 
T.sub.g 
Average 
Material Additive (LOI %) 
(.degree.C.) 
(j/m) 
__________________________________________________________________________ 
Bisphenol A (BPA) 
None 27 150 800 
polycarbonate 
BPA polycarbonate 
3.7 mole % TPPO* 
31 130 700 
BPA polycarbonate 
7.4 mole % TPPO 
33 116 50 
5.0 Mole % Phosphine 
None 33 152 650 
oxide/BPA 
copolycarbonate 
__________________________________________________________________________ 
*Triphenylphosphine oxide 
.sup.1 Performed according to ASTM D2863. 
.sup.2 Performed according to ASTM D256 using a modified testing procedur 
having a notch radius of 0.015 inches. 
The phosphine oxide substituted polycarbonate was formed as in Example 2, 
and the TPPO was added as a blend in polycarbonate at the mole percent 
loading indicated in the above table. The TPPO/polycarbonate blend is 
known in the art. As can be seen in the above table, the LOI of phosphine 
oxide substituted polycabonate is improved over that of the corresponding 
polycarbonate not containing the dihydroxyarylphosphine oxide units and 
the notched Izod values are not sacrificed by incorporating the preferred 
structural units into the polycarbonate. The LOI test performed according 
to ASTM D-2863 measures the percentage of oxygen in nitrogen necessary to 
sustain the burning of the material tested. The greater the LOI %, the 
more oxygen needed, hence the higher the flame retardency of the polymer 
being tested.