I
H. W. COOVER, Jr., RICHARD L. McCONNELL, and NEWTON H. SHEARER, Jr. Research Laboratories, Tennessee Eastman Co., Division of Eastman Kodak Co., Kingsport, Tenn.
Flame-Resistant Polymers Polyphosphonarnides f r o m Phosphonic Diamides Products useful for stabilizing poly(viny1 chloride) against light and for flameproofing are easily made
A condensation rate of phenylphosphonic diamide (melting point STUDY O F THE
189' C.) in the range of 200' to 300' C., indicated that 1 mole of ammonia was lost per mole of amide and resulted in a polymer having the probable structure, 0
(-!-TiH-)*.
I
GHa The extreme insolubility, the fact that fibers were obtainable from some products, and the second-order reaction kinetics (indicating an intermolecular reaction) also substantiate the structure shown. Products prepared below 280' C. were probably low molecular Lveight polymers which may have contained some dimeric material. I n preparing these condensation products, phenylphosphonic diamide was melted in an atmosphere of nitrogen with stirring. Then vacuum was gradually applied to remove the evolved ammonia, and the reaction mixture was heated to the desired temperature. The reactions were continued until ammonia was no longer evolved at the curing temperature. Temperature range studied was about 200" to 400' C . In addition, the condensation of some ,?'-substituted amides was invesIigated. Finally, polymers obtained by condensation of phenylphosphonic diamide or phenylphosphonic dichloride with urea and with thiourea were studied.
polymer formed at 280' C. was white and, when cooled, could be crushed to a powder that was partially soluble in acetone and dimethylformamide. The polymers formed at temperatures above 280" C., however, were generally insoluble in acetone but still partially soluble in dimethylformamide. Products formed at all temperatures used were insoluble in Tetralin, a 60:40 phenol - tetrachloroethane mixture, benzene, ethyl alcohol, ethyl acetate. and water. Fibers drawn from melts of phenylphosphonic diamide polymers cured at 300" to 350' C. were short and brittle. These melts were viscous, opaque materials which formed white. friable solids when cooled. When the condensation was completed at 400' C. or above, the viscous mass solidified to a glass which was porous, brittle, and nearly colorless. I t was insoluble in the usual solvents and did not fuse well, even in a Bunsen flame. This insolubility and infusibility may indicate a highly cross-linked material. Molecular weight determinations were difficult because all the condensation products were extremely insoluble in suitable solvents. Nitrobenzene and tetrachloroethane were used to determine molecular weights ebulliometrically on some products obtained from condensations up to 275' C. The values obtained indicated average molecular weights of 300 to 400 and thus the 0
I1 I
(-P-NH-)
Polymers from Phenylphosphonic Diamide The condensation of phenylphosphonic diamide with itself to form polymeric products ( 2 ) is illustrated by
C&,
presence of two or three units. Such low molecular weight products might be in the form of a cyclic dimer, H
1
H
I1 or a cyclic trimer,
H-N
/\ N-H l~
O=P
P=O
H I11
Molecular weights were not obtainable on products cured above 300' C. because the materials were extremely insoluble; however, the values were probably higher than 300 to 400. Inherent viscosities at 25' C. using 0.25% solutions in dimethylformamide were about 0.04. Such values indicate rather low molecular weights but since about 30% of the material was insoluble, the viscosity determinations do not represent all products which are formed. The condensation products prepared at the various temperatures were highly crystalline. Peaks in the x-ray diffraction patterns were sharper than those normally observed for high molecular
Analyses o f Infrared Spectra of Phenylphosphonic Diamide and Its Polymers Absoration Band. u Monomer 3.0;
3.15
Polymer, C.
200-300'
3.2
Polymer, 400' C.
3.2
Assignment
N-H
(doublet) 6.95 8.6
...
The nature of the product depended on the maximum temperature used. The
41 2
INDUSTRIAL A N D ENGINEERING CHEMISTRY
13.35;14.40 14.1
6.95 8.8 10.3-10.5 13.35;14.45 13.95
6.95
... ...
13.35;14.46 13.95
P-CfiHs
P=O P-N-P c6H5-
P-N
FLAME-RESISTANT P O L Y M E R S I00IL 80
c (Theor NH, lrom 0 I mole amide= 100 m e q )
I . - L - l - A 100 200
0
I_-/
300
400
Time Min
Figure 1. A temperature of 200°C. i s not high enough to complete condensation of phenylphosphonic diamide
weight polymers. Thus, at least part of the condensation products may have been low molecular weight compounds. The shift of the N-H band in the infrared pattern to 3.2 microns may be caused by strong hydrogen bonding. The polymers prepared in the 200' to 300' C. range had a broad band at 8.8 microns, characteristic of P=O groups; however, this band was slightly outside the spectral region in which the P=O absorption band usually appears. The spectra of the polymers prepared at 400' C. were generally quite featureless and had no P=O band. Compounds with P-0-P structures have a broad band in the 10.3- to 11.0micron range. A similar band at 10.3 to 10.5 microns, probably resulting from the P-N-P structure, appeared in the polymers prepared a t 200' to 300' C. This band was not observed for the polymers prepared at 400' C. The rates of evolution of ammonia a t 200', 225', 250') and 300' C. were studied. The phenylphosphonic diam-
ide was placed in a flask and stirred as a stream of nitrogen was passed through a capillary tube. A metal bath preheated to the desired temperature was placed under the flask. The ammonia evolved was passed through a cold-water condenser and then dispersed through a fritted-glass disk into a saturated aqueous solution of boric acid. The evolution of ammonia was so vigorous initially that two absorption towers connected in series were required to prevent loss of ammonia. The boric acid solutions containing ammonia were titrated with 0.5N hydrochloric acid solution using Sher's two-step indicator (8). Rates of evolution of ammonia at 200°, 225', and 250' C. are shown in Figures 1, 2, and 3. At 225' and 250°, as well as a t 300' C., approximately 1 mole of ammonia was obtained for each mole of phenylphosphonic diamide used. T h e loss of this amount of ammonia is compatible with structures I, 11, or 111. The lowest temperature (ZOO0 C.) was not high enough above the melting point to obtain a rapid evolution of ammonia. When the rates of evolution of ammonia were considered, the kinetic data indicated a second-order reaction (Figure 3) ; thus the reaction is probably bimolecular, indicating an intermolecular rather than an intramolecular condensation. O n the basis of the rate constants obtained for the condensations a t 225' and 250' C., the heat of activation was calculated to be about 14 kcal. per mole. Samples of the polymeric phenylphosphonic diamide cured at 400' C. were difficult to combust; hence, quan-
titative analyses of this material, especially in the carbon determination were inaccurate. The carbon value was always several per cent lower than the theoretical value. These combustions always left a large amount of ash. I t is quite probable that much carbon was trapped in this ash. Tungsten oxide, which is often useful in the combustion of samples that are difficult to decompose completely, did not change the carbon and hydrogen values. The values found for phosphorus were in the correct range. The nitrogen analyses on the materials condensed above 300' C. were usually low, indicating that more than 1 mole of ammonia was lost per mole of diamide. The gases evolved during condensations of phenylphosphonic diamide at temperatures ranging from 200' to 395' C. were studied by means of a mass spectrometer. Ammonia and water were detected in the gases evolved from condensations up to 245' C. ; from those between 250' and 395' C., benzene and hydrogen were also detected. The loss of benzene would help account for the low carbon analyses. The loss of benzene, hydrogen, and water would indicate an attempt by the polymer to reach a phosphorus-nitrogen-phosphorus structure and would also account for the cross-linking of the polymer.
Polymers from KSubstituted phenylphosphonic Diamides
'
P-
A similar condensation was observed with N,N' dimethyl P phenylphos-
-
- -
0.40r
250°C. (0.05 mole)
k
u
3
030-
0
I
I
= 0.125 mold' sec:'
225°C (005 mole) k = 0 071 mold' sec-'
Z
0 0
200°C (0.10 (010 mole)
amide =
!
I
50
100
k
I
I
I
150 Time, Min.
200
250
2. For phenylphosphonic diamide at 225' and 250°C., 1 mole of ammonia i s evolved per mole of starting Figure
I
0
io0
200 Time, Min.
= 00012 m o l i ' sec:' sec-'
I
300
400
Figure 3. Straight lines obtained in this plot indicate secondorder kinetics
material VOL. 52, NO. 5
MAY 1960
413
phonic diamide, methylamine liberated rather than ammonia:
being
A
IV The low melting, solid monomer was prepared from phenylphosphonic dichloride and liquid methylamine (analysis calculated for CP,H~~NZ~P: P, 16.84. Found: P, 16.65). Possible structures for the condensation product include a linear polymer as well as cyclic dimer and trimer structures similar to I1 and 111. The polymer was a glassy, amber-colored material which melted at 106' to 120' C. and was soluble in chloroform and methanol but insoluble in benzene. When water was added to a methanolic solution, the solution became warm and turned milky; hence, water probably hydrated this condensation product in a manner similar to that described for oxyphosphazobenzene (7). The condensations of phenylphosphonic diamide and N,N'-dimethyl-Pphenylphosphonic diamide with liberation of ammonia or methylamine are analogous to the pyrolysis of N,N',P-triphenylphosphonic diamide, in which aniline is liberated to form a dimer of oxyphosphazobenzene ( 7 ) .
phenylphosphonic diamide was prepared by bubbling dimethylamine through a solution of phenylphosphonic dichloride in ether. It is a white crystalline solid having a melting point of 82' to 84' C. after crystallization from a mixture of hexane and benzene (analysis calculated for C I O H I ~ N Z O PC, : 56.59; H, 8.08; N, 13.20; P, 14.60. Found: C, 56.40; H, 7.92; N, 13.16; P, 14.59). N,N,N',A7' - Tetramethyl - P chloromethylphosphonic diamide was prepared from anhydrous dimethylamine and chloromethylphosphonic dichloride in ethyl ether. I t is a white, hygroscopic, crystalline solid having a melting point of 40' C., and a boiling point of 110' to 112' C. a t 2.5 mm. (analysis calculated for CSH14ClNtOP: C, 32.53; H , 7.64; P, 16.78. Found: C, 32.25; H, 7.39; P, 16.85). Other completely substituted phosphonic diamides are reported (3, 5).
[
$CHCONH-]
It is thought that a condensation product similar to the phenylphosphonic diamide type was obtained from the condensation of chloromethylphosphonic dichloride and ammonia in 1,2,4-trichlorobenzene. I n this case, the chloromethylphosphonic diamide formed in situ was not isolated but was polymerized by refluxing the mixture (210' C.). This condensation product was a tan, CsHj
I
N
--"a
A
(4)
VI Evolution of ammonia from the mixture of phenylphosphonic diamide and urea began at 150' C. When the reaction was conducted at 200' C. under reduced pressure, the polymer obtained was a clear, light yellow, hard resin which was slightly soluble in acetone and moderately soluble in dimethylformamide. A similar polymer resulted when an excess of the phenylphosphonic diamide was used. Condensation of phenylphosphonic dichloride with urea or thiourea resulted in the loss of hydrogen chloride and the subsequent formation of a cream-colored, polymeric material. The reaction with urea began at 115' C. and was very vigorous in the initial stages; however, after a short time at 115' C. a white solid formed. A temperature of about 200' C. was necessary in order to obtain a melt and thus continue the condensation. The polymer was partially soluble in dimethylformamide and insoluble in acetone and water. When the product was heated in a flame, ammonium chloride was evolved Polymers with similar properties were obtained with thiourea; however, hydrogen chloride was not evolved copiously until the reaction temperature reached approximately 140' C. A similar reaction is reported where urea and chloromethylphosphonic, dichloromethylphosphonic, or trichloromethylphosphonic dichloride were used ( 4 )'
Polymers from Chloromethylphosphonic Diamide
O
+
C B H ~ P ( O ) ( N H ~ )NH2CONHZ Z w
0
Acknowledgment The authors thank R. L. Combs for assistance in interpreting kinetic data. I t was reported that this product could be converted back to the diamide by heating with excess aniline at 125' C. These reactions were repeated and verified. Similar attempts to convert the phenylphosphonic diamide polymers (cured above 300' C.) back to phenylphosphonic diamide using ammonia were not successful. The tendency for unsubstituted or monosubstituted phosphonic diamides to condense and lose ammonia or an amine is in marked contrast to the stability of the completely substituted phosphonic diamides; for example, iV,X,N',N' - tetramethyl - P - phenylphosphonic diamide and N,N,N',N'tetramethyl - P - chloromethylphosphonic diamide are stable and distillable because no hydrogen atom is present on either nitrogen atom to allow loss of an amine. N,N,N',.V' - Tetramethyl - P -
4 14
powdery material which gradually dissolved in water. The preparation of polymers by interaction of phosphoryl chloride and ammonia was reported by Truhlar and Pantsios ( 9 ) and also by Malowan and Hurley ( 6 ) . One of the structures presented by Truhlar and Pantsios was 0
(-!-NH-)*
I
NHz which is similar to one of the structures (I) proposed for the phenylphosphonic diamide polymers.
Literature Cited (1) Coover, H. W., Jr. (to Eastman Kodak Co.), U. S . Patent 2,642,413 (June 16, 1953). (2) Dickey, J. B.. Coover, H. W., Jr. (to Eastman Kodak Co.), U. S. Patent
2,666,750 (Jan. 19, 1954). (3) Freedman, L. D., Doak, G. O., J . Am. Chem. Soc. 77,6635 (1955). ( 4 ) Haven, A . C., Jr. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2,716,639 (Aug. 30, 1955). (5) Kosolapoff, G. M., Payne, L. B., J. Org. Chem. 21,413 (1956). (6) Malowan, J. E., Hurley, F. R. (to Monsanto Chemical Co.), U. S. Patent 2,596,935 (May 13, 1952). (7) Michaelis, A,, van Gaza, B., Rehse, W., Ann. 407, 316 (1915). (8) Sher, I. H., Anal. Chem. 27, 831 (1955). 1 9 R. ) Truhlar. J.. U. Pantsios. A. 2,582,181 A. fto F. Hlavatyj, S. Patent \
Polymers from Phenylphosphonic Diamide and Urea or Thiourea Polymers were also obtained when phenylphosphonic diamide was treated with urea ( 7 ) . A likely reaction path is
INDUSTRIAL AND ENGINEERING CHEMISTRY
z
(Jan. 8, 1952). RECEIVED for review April 7, 1959 ACCEPTED January 6,1960 Division of Paint, Plastics, and Printing Ink Chemistry, 134th Meeting? ACS, Chicago: Ill., September, 1958.
