Polymerization of Hexachlorocyclotriphosphazene - American

66 Polymerization of Hexachlorocyclotriphosphazene JOHN W. FIELDHOUSE and DANIEL F. GRAVES

Downloaded by UNIV OF ARIZONA on January 7, 2013 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch066

The Firestone Tire and Rubber Company, Central Research Laboratories, 1200 Firestone Parkway, Akron, OH 44317

Hexachlorocyclotriphosphazene (or simply trimer) can be thermally polymerized i n bulk or s o l u t i o n at 200-270ºC producing h y d r o l y t i c a l l y unstable polydichlorophosphazene (or simply chloropolymer)· A l l c o c k (1,2) obtained chloropolymer soluble in o r ganic solvents by l i m i t i n g the conversion of trimer to chloropolymer. This discovery permitted the chloropolymer to be converted to h y d r o l y t i c a l l y stable polyphosphazenes by chlorine s u b s t i t u t i o n with an approp r i a t e nucleophile. Polymerization c a t a l y s t s such as s u l f u r (3),water (4,5,6), oxygenated organics (7-10) and silica from the surface of glass (11,12) have been used to promote the polymerization. Many of these c a t a l y s t s promote the formation of crosslinked chloropolymer at conversions above 50 percent, thus rendering them unsuitable for r e a c t i o n with nucleophiles. We have discovered that boron h a l i d e s or boron halide•triarylphosphate complexes polymerize trimer at 160-250ºC to soluble chloropolymer i n y i e l d s up to 100 percent. The trimer used i n t h i s study was p u r i f i e d by sublimation at 130-140ºC and 20-30 mm Hg vacuum. Sublimation under these conditions allows entrapped hydrogen chloride to escape. Trimer (30g) and c a t a l y s t s were placed i n a 35 ml pyrex tube ( p r e v i o u s l y washed with 20% aqueous NaOH, water and then heated at 350ºC/24 hours) and sealed under vacuum p r i o r to polymerization. Using a boron t r i c h l o r i d e to trimer molar r a t i o of 1:15 almost 100% conversion to chloropolymer could be obtained i n 16 hours at 180 G or i n 2 hours at 250°C (D.S.V.=0.30 d l / g at 1.00% i n cyclohexane). At 200 G using a molar r a t i o of 1:1280 a higher molecular weight chloropolymer was obtained (D.S.V.=1.17 d l / g at 1.00% i n cyclohexane). Boron tribromide and ?

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© 1981 American Chemical Society In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


316

PHOSPHORUS CHEMISTRY

phenylboron d i c h l o r i d e gave r e s u l t s comparable to boron t r i c h l o r i d e , although the former i s faster and the l a t t e r i s slower than boron t r i c h l o r i d e . Boron halides form complexes with phosphorus oxyhalides (13) and triarylphosphates (14,15)» Compar ed to boron t r i c h l o r i d e , boron trichloride*phosphorus oxychloride at comparable conditions reduced the rate of polymerization about two f o l d , whereas the molec u l a r weight, as measured by d i l u t e s o l u t i o n v i s c o s i t y remained unchanged. Use of boron trichloride·triphenyl phosphate ( r e c r y s t a l l i z e d from a 1:1 by weight carbon t e t r a c h l o r i d e s o l u t i o n ) 1 gave high molecular weight chloropolymer (2.5 d l / g , 1% i n chloroform) at a c a t a l y s t to trimer molar r a t i o of 1:5600 and low molecular weight chloropolymer (0.03 d l / g , 1% i n cyclohexane) at a c a t a l y s t to trimer molar r a t i o of 1:38. A comparison of c a t a l y t i c a c t i v i t y o f the t r i phenyl phosphate complexes of boron t r i f l u o r i d e , b o r o n t r i c h l o r i d e and boron tribromide showed that compara ble rates of polymerization were obtained using the chloride or bromide complexes. The f l u o r i d e complex gave about h a l f the rate of the bromide or c h l o r i d e ; comparable molecular weights were obtained i n a l l three cases. The molecular weight of the chloropolymer made v i a 1 i s r e l a t i v e l y i n s e n s i t i v e to the time and temp erature of the polymerization. This i s shown i n Tables I and I I . Table I . Polymerization Of 30g Trimer Using 0.11 mmol 1 At 220 0 DSV % Con Hours v e r s i o n Ό

Table I I . Polymerization Of 30g Trimer Using 0.22 mmol 1

-

Hours

% G o n

_

T°C v e r s i o n

—

(7f )

90 160 30 0.60 28 0.92 64 180 64 0.52 53 0.97 16 220 80 0.45 0.93 55 7 250 89 0.63 67 0.95 83 0.90 Attempted homo- or co-polymerization of octachlorocyclotetraphosphazene (tetramer) with trimer at 220 G gave no conversion of tetramer i n t o chloro polymer. At a molar r a t i o of 1:1 trimer to tetramer, there was no change i n chloropolymer molecular weight, but a reduction i n the rate of polymerization (86% conversion o f 100% trimer vs. 20% conversion using 1:1 trimer-tetramer).

10.0 18.0 24.0 40.0

In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


66.

FIELDHOUSE

A N D GRAVES

Hexachlowcyclotriphosphazene

317

Complex 1 i s reported (14) to be thermally stable at 200 C but decomposes rather thaa d i s s o c i a t e s at 300 C. This was confirmed i n our laboratory v i a thermogravimetric a n a l y s i s when only 10% weight loss occurred below 175 C hut a r a p i d loss occurred between 200-250°C. ^ F NMR (reference i s 85% HJPO^) was used to confirm that thermal rearrangement of 1 (-27·8ρρπι) occurred to produce 2 (-5·5ρρπΟ and 3 (1·8 ppm) i n a r a t i o of 1.74:1 r e s p e c t i v e l y . A mass spectrograph showed 2 and 3 t o be diphenyl chlorophosphate and phenyl dichlorophosphate r e s p e c t i v e l y , which were shown to not i n i t i a t e polymerization. The remaining fragments from t h i s rearrangement may be phenyl dichloroborinate 4 and diphenyl chloroboronate 5 as shown i n Scheme I . Scheme I 0 Q Λ

n i

oon°n

( o) P 0:Bci ^^ a

5

=

CI

5

»/ h

0

,P.

n i

υ

0

ι

a

if >1

*

a

d

P i

0

1

*

CI

\

I

B-OFh +

,B PhO X

Cl

OPh

*(?) 5(?) An equilibrium mixture of 4 and 5 was prepared by the ligand exchange of boron t r i c h l o r i d e and t r i p h e n y l borate (16) and found t o be an e f f e c t i v e c a t a l y s t . T h i s suggests our e f f e c t i v e c a t a l y s t may be produced by the i n s i t u rearrangement o f 1 to give 4 and/or 5 which then i n i t i a t e s the polymerization. The Ρ NMR spectra of a polymerization o f a 1:1 molar r a t i o o f trimer and 1 i s shown i n Figure 1. A small amount o f 1 remains (-27*4ppm) along with unpolymerized trimer (19·77ρρπύ and tetramer (-6.7ppm). The sharp s i n g l e t at -18.3ppm represents i n t e r n a l -PClp- u n i t s . The sharp s i n g l e t at -4.87 represents diphenyl chlorophosphate 3· Based on model l i n e a r phosphorus compounds (17,18), the shoulder of peaks at -14 t o -18ppm may represent -PClp- u n i t s adjacent to a C1^P«N- group while the C1^P=N- group might be at 3»08ppm. A d d i t i o n a l studies"* are needed to con c l u s i v e l y elucidate the mechanism o f i n i t i a t i o n . The hydrolysis o f trimer produces hydrogen chloride and 2,2-dihydroxy-4,4,6,6-tetrachlorocyclotriphosphazeae 6 which may be present i n impure trimer. A Ρ NMR o f 6, prepared according t o Stokes (19), i s shown i n Figure 2 . Since 1 i s s e n s i t i v e to 7

0


PHOSPHORUS CHEMISTRY


318

(NPCI ) 2

3

+ l(PhO)

3

P=0-BCI

220°C^ 3

21 H R S

-18.3

308 19.77

1

Figure 1.

(NPCi ) 2

3

31

The Ρ NMR (CDCh) of the polymerization of l mol trimer with 1 mol boron trichloride Hripheny I phosphate after 21 h at 220° C.



66.

FiELDHOUSE A N D GRAVES

CI CI ρ \f N

Hexachlorocyclotriphosphazene

25°C

N

π

1

CKp

11

π

+

EXCESS

P-CI

Figure 2.

H 0 2

2

31

EfoO

The Ρ NMR (THF) of

Η X

»

9,0H p

N ® N I Jws\ll X

X

n

i

Ckp© ©p.CI

2,2-dihydroxy-4,4,6,6-tetrachlorocyclotriphosphazene.


319

PHOSPHORUS CHEMIST:

320

most p r o t i c materials, we expected 6 to hydrolyze 1. Reaction of 2 moles 1 with 1 mole of 6 gave a t o t a l conversion of 6 to trimer, along with by product t r i phenyl phosphate. A s i m i l a r r e a c t i o n occurred be tween boron t r i c h l o r i d e and 6, thus showing the great propensity f o r boron t r i c h l o r i d e to 'rechlorinate hydrolyzed cyclophosphazenes. 1


Acknowledgement « The authors wish to thank Dr. Tom Antkowiak f o r h i s guidance i n t h i s work and The Firestone T i r e and Rubber Company f o r permission to publish. L i t e r a t u r e Cited 1. A l l c o c k , H . R . ; Kugel, R.L. J.Am. Chem. Soc., 1965, 87, 4216-7. 2. A l l c o c k , H . R . ; Kugel, R.L.; Valan, K.J.Inorg. Chem. 1966, 5, 1 7 0 9 - 1 5 . 3. MacCallum, J.R.; Tanner, J.J.Pol. S c i 1969, 7, 7 4 3 - 7 4 7 . 4. A l l c o c k , H . R . ; Gardner, J.E.; Smeltz, Κ.M. M a c r o molecules 1975, 8 (1), 36-42. 5 . Korsak, V.V.; Vinogradova, S . V . ; Tur, D . R . ; Kasarova, N . N . ; Komarova, L.I.; Gilman, L.M. A c t a . Polymerica 1979, 30 (5), 245-8. 6 . U . S. 4,137,330. 7. Konecny, J.O.; Douglas, C . M . J.Pol. S c i . 1959, 36, 195-203. 8. Konecny, J.O.; Douglas, C . M . ; Gray, M.J. J. Pol. Sci. 1960, 42, 383-90. 9. G i m b l e t t , F . G . R . Polymer 1960, 1, 418-24. 10. MacCallum, J.R.; Werninck, A . J.Pol. Sci.1967, A-1 5, 3061-70. 11. Gimblett, F . G . R . P l a s t . I n s t . Trans. 1960,28, 65-73. 12. Emsley, J.; Udy, P . B . Polymer 1972, 13, 593-4. 13. Peach, M . Ε . ; Waddington, T . C . J.Chem. Soc. 1962, 3450-3. 14. Frazer, M.J.; Gerrard, W.; P a t e l , J . K . J.Chem. Soc. 1960, 726-750. 15. A l l c o c k , H . R . ; L e v i n , M . ; Fieldhouse, J.W. A c t a . C r y s t a . 1981. 16. C o l c l o u g h , T . ; Gerrard, W.; Lappert, M . F . J. Chem. Soc. 1955, 907-11. 17. Fluck, Ε . Z . Anorg. Chem. 1962, 315, 181. 18. Becke-Goehring, M.; Fluck, E. Angew. Chem. ( I n t . E d . ) 1962, 1, 281. 19. Stokes, H.Ν. Amer. Chem. J.1985, 17, 275-290. RECEIVED

June 30, 1981.


Polymerization of Hexachlorocyclotriphosphazene - American

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