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(2)(a) S.0.Grim and W. McFarlane, Nature (London),208,995(1964);(b) S. 0.Grim, W. McFarlane, E. F. Davidoff, and T. J. Marks, J. fhys. Chem., 70, 581 (1966). (3)J. B. Hendrickson, M. L. Maddox, J. J. Sims, and H. D. Kaesz, Tetrahedron, 20,449 (1964). (4)C.E. Griffin and M. Gordon, J. Organomet. Chem., 3, 414 (1965). (5)G.A. Gray, J. Am. Chem. Soc., 95,7736 (1973).
(6)(a) T. A. Albright, W. J. Freeman, and E. E. Schweizer, J. Am. Chem. Soc., 97,2942 (1975);(b) J. Org. Chem., 40,3437 (1975). (7)N. J. De'ath and S. Trippet Chem. Commun., 172 (1969). (8)J. P. Albrand, D. Gagnaire, and J. B. Robert, Chem. Commun., 1469 (1968). (9)S. 0.Grim, W. McFarlane, and T. J. Marks, Chem. Commun., 1191 (1967).
Synthesis and Thermolysis of Poly(2,2-dimethyltrimethylene phenylphosphinate) Gurdial Singhl Carothers Research Laboratory, Textile Fibers Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898 Received J u l y 25,1978
Poly(2,2-dimethyltrimethylenephenylphosphinate) has been synthesized through the ring-opening polymerization of 2,2-dimethyltrimethylenephenylphosphonite using CH3I as an initiator. The structure of the polymer has been established by NMR spectroscopy, and its thermal and other properties are reported. Its thermolysis at 300 "C gave cyclic 2,2-dimethyltrimethylenephenylphosphinate, whose conformational analysis has been conducted from lH NMR spectral data.
Ring-opening polymerization of cyclic phosphonites to polyphosphinates has been reported in literature. For example, Petrov2 and Mukaiyama3 and their co-workers prepared poly(trimethy1ene phenylphosphinate) from the corresponding cyclic phosphonite a t 120-200 OC using CH31as an initiator. However, only low molecular weight polymer (13200) was obtained,2 presumably due to decomposition at these temperatures. Assuming that the low molecular weight polymer resulted due to @-elimination,>P(=O)OCH&H,>P(=O)OH CH*=CH-, we have prepared poly(2,2dimethyltrimethylene phenylphosphinate) in which both of the @-hydrogensare substituted by methyl groups. This paper describes the thermolysis of poly(2,2-dimethyltrimethylene phenylphosphinate) and compares it with that of poly(trimethylene phenylphosphinate).
-
+
Scheme I
2
3
4
Results and Discussion structure in which the phenyl group is in the axial arrangePoly(2,2-dimethyltrimethylenephenylphosphinate) was ment. The phosphonium salt intermediate 2 probably has the prepared by the reaction shown in Scheme I. same stereochemistry as the cyclic phosphonite; that is, the The reaction of the cyclic phosphonite 1 with CH31proceeds via the phosphonium salt intermediate 2,which undergoes phenyl group is in the axial position. Arbuzov rearrangement to give phosphinate 3. Both 2 and 3 Poly(2,2-dimethyltrimethylene phenylphosphinate) were isolated and identified by their NMR spectra (Figure 1). (4). 4 is a colorless polymer. The low molecular weight polymer The rearrangement of the phosphonium salt to the phosphiis a viscous liquid, but the high molecular weight polymer is nate is quite facile as it occurred even when running the NMR usually a glassy solid. A typical polymer, g,,= 16 000, has T , = 4 "C and T , = 160 OC. Its structure has been established spectrum. The spectrum of 3 shows the OCH2 protons to be magnetically nonequivalent. Heating to 100 "C in toluene did by its NMR spectrum (Figure l),which shows multiplets of not change its spectrum, suggesting that the nonequivalence equal area for the CH2 and CH20 groups bonding to phosof the methylene protons is due to chiral phosphorus and not phorus. The polymer was shown by X-ray analysis to be mainly amorphous. The lack of crystallinity is attributed to to restricted rotation around the P-0 bond. Phosphonite 1 is known to exist in the chair c o n f ~ r m a t i o n , ~ ~the ~ bulky groups on phosphorus and close proximity of the but different configurations have been assigned at the phosphosphorus moieties along the polymer chain. phorus atom. Gagnaire et al.4 originally assigned the phenyl The polymer is stable up to about 250 "C, but decomposes substituent to the equatorial position on steric grounds. at higher temperatures to give cyclic 2,2-dimethyltrimethylene However, from NMR studies of cyclic phosphonites, Verkade phenylphosphinate ( 5 ) in almost quantitative yield (eq 1).The and Bentrude and their c o - w o r k e r ~assigned ~,~ the phenyl CH, group to the axial position in 1. Bentrude et a1.6 showed that \ 3 J p depends ~ ~ ~ on the dihedral angle POCH and the orien3oo cc HZC-C-CH3 tation of the lone pair on phosphorus. If the substituent is 41 1 (1) 0\p, CH2 axial, 3 J p ~=, 2 Hz and 3 J p H , = 10 Hz; and if the substituent is equatorial, 3 J p ~ RZ, 2 Hz and 3 J p ~=, 20 Hz. In phosphonite ' S C & \o 1 the 3 J p O C H couplings are 3 and 10.2 Hz for the axial and 5 equatorial protons, respectively, which are consistent with the 0022-3263/79/1944-1060$01.00/0
0 1979 American Chemical Society
J . Org. Chem., Vol. 44, No. 7, 1979
Poly(2,2-dimethyltriniethylene phenylphosphinate)
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NMR spectrum of 5 (Figure 1)shows CH2 and CH20 groups attached to the phosphorus atom. The decomposition of 4 to 5 does not appear to be an "unzipping" reaction involving an attack by the iodide carbon on the phosphorus atom because that would involve a highly sterically hindered transition state. Evidence against this mechanism is provided by the fact that the monomeric phosphinate 3, on heating to 300 "C, did not decompose to give 5 and CH3I. Instead, a dark brown, nondistillable product was formed. The decomposition of the polymer to 5 most probably occurs via homolytic cleavage of the P-C bond and subsequent closing of the ring. We prepared poly(trimethy1ene phenylphosphinate) (8, eq
;;li
C6Hj
7
8
2) to compare its thermal stability with that of the sterically hindered polyphosphinate 4. Surprisingly, 8 did not decompose even when heated at 300 "C for 20 min. On the other hand, its monomeric species 3iodopropyl methylphenylphosphinate (7) decomposed at 150-160 "C to give trimethylene bis(methylpheny1phosphinate) (9) and 1,3-diiodopropane presumably via a bimolecular reaction (eq 3). 0
1I
2CHaPOCH2CH2CHZI
I C&%
8.0
7.0
6.0
5.0
3.0
4.0
2.0
1.0
0
PFM ( 1 1
Figure 1. 'H NMR spectra of phosphorus compounds
7
"3%
ICH30
/>G
