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Flame retardant polyphosphate esters: 2. Condensation polymers of bisphenol A with alkyl phosphorodichloridates: synthesis, characterization and thermal studies

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Flame retardant polyphosphate esters: 2. Condensation polymers of bisphenol A with alkyl phosphorodichloridates: synthesis, characterization and thermal studies
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  Flame retardant polyphosphate esters: 2. Condensation polymers of bisphenol A with alkyl phosphorodichloridates: synthesis, characterization and thermal studies K. Kishore, K. S. Annakutty and I. M. Mallick Department of Inorganic and Physical Chemistry, Indian Institute of Science, Banga/ore 560 012, India Received 22 May 1987; revised 31 August 1987; accepted 8 September 1987) Polyphosphate esters based on bisphenol A and alkyl phosphorodichloridates have been synthesized and characterized by i.r. and n.m.r, spectroscopy. The molecular weights were calculated from 3~p n.m.r. The thermal stability of the polymers were analysed by thermogravimetry. Keywords: flame retardancy; polyphosphate esters; bisphenol A; alkyi phosphorodichloridates; i.r. and n.m.r, spectroscopy; thermogravimetry) INTRODUCTION The synthesis and characterization of polyphosphates from various bisphenols and aryl phosphorodichloridates have already been reported in a previous paper ~. The polyphosphates derived from alkyl phosphorodichlo- ridates have received much less attention compared with those derived from aryl phosphorodichloridates 2-12. A systematic study on the synthesis and properties of these polymers will reveal their potential as flame retardants. In the present communication, condensation polymers of bisphenol A with different alkyl phosphorodichloridates have been synthesized (scheme 1) and characterized by i.r. and n.m.r, spectroscopy. The molecular weights of these polymers were determined by 3~p n.m.r, spectroscopy and thermal stability by thermogravimetry. A typical procedure for the synthesis of polymer I is as follows: bisphenol A (50 mmol) was taken in dry benzene (30 ml) and refluxed with methyl phosphorodichloridate (55 mmol) in the absence of moisture for about 48 h with constant stirring. The polymer was separated and purified by repeated reprecipitation of CHC13 solution by pentane; the yield was around 80?/0. The polymer, dissolved in CHC13 solution, was then refluxed with methanol (10ml) for another 3h; the polymer was separated by adding excess of pentane. The other polymers (II-VI) were also prepared according to the same procedure except that they were refluxed with the corresponding alcohols instead of methanol (scheme 1). The details of the techniques used were the same as previously described ~. EXPERIMENTAL The bisphenol A was obtained commercially and used after recrystallization from toluene. The alkyl phosphorodichloridates were prepared from the alcohols and POCI 3 according to the procedure reported la'14. RESULTS AND DISCUSSION The various polymers synthesized are shown in scheme 1; polymers III-VI being new. The polycondensation was carried out in solution in the absence of any acid acceptor. The ratio ofbisphenol to phosphorodichloridate was kept at 1:1.1 as in the previous cases 1. CH3 0 HO OH + el ~P~CI I CH3 OR 0 CI~P-- I RO CH3 0 1 CH 3 RO _In ROH I, R=CH3 II, R = C2Hs III, R = n-C3H7 IV, R=n-C4H9 V, R = iso- C4He VI, R = iso - CsHll Scheme 1 0032-3861/88/040762-03503.00 © 1988 Butterworth Co. (Publishers) Ltd. 762 POLYMER, 1988, Vol 29, April O I- CH3 O -I RO-- P'--I- 0-~'~ ~ I ) ~ C---~ ~ I )~--O--P--i--O R I/ I I| RoL CH3 RO J n  Figure 1 H~C30--P C O--P OC3H 7 I | ~J I ~-~J I| OCaH7 CH OC HTJ n I I 4000 3000 2000 1600 1200 800 Wavenumber (cm 1 ) I.r. spectrum of polymer IlI TaMe 1 tH n.m.r, spectral data of polymers Chemical shift values (ppm) Bisphenol Polymer Isopropylidene Aromatic P~O-R end group 1 1.6 (s) 7.0 (s) 3.7 (d) 6.6-7.0(m) II 1.6 (s) 7.0 (s) 4.1 (m), 1.3 (t) 6.6-7.0 (m) III 1.6 (s) 7.0 (s) 3.9 (m),1-2 (m) 6.6-7.0 (m) IV 1.6 (s) 7.0 (s) 3.9 (m),0.6-2.0 (m) 6.6-7.0 (m) V 1.6 (s) 7.0 (s) 4.0 (m), 1.7-2.1 (m) - 0.9((1) VI 1.6 (s) 7.0 (s) 4.0 (m), 1.2-2.1 (m) - 0.9(d) The i.r. spectra of the polymers were similar except in the case of the absorptions of the alkyl group, and a typical spectra is shown in Figure 1. The spectra show strong absorptions of Vp~o at 1300 cm-1, Vv_o_c( .... ie) at 1180 and 960 cm-1 and Vp_o_C(aliphatic) at 1000 cm-1, and 15 support the polyphosphate structure . Polymers I-IV showed the presence of some bisphenol end groups• The 1H n.m.r, spectral data of all the polymers are summarized in Table 1 representative spectra are shown in Figure 2. The spectrum of I shows a singlet at 1.66 for the isopropylidene protons, a double at 3.96 for the P-O-CH a protons (a Jell = 12 Hz) and a singlet at 7.06 for the aromatic protons• The spectrum of the other polymers differ from I only in the splitting pattern of the aliphatic group. In all cases, the P-O-R groups of the repeat units have merged with that of the chain ends. The 13 C spectra of the polymers show the resonances corresponding to all the carbons of the given polyphosphate structure Figure 3, Table 2). The P-O-R groups of the chain end could not be distinguished from those of the repeat unit. The 31p n.m.r, spectra show two signals at - 5.0 and - 11.06; Figure 4, Table 3) the one at -5.06 corresponds to P at the chain ends which is attached to two alkoxy and one aryloxy groups and the one around - 11.06 corresponds to P in the repeat units which is attached to two aryloxy and one alkoxy groups 16. The molecular weights of these polymers were determined from 31p n.m.r, spectral data. Since the polymers contain P-O-R groups in both repeat unit and Flame retardant polyphosphate esters: K. Kishore et al. chain ends, the 1H n.m.r, was not used for molecular weight calculation. For polymer I, the integration of P in the repeat unit to that at the chain end is found to be 1:1 Figure 4) and the molecular weight is ~ 1000. The molecular weights obtained for the other polymers are given in Table 3. The thermograms of the various polymers are shown in Figure 5 and the data are summarized in Table 4. All the polymers start degrading between 180°C and 230°C and show a two-step degradation. Pyrolysis gas chromatog- raphic studies on polymer I showed that the first step corresponds to the formation of various phenols and phosphates with some amount of char remaining which subsequently carbonizes in the second step. The different alkyl substituents were found to cause little change to the thermal stability and char yield of the polymers. I [ I I I | I I ,, o CH= o I---I --~-VTI ~-~y- --[ OR L CH= OR Jn I, R = CH 3 IV, R = CH2CH2J~CH2CH3 I I [ i i I I I I 8 7 6 5 4 3 2 8 (ppm) Figure 2 XH n.m.r, spectrum of polymers I and IV I 0 f 2 3 O 3 CH= C 3 OCH=CH=CH:tCH3] n • b c d-- C 3 I I I g I 160 140 120 80 Figure • CDCl3 C-a i-6 C-c t I i i I 60 40 20 0 8 (ppm) Broad band decoupled t 3 C n.m.r, spectrum of polymer IV POLYMER, 1988, Vol 29, April 763  Flame retardant polyphosphate esters. K. Kishore et al. Table 2 1 a C n.m.r, chemical shift values (ppm) of the polymers Polymer C- 1 C-2 C-3 C-4 C-5 C-6 C-a C-b C-e C-d I 150.8 119.6 129.7 148.7 42.3 30.9 49.0 - _ _ II 154.0 119.6 128.2 148.6 42.4 31.1 58.5 16.0 - _ III 154.0 119.6 128.2 148.7 42.0 31.0 58.5 23.6 - IV 153.9 119.6 128.0 148.6 42.2 31.0 58.5 32.2 18.5 13.5 V 150.7 119.6 128.0 148.5 42.5 30.2 66.7 31.4 18.6 - VI 150.9 119.7 128.1 148.0 42.3 30.9 59.6 40.8 24.5 22.3 /.-- .~,CH3 V, R CHzCH ~'CH SO CH3 0 r 1 O--P O C O--P OR I ~MI H .... I, R=CH~ I I I I I I I I I 10 0 -20 -40 60 (ppm) Figure 4 3tp n.m.r, spectra of polymers I and V Table 3 alp n.m.r, spectral data of the polymers Chemical shift values (ppm) Ratio of P at the P in the integration Molecular Polymer chain end repeat unit (Pend/Prepeat) weight I -5.0 -11.6 1:1 1050 II -5.0 - 10.5 1:1 1120 III -6.0 -11.6 1:1 1200 IV -5.9 -11.4 12 1970 V -6.5 -12.0 12 1970 VI -5.1 -11.0 2:3 1730 CONCLUSIONS The structure of the polyphosphate esters, based on bisphenol A and alkyl phosphorodichloridates, were confirmed spectroscopically. The thermal stability of the polymers were found not to be affected much by the change in the alkyl pendent group. REFERENCES 1 Annakutty, K. S. and Kishore, K. Polymer 1988, 29, 756 2 Helferich, B. and Sehmidt, H. G. Chem Ber 1959, 29, 2051 3 Rabek, T. and Prot, T. Polimery 1964, 9(2), 513 4 Togepast, N. O., Nijverheid, N. O. and Verker, H. Neth. Pat. 6411549, 1965 20 40 _o .} N 60 80 lOOt~ , I 0 200 400 600 800 1000 Temperature (°C) Figure 5 Thermogravimetric traces of polymers I-VI in argon. I, ; II, - .... ; III, --..--; IV,--0--; V, ---; VI, --x-- Table 4 Thermogravimetric data of the polymers Temperature (°C) corresponding to Char Inception l weight offast 50 weight percentage Polymer loss degradation loss at 700°C I 180 230 310 14 II 180 230 300 12 III 190 230 320 20 IV 210 220 310 21 V 180 210 300 13 VI 170 220 330 20 5 Kalk, C. F. Ger. Pat. 1439408, 1966 6 Masai, A. and Muryama, K. F. Jpn. Pat. 7141699, 1971 7 Nawada, K., Tsumewaki, K. and Watamable, K. Jpn. Pat. 7142231, 1971 8 Chimura, K., Iwata, H. and Honda, H. Jpn. Pat. 74 10 242, 1972 9 Chimura, K., Iwata, H. and Honda, H. Jpn. Pat. 74 74 733, 1974 10 Sundermann, R., Rotleff, G. and Grigat, E. Ger. Pat. 2 549 569, 1977 11 Yoshioka, A., Seki, T. and Iwara, Y. Jpn. Pat. 78 105 555, 1978 12 Okamoto, K. Jpn. Pat. 76 28 856, 1976 13 Grunze, H. H. Chem Ber 1959, 97, 850 14 Jauhiannen, J. P. and Lindberg, J. J. Fimm Chem Lett 1976, 8, 185 15 Thomas, L. C. in 'Interpretation of the Infrared Spectra of Organophosphorus Compounds', Heyden, London, 1974 16 Wan Wazer, J. R., Callis, C. F., Shoolery, J. N. and Jones, R. C. J Am Chem Soc 1956, 78, 5715 764 POLYMER, 1988, Vol 29, April
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