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Special features of the catalysis of cyclotrimerization of isocyanates in the presence of o-aminophenols and reasons for the “autoinhibition” of this reaction
1909
Catalysis of cyclotrimerization of isocyanates
10. A. Ye. CHALYKH, Vysokomol. soyed. B16: 584, 1974 (Not translated in Polymer Sci. U,S.S.R.) I 1. Yu. A. SHARONOV and M. V. VOLKENSHTEIN, Fizika tverdogo tela 5: 590, 1963 12. L. V. SOKOLOVA and A. V. DANCHENKO, Vysokomol. soyed. A23: 213, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 1,238, 1981) 13. L. V. SOKOLOVA, O. A. CHESNOKOVA, O. A. NIKOLAYEVA and V. A. SHERSHNEV, Vysokomol. soyed. A27: 352, 1985 (Translated in Polymer Sci. U.S.S.R. 27: 2,392, 1985) 14. M. F. BUKHINA, Kristalizatsiya kauchukov i rczin (Crystallization of Rubbers and Rubber Products). p. 81, Moscow, 1983 15. N. V. MIKHAILOVA and V. N. NIKITIN, Vysokomol. soyed. A l l : 2432, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 11, 2764, 1969) 16. A. S. KUZM1NSKII, S. M. KAVUN and V. P. KIRPICHEV, Fizikokhimicheskie osnovy polucheniya, pererabotki i primeneniya elastomerov (Physicochemical Basis of the Production, Reprocessing, and Application of Elastomers). p. 34, Moscow, 1966 17. L. V. SOKOLOVA and G. A. VORONOVA, Vysokomol. soyed. A28: 934, 1986 (Translated in Polymer Sci. U.S.S.R. 28: 5, 1041, 1986) 18. L. V. SOKOLOVA, O. A. CHESNOKOVA and V. A. SHERSHNEV, Dokl. Mezbdunar. konf. po kauchuku i rezine (Paper of International Conicrence on Rubbers and Rubber Products). A-38, Moscow, 1984
Polymer Science U.S.S,R. Vot. 29, No. 8, pp. 1909-1917, 1987 Printed in Poland
0032-3950/87 $ 10.00 + .00 ~3 1988 Pergamon Press plc
SPECIAL FEATURES OF THE CATALYSIS OF CYCLOTRIMERIZATION OF ISOCYANATES IN THE PRESENCE OF o-AMINOPHENOLS AND REASONS FOR THE"AUTOINHIBITION" OF THIS REACTION* I. G. ROZDINA, R. P. TIGER, YE. A. CHERNOVA a n d S. G. ENTELIS Institute of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 21 April 1968) It is established that the reason for the catalytic activity of o-aminophenols in the cyclotrimerization of isocyanates is the presence in the catalyst molecule of intramolecular hydrogen bonds O - H...N. The activation of the phenyl hydroxyl group due to this results in consumption of the catalyst in the formation of the corresponding urethane, w~aich is reflected in the kinetics in the form of "autoinhibition" of cyclotrimerzation. THE cyclotrimcrization of isocyanates has recently b e c e m e extremely p o p u l a r in the modification of p o l y u r e t h a n e s a n d for the p r o d u c t i o n of new heat resistant polymers [1-4]. Because of cyclotrimerization of the N C O groups in the p o l y u r e t h a n e n e t w o r k * Vysokomol. soyed. A29: No. 8, 1737-17430 1987.
1910
I . G . ROZDXNAet al.
new (together with triol) branching centres of isocyanurate nature arise, which have significantly higher thermal stability and decreased combustibility compared with the polymer material. The method involving a combination of urethane formation and cyclotrimerization the kinetic model of which was developed fairly recently [5, 6] is the most promising. The main problem in practical application of this process, which is of interest in the production of rigid and elastic polyurethane isocyanurates, is the selection of catalyst systems giving selected urethane formation and eyclotrimerization. It is known that most catalysts for the cyclotrimerization of isocyanates also catalyse urethane formation [7]. Mannich bases, i.e. o-aminophenols, of which the most active is 2,4,6-tri-(dimethylaminomethyl) phenol (commercial grade DMR-30) have been proposed [8] and have been applied [l, 9, 10] as extremely effective cyclotrimerization catalysts, which have only a weak effect on the urethane formation process
OH I (Cti3)2NCH2--(~--CH~N(CHa)2 I CH2 I N(CH3)2 . I The first attempts at quantitative investigation of the catalysis of cyclotrimerization in the presence of compound I showed [11] that in contrast to most catalyst systems the reaction occurs without an induction period, but it's kinetics do not obey simple laws. The main feature of the reaction is rapid retardation as the reaction proceeds, in spite of the fairly high initial reaction rate. In some cases almost complete stoppin~ of the cyclotrimerization reaction was observed, which, when the process is combined with urethane formation, almost eliminates the possibility of using compound I as a selective catalyst. This work was concerned with investigating the special features of the catalysis of the cyclotrimerization under the action o-aminophenols and the nature of their catalytic activity, but mainly with the reason for the inhibition of the reaction as it proceeds. The cyclotrimerization of m-chlorophenyl isocyanate which takes place in dioxane or carbon tetrachloride in the presence of l, 2,6-bis-(dimethylaminomethyl) phenol (II), 2,6-dimethyl-4-(dimethylaminomethyl) phenol (liD, dimethylbenzylamine (IV), and p-cresol (V) served as a model reaction. Compounds (IV) and (V) were considered as fragments o,f aminophenols simulating, on combined use, catalysis in the presence of compounds (I) and (II). The m-chloropl~enylisocyanate used was chemically pure, and was vacuum distilled at 470°C and 133-266 Pa pressure and stored under argon in sealed ampoules. Compound (I), which is produced by the American firm Ferak, was vacuum distilled for use. Compounds (II) and (II1)were synthesized using the method given by Adams [12]. The purity of the products was established by elemental analysis. Compound (IV) was distilled at 68°C and 2"12 kPa pressure. Compound
Catalysis of cyc[otrlmedzatlon of isocyanates
1911
(V), which was chemically pure, was distilled at 205.YC. The peroxides were removed from the dioxide (chemically pure) by passing through an A1203 column, treating with KOH for several days, and boiling for 3-4 hr over Na, followed by distillation. The fraction of boiling point 101'C was used. The contents of impurity aromatic compounds was monitored by UV spectroscopy. The water content, as determined by the Fisher method was 0.04 %. The carbon tetrachloride, which was chemically pure, was purified free of carbon disulphide by boiling in dilute NaOH, then washed with several portions of water, dried over calcined CaCI2, and redistilled. The fraction boiling at 76.8 'C was used. A model R-20 spectrophotometer was used in the IR studies at 25°C in a thermostated CaF2 cell of thickness 0.1 and 0.02 mm over the range 1500-3800 cm-L Observation of kinetic catalytic transformation of isocyanite was carried out up to the disappearance of the band for the stretcifing vibrations of the CO group (v=2260 cm -a) of the isocyanate. The kinetics of formation of the trimer (v = 1720 cm -~) the dimer (v= 1780 cm -~) and urethane 0' = 1750 cm -I) could not be followed quantitatively because of the marked overlap of the bands for the stretching C = O vibrations. The PMR spectra were recorded at 25'~C on a "Bruker" SXP400 spectrometer at a frequency of 90 Hz, using tetramethylsilane as an internal standard. Quantum chemical calculations of the electronic structure of 4,6-dimethyl-2-(dimethylamino)methyl phenol, the simplest analogue of compound (1), were carried out by the CNDO/BW method [13], with optimization of the geometry using a procedure inw)lving Davidson-Fletcher-Powell minimization [14]. The geometrical structure of the aminophenol molecule was optimized as a whole with the exception of the structure of the benzene ring and the CHa group in the ortho- and para-positions in relation to the OH group. Figure 1 gives typical kinetic curves for cyclotrimerization of isocynate in the presence of c o m p o u n d (1). The reaction has no i n d u c t i o n period and has variable order with respect to m o n o m e r as a characteristic feature. At low c o n c e n t r a t i o n s of catalyst, in spite of the relatively high initial rate, the process does not go to completion, ilnitating s p o n t a n e o u s " a u t o i n h i b i t i o n ' . The order of the reaction with respect to the catalyst is a b o u t 2.3. Similar relationships are observed in catalysis by c o m p o u n d (ll), whereas the catalytic activity of c o m p o u n d (!II) is less by several orders or magnitude, similar to the activity of c o n v e n t i o n a l tertiary amines such as t r i b u t y l a m i n e and c o m p o u n d (IV). In the presence of c o m p o u n d s (IIl) or (IV) the reaction takes places in 2-3 days u n d e r the same conditions, the selectivity of these catalysts being significantly lower, and,
[M],mol#c 0.q~-
2 0.2 t2 ~ ~ ~ ~ l
I
80 T i m e ~rain
I 160
} ~32_.
3 .,.1o 3
g5
29
33
37 vxlO-fcm -r
FIG. 1 Fio. 2 FIG. 1. Typical kinetic curves for the decrease in concentration in polymer in the presence of compound I in dioxane (1, 2) and CC14 (3, 4); [I]o=9"7 x 10 -a (•); 4.98 x 10 -2 (2); 4-5 x 10 -2 (3) and 8"4 × 10 -2 mole/l. (4). Fro. 2. IR Spectra of solutions of compounds I (1) and III (2) in CCI.~in the region of the stretching vibrations of the OH groups. Layer thickness 2 cm, concentration of solutions c× 104=5.05 (1) and 8'30 mole]l. (2).
1912
1[. O. I~OZDINAet at.
depending on the concentration of the reagents, the nature of the solvents, and the reaction conditions amongst the products, different quarttities of the c)clic dimer of the isocyanate are observed as well as the trimer. A unique difference between compounds (II) and ( l i d is that art intramolecular hydrogen bond cannot form between the phenol hydroxyl and the amino group in the o r t h o position, as occurs ill compounds (I) and (H)
/ II . . . . . . N
/ o / \cu3 I / n-(~-cu2 \// I W A where R = R ' and is CH2N(CH3)2 in compound (I) and R is CHzN(CH3)2 and R ' is CH3 in compound (II). Figure 2 shows the I R spectra of compounds (I) and (III) in the region of the stretching vibrations of the OH group at concentrations which exclude intermolecular association. It can be seen that the frequency of the vibrations for the OH group in compound (I) is displaced by more than 400 c m - 1, which indicates the absence of a strong hydrogen bond. It is known that the presence of intramolecular hydrogen bonding is generally characteristic of such compounds. In some mono- and binuclear aminophenol and naphthols displacement of the vibration frequency of the OH groups attains 200-500 cm -1 [15, 16], and in the IR spectra of such a compound as 1-dimethylaminomethyl-2-naphthol, bands for absorption of OH group are generally not observed [17]. The works of Koll et al. [18-20] have shown that in many Mannich bases the hydrogen bond is so strong that, depending on their structure and medium, complete transfer of a proton from oxygen to nitrogen is possible with the formation of a stable zwitterion structure, i.e. 0-
H+N(CII3)2
I
/
--()-oH2-, I B
which has a significant dipole moment. It must be noted that a structure of type B is similar to the structure of a zwitterion, the formation of which is often postulated in considering opening of the epoxide ring on interaction of x-oxides with tertiary amines, i.e.
\
/
CtI~--Ct]~
Catalysis of~cyclotrlmerlzation of isocyanates
1913
Q u a n t u m chemical calculations indicate that particles of this type have a cis structure [11, 21], but their formation in the absence of proton donors is disadvantageous from the energy point view [22]. In the presence of p r o t o n donors (for example an alcohol R ' O H ) in principle ion pairs of type [RaN - CH2CH2OH] + ' O R - can be formed, although q u a n t u m chemical calculations ( C N D O / /BW) for such a system show [22] that a potential curve with a single minimum, is characteristic of this ion pair, corresponding to an almost symmetrical position of the proton between the two electron d o n o r centres ( R a N - C H 2 C H z O . . . H . . . O R ' ) , i.e. where the potential curve is typical of a strong hydrogen bond. Tertiary amine epoxide systems in the presence of proton donors are the most active catalysts of cyclotrimerization reactions [7]. The presence of intramolecular hydrogen bonding in the o-aminophenols brings them close to amine-epoxide systems and is evidently the reason for their ability to bring about the cyclotrimerization of isocyanates.
The quantum chemical calculations on the structure of a model o-aminophenol, i.e. 4,6-dimethyl-2-(dimethylaminomethyl)phenol, given within the framework of this work, shows that the minimum of the total energy of the system corresponds to a structure with an intramoleculat h~drogen bond 0
1"02
1"33
It . . . .
\
/
CHa qo = - - 0.(353
N C fl~--
1.56
\//
CH,,
Ctla
qu = ÷ 0.457 qN ~--- - - 0'589
I CHs A special feature of this structure is the strong polarization of the phenol hydroxile group (/t,=4.23 Debye). The increase in the OH bond length is 0.06 A. The negative charge on the oxygen pattern, as in the formation of a hydrogen bond, is significantly higher than the charge on the free hydroxyl group, which can result in an increase in the reactivity of the o-aminophenol as a nucleophilic reagent in relation to the NCO group. The quantity Aqo, compared with a hydrogen hydroxyl group, is 0.08 a.e. Allowance for the effect of the medium can result in a strengthening of the polarization of the hydrogen bond or to displacement of the equilibrium O H - N ~ O - . . . N H + in the direction of complete transfer of a proton with formation of a binary structure (B), which has a theoretical valhe of the dipole moment for 4,6-dimethyl-2-(dimethylaminomethyl) phenol of 9.74 D. A hydrogen bond, similar to the hydrogen bond in o-aminophenols, but of intermolecular nature, is formed in phenol-tertiary amine systems, in particular between compounds (IV) and (V). Investigation of the cyclotrimerization Of isocyanate in the presence of IV and V shows that this pair, although significantly less active and less selective than I and II, does catalyse cydotrimerization significantly more actively than IV alone. In the presence of the 1V + V system, depending on the amine : p-cresol ratio,
J together with the trimer, the uretlmne m - C 1 - C 6 H 4 N C - O C 6 H 2 ( C H a )
is formed,
III HO and possibly also traces of allophanate, as a result of which compound V is consumed
I . G . ROZDINAet al.
1914
during the process. A typical case of the activation of the O H group of compound V under the action of a tertiary amine, which is necessary for adding it to isocyanate at the N = C bond is available [23]. It follows from the above experimental data and theoretical calculations that the reason for retardation of trimerization as far as complete inhibition of the process in the presence of amino phenols must be the consumption of catalyst in the formation of the corresponding urethane, which takes place at a comparable rate, and possibly also of allophanate, which is a product of the interaction of urethane with isocyanate. The use of I R spectroscopy for identifying urethane or allophanate (stretching vibrations of C = O) against a high intensity background located close (3v = 20 c m - 5 ) to the bagtd for the R N C O trimer is difficult. High resolution N M R is more effective in this connection, and not only enables the fact of the catalyst consumption to be established but provides a means of following the nature of the change in concentration of the original, intermediate, and final products with time. The P M R spectrum of catalyst I shows signals for the protons of the groups OH, Ph, CH2 and CHa. Figure 3 shows a fragment of a P M R spectrum of catalyst ] for the range O= 8-11 ppm, where a signal for the proton of the catalyst hydroxyl group is present. It can be seen that the signal for the O H group of the catalyst (6=9"9l ppm) at the moment of introducing hydrocyanate into the system disappears, and two new
I~Pel.uR.
iS-"
- 0"2
120 i
60
- - ,
I
I
11
10
J~
~ppm
9
"I~g ,
0
1£
" 0.1
I
Time, min
82
FIG. 4 FIG. 3. Fragment of PMR spectrum of catalyst I in CC1, (1), and kinetics of change of form and intensity of peaks at 6x = 10"62 (a) and fi2= 10'35 ppm (b) after introduction of isocyanate at time t = l (2) and 2 rain (3) and 2 hr (4). [M]o=0"5, [I]o=8"0 × 10 -2 mole/l. FIG. 4. Nature of the change in intensity of the signals for protons of the CH2 groups at 6= 3"1 (1), 3"4 (2), 3.28 ppm (3), &nd the CHa groups at 5= 2.21 (4), 2.16 (5), and 2.14 ppm (6) during cyclotrimerization. [M]o=0"21, [I]o=8"5 × 10 -2 mole/1, and (7) kinetic curve for decrease in monomer content in CCI4. ([M])o=0'21, [I]o= 8'44 x 10 -2 mole/1.). FIG. 3
Catalysis of cyclotrimerization of isocyanates
1915
peaks arise with 5 = 10.6 and 10.4 ppm respectively, which can be assigned to signals from the proton bonded to the nitrogen in the final product (urethane) and the proton of the OH group of the intermediate product, so-called preurethane. During the process the signal from the proton of the N H group of urethane increases, and that of the intermediate product decreases. At the end of the reaction a single signal is observed in the N M R spectrum corresponding to the proton of the NH group of urethane, which indicates compl:te disappearance of the catalyst. The P M R spectrum of catalyst I also has a series of very clear signals from the protons of the CH2 and CH3 groups, and the changes of some of these with time can be followed easily (Fig. 4). The intensities of the signals of the CH2 (5=3.1 and 3.4 ppm) and CH3 (5=2.1 ppm) groups, which belong to the original catalyst I, decrease steadily, and the signals for the CH2 groups (5= 3-28 ppm) and CHa (5=2.16 and 2-14 ppm) groups, arising on introduction of a monomer into the system, pass through maxima. It would appear that the signals for the protons of the CH2 group with =3.28 ppm and for the CHa with 5=2.16 and 2.14 ppm are superpositions of the corresponding signals of the intermediate product, the concentration of which should pass through a maximum, and the final product, the concentration of which should increase steadily until the process has completely finished. Because of the closeness of the structures cf the intermediate "preurethane" (C) and phenylurethane (D) the signals for the protons of the CH2 and CHs group should almost coincide. On this principle, the production of information on the nature of the changes in intensity of the signals from the CH2 and CHa groups in structures C and D 0
'% / C..-~N
PhCI
I CH3 0 . . . H...N /
0
~:
,/
l'hf3
C-- N l
/(3t3 •. . i t . . . N
%/'
% .J
R
l R
c
D
taken in isolation is not possible. It must be noted (Fig. 4, curve 7) that after complete consumption of the catalyst, which can be judged from "restriction" with time of the intensities of all the P M R spectrum signals, characteristic of compound I and of the products of its interaction with RNCO, the consumption of monomer almost ceases. The slow loss of monomer at the end of the reaction can be due to trimerization catalysed by the (CHa)zN- CH2-groups of urethane formed from compound 1. The above experimental data are in agreement with a scheme in accordance with which, during the first stage, because of intramolecular hydrogen bonding and activation of the OH-group of the catalyst, the catalyst is added to the isocyanate with the
1916
I . G . ROZDINAet at,
formation of an intermediate product, which is able either to give corresponding urethane because of intramolecular regrouping with transfer of a proton, or can add the following molecules of isocyanate, leading to chain growth with subsequent cyclization at the trimer stage ,D I+M~B+3~T+ C here M and T are the m o n o m e r and cyclic trimer of the isocyanate respectively. It is doubtful whether a matrix mechanism of catalysis, which is characteristic of processes of cyclotrimerization in certain catalyst system [24], is realized with aminophenols. Although the o-aminophenols at the concentrations used can undergo self-association and solution, their complex formation with the trimer and the effect of the latter of the reaction kinetics has not been established. Allowing for the consumption of catalyst during cyclotrimerization in uiethane formation and the consequent complication of the primary kinetic laws, quantitative analysis of the kinetic scheme and the mechanism of the cyclotrimerization does not yet seem possible. It should be noticed in conclusion that the use of o-aminophenols as catalysts for the hardening of oligomers with terminal N C O groups and also for combined urethane formation and cyclotrimerization can result in blocking of some of the reactive N C O groups, and the appearance of side chain in the system, not included in the structure of the network, and consequently, to changes in the expected properties of the polymers formed. Translated by N. SrAND~I~ REFERENCES
1. T. NAWATA, J. E. KRESTA and K. C. FRISH, J. Cellular Plast. 11: 267, 1975 2. A. DEION, Advances in Urethane Science and Technology, vol. 8, p. 1, Westport, 1981 3. R. J. LOCKWOOD and L. M. ALBERINO, Advances in Urethane Science and Technology, vol. 8, p. 171, Westport, 1981 4. Ts. M. FRENKEL, V. A. PANKRATOV, V. V. KORSHAK and S. V. VINOGRADOVA, Kompozi~sionnye polimernye materialy (Composite Polymer Materials). No. 26, Kiev, 1985 5. I. G. ROZDINA, V. B. SVALOVA, V. V. YEVREINOV, R. P. TIGER and S. G. ENTELIS, Khim. fizika 3: 1002, 1984 6. I. G. ROZDINA, V. V. YEVREINOV, R. P. TIGER and S. G. ENTELIS, Kompozitsionnye polimernye materialy (Composite Polymer Materials), No. 26, p. 65, Kiev, 1985 7. R. P. TIGER, L. I. SARYNINA and S. G. ENTF_,LIS, Uspekhi khim. 41: 1672, 1972 8. L. NICOLAS and G. T. GMITTER, J. Cellular Plast. 1: 85. 1965 9. Yu. O. AVERKO-ANTONOVICH, L. A. AVERKO-ANTONOVICH, I. N. BAKIROVA, L. A. ZENITOVA, K. S. FRISCH, K. J. PATEL and R. D. MARSH, J. Cellular Plast. 6: 1, 1970 I0. P. A. KIRPICHNIKOV, A. G. LIAKUMOVICH and G. M. RAKHMATULINA, Tez. dokl. XII. Mendeleyevskogo s'ezda po obshchei prikladnoi khimii (Thesis of Paper of Twelfth Mendeleyev Congress on General and Applied Chemistry), Vol. 2, Moscow, 1981 11. R. P. TIGER and S. G. ENTELIS, Advances in Urethane Science and Technology, vol. 8, p. 19, Westport, 1981 12. R. ADAMS, Organicheskie reaktsii (Organic Reactions). Moscow, 1948
Dinitrofluorenone-containing polyesters
1917
13. 14. 15. 16. 17. 18. 19. 20. 21.
R. J. llOYD and M. A. WHITEHE, AD, J. Chem. Soc. Dalton Trans., I, 73, 1972 R. FLETCHER and M. J. D. POWEI,L, Computer J. 6: 163, 1963 A. W. BAKER and A. T, S H U I ~ I N , J. Amer. Chem. Soc. g0: 5358, 1958 A. G. MORITZ and G. M. BADGER, Spectrochim. Acta 13: 672, 1959 M. C. FLETT, Spectrochim. Acta 10: 21, 1957 A. KOLL, Bull. Soc. Chim. Belg. 92: 313, 1983 A. KOLL, M. ROSPENK and L. SOBCZUK, J. Chem. Soc. Faraday Trans. 77: 2309, 1981 J. RESPENK and A. KOLL, Bull. Soc. Chim. Belg. 92: 329, 1983 N. V. KOZAK, Yu. N. NIZELSKII, Yu. A. TISHCHENKO and T. E. LIPATOVA, Teoret. i eksper, khim. 18: 331, 1982 22. Ye. A. CHERNOVA, O. G. TARAKANOVA and A. K. ZHITINKINA, Kompozitsionnye polimernye materialy (Composite Polymer Materials), No. 26, p. 48, Kiev, 1985 23. S. G. ENTF,LlS and O. V. NESTEROV, Uspekhi khim. 35: 2178, 1966 24. S. G. ENTELIS, I. G. BADAYEVA, S. P. BONDARENKO and R. P. TIGER, Problemy khimicheskoi kinetiki (Problems of Chemical Kinetics). p. 149, Moscow, 1979
Polymer Science U.S.S.R. Vol. 29, No. 8, pp. 1917-1923, 1987 Printed in Poland
0031-3950/87 $10.00+ .00 ~ 1988 Pergamon Press plc
SYNTHESIS AND CHARGE-TRANSFER SPECTRA OF DINITROFLUORENONE-CONTAINING POLYESTERS* I. I. PASHKIN, V. A. TVF_RSKOI,A. M. ANDRIEVSKII a n d A. N . PRAVEDNIKOV (dec.) L. V. Lomonosov Institute of Fine Chemical Technology, Moscow
(Received 22 April, 1986) n-Electron acceptor polyesters are synthesized by polycondensation of the cesium salt of 4,5-dinitrofluorenone-2,7-dicarboxylic acid with ~,co-dibromoalkanes and p-xylylene dibromide. The propelties of the polyesters depend on the length of the hydrocarbon residue between the acceptor fragments. The charge-transfer complexes of the synthesized polyesters with N-ethyl carbazole, poly-N-vinyl carbazole, and poly-N-epoxypropyl carbazole are studied and it is established that in all cases their 1 : 1 complexes are formed. The stability constants are only weakly dependent on the length of the methylene chain of the polyesters. T i m e s t a b l i s h m e n t o f p o l y m e r m a t e r i a l s with special e l e c t r o p h y s i c a l p r o p e r t i e s , in p a r t i c u l a r the synthesis o f p o l y m e r s o f high p h o t o e l e c t r i c sensitivity, is an u r g e n t and p r a c t i c a l l y i m p o r t a n t t r e n d in t h e m o d e r n c h e m i s t r y o f high m o l e c u l a r weight c o m p o u n d s [1 ]. A l a r g e n u m b e r o f p h o t o e o n d u c t i n g p o l y m e r s have n o w b e e n p r o d u c e d , b u t these a r e m o s t l y tr-electron d o n o r s , w h e r e a s n - e l e c t r o n a c c e p t o r p o l y m e r s have * Vysokomol. soyed. A29: No. 8, 1744--1748, 1987.
Catalysis of cyclotrimerization of isocyanates
10. A. Ye. CHALYKH, Vysokomol. soyed. B16: 584, 1974 (Not translated in Polymer Sci. U,S.S.R.) I 1. Yu. A. SHARONOV and M. V. VOLKENSHTEIN, Fizika tverdogo tela 5: 590, 1963 12. L. V. SOKOLOVA and A. V. DANCHENKO, Vysokomol. soyed. A23: 213, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 1,238, 1981) 13. L. V. SOKOLOVA, O. A. CHESNOKOVA, O. A. NIKOLAYEVA and V. A. SHERSHNEV, Vysokomol. soyed. A27: 352, 1985 (Translated in Polymer Sci. U.S.S.R. 27: 2,392, 1985) 14. M. F. BUKHINA, Kristalizatsiya kauchukov i rczin (Crystallization of Rubbers and Rubber Products). p. 81, Moscow, 1983 15. N. V. MIKHAILOVA and V. N. NIKITIN, Vysokomol. soyed. A l l : 2432, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 11, 2764, 1969) 16. A. S. KUZM1NSKII, S. M. KAVUN and V. P. KIRPICHEV, Fizikokhimicheskie osnovy polucheniya, pererabotki i primeneniya elastomerov (Physicochemical Basis of the Production, Reprocessing, and Application of Elastomers). p. 34, Moscow, 1966 17. L. V. SOKOLOVA and G. A. VORONOVA, Vysokomol. soyed. A28: 934, 1986 (Translated in Polymer Sci. U.S.S.R. 28: 5, 1041, 1986) 18. L. V. SOKOLOVA, O. A. CHESNOKOVA and V. A. SHERSHNEV, Dokl. Mezbdunar. konf. po kauchuku i rezine (Paper of International Conicrence on Rubbers and Rubber Products). A-38, Moscow, 1984
Polymer Science U.S.S,R. Vot. 29, No. 8, pp. 1909-1917, 1987 Printed in Poland
0032-3950/87 $ 10.00 + .00 ~3 1988 Pergamon Press plc
SPECIAL FEATURES OF THE CATALYSIS OF CYCLOTRIMERIZATION OF ISOCYANATES IN THE PRESENCE OF o-AMINOPHENOLS AND REASONS FOR THE"AUTOINHIBITION" OF THIS REACTION* I. G. ROZDINA, R. P. TIGER, YE. A. CHERNOVA a n d S. G. ENTELIS Institute of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 21 April 1968) It is established that the reason for the catalytic activity of o-aminophenols in the cyclotrimerization of isocyanates is the presence in the catalyst molecule of intramolecular hydrogen bonds O - H...N. The activation of the phenyl hydroxyl group due to this results in consumption of the catalyst in the formation of the corresponding urethane, w~aich is reflected in the kinetics in the form of "autoinhibition" of cyclotrimerzation. THE cyclotrimcrization of isocyanates has recently b e c e m e extremely p o p u l a r in the modification of p o l y u r e t h a n e s a n d for the p r o d u c t i o n of new heat resistant polymers [1-4]. Because of cyclotrimerization of the N C O groups in the p o l y u r e t h a n e n e t w o r k * Vysokomol. soyed. A29: No. 8, 1737-17430 1987.
1910
I . G . ROZDXNAet al.
new (together with triol) branching centres of isocyanurate nature arise, which have significantly higher thermal stability and decreased combustibility compared with the polymer material. The method involving a combination of urethane formation and cyclotrimerization the kinetic model of which was developed fairly recently [5, 6] is the most promising. The main problem in practical application of this process, which is of interest in the production of rigid and elastic polyurethane isocyanurates, is the selection of catalyst systems giving selected urethane formation and eyclotrimerization. It is known that most catalysts for the cyclotrimerization of isocyanates also catalyse urethane formation [7]. Mannich bases, i.e. o-aminophenols, of which the most active is 2,4,6-tri-(dimethylaminomethyl) phenol (commercial grade DMR-30) have been proposed [8] and have been applied [l, 9, 10] as extremely effective cyclotrimerization catalysts, which have only a weak effect on the urethane formation process
OH I (Cti3)2NCH2--(~--CH~N(CHa)2 I CH2 I N(CH3)2 . I The first attempts at quantitative investigation of the catalysis of cyclotrimerization in the presence of compound I showed [11] that in contrast to most catalyst systems the reaction occurs without an induction period, but it's kinetics do not obey simple laws. The main feature of the reaction is rapid retardation as the reaction proceeds, in spite of the fairly high initial reaction rate. In some cases almost complete stoppin~ of the cyclotrimerization reaction was observed, which, when the process is combined with urethane formation, almost eliminates the possibility of using compound I as a selective catalyst. This work was concerned with investigating the special features of the catalysis of the cyclotrimerization under the action o-aminophenols and the nature of their catalytic activity, but mainly with the reason for the inhibition of the reaction as it proceeds. The cyclotrimerization of m-chlorophenyl isocyanate which takes place in dioxane or carbon tetrachloride in the presence of l, 2,6-bis-(dimethylaminomethyl) phenol (II), 2,6-dimethyl-4-(dimethylaminomethyl) phenol (liD, dimethylbenzylamine (IV), and p-cresol (V) served as a model reaction. Compounds (IV) and (V) were considered as fragments o,f aminophenols simulating, on combined use, catalysis in the presence of compounds (I) and (II). The m-chloropl~enylisocyanate used was chemically pure, and was vacuum distilled at 470°C and 133-266 Pa pressure and stored under argon in sealed ampoules. Compound (I), which is produced by the American firm Ferak, was vacuum distilled for use. Compounds (II) and (II1)were synthesized using the method given by Adams [12]. The purity of the products was established by elemental analysis. Compound (IV) was distilled at 68°C and 2"12 kPa pressure. Compound
Catalysis of cyc[otrlmedzatlon of isocyanates
1911
(V), which was chemically pure, was distilled at 205.YC. The peroxides were removed from the dioxide (chemically pure) by passing through an A1203 column, treating with KOH for several days, and boiling for 3-4 hr over Na, followed by distillation. The fraction of boiling point 101'C was used. The contents of impurity aromatic compounds was monitored by UV spectroscopy. The water content, as determined by the Fisher method was 0.04 %. The carbon tetrachloride, which was chemically pure, was purified free of carbon disulphide by boiling in dilute NaOH, then washed with several portions of water, dried over calcined CaCI2, and redistilled. The fraction boiling at 76.8 'C was used. A model R-20 spectrophotometer was used in the IR studies at 25°C in a thermostated CaF2 cell of thickness 0.1 and 0.02 mm over the range 1500-3800 cm-L Observation of kinetic catalytic transformation of isocyanite was carried out up to the disappearance of the band for the stretcifing vibrations of the CO group (v=2260 cm -a) of the isocyanate. The kinetics of formation of the trimer (v = 1720 cm -~) the dimer (v= 1780 cm -~) and urethane 0' = 1750 cm -I) could not be followed quantitatively because of the marked overlap of the bands for the stretching C = O vibrations. The PMR spectra were recorded at 25'~C on a "Bruker" SXP400 spectrometer at a frequency of 90 Hz, using tetramethylsilane as an internal standard. Quantum chemical calculations of the electronic structure of 4,6-dimethyl-2-(dimethylamino)methyl phenol, the simplest analogue of compound (1), were carried out by the CNDO/BW method [13], with optimization of the geometry using a procedure inw)lving Davidson-Fletcher-Powell minimization [14]. The geometrical structure of the aminophenol molecule was optimized as a whole with the exception of the structure of the benzene ring and the CHa group in the ortho- and para-positions in relation to the OH group. Figure 1 gives typical kinetic curves for cyclotrimerization of isocynate in the presence of c o m p o u n d (1). The reaction has no i n d u c t i o n period and has variable order with respect to m o n o m e r as a characteristic feature. At low c o n c e n t r a t i o n s of catalyst, in spite of the relatively high initial rate, the process does not go to completion, ilnitating s p o n t a n e o u s " a u t o i n h i b i t i o n ' . The order of the reaction with respect to the catalyst is a b o u t 2.3. Similar relationships are observed in catalysis by c o m p o u n d (ll), whereas the catalytic activity of c o m p o u n d (!II) is less by several orders or magnitude, similar to the activity of c o n v e n t i o n a l tertiary amines such as t r i b u t y l a m i n e and c o m p o u n d (IV). In the presence of c o m p o u n d s (IIl) or (IV) the reaction takes places in 2-3 days u n d e r the same conditions, the selectivity of these catalysts being significantly lower, and,
[M],mol#c 0.q~-
2 0.2 t2 ~ ~ ~ ~ l
I
80 T i m e ~rain
I 160
} ~32_.
3 .,.1o 3
g5
29
33
37 vxlO-fcm -r
FIG. 1 Fio. 2 FIG. 1. Typical kinetic curves for the decrease in concentration in polymer in the presence of compound I in dioxane (1, 2) and CC14 (3, 4); [I]o=9"7 x 10 -a (•); 4.98 x 10 -2 (2); 4-5 x 10 -2 (3) and 8"4 × 10 -2 mole/l. (4). Fro. 2. IR Spectra of solutions of compounds I (1) and III (2) in CCI.~in the region of the stretching vibrations of the OH groups. Layer thickness 2 cm, concentration of solutions c× 104=5.05 (1) and 8'30 mole]l. (2).
1912
1[. O. I~OZDINAet at.
depending on the concentration of the reagents, the nature of the solvents, and the reaction conditions amongst the products, different quarttities of the c)clic dimer of the isocyanate are observed as well as the trimer. A unique difference between compounds (II) and ( l i d is that art intramolecular hydrogen bond cannot form between the phenol hydroxyl and the amino group in the o r t h o position, as occurs ill compounds (I) and (H)
/ II . . . . . . N
/ o / \cu3 I / n-(~-cu2 \// I W A where R = R ' and is CH2N(CH3)2 in compound (I) and R is CHzN(CH3)2 and R ' is CH3 in compound (II). Figure 2 shows the I R spectra of compounds (I) and (III) in the region of the stretching vibrations of the OH group at concentrations which exclude intermolecular association. It can be seen that the frequency of the vibrations for the OH group in compound (I) is displaced by more than 400 c m - 1, which indicates the absence of a strong hydrogen bond. It is known that the presence of intramolecular hydrogen bonding is generally characteristic of such compounds. In some mono- and binuclear aminophenol and naphthols displacement of the vibration frequency of the OH groups attains 200-500 cm -1 [15, 16], and in the IR spectra of such a compound as 1-dimethylaminomethyl-2-naphthol, bands for absorption of OH group are generally not observed [17]. The works of Koll et al. [18-20] have shown that in many Mannich bases the hydrogen bond is so strong that, depending on their structure and medium, complete transfer of a proton from oxygen to nitrogen is possible with the formation of a stable zwitterion structure, i.e. 0-
H+N(CII3)2
I
/
--()-oH2-, I B
which has a significant dipole moment. It must be noted that a structure of type B is similar to the structure of a zwitterion, the formation of which is often postulated in considering opening of the epoxide ring on interaction of x-oxides with tertiary amines, i.e.
\
/
CtI~--Ct]~
Catalysis of~cyclotrlmerlzation of isocyanates
1913
Q u a n t u m chemical calculations indicate that particles of this type have a cis structure [11, 21], but their formation in the absence of proton donors is disadvantageous from the energy point view [22]. In the presence of p r o t o n donors (for example an alcohol R ' O H ) in principle ion pairs of type [RaN - CH2CH2OH] + ' O R - can be formed, although q u a n t u m chemical calculations ( C N D O / /BW) for such a system show [22] that a potential curve with a single minimum, is characteristic of this ion pair, corresponding to an almost symmetrical position of the proton between the two electron d o n o r centres ( R a N - C H 2 C H z O . . . H . . . O R ' ) , i.e. where the potential curve is typical of a strong hydrogen bond. Tertiary amine epoxide systems in the presence of proton donors are the most active catalysts of cyclotrimerization reactions [7]. The presence of intramolecular hydrogen bonding in the o-aminophenols brings them close to amine-epoxide systems and is evidently the reason for their ability to bring about the cyclotrimerization of isocyanates.
The quantum chemical calculations on the structure of a model o-aminophenol, i.e. 4,6-dimethyl-2-(dimethylaminomethyl)phenol, given within the framework of this work, shows that the minimum of the total energy of the system corresponds to a structure with an intramoleculat h~drogen bond 0
1"02
1"33
It . . . .
\
/
CHa qo = - - 0.(353
N C fl~--
1.56
\//
CH,,
Ctla
qu = ÷ 0.457 qN ~--- - - 0'589
I CHs A special feature of this structure is the strong polarization of the phenol hydroxile group (/t,=4.23 Debye). The increase in the OH bond length is 0.06 A. The negative charge on the oxygen pattern, as in the formation of a hydrogen bond, is significantly higher than the charge on the free hydroxyl group, which can result in an increase in the reactivity of the o-aminophenol as a nucleophilic reagent in relation to the NCO group. The quantity Aqo, compared with a hydrogen hydroxyl group, is 0.08 a.e. Allowance for the effect of the medium can result in a strengthening of the polarization of the hydrogen bond or to displacement of the equilibrium O H - N ~ O - . . . N H + in the direction of complete transfer of a proton with formation of a binary structure (B), which has a theoretical valhe of the dipole moment for 4,6-dimethyl-2-(dimethylaminomethyl) phenol of 9.74 D. A hydrogen bond, similar to the hydrogen bond in o-aminophenols, but of intermolecular nature, is formed in phenol-tertiary amine systems, in particular between compounds (IV) and (V). Investigation of the cyclotrimerization Of isocyanate in the presence of IV and V shows that this pair, although significantly less active and less selective than I and II, does catalyse cydotrimerization significantly more actively than IV alone. In the presence of the 1V + V system, depending on the amine : p-cresol ratio,
J together with the trimer, the uretlmne m - C 1 - C 6 H 4 N C - O C 6 H 2 ( C H a )
is formed,
III HO and possibly also traces of allophanate, as a result of which compound V is consumed
I . G . ROZDINAet al.
1914
during the process. A typical case of the activation of the O H group of compound V under the action of a tertiary amine, which is necessary for adding it to isocyanate at the N = C bond is available [23]. It follows from the above experimental data and theoretical calculations that the reason for retardation of trimerization as far as complete inhibition of the process in the presence of amino phenols must be the consumption of catalyst in the formation of the corresponding urethane, which takes place at a comparable rate, and possibly also of allophanate, which is a product of the interaction of urethane with isocyanate. The use of I R spectroscopy for identifying urethane or allophanate (stretching vibrations of C = O) against a high intensity background located close (3v = 20 c m - 5 ) to the bagtd for the R N C O trimer is difficult. High resolution N M R is more effective in this connection, and not only enables the fact of the catalyst consumption to be established but provides a means of following the nature of the change in concentration of the original, intermediate, and final products with time. The P M R spectrum of catalyst I shows signals for the protons of the groups OH, Ph, CH2 and CHa. Figure 3 shows a fragment of a P M R spectrum of catalyst ] for the range O= 8-11 ppm, where a signal for the proton of the catalyst hydroxyl group is present. It can be seen that the signal for the O H group of the catalyst (6=9"9l ppm) at the moment of introducing hydrocyanate into the system disappears, and two new
I~Pel.uR.
iS-"
- 0"2
120 i
60
- - ,
I
I
11
10
J~
~ppm
9
"I~g ,
0
1£
" 0.1
I
Time, min
82
FIG. 4 FIG. 3. Fragment of PMR spectrum of catalyst I in CC1, (1), and kinetics of change of form and intensity of peaks at 6x = 10"62 (a) and fi2= 10'35 ppm (b) after introduction of isocyanate at time t = l (2) and 2 rain (3) and 2 hr (4). [M]o=0"5, [I]o=8"0 × 10 -2 mole/l. FIG. 4. Nature of the change in intensity of the signals for protons of the CH2 groups at 6= 3"1 (1), 3"4 (2), 3.28 ppm (3), &nd the CHa groups at 5= 2.21 (4), 2.16 (5), and 2.14 ppm (6) during cyclotrimerization. [M]o=0"21, [I]o=8"5 × 10 -2 mole/1, and (7) kinetic curve for decrease in monomer content in CCI4. ([M])o=0'21, [I]o= 8'44 x 10 -2 mole/1.). FIG. 3
Catalysis of cyclotrimerization of isocyanates
1915
peaks arise with 5 = 10.6 and 10.4 ppm respectively, which can be assigned to signals from the proton bonded to the nitrogen in the final product (urethane) and the proton of the OH group of the intermediate product, so-called preurethane. During the process the signal from the proton of the N H group of urethane increases, and that of the intermediate product decreases. At the end of the reaction a single signal is observed in the N M R spectrum corresponding to the proton of the NH group of urethane, which indicates compl:te disappearance of the catalyst. The P M R spectrum of catalyst I also has a series of very clear signals from the protons of the CH2 and CH3 groups, and the changes of some of these with time can be followed easily (Fig. 4). The intensities of the signals of the CH2 (5=3.1 and 3.4 ppm) and CH3 (5=2.1 ppm) groups, which belong to the original catalyst I, decrease steadily, and the signals for the CH2 groups (5= 3-28 ppm) and CHa (5=2.16 and 2-14 ppm) groups, arising on introduction of a monomer into the system, pass through maxima. It would appear that the signals for the protons of the CH2 group with =3.28 ppm and for the CHa with 5=2.16 and 2.14 ppm are superpositions of the corresponding signals of the intermediate product, the concentration of which should pass through a maximum, and the final product, the concentration of which should increase steadily until the process has completely finished. Because of the closeness of the structures cf the intermediate "preurethane" (C) and phenylurethane (D) the signals for the protons of the CH2 and CHs group should almost coincide. On this principle, the production of information on the nature of the changes in intensity of the signals from the CH2 and CHa groups in structures C and D 0
'% / C..-~N
PhCI
I CH3 0 . . . H...N /
0
~:
,/
l'hf3
C-- N l
/(3t3 •. . i t . . . N
%/'
% .J
R
l R
c
D
taken in isolation is not possible. It must be noted (Fig. 4, curve 7) that after complete consumption of the catalyst, which can be judged from "restriction" with time of the intensities of all the P M R spectrum signals, characteristic of compound I and of the products of its interaction with RNCO, the consumption of monomer almost ceases. The slow loss of monomer at the end of the reaction can be due to trimerization catalysed by the (CHa)zN- CH2-groups of urethane formed from compound 1. The above experimental data are in agreement with a scheme in accordance with which, during the first stage, because of intramolecular hydrogen bonding and activation of the OH-group of the catalyst, the catalyst is added to the isocyanate with the
1916
I . G . ROZDINAet at,
formation of an intermediate product, which is able either to give corresponding urethane because of intramolecular regrouping with transfer of a proton, or can add the following molecules of isocyanate, leading to chain growth with subsequent cyclization at the trimer stage ,D I+M~B+3~T+ C here M and T are the m o n o m e r and cyclic trimer of the isocyanate respectively. It is doubtful whether a matrix mechanism of catalysis, which is characteristic of processes of cyclotrimerization in certain catalyst system [24], is realized with aminophenols. Although the o-aminophenols at the concentrations used can undergo self-association and solution, their complex formation with the trimer and the effect of the latter of the reaction kinetics has not been established. Allowing for the consumption of catalyst during cyclotrimerization in uiethane formation and the consequent complication of the primary kinetic laws, quantitative analysis of the kinetic scheme and the mechanism of the cyclotrimerization does not yet seem possible. It should be noticed in conclusion that the use of o-aminophenols as catalysts for the hardening of oligomers with terminal N C O groups and also for combined urethane formation and cyclotrimerization can result in blocking of some of the reactive N C O groups, and the appearance of side chain in the system, not included in the structure of the network, and consequently, to changes in the expected properties of the polymers formed. Translated by N. SrAND~I~ REFERENCES
1. T. NAWATA, J. E. KRESTA and K. C. FRISH, J. Cellular Plast. 11: 267, 1975 2. A. DEION, Advances in Urethane Science and Technology, vol. 8, p. 1, Westport, 1981 3. R. J. LOCKWOOD and L. M. ALBERINO, Advances in Urethane Science and Technology, vol. 8, p. 171, Westport, 1981 4. Ts. M. FRENKEL, V. A. PANKRATOV, V. V. KORSHAK and S. V. VINOGRADOVA, Kompozi~sionnye polimernye materialy (Composite Polymer Materials). No. 26, Kiev, 1985 5. I. G. ROZDINA, V. B. SVALOVA, V. V. YEVREINOV, R. P. TIGER and S. G. ENTELIS, Khim. fizika 3: 1002, 1984 6. I. G. ROZDINA, V. V. YEVREINOV, R. P. TIGER and S. G. ENTELIS, Kompozitsionnye polimernye materialy (Composite Polymer Materials), No. 26, p. 65, Kiev, 1985 7. R. P. TIGER, L. I. SARYNINA and S. G. ENTF_,LIS, Uspekhi khim. 41: 1672, 1972 8. L. NICOLAS and G. T. GMITTER, J. Cellular Plast. 1: 85. 1965 9. Yu. O. AVERKO-ANTONOVICH, L. A. AVERKO-ANTONOVICH, I. N. BAKIROVA, L. A. ZENITOVA, K. S. FRISCH, K. J. PATEL and R. D. MARSH, J. Cellular Plast. 6: 1, 1970 I0. P. A. KIRPICHNIKOV, A. G. LIAKUMOVICH and G. M. RAKHMATULINA, Tez. dokl. XII. Mendeleyevskogo s'ezda po obshchei prikladnoi khimii (Thesis of Paper of Twelfth Mendeleyev Congress on General and Applied Chemistry), Vol. 2, Moscow, 1981 11. R. P. TIGER and S. G. ENTELIS, Advances in Urethane Science and Technology, vol. 8, p. 19, Westport, 1981 12. R. ADAMS, Organicheskie reaktsii (Organic Reactions). Moscow, 1948
Dinitrofluorenone-containing polyesters
1917
13. 14. 15. 16. 17. 18. 19. 20. 21.
R. J. llOYD and M. A. WHITEHE, AD, J. Chem. Soc. Dalton Trans., I, 73, 1972 R. FLETCHER and M. J. D. POWEI,L, Computer J. 6: 163, 1963 A. W. BAKER and A. T, S H U I ~ I N , J. Amer. Chem. Soc. g0: 5358, 1958 A. G. MORITZ and G. M. BADGER, Spectrochim. Acta 13: 672, 1959 M. C. FLETT, Spectrochim. Acta 10: 21, 1957 A. KOLL, Bull. Soc. Chim. Belg. 92: 313, 1983 A. KOLL, M. ROSPENK and L. SOBCZUK, J. Chem. Soc. Faraday Trans. 77: 2309, 1981 J. RESPENK and A. KOLL, Bull. Soc. Chim. Belg. 92: 329, 1983 N. V. KOZAK, Yu. N. NIZELSKII, Yu. A. TISHCHENKO and T. E. LIPATOVA, Teoret. i eksper, khim. 18: 331, 1982 22. Ye. A. CHERNOVA, O. G. TARAKANOVA and A. K. ZHITINKINA, Kompozitsionnye polimernye materialy (Composite Polymer Materials), No. 26, p. 48, Kiev, 1985 23. S. G. ENTF,LlS and O. V. NESTEROV, Uspekhi khim. 35: 2178, 1966 24. S. G. ENTELIS, I. G. BADAYEVA, S. P. BONDARENKO and R. P. TIGER, Problemy khimicheskoi kinetiki (Problems of Chemical Kinetics). p. 149, Moscow, 1979
Polymer Science U.S.S.R. Vol. 29, No. 8, pp. 1917-1923, 1987 Printed in Poland
0031-3950/87 $10.00+ .00 ~ 1988 Pergamon Press plc
SYNTHESIS AND CHARGE-TRANSFER SPECTRA OF DINITROFLUORENONE-CONTAINING POLYESTERS* I. I. PASHKIN, V. A. TVF_RSKOI,A. M. ANDRIEVSKII a n d A. N . PRAVEDNIKOV (dec.) L. V. Lomonosov Institute of Fine Chemical Technology, Moscow
(Received 22 April, 1986) n-Electron acceptor polyesters are synthesized by polycondensation of the cesium salt of 4,5-dinitrofluorenone-2,7-dicarboxylic acid with ~,co-dibromoalkanes and p-xylylene dibromide. The propelties of the polyesters depend on the length of the hydrocarbon residue between the acceptor fragments. The charge-transfer complexes of the synthesized polyesters with N-ethyl carbazole, poly-N-vinyl carbazole, and poly-N-epoxypropyl carbazole are studied and it is established that in all cases their 1 : 1 complexes are formed. The stability constants are only weakly dependent on the length of the methylene chain of the polyesters. T i m e s t a b l i s h m e n t o f p o l y m e r m a t e r i a l s with special e l e c t r o p h y s i c a l p r o p e r t i e s , in p a r t i c u l a r the synthesis o f p o l y m e r s o f high p h o t o e l e c t r i c sensitivity, is an u r g e n t and p r a c t i c a l l y i m p o r t a n t t r e n d in t h e m o d e r n c h e m i s t r y o f high m o l e c u l a r weight c o m p o u n d s [1 ]. A l a r g e n u m b e r o f p h o t o e o n d u c t i n g p o l y m e r s have n o w b e e n p r o d u c e d , b u t these a r e m o s t l y tr-electron d o n o r s , w h e r e a s n - e l e c t r o n a c c e p t o r p o l y m e r s have * Vysokomol. soyed. A29: No. 8, 1744--1748, 1987.