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o f compositions. Therefore, it m a y be assumed that'repulsion of the components of the macrochain increases the unperturbed dimensions of the Coils o f the copotymers as compared with those calculated from the additivity law. The authors wish to thank A. G. Morozov for a useful discussion of the contents of the paper. Translated by A. CROZY

REFERENCES

1. M. A, PONOMAREVA, Dissert. Cand. Chem. Sei. INEOS, Akad. Nauk SSSR, Moscow, 1985 2, Ye. A. PISKAREVA, Ye. G. ERENBURG and I. Ya. PODDUBNYI, Vysokomol. soyed. A20: 784, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 4, 883, 1978) 3. A. RUDIN, G. W. BENNET and J. R. MeLAREN, J. Appl. Polymer SCi. 13: 2371, 1969 4. M. R. AMBLER, J. Polymer Sci. Polymer Chem. Ed. 11: 191, 1973 5. K.-Q. WANG, S. I. ZHANG, J, XU and Y. LI, J. Liquid Chromatogr. 5:. 1899, 1982 6. A. R. WEISS and E. COHN, J. Polymer Sci. B7: 349, 1969 7. H~ Kli. MAHABADI, J. Appl. Polymer Sci. 30: 1535, 1985 8. M. KUBIN, Collect. Czechosl. Chem. Communs .51: 1636, 1986 9. E. Sh. GOL'BYERG, I. M. RAIGORODSKII, A. I. KUZAYEW and I. Ya. SLONIM, Vysokomol, soyed. A26: 1369, 1984 (Translated in Polymer Sci. U.S,S.R. 26: 7, 1529, 1984) 10. G. SITARAMAHIAH, J. Polymer Sci. A, 8, 2743, 1965

Polymer Sclence U.S.S.R. Vol. 31, No. 6, pp. 1272-1277, 1989 Printed in Poland

0032-3950/89 $10.00+ .00 © 1990 Pergamon press pie

VISCO-ELASTICITY OF INTERPENETRATING POLYMERIC NETWORKS BASED ON DHSOCYANATES* Yu. S. LIPATOV, V. F. ROSOVITSKII,YU. N. NIZEL'SKI1, A. M. FAINLEIB and Yu. V. MASLAK Institute of Chemistry of High Molecular Weight Compounds, Ukr. S.S.R. Academy of Sciences • (Received 10 D e c e m b e r 1987)

Dynamic mechanical spectroscopy has been employed to study the visco-elasticity of interpenetrating networks the components of which are network polyisocyanurate and partially erosslinked or crossliakcd polycarbodiimide obtained respectively from hexamethylerie diisocyanate and 4,4'-diphenylmcthane diisocyanate. Networks have been investigated with a content of polycarbodiimide in the polyisocyanurate matrix from 1 to 20~/o by weight. The presence for all samples of the networks of a single 'vitrification peak and also the linear dependence of Ts on the concentration of polycarbodiimide indicate the compatibility of the ~network components. :L Vysokotn0L soyed. A3|: No. 6, 1162-1166, 1;989.

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SELECTIVEcatalysts and catalytic systems of the diisocyanates O = C = N - R - N = C = O may give network polyisocyanurates [1] and linear polycarbodiimides [2, 3] also capable of forming network structures at raised temperatures through the reactive carbodiimide groups [2, 3]. It is known [4] that polycarbodiimides combine well with other polymers. It was, therefore, of interest to obtain from polyisocyanurates and polycarbodiimides interpenetrating polymeric networks (IPN). The literature known to us does not describe IPNs obtained by polymerization of monomers of the same nature• A difference may be expected in the properties Of such polymeric composition from those traditionally obtained from different monomers such as, for example, the IPNs described in [5] based on diisocyanates and some polar monomers. The reactions underlying the formation of the 1PNs from diisocyanates are represented by the following general scheme: %.

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Yu, S. L~ATOVet al.

In the present work we study the dynamic mechanical characteristics o f the polymeric composites obtained enabling their structural organization to be judged. The substances used in the work were purified before the experiments. Hexamethylene diisocyanate (HMDI) was distilled in vacuo, BP 159°C/2 kPa, n~s 1.4510. 4,4'-Diphenylmethane diisocyanate (MDI)was recrystallized from heptane, MP 39-40°C. The phenylglycidyl ether was distilled in m c u o , BP 79-81°C/0.14 kPa. Triethylamine was distilled at 85°C The starting components of the IPNs were pol~hexamethylene isocyanurate (PIC). (II, R,~ - ( C H 2 ) s - ) obtained by polycyclotrimerization of HMDI and polyphenylenemethane carbodiimide (PCD) (I, R - - < ~ _ _ ~ - C H = - < ~ _ _ _ ~ - , n--100) synthesoized by the technique in [3] from MDI. The IPN samples.were obtained by dissolving the synthesized PCD in HMDI followed by polymerization of the latter in presence pf the catalytic system triethylamine-phenylglycidyl ether. The technique employed is characteristic of the synthesis of hemiIPNs. Since in our case the selective preparation of PICs in bulk requires a raised temperature [1] during their synthesis in presence of linear PCD the latter was subjected to the appropriate thermal threatment resulting in its crosslinking. Two types of IPN were synthesized, one of the components of which was the polyisocyanurate network and the se~:ond polycarbodiimide with a different degree of crosslinking depending on the regime of curing of the system. We investigated IPNs with a content of PCD in the polyisocyanurate matrix 1-20% by weight. The samples were cured at 393 K for 6 hr (IPN-I) and with further stepped rise in temperature from 393 to 523 K for 14 hr (IPN-2). The completeness of curing of the composites was checked by IR spectroscopy from the characteristic absorption bands 2270 and 2130 cm -t belonging respectively to the vibrations of the groups N C O - and -N=C=Nand the process of obtaining the composites was continued until their practically complete depletion. The samples obtained were monolithic, transparent composites. The dynamic mechanical characteristics of the composites were studied by the method of longitudinal vibrations with an apparatus produced in the Institute of Chemistry of High Molecular Weight Compounds, Ukr. S.S.R. Academy of Sciences, and described in [8]. Frequency of vibrations 100 Hz, temperature range 290-600 K and scanning rate 1 K/rain. We determined the temperature dependences of the tangent of the angle of mechanical losses tan &, the elasticity modulus E' and the loss modulus E". Figure 1 presents the I R spectra of PIC and IPN-2 obtained by curring the system containing 8 0 ~ H M D I and 2 0 ~ P C D (the I R spectra o f the other composites are similar to that presented). In the spectrum of P I C (Fig. la) two bands stand out cleady at 1460 and 1690 cm -1 characteristic of isocyanurate cycles [6]. The asymmetri-

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Visco-elasticity of interpenetrating polymeric networks

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Fio. 2. Temperature dependence of the elasticity modulus E' (a) and the tangent of mechanical losses tan &(b) for PIC (1), linear PCD (2), thermallytreated PCD at 393 K for 6 hr (3), thermally treated PCD for 14 hr at 393-523 K (4). city of the band ~ C = O of the isocyanurate cycle (1690 cm-~) in the spectrum of PIC is connected with fact that the polymer HMDI, according to [7], as well as the isocyanurate cycles comprises different forms of structures containing the groups ~/C=O. The IR spectrum of the composite obtained by curing the system containing 80~o I-IMDI and 2 0 ~ PCD has bands characteristic of polyhexamethylene isocyanurate and also a band at 2130 cm -1 belonging to the residual carbodiimide groups and absorption in the region 1640 cm-x characteristic of the trimer fragments of heated carbodiimides [2, 3]. Absorption in the region 1640 cm- 1 was established from analysis of the spectral contour of the band 1690 cm- ~ using the second derivative O2D/t3vZ. Comparison of the spectra 1 and 2 (Fig. lb) suggests that in the spectrum 2 for the PIC-PCD composite absorption bands areabsent in the region 1720-1750 cm -~ characteristic of the condensation products of the isocyanates with polycarbodiimides [4]. It may from the results be cons~idered that in the experimental conditions chosen there is cyclization of the carbodiimide groups with no reaction between PCD and HMD[ so that one may exclude chemical interaction between the IPN components. Figure 2 gives the temperature dependences of the elasticity modulus ap.d the tangent of the angle of mechanical losses of PIC and PCD with different degress of crosslinking. Curve 1 corresponds to the polyhexamethylen.e isocyan.urate netx~crk (T, =388 K) and curve 2 to the starting linear PCD (Tg=388 K). With further rise in temperature (above 393 K) substantial rise is observed in the elasticity modulus associated with the reaction of polycyclodimerization of the carbodiimide groups. Further fall in the elasticity modulus is evidently connected with the completion of this reaction and subsequent rise in E' (from the temperature 508 K) is connected with the polycyclotrimerization of the groups - N = C = N [3]. Corresponding effects may also be observed in the temperature dependence of mechanical losses. To confirm the formation of chemical crosslinking we investigated the visco-elastic properties of thermally treated samples of PCD-2 (curve 3, 393 K, 6 hr) and PCD-3 (curve 4, stepped rise in temperature from 393 to 523 K for 14 hr. As to be expected

12"/6

Yu. S. LIPATOVe t al.

the glass transition temperature of the erosslinked samples (curves 3 and 4) shifted to the region of higher temperatures. The absence of an increase in the modulus above 393 K indicates the completion of the polycyclodimerization reaction as is also suggested by the absence of a peak of mechanical losses at 453 K. The difference in the glass transition points of the crosslinked samples (curves 3 and 4) confirms the different degree of their crosslinking. However, the persistence of the rise in the elasticity modulus above 513 K for all samples may indicate the incompleteness of the polycyclotrimerization reaction which agrees with the known published findings [2]. Thus, the components of the IPNs studied were the polyhexamethylene isocyanurate network with T==388 K and the networks of polycarbodiimides-PCD-2 (Ts 494 K) and PCD-3 (T,=513 K). The results of investigation of the visco-elastic properties of the composites based on networks of PIC and PCD-2 (IPN-1) and PIC and PCD-3 (IPN-2) are given in Fig. 3. The first point to note is the existence of a single vitrification peak for all the IPN samples and also the fact that the magnitudes tan ~ for the composites obtained reflect the visco-elastie properties of their constituents. However, the concentration dependences tan6" I

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F1o. 3 Fxo. 4 FIo. 3. Temperature dependence of tan ~ for PIC (f), PCD (2) and composites based on them c0ntafning 2 (3), 5 (4), 10 (5), 15 (6) and 20% (7) by weight PC]) in two regimes of curing for 6 hr at 393 K (a) and for 14 hr at 393-523 K (b). Fro. 4. T= as a function of the PCD content in composites IPN-1 (1) and IPN-2 (2). of the glass transition temperatures for IPN-1 and IPN-2 differ (Fig. 4). The dependence for IPN-1 is linear in the concentration range of PCD studied and persists on extrapolation to the region of higher PCD concentrations. The dependence for IPN-2 over the PCD concentration range studied is also of a linear character although on extrapolation to the region of higher PCD concentrations the straight line changes its slope. The presence of a single glass transition temperature, as is known [9, 10], and its linear dependence on the concentration of the components indicate their compatibi-

Visco-elasticity of interpenetrating polymeric networks

1277

lity. It may be assumed that the conditions of formation of composites correspond to the point in the phase diagram of the system in the region o f compatibility of the components. The visco-elastic behaviour o f the I P N investigated fundamentally differs from those previously studied. The first thing to note is the presence of one vitrification relaxation maximum characteristic of compatible components of linear structure. The thermodynamic criteria of the compatibility o~" such networks on formation o f IPNs have already been obtained [11]. Thus, the investigations of the visco-elastic behaviour o f polyisocyanurate, polycarbodiimide and IPNs based on them have confirmed the occurrence of reactions o f polycyclodimerization and polycyclotrimerization at raised temperatures. The compatibility o f polymers of varied structure forming interpretating networks and obtained from monomers of an identical nature has been established for the first time. Growing interest of researches in compatible polymeric systems was noted in a recently published review [12]. Translated by A. CROZY REFERENCES

1. S. V. VINOGRADOVA, V. A. PANKRATOV, Ts. M. FRENKEL', L. F. LARINA, L. P. KOMAROVA and V. V KORSHAK, Vysokomol. soyed. A23: 1238, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 6, 1374, 1981) 2. L. M. ALBERINO, W. J. FARRISSEY and A. A. R. SAYIGH, J. Appl. Polymer Sci. 21: 11999, 1977 3. V. A. PANKRATOV, V. M. LAKTIONOV, A. I. AKHMEDOV, P. N. GRIBKOVA, Ya. M. BILALOV, S. A. PAVLOVA and V. V. KORSHAK, Acta Polymerica 37: 39, 1986 4. W. NEUMANN and P. FISCHER, Angew. Chemie 74: 801, 1962 5. G. P. BELONOVSKAYA, T. I. BORISOVA, I. S. ANDRIANOVA, J. D. CHERNOVA, Yu. V. BRESK!N, L. V. KRASNER and E. V. KRUCHININA, Acta Polymerica 33: 246, 1982 6. R. MERTEN, D. LAURERER, G. BRAUN and M. DAHM, Makromolek. Chem. 101: 337, 1967 7. J. IWAKURA, K. UNO and K. ISHIKAWA, J. Polymer Sci. A2: 3387, 1964 8. V. F. ROSOVITSKII and V. V. SHIFRIN, Fizicheskiye metody issledovaniya polimerov (Physical Methods of Invesigating Polymers). p. 93, Kiev, 1981 9. Yu. S. LIPATOV and V. F. ROSOVITSKII, Dokl. Akad. Nauk SSSR 283: 910, 1985 10. D. THOMAS and L. SPERLING, Polimernye smesi (Polymer Blends). (Eds. D. Paul and S. Newman) Vol. 2, p. 26, Moscow, 1981 11. Yn. S. LIPATOV, V. V. SHIFRIN and Yu. N. NIZEL'SKII, Dokl. Akad. Nauk Ukr. SSR, B, 9, 45, 1987 12. A. A. TAGER and V. S. BLINOV, Usp. khimii 56: 1004, 1987