- Email: [email protected]
Mesomorphic polydiarylsiloxanes
2242
M.I. BuzxN et al.
REFERENCES 1. M. RICHARDSON (editor), Promyshlennye Polimernye Kompozitsionnye Materialy (Industrial Composite Polymer Materials). Moscow, 1980. 2. Yu. S. LIPATOV, Fizitheskaya Khimiya Napolnennykh Polimerov (Physical Chemistry of Filled Polymers). Kiev, 1977. 3. N. A. KNUNYANTS, M. A. LYAPUNOVA, L. I. MANEVICH, V. G. OSHMYAN and A. Yu. SHAULOV, Mekhanika Kompozitnykh Mat., No. 2, 231, 1986. 4. I. V. KRAGELSKY, M. N. DOBYCHIN and V. S. KOMBALOV, Osnovy Raschetov Na Trenie i Iznos (Friction and Wear Calculation Methods). Moscow, 1977. 5. L. E. NIELSEN and T. LEWIS, J. Polymer Sci. A-2 7: 1705, 1969. 6. L. E. NIELSEN, Proc. Phys. Soc. 69: 808, 1956. 7. L. E. NIELSEN, J. Appl. Polymer Sci. 10: 97, 1966. 8. V. DOLAROVA-SVEHLOVA, J. Macromolec. Sci. Phys. 21: 234, 1982. 9. I. V. KRAGELSKY and I. E. VINOGRADOVA, Koeffitsienty Treniya (Coefficients of Friction). Moscow, 1962. 10. A. Yn. SHAULOV and M. A. LYAPUNOVA, Dokl. Akad. Nauk SSSR. 303: 1424, 1988. 11. A. Yu. SIiAULOV, M. A. LYAPUNOVA and L. S. IVANOV, Plast. Massy, No. 7, 18, 1988. 12. S. SAHU and L. J. BROUTMAN, Razrushenie i Ustalost (Fracture and Fatigue) (edited by L. Broutman). Moscow, 1978.
Polymer Science U.S.S.R, Vol. 32, No. 11, pp. 2242-2248, 1990
Printed in GreatBritain.
0032-3950/90$10.00+ .00 © 1991PergamonPresspie
MESOMORPHIC POLYDIARYLSILOXANES* M. I. BUZIN, N. V. VASILENKO, L. M. TARTAKOVSKAYA, V. P. ZHUKOV, I. I. DUBOVIK, D. YA. TSVANKIN and V. S. PAPAPKOV A. N. Nesmeyanov Institute of Hetero-organic Compounds S.S.S.R.; Institute of Synthetic Polymer Materials, Academy of Sciences of the U.S.S.R. (Received 25 October 1989)
Linear polyphenyltolylsiloxanesare studied by calorimetric and X-ray diffraction methods. It is established that these polymers, as also polyphenylsiloxane, pass, on melting, into the mesomorphic state, which is stable up to their decomposition temperature. It is observed that the mesomorphic state can promote crystallization, but can also hinder it. IT HAS been established recently that linear polyorganosiloxanes with symmetrical side substituents on the silicone a t o m show a tendency towards the formation of thermotropic mesophases. The m e s o m o r p h i c state has been observed in polydiethylsiloxane [1, 2], polydipropylsiloxane [3], and polydiphenylsiloxane [4]. The nature of the mesophases appearing in such polymers, which contain no mesogenic groups in their chemical structure, is not completely clear. In view of this it is of interest to explain the effect of the type of substituent on the silicon a t o m and disturbance of the structural regularity of the macromolecules on their ability to form mesophases. We studied *Vysokomol soyed. A32: No. 11, 2340-2345, 1990.
Mesomorphic polydiarylsiloxanes
2243
polydiethylsiloxane containing phenyl and tolyl substituents on the silicone atom from this point of view. This work deals with the general characteristics of mesomorphic and crystalline phases and phase transformations in these polymers. The polymers studied differ in the position of the methyl substituent on the phenyl group (presence of meta- or para-substituent) and in the ratio of the tolyl and phenyl groups. The polymers were obtained by a previously described method [5], i.e. by polymerization of the corresponding organocyclotrisiloxane, having different ratios of the diphenylphenyltolyl, and ditolylsiloxane units in the presence of a,to-dipotassiumoxy-poly(pheny)-(p-tolyl)siloxane. The catalyst was deactivated by introduction of trimethylchlorosilane. The polymers were separated by extraction of the monomer part with methylethylketone and subsequent precipitation of the toluene solution in ethanol. The polymers synthesized were soluble in chloroform, carbon tetrachloride, and xylene. The absence of monomer in the polymers was checked by GLC, using an internal standard, i.e. methyltriphenylsilane on a LKhM-8-MD chromatograph a I x 0.004 m column solid phase-Inerton AW-HMD, liquid phase SE30 (5%), thermostat temperature 350°C, gas flow rate 3600 ml/h. The structure of the original rings, and the notation and characteristics of the polymers studied are shown Table 1. As can be seen from the table, the polydiarylsiloxanes studied, which have different types of units, can be represented as copolymers with the units Ph2SiO, Tol(Ph)SiO and TolESiO. We note that anionic polymerization of the rings, because of the nonstereospecific character of the reactions, possible inter-chain exchange, and depolymerization, which, as shown in [6] occurs at different polymerization stages, results in the formation of a polymer with a considerable degree of randomization of the macromolecule structure. However, in spite of this all the polymers can be crystallized [7, 8]. The crystallinity and the perfection of the crystalline phase depend both on the ratio of the phenyl and tolyl groups, and on the conditions under which the samples are obtained: reprecipitation, formation of films from solution, crystallization from the melt. This problem is considered in greater detail below. TABLE1. POLYDIARYLSILOXANES Original organocyclotrisiloxane
Designation of polymer
Intrinsic viscosity of chloroform*
i---[Ph2SiO]3-q
PDPS
t--[(m-Tol)2SiO]3--I
PDMTS
1.0
r-[Ph2SiO]E-[Ph(m-Tol)SiO]--1
m-T-1
0.4
l---[PhESiO12-[(m-Tol)2SiOl-q
m-T-2
1.0
i--[PhESiO]-[(m-Tol)ESiO]z-q
m-T-4
0.6
r--[(p-Tol)2SiO]3--q
PDPTS
t--[Ph2SiO]2-[Ph(p-Tol)SiO]--1
p-T-1
0.9
t--[Ph2SiO]2-[(p-Tol)2SiOl-n
p-T-2
0.3
r--[Ph(p-Tol)SiO]3-~
p-T-3
0.7
*Concentration of solution 1%, temperature 25°C. \
The diffraction patterns of the homopolymers and copolymers with m- and p-tolyl groups are shown in Fig. 1. A special feature in the melting of all the polymers studied is their transformation after melting of the crystalline phase not into an isotropic melt, but into the mesomorphic state. X-ray diffraction shows that this transformation is characterized by the disappearance of crystalline
M . I . Buzm et al.
2244 I, relative units
(a)
I
tO
I
20
I
,i0 Z6*
tO
gO
20*
,1
,P
I
I
tO
20
I
26*
FIG. 1. Diffraction patterns of polydiarylsiioxanes:(a, c) crystallinepolymers with different contents of m-tolyl (a) and p-tolyl groups (c); (b) PDMTS. a: (1) PDPS from reaction mixture, (2) PDPS, crystallized by cooling from the mesophase, (3) m-T-l, (4) m-T-2, (5) m-T-4; b: (1) 25, (2) 110, (3) 130, (4) 160, (5) 25°C; c: (1) PDPS, (2) p-T-3 (3), (3) p-T-1. (a, b) peaks in left-hand part of diffraction pattern doubly reduced. reflections, but a sharp reflection in the region of the angles 20 = 8--8.5 ° is retained. The diffraction patterns of PDMTS in the crystalline and mesomorphic states are shown in Fig. lb. The diffraction patterns of the remaining polymers studied above the melting point are similar in form to that of mesomorphic PDMTS. On melting, the optical texture observed in polymer films in polarized light with cross and parallel nicol prisms is preserved, although in many cases the colour of the optically anisotropic domains is changed because of the change in magnitude of the birefringence. Microphotographs of a series of polymers in the crystalline and mesomorphic states are shown in Fig. 2.
Mesomorphic polydiarylsiloxanes
n
2245
in
[]
301zro L
I
Fio. 2. Microphotographs of polydiarylsiloxanes at various temperatures in polarized light: (a-d) with crossed nicol prisms; (e-h) with parallel nicol prisms: (a, b, e, d) m-T-4, (c, d, g, h) PDMTS. Temperature: (a, c, e, g) 25°C, (b, f) 90°C, (d, h) 160°C.
Comparison of the diffraction patterns of the polymers provides a basis for making a number of qualitative notes on their structure. Thus, from a comparison of the diffraction patterns of PDPS and PDMS (Fig. la and b) it can be seen that these polymers have different crystal lattices. Comparison of the diffraction patterns of the copolymers shows that the tolyl and the phenyl substituent enter into the crystals, the structure of which is close to that of homopolymer crystals. The diffraction pattern of the copolymer m-T-1 is similar to that of defective PDPS crystals, formed during polymerization (Fig. la), but differs from that of the more perfect PDPS crystals. Evidently the introduction of the bulky m-tolyl group leads to disappearance of the crystalline PDPS lattice, which is accompanied by a change in the position of the inter-chain crystal reflections (Table 2). The diffraction pattern of the copolymer m-T-4 is similar to that of the homopolymer PDMTS (Fig. la and b). This indicates that the phenyl groups, which are smaller in volume, enter into the lattice formed on packing of the m-tolyl groups. The diffraction pattern of the copolymer m-T-2 is close to that of the copolymer m-T-1 (Fig. la), although it differs from it in that it has a reflection at 20 = 21 °, which is not observed in any of the other copolymers of the series considered. The replacement of the phenyl groups by p-tolyl groups also results in disturbance of the PDPS crystal lattice (Fig. lc; Table 2). The maximum distortions are observed on introducing three p-tolyl substituent.
2246
M . I . BUZIN et al.
TABLE2. VALUESOFTHEINTERPLANEDISTANCESd INPOLYARYLSILOXANES Polymer PDPS m-T-1 m-T-4 PDMTS n-T-1
T, °C
Phase
d,/~
25 270 25 140 25 90 25 160 25 200
cystalline mesomorphic crystalline mesomorphic crystalline mesomorphic crystalline mesomorphic crystalline mesomorphic
10.2 10.3 10.4 10.5 12.1 (10.4") 10.8 12.4 (10.9") 11.2 10.6 (9.6*) 10.8
*The second reflection is shown in brackets. The crystal lattice distortion obtained on replacing the phenyl groups by tolyl groups is manifested not only in changes in the diffraction patterns, but also can be clearly followed from the change in temperature and the heat of melting of the copolymers compared with the homopolymers. These data are shown in Fig. 3. They apply to the most perfect of the crystalline specimens, the conditions of production of which differ for the different polymers studied (see below). Replacement of one phenyl group by a tolyl group results in a sharp decrease in the temperature and heat of melting of the copolymer, especially in the case of the m-tolyl group. The curves for the given parameters as a function of the tolyl group content have an extreme character, with a minimum, in the case of the heat of melting, at a ratio of the phenyl and m-tolyl groups of 2: 4, and in the case of the melting point at a ratio of 4:2. The introduction into the homopolymer of different side substituents can result not only in an increase in the defectiveness of the crystals, but also to a decrease in their size. Both these effects are evidently due to a decrease in the temperature and heat of melting of the copolymers compared with the homopolymers. The smaller values of the heat of melting of the copolymers can also be due to their smaller degree of crystallinity. Unfortunately, accurate determination of their crystallinity is difficult: there is no jump in the heat capacity in the glass formation region on the DSC thermograms, and the positions of the inter-chain mesomorphic and crystalline reflections in the region of the angles 20 = 8-8.5 ° on the diffraction patterns almost coincide. The amorphous halo indicating inter-chain distances in the amorphous regions, is probably located at the same 20 angles. A characteristic feature of all the polymers studied is preservation of the mesomorphic state after melting as far as decomposition, which occurs above 400°C. Preservation of the optically anisotropic regions observed under the polarization microscope, and also preservation of the sharp mesomorphic reflection on the diffraction patterns is an indication of this. Moreover, the intensity of the mesomorphic reflection on the diffraction patterns is directly related to the temperature (Fig. lb), as was observed previously with PDPS, and can be explained in terms of thermal expansion [4]. In conclusion, some words are in order on the effect of conditons of crystallization on the crystalline structure of the samples studied. We compared the heat and temperature of melting of samples taken directly from the reaction mixture, reprecipitated samples, samples in the form of films crystallized from solution in chloroform, and also samples crystallized on cooling from a mesomorphic melt. It was established that in all cases, apart from m-T-4, which gives the optimum structure on crystallization from solution, crystallization from the mesomorphic state promotes a specific improvement in the crystalline phase of the polymers and a corresponding increase in their heats
Mesomorphic polydiarylsiloxanes
2247
and temperatures of melting. This is manifested most clearly in the melting thermograms of the homopolymers shown in Fig. 4. During syntheses PDPS is deposited from the reaction mixture in
260" I
II 7-,°C
O, J/g
II II I I I I
/ ~o "
i I
,~o
20
/I Ii
250
j
220*eJa° II
T:
I/0"
125*
150 (c)
(b) .
d FIG. 3
n
6
l
//
75
I
a
J
/50
/00
/A
200
~
I
250 T,° C
FIG. 4
FIG. 3. Temperature (a, b) and heat of melting (c, d) of polyphenyltolylsiloxanes as a function of the number of tolyl groups n in the original organocyclotrisiloxane (Table 1): (a, c) polyphenyl (m-tolyl) siloxanes; (b, d) polyphenyl (p-tolyl) siloxanes. FIG. 4. DSC thermograms of polydiarylsiloxanes at a scanning rate of 8-day/min: (a) m-T-4, (b) PDMTS, (c) PDPS. The full lines denote the original samples, and the broken lines samples crystallized from the melt.
the form of a fairly disordered crystalline powder, the diffraction pattern of which is shown in Fig. la. The heat of melting of this sample is 18.9 J/g. Melting and subsequent crystallization on cooling lead to improvement of the crystal lattice (Fig. la) and to an increase in the heat of melting to 39 J/g and displacement of the melting point (position of the melting peak maximum on the thermograms) from 220 to 60°C. The heat of melting of the PDMTS sample in the form of a film obtained from solution is 3.4 J/g, and the melting point is 120°C, whereas in crystallization from the mesophases the heat and temperature of melting increase to 26 J/g and 140°C respectively (see also the diffraction patterns in Fig. lb). The above facts are an additional example showing that the mesophase promotes crystallization, which has also been demonstrated previously in the case of polydiethylsiloxane [1] and poly-b/strifluoroethoxyphosphazene [9]. The reason for this is the closeness of structure of the mesomorphic and crystalline phases and the fair mobility of macromolecules in the mesomorphic phase, which means that ordered regions have become possible. In contrast to both homopolymers, the copolymer m-T-4 does not appreciably crystallize on cooling from the mesomorphic melt: no melting point peak is observed on the DSC thermograms of the crystalline films on repeated heating (Fig. 4), and the diffraction pattern of the sample on lowering the temperature to room temperature remains identical with that of the mesomorphic polymer above the melting point. This can evidently be explained by the difference in structure of the mesomorphic and crystalline phases of the copolymer and the difficulty of crystallization from a high viscosity mesomorphic phase.
2248
M . I . BoztN et aL
Accordingly, polyphenyltolylsiloxanes are a new example of thermotropic mesomorphic polymers containing no mesogenic groups in their structure. In spite of the irregularity of the structure of their macromolecules, the thermotropic mesophases formed by them are stable over a wide temperature range, as far as decomposition of these polymers. A further, more detail study of the crystalline and mesomorphic phases of these polymers can promote an explanation of the nature of the mesomorphic state in linear polyorganosiloxanes.
Translated by N. STANDEN REFERENCES 1. C. L. BEATTY, J. M. POCHAN, H. F. FROIZ and D. F. HINMAN, Macromolecules 8: 547, 1975. 2. V. S. PAPKOV, Ju. K. GODOVSKY, V. M. LITVINOV, V. S. SVISTUNOV and A. A. ZHDANOV, J. Polymer Sci. A-1 22: 3617, 1984. 3. Yu. K. GODOVSKII, M. M. MAKAROV, V. S. PAPKOV and N. N. KUZMIN, Vysokomol. soyed. B27: 164, 1985 (not translated in Polymer Sci. U.S.S.R.). 4. D. Ya. TSVANKIN, V. Yu. LEVIN and V. S. PAPKOV, Vysokomol. soyed. A21:2126 1979 (translated in Polymer Sci. U.S.S.R. 21: 9, 2348, 1979). 5. V. V. KORSHAK, A. A. ZHDANOV, L. M. TARTAKOVSKAYA, N. G. VASILENKO, T. M. BABCHINITSER, L. G. KAZARYAN, L. B. ITSIKSON and A. A. FILIPPOV, Vysokomol. soyed. B27: 300, 1965 (not translated in Polymer Sci. U.S.S.R.). 6. N. G. VASILENKO, L. M. TARTAKOVSKAYA, V. P. LAVRUKHIN and A. A. ZHDANOV, Vysokomol. soyed. A31: 2026, 1989 (translated in Polymer Sci. U.S.S.R. 31: 10, 2225, 1989). 7. N. G. VASILENKO, L. M. TARTAKOVSKAYA, T. M. BABCHINITSER, N. V. ERMILOVA and A. A. ZHDANOV, Vysokomol. soyed. A31: 1585, 1989 (translated in Polymer Sci. U.S.S.R. 31: 8, 1737, 1989). 8. T. M. BABCHINITSER, L. G. KAZARYAN, L. M. TARTAKOVSKAYA, N. G. VASILENKO, A. A. ZHDANOV and V. V. KORSHAK, Polymer 26: 1527, 1985. 9. V. S. PAPKOV, V. M. LITVINOV, I. I. DUBOVIK, G. L. SLONIMSKH, D. R. TUR, S. V. VINOGRADOVA and V. V. KORSHAK, Dokl. Akad. Nauk, SSSR 284: 1423, 1985.
M.I. BuzxN et al.
REFERENCES 1. M. RICHARDSON (editor), Promyshlennye Polimernye Kompozitsionnye Materialy (Industrial Composite Polymer Materials). Moscow, 1980. 2. Yu. S. LIPATOV, Fizitheskaya Khimiya Napolnennykh Polimerov (Physical Chemistry of Filled Polymers). Kiev, 1977. 3. N. A. KNUNYANTS, M. A. LYAPUNOVA, L. I. MANEVICH, V. G. OSHMYAN and A. Yu. SHAULOV, Mekhanika Kompozitnykh Mat., No. 2, 231, 1986. 4. I. V. KRAGELSKY, M. N. DOBYCHIN and V. S. KOMBALOV, Osnovy Raschetov Na Trenie i Iznos (Friction and Wear Calculation Methods). Moscow, 1977. 5. L. E. NIELSEN and T. LEWIS, J. Polymer Sci. A-2 7: 1705, 1969. 6. L. E. NIELSEN, Proc. Phys. Soc. 69: 808, 1956. 7. L. E. NIELSEN, J. Appl. Polymer Sci. 10: 97, 1966. 8. V. DOLAROVA-SVEHLOVA, J. Macromolec. Sci. Phys. 21: 234, 1982. 9. I. V. KRAGELSKY and I. E. VINOGRADOVA, Koeffitsienty Treniya (Coefficients of Friction). Moscow, 1962. 10. A. Yn. SHAULOV and M. A. LYAPUNOVA, Dokl. Akad. Nauk SSSR. 303: 1424, 1988. 11. A. Yu. SIiAULOV, M. A. LYAPUNOVA and L. S. IVANOV, Plast. Massy, No. 7, 18, 1988. 12. S. SAHU and L. J. BROUTMAN, Razrushenie i Ustalost (Fracture and Fatigue) (edited by L. Broutman). Moscow, 1978.
Polymer Science U.S.S.R, Vol. 32, No. 11, pp. 2242-2248, 1990
Printed in GreatBritain.
0032-3950/90$10.00+ .00 © 1991PergamonPresspie
MESOMORPHIC POLYDIARYLSILOXANES* M. I. BUZIN, N. V. VASILENKO, L. M. TARTAKOVSKAYA, V. P. ZHUKOV, I. I. DUBOVIK, D. YA. TSVANKIN and V. S. PAPAPKOV A. N. Nesmeyanov Institute of Hetero-organic Compounds S.S.S.R.; Institute of Synthetic Polymer Materials, Academy of Sciences of the U.S.S.R. (Received 25 October 1989)
Linear polyphenyltolylsiloxanesare studied by calorimetric and X-ray diffraction methods. It is established that these polymers, as also polyphenylsiloxane, pass, on melting, into the mesomorphic state, which is stable up to their decomposition temperature. It is observed that the mesomorphic state can promote crystallization, but can also hinder it. IT HAS been established recently that linear polyorganosiloxanes with symmetrical side substituents on the silicone a t o m show a tendency towards the formation of thermotropic mesophases. The m e s o m o r p h i c state has been observed in polydiethylsiloxane [1, 2], polydipropylsiloxane [3], and polydiphenylsiloxane [4]. The nature of the mesophases appearing in such polymers, which contain no mesogenic groups in their chemical structure, is not completely clear. In view of this it is of interest to explain the effect of the type of substituent on the silicon a t o m and disturbance of the structural regularity of the macromolecules on their ability to form mesophases. We studied *Vysokomol soyed. A32: No. 11, 2340-2345, 1990.
Mesomorphic polydiarylsiloxanes
2243
polydiethylsiloxane containing phenyl and tolyl substituents on the silicone atom from this point of view. This work deals with the general characteristics of mesomorphic and crystalline phases and phase transformations in these polymers. The polymers studied differ in the position of the methyl substituent on the phenyl group (presence of meta- or para-substituent) and in the ratio of the tolyl and phenyl groups. The polymers were obtained by a previously described method [5], i.e. by polymerization of the corresponding organocyclotrisiloxane, having different ratios of the diphenylphenyltolyl, and ditolylsiloxane units in the presence of a,to-dipotassiumoxy-poly(pheny)-(p-tolyl)siloxane. The catalyst was deactivated by introduction of trimethylchlorosilane. The polymers were separated by extraction of the monomer part with methylethylketone and subsequent precipitation of the toluene solution in ethanol. The polymers synthesized were soluble in chloroform, carbon tetrachloride, and xylene. The absence of monomer in the polymers was checked by GLC, using an internal standard, i.e. methyltriphenylsilane on a LKhM-8-MD chromatograph a I x 0.004 m column solid phase-Inerton AW-HMD, liquid phase SE30 (5%), thermostat temperature 350°C, gas flow rate 3600 ml/h. The structure of the original rings, and the notation and characteristics of the polymers studied are shown Table 1. As can be seen from the table, the polydiarylsiloxanes studied, which have different types of units, can be represented as copolymers with the units Ph2SiO, Tol(Ph)SiO and TolESiO. We note that anionic polymerization of the rings, because of the nonstereospecific character of the reactions, possible inter-chain exchange, and depolymerization, which, as shown in [6] occurs at different polymerization stages, results in the formation of a polymer with a considerable degree of randomization of the macromolecule structure. However, in spite of this all the polymers can be crystallized [7, 8]. The crystallinity and the perfection of the crystalline phase depend both on the ratio of the phenyl and tolyl groups, and on the conditions under which the samples are obtained: reprecipitation, formation of films from solution, crystallization from the melt. This problem is considered in greater detail below. TABLE1. POLYDIARYLSILOXANES Original organocyclotrisiloxane
Designation of polymer
Intrinsic viscosity of chloroform*
i---[Ph2SiO]3-q
PDPS
t--[(m-Tol)2SiO]3--I
PDMTS
1.0
r-[Ph2SiO]E-[Ph(m-Tol)SiO]--1
m-T-1
0.4
l---[PhESiO12-[(m-Tol)2SiOl-q
m-T-2
1.0
i--[PhESiO]-[(m-Tol)ESiO]z-q
m-T-4
0.6
r--[(p-Tol)2SiO]3--q
PDPTS
t--[Ph2SiO]2-[Ph(p-Tol)SiO]--1
p-T-1
0.9
t--[Ph2SiO]2-[(p-Tol)2SiOl-n
p-T-2
0.3
r--[Ph(p-Tol)SiO]3-~
p-T-3
0.7
*Concentration of solution 1%, temperature 25°C. \
The diffraction patterns of the homopolymers and copolymers with m- and p-tolyl groups are shown in Fig. 1. A special feature in the melting of all the polymers studied is their transformation after melting of the crystalline phase not into an isotropic melt, but into the mesomorphic state. X-ray diffraction shows that this transformation is characterized by the disappearance of crystalline
M . I . Buzm et al.
2244 I, relative units
(a)
I
tO
I
20
I
,i0 Z6*
tO
gO
20*
,1
,P
I
I
tO
20
I
26*
FIG. 1. Diffraction patterns of polydiarylsiioxanes:(a, c) crystallinepolymers with different contents of m-tolyl (a) and p-tolyl groups (c); (b) PDMTS. a: (1) PDPS from reaction mixture, (2) PDPS, crystallized by cooling from the mesophase, (3) m-T-l, (4) m-T-2, (5) m-T-4; b: (1) 25, (2) 110, (3) 130, (4) 160, (5) 25°C; c: (1) PDPS, (2) p-T-3 (3), (3) p-T-1. (a, b) peaks in left-hand part of diffraction pattern doubly reduced. reflections, but a sharp reflection in the region of the angles 20 = 8--8.5 ° is retained. The diffraction patterns of PDMTS in the crystalline and mesomorphic states are shown in Fig. lb. The diffraction patterns of the remaining polymers studied above the melting point are similar in form to that of mesomorphic PDMTS. On melting, the optical texture observed in polymer films in polarized light with cross and parallel nicol prisms is preserved, although in many cases the colour of the optically anisotropic domains is changed because of the change in magnitude of the birefringence. Microphotographs of a series of polymers in the crystalline and mesomorphic states are shown in Fig. 2.
Mesomorphic polydiarylsiloxanes
n
2245
in
[]
301zro L
I
Fio. 2. Microphotographs of polydiarylsiloxanes at various temperatures in polarized light: (a-d) with crossed nicol prisms; (e-h) with parallel nicol prisms: (a, b, e, d) m-T-4, (c, d, g, h) PDMTS. Temperature: (a, c, e, g) 25°C, (b, f) 90°C, (d, h) 160°C.
Comparison of the diffraction patterns of the polymers provides a basis for making a number of qualitative notes on their structure. Thus, from a comparison of the diffraction patterns of PDPS and PDMS (Fig. la and b) it can be seen that these polymers have different crystal lattices. Comparison of the diffraction patterns of the copolymers shows that the tolyl and the phenyl substituent enter into the crystals, the structure of which is close to that of homopolymer crystals. The diffraction pattern of the copolymer m-T-1 is similar to that of defective PDPS crystals, formed during polymerization (Fig. la), but differs from that of the more perfect PDPS crystals. Evidently the introduction of the bulky m-tolyl group leads to disappearance of the crystalline PDPS lattice, which is accompanied by a change in the position of the inter-chain crystal reflections (Table 2). The diffraction pattern of the copolymer m-T-4 is similar to that of the homopolymer PDMTS (Fig. la and b). This indicates that the phenyl groups, which are smaller in volume, enter into the lattice formed on packing of the m-tolyl groups. The diffraction pattern of the copolymer m-T-2 is close to that of the copolymer m-T-1 (Fig. la), although it differs from it in that it has a reflection at 20 = 21 °, which is not observed in any of the other copolymers of the series considered. The replacement of the phenyl groups by p-tolyl groups also results in disturbance of the PDPS crystal lattice (Fig. lc; Table 2). The maximum distortions are observed on introducing three p-tolyl substituent.
2246
M . I . BUZIN et al.
TABLE2. VALUESOFTHEINTERPLANEDISTANCESd INPOLYARYLSILOXANES Polymer PDPS m-T-1 m-T-4 PDMTS n-T-1
T, °C
Phase
d,/~
25 270 25 140 25 90 25 160 25 200
cystalline mesomorphic crystalline mesomorphic crystalline mesomorphic crystalline mesomorphic crystalline mesomorphic
10.2 10.3 10.4 10.5 12.1 (10.4") 10.8 12.4 (10.9") 11.2 10.6 (9.6*) 10.8
*The second reflection is shown in brackets. The crystal lattice distortion obtained on replacing the phenyl groups by tolyl groups is manifested not only in changes in the diffraction patterns, but also can be clearly followed from the change in temperature and the heat of melting of the copolymers compared with the homopolymers. These data are shown in Fig. 3. They apply to the most perfect of the crystalline specimens, the conditions of production of which differ for the different polymers studied (see below). Replacement of one phenyl group by a tolyl group results in a sharp decrease in the temperature and heat of melting of the copolymer, especially in the case of the m-tolyl group. The curves for the given parameters as a function of the tolyl group content have an extreme character, with a minimum, in the case of the heat of melting, at a ratio of the phenyl and m-tolyl groups of 2: 4, and in the case of the melting point at a ratio of 4:2. The introduction into the homopolymer of different side substituents can result not only in an increase in the defectiveness of the crystals, but also to a decrease in their size. Both these effects are evidently due to a decrease in the temperature and heat of melting of the copolymers compared with the homopolymers. The smaller values of the heat of melting of the copolymers can also be due to their smaller degree of crystallinity. Unfortunately, accurate determination of their crystallinity is difficult: there is no jump in the heat capacity in the glass formation region on the DSC thermograms, and the positions of the inter-chain mesomorphic and crystalline reflections in the region of the angles 20 = 8-8.5 ° on the diffraction patterns almost coincide. The amorphous halo indicating inter-chain distances in the amorphous regions, is probably located at the same 20 angles. A characteristic feature of all the polymers studied is preservation of the mesomorphic state after melting as far as decomposition, which occurs above 400°C. Preservation of the optically anisotropic regions observed under the polarization microscope, and also preservation of the sharp mesomorphic reflection on the diffraction patterns is an indication of this. Moreover, the intensity of the mesomorphic reflection on the diffraction patterns is directly related to the temperature (Fig. lb), as was observed previously with PDPS, and can be explained in terms of thermal expansion [4]. In conclusion, some words are in order on the effect of conditons of crystallization on the crystalline structure of the samples studied. We compared the heat and temperature of melting of samples taken directly from the reaction mixture, reprecipitated samples, samples in the form of films crystallized from solution in chloroform, and also samples crystallized on cooling from a mesomorphic melt. It was established that in all cases, apart from m-T-4, which gives the optimum structure on crystallization from solution, crystallization from the mesomorphic state promotes a specific improvement in the crystalline phase of the polymers and a corresponding increase in their heats
Mesomorphic polydiarylsiloxanes
2247
and temperatures of melting. This is manifested most clearly in the melting thermograms of the homopolymers shown in Fig. 4. During syntheses PDPS is deposited from the reaction mixture in
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FIG. 3. Temperature (a, b) and heat of melting (c, d) of polyphenyltolylsiloxanes as a function of the number of tolyl groups n in the original organocyclotrisiloxane (Table 1): (a, c) polyphenyl (m-tolyl) siloxanes; (b, d) polyphenyl (p-tolyl) siloxanes. FIG. 4. DSC thermograms of polydiarylsiloxanes at a scanning rate of 8-day/min: (a) m-T-4, (b) PDMTS, (c) PDPS. The full lines denote the original samples, and the broken lines samples crystallized from the melt.
the form of a fairly disordered crystalline powder, the diffraction pattern of which is shown in Fig. la. The heat of melting of this sample is 18.9 J/g. Melting and subsequent crystallization on cooling lead to improvement of the crystal lattice (Fig. la) and to an increase in the heat of melting to 39 J/g and displacement of the melting point (position of the melting peak maximum on the thermograms) from 220 to 60°C. The heat of melting of the PDMTS sample in the form of a film obtained from solution is 3.4 J/g, and the melting point is 120°C, whereas in crystallization from the mesophases the heat and temperature of melting increase to 26 J/g and 140°C respectively (see also the diffraction patterns in Fig. lb). The above facts are an additional example showing that the mesophase promotes crystallization, which has also been demonstrated previously in the case of polydiethylsiloxane [1] and poly-b/strifluoroethoxyphosphazene [9]. The reason for this is the closeness of structure of the mesomorphic and crystalline phases and the fair mobility of macromolecules in the mesomorphic phase, which means that ordered regions have become possible. In contrast to both homopolymers, the copolymer m-T-4 does not appreciably crystallize on cooling from the mesomorphic melt: no melting point peak is observed on the DSC thermograms of the crystalline films on repeated heating (Fig. 4), and the diffraction pattern of the sample on lowering the temperature to room temperature remains identical with that of the mesomorphic polymer above the melting point. This can evidently be explained by the difference in structure of the mesomorphic and crystalline phases of the copolymer and the difficulty of crystallization from a high viscosity mesomorphic phase.
2248
M . I . BoztN et aL
Accordingly, polyphenyltolylsiloxanes are a new example of thermotropic mesomorphic polymers containing no mesogenic groups in their structure. In spite of the irregularity of the structure of their macromolecules, the thermotropic mesophases formed by them are stable over a wide temperature range, as far as decomposition of these polymers. A further, more detail study of the crystalline and mesomorphic phases of these polymers can promote an explanation of the nature of the mesomorphic state in linear polyorganosiloxanes.
Translated by N. STANDEN REFERENCES 1. C. L. BEATTY, J. M. POCHAN, H. F. FROIZ and D. F. HINMAN, Macromolecules 8: 547, 1975. 2. V. S. PAPKOV, Ju. K. GODOVSKY, V. M. LITVINOV, V. S. SVISTUNOV and A. A. ZHDANOV, J. Polymer Sci. A-1 22: 3617, 1984. 3. Yu. K. GODOVSKII, M. M. MAKAROV, V. S. PAPKOV and N. N. KUZMIN, Vysokomol. soyed. B27: 164, 1985 (not translated in Polymer Sci. U.S.S.R.). 4. D. Ya. TSVANKIN, V. Yu. LEVIN and V. S. PAPKOV, Vysokomol. soyed. A21:2126 1979 (translated in Polymer Sci. U.S.S.R. 21: 9, 2348, 1979). 5. V. V. KORSHAK, A. A. ZHDANOV, L. M. TARTAKOVSKAYA, N. G. VASILENKO, T. M. BABCHINITSER, L. G. KAZARYAN, L. B. ITSIKSON and A. A. FILIPPOV, Vysokomol. soyed. B27: 300, 1965 (not translated in Polymer Sci. U.S.S.R.). 6. N. G. VASILENKO, L. M. TARTAKOVSKAYA, V. P. LAVRUKHIN and A. A. ZHDANOV, Vysokomol. soyed. A31: 2026, 1989 (translated in Polymer Sci. U.S.S.R. 31: 10, 2225, 1989). 7. N. G. VASILENKO, L. M. TARTAKOVSKAYA, T. M. BABCHINITSER, N. V. ERMILOVA and A. A. ZHDANOV, Vysokomol. soyed. A31: 1585, 1989 (translated in Polymer Sci. U.S.S.R. 31: 8, 1737, 1989). 8. T. M. BABCHINITSER, L. G. KAZARYAN, L. M. TARTAKOVSKAYA, N. G. VASILENKO, A. A. ZHDANOV and V. V. KORSHAK, Polymer 26: 1527, 1985. 9. V. S. PAPKOV, V. M. LITVINOV, I. I. DUBOVIK, G. L. SLONIMSKH, D. R. TUR, S. V. VINOGRADOVA and V. V. KORSHAK, Dokl. Akad. Nauk, SSSR 284: 1423, 1985.