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Mesophase transitions in liquid crystal polymers
REACTIVE & FUNCTIONAL POLYMERS ELSEVIFR
Reactive & Functional Polymers 33 (1997) 225-231
Mesophase transitions in liquid crystal polymers Leszek Makaruk *, Jolanta Furman Warsaw University of Technology, Depart?nent of Chemistry ul. Noakowskiego 3, 00-664 Warsaw, Poland
Received 21 July 1996; revised version received 25 November 1996; accepted 20 December 1996
Abstract Liquid crystalline main-chain polysebacates containing mesogenic units with odd member bridging groups, as well as mesogenic units elongated by introduction into bridging groups cyclohexanone or ferrocene units, were synthesized. Bisphenols obtained from p-hydroxybenzaldehyde (or its derivatives) and various ketones by aldol condensation were used as a source of mesogenic units. The effect of the length and the structure of mesogenic units (MU) on mesophase transition temperatures was investigated. It is shown that polymers containing MU with an odd member of bridging groups exhibit Iiquid crystalline properties. Extending a mesogenic unit by the introduction of ahcyclic or ferrocenic units within the bridging group increases the mesophase transition temperatures much less than does the introduction of a third aromatic ring. Keywords:
Liquid crystal polyesters; Odd-member bridging group in mesogenic units
1. Introduction The existence of liquid crystalline arrangement of macromolecules is strictly connected with their chemical structure. In the history of development of polymers, liquid crystalline polymers (LCP) appeared relatively late on. In 1956 P.J. Flory published two theoretical works, which showed that the rigid rodlike macromolecules and semi-flexible chain molecules may form liquid-crystalline systems in solutions or in undiluted polymers [1,2]. The formation of mesophase in defined thermodynamical conditions issued from purely geometrical requirements. At this time liquid crystal polymers were unknown. Flory’s theory was soon confirmed in the investigation of synthetic polypeptide, poly(y-ben* Corresponding author.
zyl-L-glutamate), which in some solvents formed a rigid helix stabilized by hydrogen bonds [31. This was an exception. Other polymers with rigid rod-like chains did not melt without thermal decomposition and no solvent for these stiff polymers was known. The main problem was, how to reduce the melting temperature of rigid polymers below their thermal decomposition temperatures. This problem was satisfactorily solved 20 years after Flory’s presentation of his theory and it was the beginning of the major development of LCP. There are four basic methods of decreasing the melting temperature of rigid polymers used in synthesis of stiff macromolecules. Those are well described in original works and numerous monographs [4-71. All the methods introduce some disorder in the structures and symmetry of polymer chains. The first one consists of the introduction of
1381-5148/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII S1381-5148(97)00041-2
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226
& Functional Polymers 33 (1997) 225-231
kinks and bends into the rigid straight chain. For example, if the regular chain is built from the aromatic rings linked in the para position, distortions are introduced by linking some of the rings in the meta position. The second method is copolymerization (or copolycondensation) of monomers of various sizes and shapes. The third method is lateral substitution of aromatic rings building stiff chains. And the fourth method, the most commonly used, is building of macromolecular chains from rigid segments linked by flexible spacers. The rigid segments - mesogenic units (MU) - introduce liquid crystalline properties to the polymers . MUs are usually rod-like, sometimes disclike, or another shape. The most commonly used MUs in LCP are rod-like structures built from two aromatic rings joined either directly in para positions, or most frequently by the bridging unit -M-:
-N-N-
-N=N-,
T
azomethine -CH=N-, 1,2-ethylenyl %H=CH-, acethylene -C=C[4]. Some authors used four-member azine groups: -_C’N-N’Cazoxy
-CH-N-N=CHor &I $H [8]. Very rarely, other even-member bridging groups were used. The odd-member bridging groups were not used in LCP. In our earlier work from the year 1982 we used, with quite good results, a single-member bridging group, namely the carbonyl unit
‘C’ 4
[%lOl. In the present work, three- or five-member bridging units are used, as well as the bridging units elongated by introduction of cyclohexanone or ferrocene units. The effects of the length and the structure of MUs on mesophase transition temperatures were investigated. 2. Experimental
The bridging units used in LCP are usually two member groups, such as: car-c-oboxy1 ; , amide -5-f;‘, azo 0 H
1) Ho
C-H+
H&--C
i
-o-
:: C-t3H
HC-!
As the source of rigid MUs we used bisphenols obtained from p-hydroxybenzaldehyde and various ketones by the well known aldol condensation according to Scheme 1. The aldol condensation is also used for introducing cyclohexanone ring into bridging group (Scheme 2).
’ ’ -
HO-QCH=CH-!eOII
OH -
1 II,0
OH +W,O
-%-HO
:: Scheme
1.
Scheme 2.
L. Makaruk, J. Furman/Reactive
& Functional Polymers 33 (1997) 225-231
4-Hydroxybenzaldehyde (or its derivatives) and the appropriate ketone in stoichiometric quantities were dissolved in anhydrous ethanol saturated with gaseous hydrochloride and stirred at a temperature of 0-5°C during 5 h. After this time the reaction mixture was kept for 24 h in a refrigerator. The precipitated crude bisphenol was filtered, washed with cold water to neutrality and later recrystallized from ethanol or ethanol/water mixtures. The chemical structures of the synthesized bisphenols were confirmed by IR, NMR and elemental analysis. In a similar way l,l’-di(formyl)ferrocene and 4-hydroxyacetophenone were condensed [ 111. This reaction, however, occurred more slowly and with lower yield. The monomeric, pure bisphenols have no liquid crystalline properties, in spite of the fact that some low molecular liquid crystals with chalcone bridging groups are known [ 121. The bisphenol with a single-member carbonyl bridging group, 4,4’-dihydroxybenzophenone, was synthesized using anisoyl chloride and anisole according to Barclay’s method described in ‘Condensation Monomers’ [ 131. For comparison, 1,4-bis(p-hydroxybenzoyl)benzene containing three aromatic rings and two single-member carbonyl bridging groups was synthesized from terephthaloyl chloride and anisole by the method described in detail in our earlier work [9]. Polyesters were obtained from the appropriate bisphenol and aliphatic dicarboxylic acid dichloride by interfacial polycondensation as described earlier [9]. Molecular weights of synthesized polyesters were tested by means of a Perkin-Elmer vapour phase osmometer. All obtained polyesters are oligomers containing about 6-8 monomeric units. The mesophase transition temperatures were determined by means DSC calorimeter ‘Unipan’ system 605 M, by observations under a microscope in polarized light and by means of a homemade thermooptical analyzer.
227
3. Results The mesophase transition temperatures depend upon the length and the stiffness of MU, the length of flexible spacers, and upon the intermolecular interactions. Since the last factor is difficult to determine strictly, our comparison is only qualitative. Chemical structures of investigated polyesters, the length of MU with two oxygen atoms on both ends (calculated by the ‘HyperChemTM4.5’ program [14]), and the temperatures of transitions from the solid-state to liquid crystal Tm, and from the mesophase into isotropic liquid I;: are shown in Table 1. The mesophase transition temperatures for the polyester 1 are taken from the work [ 151 for comparison. The shortest MU is dioxobiphenyl unit in polyester 1. The transition temperatures T, and c are relatively high. Introduction of singlemember carbonyl group as a bridging unit decreases T, and Ti in a significant way - polyester 2. This unit was used by some authors [ 16,171 for lowering T, of rigid LCP as a ‘swivel unit’, like units containing single member oxygen or sulfur bridges. This is a misunderstanding, because the unit containing carbonyl bridging group is stiff and may be a self-dependent MU contrary to the other ‘swivel units’. This MU, after being introduced into a rigid chain of LCP, lowered T, rather as a ‘rigid bend’ (the angle between the axes of both aromatic rings in the paru position is 139“) or as a ‘unit of another shape’. The addition of the third aromatic ring linked to the MU by the second carbonyl group causes an increase of both characteristic temperatures, but not to the value observed for dioxobiphenyl unit [91.
Introduction of three-member and five-member bridging units causes further decrease of temperatures of mesophase transitions, despite the significant increase of length of MU as compared to polyester 1. The introduction of a cyclohexanonic ring into the bridging group slightly increases T, and z
228
L. Makaruk, J. Funmn/Reactive
& Functionul Polymers 33 (1997) 225-231
Table 1 Mesophase transition temperatures
Mesophase transition
Y=
R
-c-w-g,-
of polyester 6, comparing to the polyester 5, but not as much as does introduction of an aromatic ring in polyester 3. It is interesting to introduce a ferrocene unit into the bridging group [ 111. We have obtained a very extended (two times comparing to dioxobiphenyl unit) and bent MU with four aromatic
fi
rings. In this case also the mesophase transition temperatures are much lower as compared to the polyester 1. Interesting results are also obtained for the case of polyesters containing a cyclohexanonic ring - Table 2. Usually bulky substituents in the bridging unit cause disappearance of liq-
L. Makaruk, J. Furman/Reactive
& Functional Polymers 33 (1997) 225-231
229
Table 2 Mesophase transition temperatures
uid crystalline properties of a polymer. We obtamed derivatives with methyl and tert-butyl substituents, but these substituents do not cause disappearance of the mesophase [ 161. The ethoxy derivative of parahydroxybenzaldehyde is readily available as ethylvanilin. In
Table 2 it is shown, that the lateral substituents lower Tm, which could be expected, but, in addition, they cause appearance of polymesomorphism. In this case we observe on the DSC scan three endothermic peaks. Comparing visual observations in the polarized light micro-
L. Makaruk,J. Furman/Reactive & FunctionalPolymers33 (1997) 225-231
230
I
0
&.
O-W&+,
e” 0
OCH, Scheme 3.
scope with photographs in the book ‘Textures of Liquid Crystals’ [17], the smectic and nematic mesophase are recognised. In the case of ferrocene containing MUs with lateral substituents only one mesophase is observed [ 111. All the methods of decreasing the melting temperature of rigid polymers introduce disorder in the chains of LCP. Sometimes the disorder is so large, that the polymer cannot crystallize. During cooling it goes into glassy state with frozen liquid crystalline structure. During heating polymer goes over Ts into liquid crystalline rubber-like state. At higher temperatures there is viscous polymer liquid crystal, which undergoes transition into the viscous isotropic liquid. Consequently we must take into account, that in these cases the liquid crystalline behaviour is strongly connected to the relaxation phenomena typical for polymers. In addition to LCP containing MUs in the main chain, there are comb-like polymers with MUs in side chains. Synthesis of this kind of polymer is more complicated [7], but the MUs are more mobile, because there are linked only on one end. MUs containing odd member bridging groups also may be used in synthesis of comb-like polymers, for example, as in Scheme 3 [20] with mesophase transition temperatures: Tmr 64“C, Tm27o”c, T 110°C.
we may influence the thermal properties of LCP as well as by other methods mentioned above. (2) Polymers containing MU with odd (single-, three- or five-) member bridging groups exhibit liquid crystalline properties. (3) Extending the MU by introduction of alicyclic or ferrocenic unit within the bridging group increases the mesophase transition temperatures much less than does the introduction of further aromatic ring. 5. List of symbols LCP -MMU Tg Z Tm
Tml Gl2
Liquid crystal polymer Bridging group in mesogenic unit Mesogenic unit Glass-transition temperature Temperature of the transition from mesophase to isotropic liquid Temperature of the transition from solid state to liquid crystal state Temperature of the transition from solid state to smectic mesophase Temperature of the transition from smectic to nematic mesophase
Acknowledgements This work was supported by Polish Committee of Scientific Research (KBN), grant No. 7s 20505403.
4. Conclusions References (1) The chemical structure of the bridging group in MU influences the temperatures of the mesophase transitions of LCP in a significant way. By a varying the length and the structure of MU
[ 11P.J. Flory, Proc. Royal Sot. London, A234 (1956) 60. [2] P.J. Flory, Proc. Royal Sot. London, A234 (1956) 73. [3] C., Robinson, I.C. Ward and P.B. Beevers, Discuss. Faraday Sot., 25 (1958) 29.
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& Functional Polymers 33 (1997) 225-231
[4] A. Blumstein (Ed.), Liquid Crystalline Order in Polymers.
[5] [6]
[7]
[8] [9]
[lo]
[ll] [12]
Academic Press, New York, NY, 1978. A. Ciferri, W., Krigbaum and l? Meyer, Polymer Liquid Crystals. Academic Press, New York, NY, 1982. A.A. Collyer (Ed.), Liquid Crystal Polymers: From Structures to Applications. Elsevier Applied Science, LondonNew York, 1992. J. Franek, Z.J. Jedliiiski and J. Majnusz, in: H.R. Krlcheldorf (Ed.), Handbook of Polymer Synthesis, Part B. Marcel Dekker, New York, NY, 1992, pp. 1281-1351 (Chapter 20). A. Roviello and A. Sirigu, J. Polym. Sci., Lett., 15 (1979) 61. L. Makaruk and H. Polaiiska, in: A.C. Griffin and J.F. Johnson @is.), Liquid Crystals and Ordered Fluids, Vol. 4. Plenum Press, New York, NY, 1984, p. 155. L. Makaruk and H. Polahska, in: B. Sedlacek (Ed.), Morphology of Polymers. Valter de Gruyter, Berlin, 1986, p. 515. J. Furman and L. Makaruk, Polimery, 41(7-g) (1996) 424. H. Kelker and R. Hatz, Handbook of Liquid Crystals.
231
Verlag Chemie, Weinheim, Deerlield Beach, Florida, Basel, 1980, p. 94. [13] J.K. Stille and T.W. Campbell (Eds.), Condensation Monomers. Wiley, New York, NY, 1972. [ 141 Hype&hem. Release 4.5 for Windows, Molecular Modeling System, Serial No. 510-10004180, Hypercube, Inc. and Autodesk, Inc. [15] A. Blumstin, K.N. Sivaramalaishnan, R.B. Blumstein and S.B. Claugh, Polymer, 23(l) (1982) 47. [16] G.W. Calundann, M. Jaffe and A. Robert, in: Welch Conferences in Chemical Research, Proc. Synth. Polymers, Houston, Texas, November 1982, p. 247. [17] W.A. MacDonald, in: A.A. Collyer (Ed.), Liquid Crystal Polymers: From Structures to Applications. Elsevier Applied Science, London, 1992, p. 414. [18] J. Furman and L. Makaruk, Proc. SPIE, 2372 (1995) 275. [19] D. Demus and L. Richter, Textures of Liquid Crystals. VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig, 1980. [20] L. Makaruk and E. G6recka, unpublished data.
Reactive & Functional Polymers 33 (1997) 225-231
Mesophase transitions in liquid crystal polymers Leszek Makaruk *, Jolanta Furman Warsaw University of Technology, Depart?nent of Chemistry ul. Noakowskiego 3, 00-664 Warsaw, Poland
Received 21 July 1996; revised version received 25 November 1996; accepted 20 December 1996
Abstract Liquid crystalline main-chain polysebacates containing mesogenic units with odd member bridging groups, as well as mesogenic units elongated by introduction into bridging groups cyclohexanone or ferrocene units, were synthesized. Bisphenols obtained from p-hydroxybenzaldehyde (or its derivatives) and various ketones by aldol condensation were used as a source of mesogenic units. The effect of the length and the structure of mesogenic units (MU) on mesophase transition temperatures was investigated. It is shown that polymers containing MU with an odd member of bridging groups exhibit Iiquid crystalline properties. Extending a mesogenic unit by the introduction of ahcyclic or ferrocenic units within the bridging group increases the mesophase transition temperatures much less than does the introduction of a third aromatic ring. Keywords:
Liquid crystal polyesters; Odd-member bridging group in mesogenic units
1. Introduction The existence of liquid crystalline arrangement of macromolecules is strictly connected with their chemical structure. In the history of development of polymers, liquid crystalline polymers (LCP) appeared relatively late on. In 1956 P.J. Flory published two theoretical works, which showed that the rigid rodlike macromolecules and semi-flexible chain molecules may form liquid-crystalline systems in solutions or in undiluted polymers [1,2]. The formation of mesophase in defined thermodynamical conditions issued from purely geometrical requirements. At this time liquid crystal polymers were unknown. Flory’s theory was soon confirmed in the investigation of synthetic polypeptide, poly(y-ben* Corresponding author.
zyl-L-glutamate), which in some solvents formed a rigid helix stabilized by hydrogen bonds [31. This was an exception. Other polymers with rigid rod-like chains did not melt without thermal decomposition and no solvent for these stiff polymers was known. The main problem was, how to reduce the melting temperature of rigid polymers below their thermal decomposition temperatures. This problem was satisfactorily solved 20 years after Flory’s presentation of his theory and it was the beginning of the major development of LCP. There are four basic methods of decreasing the melting temperature of rigid polymers used in synthesis of stiff macromolecules. Those are well described in original works and numerous monographs [4-71. All the methods introduce some disorder in the structures and symmetry of polymer chains. The first one consists of the introduction of
1381-5148/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII S1381-5148(97)00041-2
L. Makaruk. J. Furman/Reactive
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& Functional Polymers 33 (1997) 225-231
kinks and bends into the rigid straight chain. For example, if the regular chain is built from the aromatic rings linked in the para position, distortions are introduced by linking some of the rings in the meta position. The second method is copolymerization (or copolycondensation) of monomers of various sizes and shapes. The third method is lateral substitution of aromatic rings building stiff chains. And the fourth method, the most commonly used, is building of macromolecular chains from rigid segments linked by flexible spacers. The rigid segments - mesogenic units (MU) - introduce liquid crystalline properties to the polymers . MUs are usually rod-like, sometimes disclike, or another shape. The most commonly used MUs in LCP are rod-like structures built from two aromatic rings joined either directly in para positions, or most frequently by the bridging unit -M-:
-N-N-
-N=N-,
T
azomethine -CH=N-, 1,2-ethylenyl %H=CH-, acethylene -C=C[4]. Some authors used four-member azine groups: -_C’N-N’Cazoxy
-CH-N-N=CHor &I $H [8]. Very rarely, other even-member bridging groups were used. The odd-member bridging groups were not used in LCP. In our earlier work from the year 1982 we used, with quite good results, a single-member bridging group, namely the carbonyl unit
‘C’ 4
[%lOl. In the present work, three- or five-member bridging units are used, as well as the bridging units elongated by introduction of cyclohexanone or ferrocene units. The effects of the length and the structure of MUs on mesophase transition temperatures were investigated. 2. Experimental
The bridging units used in LCP are usually two member groups, such as: car-c-oboxy1 ; , amide -5-f;‘, azo 0 H
1) Ho
C-H+
H&--C
i
-o-
:: C-t3H
HC-!
As the source of rigid MUs we used bisphenols obtained from p-hydroxybenzaldehyde and various ketones by the well known aldol condensation according to Scheme 1. The aldol condensation is also used for introducing cyclohexanone ring into bridging group (Scheme 2).
’ ’ -
HO-QCH=CH-!eOII
OH -
1 II,0
OH +W,O
-%-HO
:: Scheme
1.
Scheme 2.
L. Makaruk, J. Furman/Reactive
& Functional Polymers 33 (1997) 225-231
4-Hydroxybenzaldehyde (or its derivatives) and the appropriate ketone in stoichiometric quantities were dissolved in anhydrous ethanol saturated with gaseous hydrochloride and stirred at a temperature of 0-5°C during 5 h. After this time the reaction mixture was kept for 24 h in a refrigerator. The precipitated crude bisphenol was filtered, washed with cold water to neutrality and later recrystallized from ethanol or ethanol/water mixtures. The chemical structures of the synthesized bisphenols were confirmed by IR, NMR and elemental analysis. In a similar way l,l’-di(formyl)ferrocene and 4-hydroxyacetophenone were condensed [ 111. This reaction, however, occurred more slowly and with lower yield. The monomeric, pure bisphenols have no liquid crystalline properties, in spite of the fact that some low molecular liquid crystals with chalcone bridging groups are known [ 121. The bisphenol with a single-member carbonyl bridging group, 4,4’-dihydroxybenzophenone, was synthesized using anisoyl chloride and anisole according to Barclay’s method described in ‘Condensation Monomers’ [ 131. For comparison, 1,4-bis(p-hydroxybenzoyl)benzene containing three aromatic rings and two single-member carbonyl bridging groups was synthesized from terephthaloyl chloride and anisole by the method described in detail in our earlier work [9]. Polyesters were obtained from the appropriate bisphenol and aliphatic dicarboxylic acid dichloride by interfacial polycondensation as described earlier [9]. Molecular weights of synthesized polyesters were tested by means of a Perkin-Elmer vapour phase osmometer. All obtained polyesters are oligomers containing about 6-8 monomeric units. The mesophase transition temperatures were determined by means DSC calorimeter ‘Unipan’ system 605 M, by observations under a microscope in polarized light and by means of a homemade thermooptical analyzer.
227
3. Results The mesophase transition temperatures depend upon the length and the stiffness of MU, the length of flexible spacers, and upon the intermolecular interactions. Since the last factor is difficult to determine strictly, our comparison is only qualitative. Chemical structures of investigated polyesters, the length of MU with two oxygen atoms on both ends (calculated by the ‘HyperChemTM4.5’ program [14]), and the temperatures of transitions from the solid-state to liquid crystal Tm, and from the mesophase into isotropic liquid I;: are shown in Table 1. The mesophase transition temperatures for the polyester 1 are taken from the work [ 151 for comparison. The shortest MU is dioxobiphenyl unit in polyester 1. The transition temperatures T, and c are relatively high. Introduction of singlemember carbonyl group as a bridging unit decreases T, and Ti in a significant way - polyester 2. This unit was used by some authors [ 16,171 for lowering T, of rigid LCP as a ‘swivel unit’, like units containing single member oxygen or sulfur bridges. This is a misunderstanding, because the unit containing carbonyl bridging group is stiff and may be a self-dependent MU contrary to the other ‘swivel units’. This MU, after being introduced into a rigid chain of LCP, lowered T, rather as a ‘rigid bend’ (the angle between the axes of both aromatic rings in the paru position is 139“) or as a ‘unit of another shape’. The addition of the third aromatic ring linked to the MU by the second carbonyl group causes an increase of both characteristic temperatures, but not to the value observed for dioxobiphenyl unit [91.
Introduction of three-member and five-member bridging units causes further decrease of temperatures of mesophase transitions, despite the significant increase of length of MU as compared to polyester 1. The introduction of a cyclohexanonic ring into the bridging group slightly increases T, and z
228
L. Makaruk, J. Funmn/Reactive
& Functionul Polymers 33 (1997) 225-231
Table 1 Mesophase transition temperatures
Mesophase transition
Y=
R
-c-w-g,-
of polyester 6, comparing to the polyester 5, but not as much as does introduction of an aromatic ring in polyester 3. It is interesting to introduce a ferrocene unit into the bridging group [ 111. We have obtained a very extended (two times comparing to dioxobiphenyl unit) and bent MU with four aromatic
fi
rings. In this case also the mesophase transition temperatures are much lower as compared to the polyester 1. Interesting results are also obtained for the case of polyesters containing a cyclohexanonic ring - Table 2. Usually bulky substituents in the bridging unit cause disappearance of liq-
L. Makaruk, J. Furman/Reactive
& Functional Polymers 33 (1997) 225-231
229
Table 2 Mesophase transition temperatures
uid crystalline properties of a polymer. We obtamed derivatives with methyl and tert-butyl substituents, but these substituents do not cause disappearance of the mesophase [ 161. The ethoxy derivative of parahydroxybenzaldehyde is readily available as ethylvanilin. In
Table 2 it is shown, that the lateral substituents lower Tm, which could be expected, but, in addition, they cause appearance of polymesomorphism. In this case we observe on the DSC scan three endothermic peaks. Comparing visual observations in the polarized light micro-
L. Makaruk,J. Furman/Reactive & FunctionalPolymers33 (1997) 225-231
230
I
0
&.
O-W&+,
e” 0
OCH, Scheme 3.
scope with photographs in the book ‘Textures of Liquid Crystals’ [17], the smectic and nematic mesophase are recognised. In the case of ferrocene containing MUs with lateral substituents only one mesophase is observed [ 111. All the methods of decreasing the melting temperature of rigid polymers introduce disorder in the chains of LCP. Sometimes the disorder is so large, that the polymer cannot crystallize. During cooling it goes into glassy state with frozen liquid crystalline structure. During heating polymer goes over Ts into liquid crystalline rubber-like state. At higher temperatures there is viscous polymer liquid crystal, which undergoes transition into the viscous isotropic liquid. Consequently we must take into account, that in these cases the liquid crystalline behaviour is strongly connected to the relaxation phenomena typical for polymers. In addition to LCP containing MUs in the main chain, there are comb-like polymers with MUs in side chains. Synthesis of this kind of polymer is more complicated [7], but the MUs are more mobile, because there are linked only on one end. MUs containing odd member bridging groups also may be used in synthesis of comb-like polymers, for example, as in Scheme 3 [20] with mesophase transition temperatures: Tmr 64“C, Tm27o”c, T 110°C.
we may influence the thermal properties of LCP as well as by other methods mentioned above. (2) Polymers containing MU with odd (single-, three- or five-) member bridging groups exhibit liquid crystalline properties. (3) Extending the MU by introduction of alicyclic or ferrocenic unit within the bridging group increases the mesophase transition temperatures much less than does the introduction of further aromatic ring. 5. List of symbols LCP -MMU Tg Z Tm
Tml Gl2
Liquid crystal polymer Bridging group in mesogenic unit Mesogenic unit Glass-transition temperature Temperature of the transition from mesophase to isotropic liquid Temperature of the transition from solid state to liquid crystal state Temperature of the transition from solid state to smectic mesophase Temperature of the transition from smectic to nematic mesophase
Acknowledgements This work was supported by Polish Committee of Scientific Research (KBN), grant No. 7s 20505403.
4. Conclusions References (1) The chemical structure of the bridging group in MU influences the temperatures of the mesophase transitions of LCP in a significant way. By a varying the length and the structure of MU
[ 11P.J. Flory, Proc. Royal Sot. London, A234 (1956) 60. [2] P.J. Flory, Proc. Royal Sot. London, A234 (1956) 73. [3] C., Robinson, I.C. Ward and P.B. Beevers, Discuss. Faraday Sot., 25 (1958) 29.
L. Makaruk, J. Furman/Reactive
& Functional Polymers 33 (1997) 225-231
[4] A. Blumstein (Ed.), Liquid Crystalline Order in Polymers.
[5] [6]
[7]
[8] [9]
[lo]
[ll] [12]
Academic Press, New York, NY, 1978. A. Ciferri, W., Krigbaum and l? Meyer, Polymer Liquid Crystals. Academic Press, New York, NY, 1982. A.A. Collyer (Ed.), Liquid Crystal Polymers: From Structures to Applications. Elsevier Applied Science, LondonNew York, 1992. J. Franek, Z.J. Jedliiiski and J. Majnusz, in: H.R. Krlcheldorf (Ed.), Handbook of Polymer Synthesis, Part B. Marcel Dekker, New York, NY, 1992, pp. 1281-1351 (Chapter 20). A. Roviello and A. Sirigu, J. Polym. Sci., Lett., 15 (1979) 61. L. Makaruk and H. Polaiiska, in: A.C. Griffin and J.F. Johnson @is.), Liquid Crystals and Ordered Fluids, Vol. 4. Plenum Press, New York, NY, 1984, p. 155. L. Makaruk and H. Polahska, in: B. Sedlacek (Ed.), Morphology of Polymers. Valter de Gruyter, Berlin, 1986, p. 515. J. Furman and L. Makaruk, Polimery, 41(7-g) (1996) 424. H. Kelker and R. Hatz, Handbook of Liquid Crystals.
231
Verlag Chemie, Weinheim, Deerlield Beach, Florida, Basel, 1980, p. 94. [13] J.K. Stille and T.W. Campbell (Eds.), Condensation Monomers. Wiley, New York, NY, 1972. [ 141 Hype&hem. Release 4.5 for Windows, Molecular Modeling System, Serial No. 510-10004180, Hypercube, Inc. and Autodesk, Inc. [15] A. Blumstin, K.N. Sivaramalaishnan, R.B. Blumstein and S.B. Claugh, Polymer, 23(l) (1982) 47. [16] G.W. Calundann, M. Jaffe and A. Robert, in: Welch Conferences in Chemical Research, Proc. Synth. Polymers, Houston, Texas, November 1982, p. 247. [17] W.A. MacDonald, in: A.A. Collyer (Ed.), Liquid Crystal Polymers: From Structures to Applications. Elsevier Applied Science, London, 1992, p. 414. [18] J. Furman and L. Makaruk, Proc. SPIE, 2372 (1995) 275. [19] D. Demus and L. Richter, Textures of Liquid Crystals. VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig, 1980. [20] L. Makaruk and E. G6recka, unpublished data.