Liquid crystalline polyesters containing camphoric acid fragments

Liquid crystalline polyesters containing camphoric acid fragments

1619

diffusant molecule exceeds 8, the prepolymer is in contact not so with individual molecules of the diffusant but rather with their bulky aggregates. Individual molecules then diffuse towards the axis at a rate governed by the decomposition of the associates. Thus, to solve problems in the production of materials exhibiting a permanent refractive index gradient, one must consider the compatibility of the matrix and the diffusant, the values of coefficients characterizing the diffusion of individual components in the matrix and the possibility of association of diffusant molecules, which can lead to a shar change in the character of diffusion even when the number of repeat units in a homologous series of monomeric diffusants rises gradually. Translated by M. KuntN REFERENCES 1. YASUJI OHTSUKA and MOTOAKI YOSHIDA, U.S. Pat. 3955015 2. A. L. MIKAELYAN, Optika i spektroskopia 44: 370, 1978 3. L. D. BUDOVSKAYA, V. N. IVANOVA, G. O. KARAPETYAN, V. I. KOSYAKOV, L. Yu. TIKHONOVA and A. Sh. TUKHVATULIN, Zh. priki, khimii, 8, 1730, 1984 4. Entsiklopedia polimerov (Polymer Encyclopaedia). Vol. 1, p. 35, Moscow, 1972 5. Ye. N. ROSTOVSKII and L. D. RUBINOVICH, Karbotsepnye vysokomolekulyarnye soyedi. neniya (Carbon-Chain Macromolecular Compounds). p. 140, 1983 6. N. B. GALIMOV, V. I. KOSYAKOV, R. M. MINKOVA, L K. MOSEVICH, A. N. R A M A Z A . NOV, L. Yu. TIKHONOVA, A. Sh. TUKHVATULIN and M. L. SHEVCHENKO, Zh. prikl. khimii 54: 1552, 1981 7. T. P. STEPANOVA, L. L. BURSHTEIN, L. D. BUDOVSKAYA, Yu. G. BAKLAGINA, V. N. IVANOVA, N. A. NIKONOROVA and N. I. TKACHEVA, Zh. fiz. khimii, 9, 1949, 1984 8. V. M. OBRAZTSOVA and A. A. KRUSTALEVA, Zh. fiz. khimii, 4, 812, 1973

Polymer Science U.S.S.R. Vol. 30, No. 7, pp. 1619-1625, 1988 Printed in Poland

0032-3950]88$10.00+.00 plc

© 1989 Pergamon Press

LIQUID CRYSTALLINE POLYESTERS CONTAINING CAMPHORIC ACID FRAGMENTS* V. V. ZuYEV, I. G. DENISOV and S. S. SKOROKHODOV Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences (Received 2 March 1987) The synthesis of a number of liquid crystalline polyesters containing camphoric acid fragments is described, and conclusions are reached concerning the effect of composition on the mesomorphic properties of the generated polymers. The presence of a chiral centre in * Vysokomol. soyed. A30: No. 7, 1534-1538, 1988.

1620

V. V. Z L r r ~ et al.

the camphor ring made possible the preparation of polymers with a cholesteric mesophase. By measurements of circular dichroism it could be shown that the conformation of the polymer chain in solution is determined both by the parameters of the chain itself, and by the properties of the solvent. Differences in circular dichroism in various solvents are caused by conformational changes.

IN recent years, particular attention has been paid to the introduction of various aliphatic rings into liquid-crystalline (LC) polymers with mesogenic groups in the main chain [1]; in this way, solubility in suitable solvents can be considerably improved and temperatures of phase transitions can be reduced. The rings may contain chiral centres so that optically active polymers, cholesterics or chiral smectics can be prepared. In continuation of our previous studies of the mesogenic properties of the fragment type I [2], containing a variable central unit R, with 4-oxybenzoate side groups, we chose to introduce a eamphoric acid residue as the central unit CH~

CH3

CHs •--"C/ _OC,,(F~,OC_R_CO/F-~CO_, kt ~'~-/

O

tl

tl ~1]

O

O

R=~_J

"C/__ I

I

O

H

CIt2--CH2

I

Previously it has been shown that by the application of diacid chloride monomers, of structure corresponding to that of the mesogenic fragment, a large number of various LC polyesters of high molecular mass can be prepared by high-temperature, accpetor free, polycondensation [2] CH3

\/

ClC II

CHa

a J"

CHa

CHs

\/

CCl II

} "] O CHz--CH20

c

NaOH

O

O

CHa CH a

II

0

O

\/

I

/

co ~--~,ccl ~ X~/tl~

c f

Ctt=--Ctt.2 III CHa

CH.~

1

~

11"x'~/

L o

O

l{

'N'C/

i n lll +nHO--R--OH..--,--]--OC,

CH~--Cft,-, II

C00~OH II

CtT~

II pcl, clc//F--yo C \ c /

11~

,

HOC~OC \ C / \C / l{ ~ II t I

'

0

CHa

"'C /

\ / ~ , /

OC C

]

H C

~

CO(/

II I l ~1 ~11 o CH~--CH~ O IV

/

",',,CO--R--|-

O

| .J,,

1621

Liquid erystailine polyesterscontaining camphoric acid fragments

The synthetic method was developed with racemic derivatives. The diacid chloride III was prepared under conditions similar to those used for the preparation of camphoroylchloride [3]. By polycondensation of III with hexamethyleneglycol-l,6, decamethyleneglycol-l,10, chlorohydroquinone and hydroquinone, the corresponding polyesters TABLE l. PROPERTIES OF POLYMERS I V - V I I

Polymer

D],* dl/g

IVa IVb IVc iVd V VI VII

0.18 0.17

Calculated,

.~T& I

0"25

o.171

8100 3200

0"16 0.28!

Found,

clHt

ciHI

CI

20 [ 69"48 5"83 40 I 71.06 6"66 160 66.12 3.88 70.58 4.34 180 62.24 5.55 210 70.05 6"61 280 75.40 6"33

%

69"72

70'77 6.50 65'92 70"86 62"79 11"48 70"36 75.44

Empirical formula CaoHaoOs

Cl

5'88

-

6"54 C3,HaaOa 3"81 6 " 9 7 C 3 o H 2 1 0 8 C l 4"45 - C3oHa2Oe 5.50 11"25 C16Ht.70,CI 6"92 Ct6HtaO,t 6"38 - C22H220,t

* CHCI3; 20*.

IVa-d were prepared. With the exception of poly(p-phenylene-camphoroyl-bis-4-oxybenzoate) IVd, which does not melt without decomposition, all these polymers have low softening temperatures and do not exhibit LC properties (Table 1). By polycondensation of camphoroylchloride with chlorohydroquinone, hydroquinone and 4,4'-dihydroxydiphenyl, polymers V-VII were produced, also lacking LC properties (Table 1). CH3

FII/_ \X c,x XI\I

--I--4/

,

I X,J J .-!7..

L

ut

\x,---OC~C

u [

o

c,.

" 2 V

IH3

{/

,, -I I

CH 3

IE /

2

I x=/-

~l I

L

o /

Jn

--1

. I

I

, ! =oj.

VI

qH3 ct~ 3 cu \ , /

-IL

CH 3

,.,,X/

CO-- I - -

I

cn

['-

-x=/

oc~ac/C\c/H ,l-fCHz

VII

I

CH~

ot

C O ~

--

In view of the successful preparation by Krigbaum et al. of many LC polyesters [4], we hoped to obtain LC copolyesters by copolycondensation of 4,4'-dihydroxydiphenyl, camphoroyl chloride and the eorresonding aliphatic diacid chloride. We have chosen the diacid chloride of pimelic acid, as it had been known that its homopolymer with 4,4'-dihydroxydiphenyl forms a mesophase of nematic type. Consequently, by the introduction of a chiral constituent, a cholesteric mesophase could be obtained [5]. As the

1622

V.V. Zu'~v

et al.

chiral component we used L-camphoroyl chloride, and obtained the set of LC copolymers VIII (Fig. 1).

Ctt3

_2--% --

C

J---%,oc\ C/

\----J -- ~ /

il

J

H

\ c/ l

O CH2--CH2

-- - - ~ - /)---~,_OC(CH~)~CO_I_ -

CO-.

-,-x-~

VIII All copolyesters VIII, with LC properties, form a planar texture by cooling from isotropic melt; this texture can be "frozen" in a film by quenching. The planartexture of copolymers VIII With x>0.5 reflects light in the visible range (blue), as is often observed with low-molecular weight cholesterics [6]. We have recorded the circular dichroism (CD) spectra of the prepared films (Fig. 2). These spectra are similar in form to those obtained by Krigbaum and Watanabe with films of copolyesters of 4,4'-dihydroxydiphenyl, 3-methyladipic acid and aliphatic dicarboxylic acids [7]. L1£ , arb.un. 0

/ll

T* 2l/0

iiiiI ii I iiI

2 -o.

1

2,o

,/i

180

-I'0

03

0"6 X

ill

/[/

- M..__..._J/ 300

#00

500

,~,,nm

Fro. 1 Fro. 2 Fio. 1. Dependenceof phase transition temperatures on compositionof copolymersVIII: 1 and 2-temperatures of melting and of isotropization. FIo. 2. CD spectrum of a film of copolymerVIII-10. However, we think that some caution is due in connecting the observed spectrum solely with the circular dichroism caused by the (twisted) cholesteric structure of the films, as the planar texture itself is birefringent, with the properties of a biaxial crystal. This is indicated by the change in circular dichroism when the spectrum of the same film is recorded for the second time. At the same time, the constant wavelength of the CD maximum indicates that the main contribution to the CD effect should be ascribed to the planar cholesteric texture.

Liquid crystalline polyesters containing camphoric acid fragments

~O3,10;~9~a.cm ~/dr.ole rl 30 -

3 1/ /I

1623

[OJ, l O~3gead.cm Z/dmole

e ,lO;q m-I. crn-1 5 ~-

N \ \ -\ ' - " \ \ \

20

20-

2"5

10

10

1

280 300 2,nrn 260 FIG. 3. Absorption and CD spectra of the solutions of polymers VII (1), VIII-11 (2), VIII10 (3) and VIII.4 (4) in chloroform (a) and dioxane (b). 2qO

260

280

300

We have investigated the chiroptical properties of the copolyesters V I I I in solution (Table 2). The non-linear dependence of molar optical rotation on composition is probably due to differences in molecular mass of these copolyesters [8]. C D spectra of solutions of the eopolyesters V I I I are shown in Fig. 3. The strong solvent effect is conspicuous. For the similar alkylenearomatic polyesters, chloroform is a better solvent than dioxane [9]. At the same time, according to characteristic viscosity and molecular mass values (Table 2), camphoric acid appears as a more flexible spacer than the pimelic acid fragment. F o r the copolymers V I I I with large contents of camphoric acid, (>/55 %), TABLE 2. PROPERTIESO F COPOLYMERSVIII

Experiment No.

x,%

[MI~~*

5 13 17 23 24 33

4"65 7"53 7"08 9"58 11"0 12"6

[~] t

0"37 0"42 0"25 0'30 0"37 0"31

dl/g

4040 5000

Experiment No. 7 8 9 10" 11 12

x,%

[Ml•Z,

[rt] t, dl/g

38 43 48 52 55 65

7'0 12"44 10'8 12"54 10"5 18"6

0"30 0"41 0"41 0"18 0'25 0'25

JD

5500 3700

* .... t~aju= ~laid [x-350+ (I - x) 286](- 1); CFaCOOH. CF~COOH; 20*. the value of C D is independent of solvent and directly proportional to the contents of camphoric acid fragments. It is probably mainly determined by the disymmetric neighb o u r h o o d of the biphenyl chromophore, The C D value changes sharply on transition

1624

V.V. Z u Y E v et al. [~] • lO-J,#pad. cm 2/drnole I0 L-

J/S "4__L

!2qO/ •

250

_

280 ,~,nrn

-2 FIe. 4. CD spectra of polymer VIII-10 in various solvents: 1-100 % chloroform; 2 - 5 0 % chloroform + 50 % dioxane; 3 - 22 % chloroform + 78 % dioxane; 4-100 % dioxane.

from chloroform to dioxan¢ for the copolymer VII-10 with x = 0 . 5 2 ; this is probably caused by a change in polymer conformation, on transiton to a poorer solvent. These changes occur in a broad range of chloroform-dioxane ratios (Fig. 4) and reflect the averaged effect of solvent on polymer conformation. The copolymer with 23 % of camphoric acid is so poorly soluble in dioxane that its true CD spectrum could not be obtained (the opalescent solutions of this polymer exhibit an anomalous CD, characteristic of aggregating systems [10]). Thus the conformation of macromolecules with mesogenic groups in the main chain is determined by the relation between the quality o f solvent and the flexibility of the spacer, and may vary from the statistical coil [11] u p to an ordered conformation [12]. Viscosity of the prepared polymers was measured with the Ubbelohde viscosimeter. 3~rn was determined by the ITEK method with the instrument "Hitachi-Perkin-Elmer" model 115, in chloroform. Phase transition temperatures were determined using the Boethius melting stage with a polarizing microscope. PMR spectra were measured with the spectrometers "JEOL C60L" (60 MHz) and "Tesla BS-497" (100 MHz). Optical rotation was determined with the spectropolarimeter "Pepol-60" (Great Britain) for solutions at concentrations 0.1-0.5 mg/ml in CFaCOOH. UV and CD spectra were recorded with the instruments "Specord UV-VIS" and "Mark III" (France) for dioxan¢ solutions at concentrations 0.01-0.05 mg/ml. Camphoroyl-bis-4-oxybenzoic acid (II) was prepared in the following way. A solution containing 60 g (0.25 mols) of camphoroyl chloride in 200 ml of carbon tetrachloride was added dropwise to a solution of 72-5 g (0.53 reels) ofp-oxybenzoic acid in 600 ml 1 N NaOH for 30 rain with stirring. The solution was then further stirred for 5 hr ~t room temperature, not letting acidity to drop below pH 8. Afterwards the solution was acidified by HCI to pH 5 and the precipitate was separated by filtration. It was recrystallized twice from water and dried. The obtained product was a crystalline hydrate of II, with one molecule of water. Yield 12.5 g (11%); Tm=177-178°. PMR spectrum (100 MHz) in acetone-de, t~, ppm: a-8"06 (4H); b-7.18 (4H); c-1.19-1.09 (6H); d-0"76 (3H); e - 3.15-1.0 (5H). Calculated, %: C 63-43; H 4.88. C24H2209. Found, %: C 63.37; H 4.82. The diacid chloride of camphoroyl-bis-4-oxybenzoic acid (III) was prepared in the following way. 12.5 g (0.027 mole) were heated with 11.8 g (0.20 mole) of PCI5 in 50 ml of absolute petroether to 40° for 3 hr, until gas evolution stopped. Petrol-ether was then driven off into phosphorus oxychloride. The residual transparent yellowish liquid represented the desired product. Yield 10.4 g

Molecular mobility and relaxation processes in polyamide-6

1625

(81%). PMR spectrum (I00 MHz) in CDC12, t~, ppm: a - 8 . 0 8 (3H); b - 7 . 2 0 (4H); c-1'19; 1.09 (6H); d-0.86 (3H); e-3"15-1"0 (5H). Calculated, ~: C 60.90; H 3"83; CI 14.98. C24H1806CI2. Found, %: C 60.45; H 3.99; CI 15.08. For polycondensation, eqtuimolar amounts of diol and diacid chloride (0.002 mole each) in 4 ml of diphenyloxide were placed in a testtube, flushed for 15 rain with argon, then heated in an oil bath to 160° in a stream of argon for 2.5 hr. The polymer was then precipitated into toluene, filtered and reprecipitated twice from chloroform or from the mixture CF3COOH : CHC13 (I : I by volume) into methanol. Polymer yield 95-98 %. Translated by D. DOSKOg~ILOVA

,REFERENCES I. M. POLK and M. NANDU, J. Polymer Sci. Polymer Chem. Ed. 24: 1923, 1986 2. A. Yu. BILIBIN, V. V. ZUYEV and S. S. SKOROKHODOV, Makromolek. Chem. Rapid Commun. 136: 601, 1985 3. J. BREDT, Ber. 45: 1419, 1912 4. W. R. KRIGBAUM, J. WATANABE and T. ISHIKAWA, Macromoleeules 16: 1271, 1983 5. V. P. SHIBAEV and N. A. PLATE, Advances Polymer Sei. 60/61: 173, 1984 6. V. A. BELYAKOV, A. S. SONIN, Optika kholestericheskikh zhidkikh kristallov (Optics of Cholesterie Liquid Crystals). p. 360, Moscow, 1982 7. J. WATANABE and W. R. KRIGBAUM, J. Polymer Sci. Polymer Phys. Ed. 23: 565, 1985 8. E. CHIELLINI, R. SOLARO, G. GALLI and A. LEDWITH, Advances Polymer Sci. 62: 143, 1985 9. R. W. LENZ, Recent Advances in Liquid Crystalline Polymers (Ed. L. L. Chapov), p. 3, L.-N.Y., 1985 10. D. KELLER and C. BUSTAMANTE, J. Chem. Phys. 84: 2981, 1986 11. A. BLUMSTEIN, G. MAllET and S. VILASUGAR, Macromolecules 14: 1543, 1984 12. E. CHIELLINI and G. GALLI, Faraday Disc. Chem. Soc. 79: No. 16, 1, 1985

Polymer Science U.S.S.R. Vol. 30, No. 7, pp. 1625-1631, 1988 Printed in Poland

0032-3950/88 $10.00+.00 © 1989 Pergamon Press plc

EFFECT OF THE 7*--+~-STRUCTURAL TRANSITION, OCCURRING IN THE PRESENCE OF MINERAL ACIDS, ON THE MOLECULAR MOBILITY AND RELAXATION PROCESSES IN POLYAMIDF_,-6* O. V. STARTSEV, A. L. IORDANSKll a n d G. YE. ZAH