Intramolecular ordering of copolymers containing cholesterol

:Polymer ScienceU.S.S.R. Vol. 20, pp. 1555-1560. ~ ) Pergamon Press Ltd. 1979. Printed in Poland.

0032-3950/78/0601-1555507.5010

INTRAMOLECULAR ORDERING OF COPOLYMERS CONTAINING CHOLESTEROL* W. I . BORISOVA, L. L. :BuRSHTEII~, T. P. STEPAI~OVA, YA. S. FREIDZON and

V. P. SHIBAYEV :Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences M. V. Lomonosov State University, Moscow

(Received 30 August 1977) A study was made of dielectric polarization in dilute copolymer solutions of cholesterol ester of N-nmthacryloyl-co-aminolauric acid with n-butyhnethacrylate and n-decylmothacrylate and homopolymers. It was shown that conformation properties and intramolecular ordering in copolymers containing cholesterol are determined not only by the concentration of mesogenic groups in the macromolecule, but also by :specific features of dispersion interactions of alkyl radictfls of aliphatie comonomers. A STUDY of the intramolecular mobility and conformation properties of cholesterol ester maerolno]ecules of poly-N-methacryloyl-og-aminolauric acid (CPMALA) CIt3 ~

(3II3

(:[{:~

C|[ 3

(I.L_ --CII---(C ' [ t,).~- Ctt

-

a n d m a n y comb-like model polymers shows t h a t elements of structural organization at the molecular level are formed as a result of interactions between side chains [1]. The presence in side branches of amide and cholesterol groups predetermines the formation of intramolecular hydrogen bonds and the strong dispersion interaction of cholesterol groups. As a result certain structural elements are contained in a molecular sphere at an isolated molecular level, which m a y be regarded as the initial stage of formation of liquid crystalline order in a pol ym er in the condensed state [2-4]. The problem arises to what ext ent the formation o f an intramolecular order depends on the 6oncentration and mutual arrangement of mesogenic groups in the polymer chain. An analysis was made of this effect while investigating intramolecular mobility and conformation properties of CMALA eopolymers of different compositions. Copolymers of CMALA with but yl m et hacryl at e (CI~[ALA:MA-4) were used containing CMALA in proportions of 40 and 67 mole%. The following were * Vysokomol. soyod. A20: No. 6, 1380-1384, 1978. 1555

1556

T . I . BORISOVAet al.

also examined: copolymers of CMALA with decyl methacrylate (CMALA:MA-10) containing 31 and 80 mole% CMALA and homopolymers of CPMALA, PMA-4 and PMA-10. Synthesis of all polymers and copolymers investigated wa~ described previously [4, 5]. Parameters of intramolecular mobility: relaxation time ~ and activation energy U were determined by studying relaxation of dipole polarization of dilute polymer solutions i~ toluene. Methods of measurement were given previously [1]. Conformation properties were analysed using dipole moments and methods of measurement and calculation were dealt with in a separate paper [6]. As an example of initial experimental results Fig. ]a shows temperature dependences of e" for some of the homopolymers and copolymers studied.

C% 10 _l~9 v a

8

b 1

2 ¢536k7

/\-I \\ \

I

I

-60

-2O

2.

I

]

2O

60

-'-o5

T,°C

I

E

3

0

r

IO~T, °K -~

FIc. 1. Dependence of a" and r (b) on temperature: 1-- CPMALA; 2-- CMALA: MA-4 (67 : 33); 3--CMALA:MA-4 (40:60); 4--CMALA:MA-10 (80:20); 5--CMALA:MA-10 (31:69); 6-PMA-10; 7--PMA-4. Temperature dependences of relaxation time of dipole polarization (Fig. lb) are shown using the temperature-frequency relations of #' and # of all copolymers and homopo]ymers; these indicate t h a t the range of variation of ~ on transition from PMA-4, PMA-10 homopolymers to CPMALA exceeds two orders of magnitude, which is direct evidence of the varying degree of intramolecular ordering in these systems. When analysing parameters of molecular mobility (r and U) from the variation of which the degree of orientation order m a y be evaluated, it is interesting to examine/,he concentration of mesogenic groups of CMALA in the copolymer and tl~e chemical structure of the second component. Figure 2a shows t h a t an increase in the number of mesogeiiie groups in the chain increases relaxation time.

Copolymers containing cholesterol

1557

tIowever, the variation of this p a r a m e t e r of intramolecular mobility is d e t e r m i n e d b y the concentration of CMALA in eopolymers. Thus for copolymers of C M A L A : :MA-4 up to about 50% CIV[ALA content the variation of log~--x~ is linear a n d takes place within the range of the same order of m a g n i t u d e . The value of ~ a t 20 ° increases from 5 Nsec in PMA-4 to 19 Nscc in a CMALA copolymer w i t h ])IPOLE

)IOMENTS

O~

CMALA:MA-4 AT

Polymer

]

PMA-4 CMALA : MA-4 (40 : 60) CMALA : MA-4 (67 : 33) CPMALA

! i _

(!OPOLYSIEr~S

IN

TOLUENE

20 °

~.- - - ': 1-50 2.23 3.57 7.fi0

i ' : i

--,~

I

~/5~

I

1.9 6.8 14.8 42.2 __

0,23 0.20 [ 0.18 .] 0.17 _]

x e = 4 0 % . The value of r increases most m~rkedly in th:~ region of CSfALA values of 50 to 100%. R e l a x a t i o n times in this r:mge of concentration Lqerease to 1380 Nsec. Such a sudden variation of r m a y be a direct reflection of a new order of magnitude, which is due to the specific interaction of cholesterol radicals, a n d a corresponding variation of the conformation state of the chain. This effect m a y be directly recorded according to the t y p e of dependence between -the average dipole m o m e n t per m o n o - u n i t of the polymer chain M2/N and the composition of the eopolymer [4]

.zfl~/N-- :~:.,g~2 where 342 is the average square of the dipqle m o m e n t of the whole chMn; N, ~he n u m b e r of chain units; x2, molar concentration of the CMALA eomonomer,/10, dipole m o m e n t of the mono-unit; g, correlation para.meter determining the conf o r m a t i o n state of the chain. Values of J142/~Y were eMeulated by a ~nethod previously described [7]. Experimental values of specific increments of dielectric constant e and specific volume fi, required to calculate J~2/N and the value of ~I2/N for a CMALA : MA-4 copolymcr were t a b u l a t e d \

w2 /w,=o

\

w2 /w,=0

where e12, e~, v~2 a n d v~ are the dielect.rfc eo,astant and the specific volume of the solution a n d solvent, w2, weight eonccntration of the polymer in solution. Figure 2b shows the relation between Jq2/N and x 2 of CMALA:MA-4 eopolymers. These results show t h a t a sudden increase in ~ / N also occurs with eoneentrations of CMALA>50°/o, which is direct evidence of specific interactions influencing the conformation state of the chMn under these conditions. This effect m a y be explained b y the fact t h a t on increasing the concentration of CMALA in the copolymer chain, comparatively short side chains of MA-4 do n o t

"1558

T . I . BORZSOV~e~ a l .

prevent £he convergence and interaction of cholesterol end groups, resulting in mutual adjustment inside the sphere and the formation of elements of structurM order in macromolecules. Results indicate that the formation of an intramolecular structure in the sphere b y the interaction of cholesterol radicals starts from 50 mole% CMALA. -Logr 8 -

a A

6 50 -HZ

•

t nv • 2

2

loc 'r [

25

7-8~7"# ~ I

I

,.50

100

CIdALA , mole %

Fro. 2

I

I

I

I

2

6

I0

lZ/

I 18/7

FIG. 3

l~zo. 2. Relation between relaxation time (a), average square dipole moment (b) and the composition of copolymers: 1--CMALA:MA-10, 2--CMALA:MA-4. Fzo. 3. Relation between the relaxation of dipole polarization in comb-like PMA-n and the length of the aliphatie radical (toluene, T = 10°). In CMALA:MA-10 copolymers an increase in the contents of mesogenie g r o u p s also produces an increase in v. However, as shown b y Fig. 2a, the concentration dependence of T in this ease has typical features. In ~ L A : ] Y [ A - 1 0 copolymers the range of comparatively slight change of v reaches 80% CMALA. Thus, on transition from P ~ A - 1 0 to a copolymer with x2----80%, ~ only increases from 12 to 30 nsec. For a copolymer with MA-4 of the same concentration v is 125 Nsec, i.e. the effect of the concentration of mesogenic groups on ~ in copolymers with M_&-10 is much more weakly expressed than in copolymers with ~A-4. T h i s results in the conclusion that the formation of intramolecular structure in

Copolymers conSaining eholesterm

1559

spheres with cholesterol groups is largely determined by the chemical structure of co-monomers. Analysing the dependence of r on CI~[ALA contents in copolymers with ~/[A-4 and M[A-10, the difference in kinetic properties of homopolymers of P~c[A-n deries shguld also be taken into account. It is known that the relaxation time of dipole polarization depends on the length of the side chain [8] in comb-like polymers with aliphatic side groups. Figure 3 shows the dependence of ~ on the number of carbon atoms in the side chain, which indicates an increase of r with a lengthU, kca//mole

f

! !

/0-

I /

5

I 50 Oi~,ALA , mole %

I

r I00

JFIG. 4. Relation between activation energy and tile composition of eopolymers of CMALA: :MA-10 (1) and CMALA:MA-4 (2).

ening of the side chain. It is in~eresting to note that the greatest variation of z from n is observed in the region of n value of --8-10. Any subsequent elongation of the aliphatie radical affects parameters of intramolecular mobility to a much lower extent. This clearly demonstrates the orientation order established on the intramolecular level as a result of a further dispersion interaction of hydrocarbon radicals in comb-like polymers, starting from n = 1 0 . This interaction also takes place in CMALA:~IA-10 eopolymers of all concentrations, since there are 11 CH 2 groups in the mono-unit of CMALA. This m a y also explain the difference in the dependence of relaxation time on coneentration in CMALA :3[A-4 and C3IALA: :MA-10 copolymers. In the range of low concentrations of CI~[ALA, where the behaviour of the system is determined by kinetic properties of 1~3IA-4 and PMA-10 homopolymers, further dispersion interactions result in increased relaxation times in CMALA.MA-10 copolymers, compared with CMALA:3IA-4 copolymers. At the s~lne time when x2~-50 mole%, the ratio of r in C3'LA_LA:MA-4 and CPMALA.){A-10 copolymers changes inversely: relaxation times of dipole polarization in CMALA:MA-4 become more considerable than CMALA.MA-10. This is due to the fact that starting from x2=50 mole%, specific interaction of cholesterol end radicals takes place in CMALA:~IA-4 copolymers. In C_~IALA: MA-10 copolymers the mutual adjustment of mesogenic groups is impeded by screening with relatively long aliphatic radicals. The difficulty involved in the interaction of mesogenic groups is apparent in lower z values in CMALA: MA-10 eopolymers, compared with CMALA :i~[A-4 in the region of x2> 50 mole %

1560

T. I. BORISOVAet al.

The relation between activation energy U of the relaxation of dipole polarization and CMALA concentration in CMALA:MA-4 and CMALA.MA-10 copolymers is also typical from this point of view (Fig. 4). When x2~50 mole %, the valuo of U in copolymers with MA-10 is higher than in CMALA:MA-4, which is in satisfactory agreement with further interactions between alpihatic radicals in C~ALA:MA-10 copolymers. On transition from PMA-10 to copolymers with x2~--80~o, this value remains approximately constant. The weak concentration dependence of • is evidence of the stability of intramolecular structure. A sudden increase in z and U only begins after x,~----~0°/o. Consequently, in CMALA :MA-10 copolymers the interaction of cholesterol end groups and the formation of elements of structural order is only possible ~vith a high degree of saturation of the polymer sphere b y mesogenie groups. In contrast to this, in CMALA:MA-4 constant activation energy is observed in the concentration range, where relaxation time increases and the conformation state of the chain changes. This points to the entropy nature of variation of T in this range of concentration, which reflects mutual adjustment and interaction of cholesterol groups in copolymers with MA-4. Results concerning parameters of intramolecular mobility and dipole moments of copolymers of different chemical structures enable the type of formation of elements of structural order inside a macromolecular sphere to be analysed and the effect of variofis interactions in this process, indicated. In addition to the concentration of mesogenic groups in side chains, it is essential to consider structural factors, determining the type of intramolecular interaction and controlling the possibility of mutual adjustment of cholesterol radicals inside the molecular sphere. Translated by E. SEMERE

REFERENCES I. T. I. BORISOVA, L. L. BURSHTEIN, T. P. STEPANOVA, Ya. S. FREIDZON and V. P . SHIBAYEV, Vysokomol. soyed. A19: 552, 1977 (Translated in Polymer Sei. U.S.S.R.

19: 3, 637, 1977) 2. V. P. SHIBAYEV, Ya. S. FREIDZON, I. M. AGRANOVICH, V. D. PAUTOV, Ye. V~ ANUFRIYEVA and N. A. PLATE, Dokl. A N S S S R 232: 401, 1977 3. Ye. V. ANUFRIYEVA, V. D. PAUTOV, Ya. S. FREIDZON and V. P. SHIBAYEV, Vysokomol, soyed. A19: 755, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 4, 875, 1977) 4. V. P. SHIBAYEV, Ya. S. FREIDZON and N. A. PLATE, Dokl. AN S~SR 227: 1412, 1976 5. V. P. SHIBAYEV, Ya. S. FREIDZON and N. A. PLATE, Vysokomol. §oyed. A2O: 82, 1978 (Translated in Polymer Sci. U.S.S.R. 20: l, 1978} 6. T. I. BORISOVA, L. L. BURSHTEIN, T. P. STEPANOVA, Ya. S. FREIDZON, V. P. SHIBAYEV and N. A. PLATE, Vysokomol. soyed. BI8: 628, 1976 (Not translated in Polymer

Sci. U.S.S.R.) 7. G. P. M I K H A I L O V , L. L. B U R S H T E I N and V. P. M A L I N O V S K A Y A , Vysokomol. soyed. All: 548, 1969 (Translated in Polymer Sci. U.S.S.R. II: 3, 623, 1969) 8. T. I. BORISOVA, L. L. B U R S H T E I N , V. P. M A L I N O V S K A Y A , T. P. S T E P A N O V A , N. A. P L A T E and V. P. S H I B A Y E V , Vysokomol. soyed. A14: 2106, 1972 (Translated in Polymer Sei. U.S.S.R. 14: 10, 2474, 1972}