The IR data confi rm the ionic character of the acid â amine bonds. The blends with low ... of the intermolecular donor â acceptor interactions in the case of ...
~
Polymer Sci ence, Ser. À , Vttl. 4 1, htrt. 3, 1999, pp . 337- 345. Translated ~ãî ò Vy sokomol ekulyur nye Soedineniyu, Ser. À, Vol. 4 1, No. 3, 1999, pp. 488- 497, Ori 1;i nul ßèü;ñø è Text Copyri ght Î~' 1999 by Burmutov, Bar nattovu, Chcnskuya, Grttkhovtkuyu, Shi baev Ent; l i sh Trunsluttttn Copyi tght Ñ 1999 Üò Ì À È Ê " Í ï óêî l l nterp er todtca " (Russi a ).
P H A SE ST R U C T U R E A N D T R A N SF O R M A T I O N S
Å .  .  à ï ï à 1î ÷ '" , Ì . V .  à ï ï à ( î ÷à '", Ò .  . Ñ Üåï 8Êà ó à "" " , Ò . Å . G r o k h o v sk a y a * , a n d V . P . Sh i b a ev * * D epa r tm ent of Ñéåò è 1ãó, M osco w Sta te Uni versi ty, Vo rob 'evy g ory, M oscow, 119899 Russi a * * I nsti tute of Syntheti c Po ly meri c M a teri a ls, Russi a n A cademy of Sci en ces, Prof soy uznay a ul . 70, M oscow, 117393 Russi a Received June 9, 1998; Revi sed M anuscri pt Received September 24, 1998
A bst r act — T he phase state and structure of the blends of octadecylami ne (ODA ) wi th à nematic ionogenic ?.Ñ copolymer contai ni ng mesogenic (hydroxycyanobiphenyl ) and i onogenic (30% acrylic acid) groups were studied by IR spectroscopy. T he IR data confi rm the ioni c character of the acid—ami ne bonds. The blends with l ow ODA concentrations (5—15 mol %) show evidence of the S>-phase inducti on caused Úó the f ormati on of i ntraand i ntermolecular ionic associates. T he further increase i n the ODA content (24- 29 mol %) l eads ãî the appearance of the Sz- and S~ phases. T he effect of the mol ecul ar mass of i onogenic copolymers on the phase state of the blend was studied by GPC. A s the molecular mass i ncreases, the concentr ation interval of the nematic phase formati on narrows, the interval of the 5ä-phase broadens, and the system exhi bits à trend of forming ò î ãå ordered phases.
containing electron-donor (carbazole) and electronacceptor (nitrophenyl) groups. In [9—11] we have reported on the induction of à smectic phase in þ ï î genic 1 Ñ copolymers containing nematogenic groups
INTRODUCTION À conventional method of obtaining thermotropic comb-shaped I.Ñ polymers consists in the chemical attachment of mesogenic groups to the aliphatic side chains of à base comb-shaped polymer (Fig. l a) [ 1, 2] . In recent years, some new methods have been developed for the synthesis of comb-shaped ÜÑ polymers, which are based on the special non-covalent interactions (electrostatic and donor—acceptor interactions, intra- and intermolecular hydrogen bonds) in an 1.Ñ polymer system [3—20] .
(à)
Kato and Frechet [3, 4] developed à new concept of obtaining elongated mesogenic groups composed of two molecules linked by hydrogen bonds. Thi s method allows the new mesogenic groups to be obtained with à markedly increased anisodiametry. Wiesemann and Zentel [5, 6] obtained I. Ñ elastomers using the ability of the þ ï -containing I. Ñ polymers (and their blends with an amorphous ionomer) to feature à physical network by forming ionic clusters. Kosaka and Uryu [7, 8] demonstrated à high effi ciency of the intermolecular donor—acceptor interactions in the case of equimolar blends of two nematic polymers T he work was supported by the Russian Foundation for B asic Research, proj ects nos. 96-03-33820 àï 4 98-03-33390.
çï
(ñ)
F i g . 1. Sc h e m a t i c d i a g r am o f d i f er en t v ar i a n ts o f th e c o m b l i k e 1 Ñ p o l y m e r str u c t u r e .
~
BARMATOV et al.
338
and acrylic acid f ragments. The eff ect was related (î increasing rigidity of the polymer chain as à result of formation of the intramolecular hydrogen cycles. Finally, it is necessary to mention the works of Paleos et al. [ 12, 18] , Uj iie et al. [ 13, 14] , Bazuin et al. [ 15—17] , and ÒàÃãî êå et al. [ 19, 20] devoted to creation of the mesomorphous polymers of à new type based on the self -organization of two fragments— à polymer matrix and à low-molecular-mass amine, each component alone being uncapable of f orming an ÜÑ phase (Fig. 1Ü) [ 15—20] . À polymer matri x in these systems is usual ly represented by polyacids (PA A [ 15—20] , PM A A [ 19] , polymalonic acid, poly(vinylsulf onates) [ 16] , etc) . The choice of amines off ers à greater variety— 1ãî ò primary to tertiary amines having different structures of the lyophobic part of the molecule, which is provided by including one or two aromatic or cyclohexane rings and long aliphatic " tails" into the amine
The purpose of this work was to study the ionic complexes of an ionogenic copolymer, containing about 30 mol % acrylic acid, and à low-molecular-mass surfactant— octadecylamine (ODA ). Study of the phase diagrams of the ionogenic copolymer—low-molecularmass amine system al lowed us to reveal the eff ect of the low-molecular-mass nonmesogenic additive, noncovalently bound to the backbone, on the structure and thermal stability of these ionic complexes. In order to establish the infl uence of the polymer chain length on the properties of the |î ï |ñ complexes, we have studied the blends of ODA with ionogenic copolymers having different molecular masses. ÅÕÐÅ % Ì ÅÍ ÒÀ? The ÜÑ copolymers were synthesized by the radical copolymerization of 1,4- (4-ñóàï î -4-biphenyloxy)butyloxycarbonylethylene (ÑÂ) with acrylic acid (ÀÀ ). The process was conducted in absolute THF and initiated by A IBN (2%) . The concentration of À À in the monomer mixture was 30 mol %. The fi nal copolymer was boiled f or à prolonged time in ethanol to eliminate the residual monomers and low-molecular-mass products, and then precipitated with methyl alcohol f rom à chlorof orm solution. The copolymer is well soluble in chlorof orm and THF. Fractional precipitation of the product yielded several fractions of the copolymer studied (Table 1). The I R spectra were measured on à Specord Ì -80 spectrophotometer (K arl Zeiss, Germany) linked to à computer. The spectra were acquired and processed using the SPECTRA program package. The copolymer composition was determined by the methods of elemental analysis. The complexes of þ ï î genic copolymers with ODA (Ò = 55—57' Ñ according
molecule. Reactions between polyacids and amines usually proceed with the f ormation of ionic complexes, which leads to the appearance of new structures susceptible (î thermotropic and/î ã lyotropic mesomorphi sm. A ccording to [ 19] , this mesomorphi sm is related to à pronounced diphilic character of the system and the related microsegregation processes, rather than to the rigidity or geometric anisotropy of the side groups. The above examples give convincing evidence f or the interest in studying polymeric L Ñ systems based on the principles of molecular recognition and self-organization. In this connection, it is of importance to study the propert ies of comb-shaped 1 Ñ polymers based on à mi xed principle, whereby one part of à polymer macromolecule is constructed by the covalent binding of side groups, and the other, by electrostatic interactions (Fig. l c).
to Aldrich) were prepared by di ssolving mechanical mixtures of various compositions in chlorof orm , f ollowed by the drying in vacuum at 60—70' Ñ.
I
I
CH —COO—(CHg)4—0 I
The molecular masses of copolymers were determined by GPC (Knauer) by referencing to à PS standard. The microcalorimetric measurements were conducted on M ettler diff erential scanning calorimeter operated at à sample heating rate of 10 Ê/min. T he microscopic investigations were performed on à Polar P-211 polarization microscope equipped with à M ettler
l 00 - .ñ
0
1
ÑÍ
ÑÎ Î
0+ Í ~Õ (ÑÍ 2) ä ÑÍ ~
1
(õ = 27- 3 1 mol %).
Ò à Û å 1.
M o l e c u l a r - m a s s c h ar a c t e r i st i c s ( G P C , P S st a n d ar d ) a n d f r ac t i o n a l c o m p o s i t i o n o f c o p o l y m e r s
Fracti on
Ì „ õ 10~
Ì ,„ õ 10-'
Є
Ì „ /Ì „
À À . m ol %
8.20
12.60
51
1.5 3
27
5 .69
7 .32
çî
59
.29
28
2 .5 2
~ .ã ~
~ç
25
26
* C al cu l ated f ro m G PC d at a.
P A T V M F R ÑÃ 1Ð Û Ñ Ð
ñ
ë
÷û
û
i oaa
PHASE STATE OF IONOGENIC LIQUID-CRYSTALLINE COPOLYMER BLENDS
FP-82 hot stage. The Õ-ray diffraction patterns were recorded on an URS-55 spectrometer using CuK radiàêî ï p = 1.54 À).
Phase Transi ti ons, Composi ti on, and Molecular-Mass Characteri sti cs of Ðòàñéî ï à1åé i onogeni c LC Polymers The sample complexes were prepared f rom the fractions of the ionogenic copolymer obtained by the method of f ractional precipitation. A s is seen f rom Table 1, the copolymers have rather low molecular masses. The weight-average values of the degree of polymerization, determined by GPC with the aid of PS standards, fall within the interval of 13—5 1 monomer units. A nal ogous measurements based on the al ternative standards, represented by f ractions of an acrylic polymer with cyanobiphenyl mesogenic groups and by à hydrogenated analog of the corresponding monomer (characterized by the light scattering data) [2 1] , showed that using the PS standards may lead to the hal f -understated values of the molecular masses. Similar results f or the ionogenic ÜÑ copolymers studied in this work were obtained in [ 10] where the molecular masses were determined by à combined method based on the measurements of sedimentation and diffusion. Thus, the copolymer fractions obtained by the method of fractional precipitation are characterized by à rather narrow molecular-mass distribution and cover the entire range of masses f rom oligomers (fractions 2 and 3) to polymers (fraction 1). The nonfractionated copolymer sample, containing 31 mol % À À , forms à nematic phase with à clarifi cation temperature of 96' Ñ and à glass transition temperature of 40' Ñ. According to the data of DSC, polarization microscopy, and Õ-ray diffraction analysi s, all fractions are also capable of forming mesophases of the nematic type, Figure 2 (curve 1) shows à typical DSC
curve for the second copolymer fraction. A s à rule, an increase in the degree of polymerization in 1 Ñ polymers is accompanied by increasing phase transi tion temperatures. Figure 3 shows the plots of the transition temperatures versus the degree of polymerization f or an ionogenic ÜÑ copolymer. Taking into account that the À À f raction in the copolymers amounts on the average to 28 mol % and varies only slightly on the passage from high- to low-molecular-mass f ractions, we may ascertain that the observed increase in the transition temperatures is caused by increasing molecular masses of the samples, rather than by compositional inhomogeneity of the copolymers. Thus, the sample blends were prepared from three well characterized f ractions of ionogenic ÜÑ copolymers having diff erent molecular masses at à nearly the same composition. The Nature of Nonñoèàlånt I nteracti ons i n the Blends of Ionogeni c Copolymer wi th Low M olecular-Mass Ami ne A s reported previously [9—11] , the phase state of an ionogenic 1. Ñ copolymer used as à matrix for' the blend preparation is signifi cantly affected by the intramolecular hydrogen bonds. I n thi s work, the character of hydrogen bonds f ormed in the ionic copolymers studied and in their blends with ODA was studied by the method of IR absorption spectroscopy. Figure 4 (curve 1) shows the IR spectrum of f racti on 3 of the ionogenic copolymer. A s is seen, the region of 1650—1750 cmã ' contains à number of overlapping absorption bands related to the stretching vibrations of carbonyl entering into the ester and carboxyl groups. To study the type of hydrogen bonds in the copolymers, we have used the diff erence spectra obtained by subtracting the IR spectrum of ÑÂ homopolymer (curve 2) from the spectra of ionogenic
î õ
20
40
60
80
100
7. ' ñ F i g . 3 . T h e p l o t o f p h a se tr an si t i o n t em p er atu r e v e r su s d eg r ee o f p o l y m er i z a ti o n o f i o n o g en i c L Ñ c o p o l y m er s. B l ac k p o i n t s sh o w th e d at a f o r t h e n o n f r ac t i o n ate d sam p l e . Í å ãå a n d i n F i g . 9 : 1 = i so t r o p i c m e l t ; G = g l ass .
F i g. 2. D SC cur ves: ( 1) fr acti on 2 of i o nogeni c 1. Ñ copol y m er ; (2) bl end of f racti on 2 w ith 2 8 m ol % O D A ; (3 ) b lend o f fr acti on 1 w i th 27 mol % O D A . PO L Y M E R SC IE N C E
Ser i es À
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~
340
B A RM A T OV et al .
copolymers. T he spectra were normalized with respect to the bands at - 1600 and - 1500 cm- ' belonging to the skeletal vibrations of benzene rings. Using this procedure allowed the absorption component due to the ester fragment of à mesogenic group to be eliminated from the spectrum of copolymer, af ter which the resulting spectrum contains only the bands of vibrations belonging to the ÑÎ Î Í groups (curve 3). The diff erence spec-
í -î
ä ~
"î
î
Î
trum exhibits à broad absorption band in the region of 3200 cmã ' , which is attributed to the stretching vibrations of the Î Í bonds (voz), and two characteristic bands corresponding to vco = 1748 and 1704 cmã ', assigned [22, 23] to the free and hydrogen-bonded ÑÎ Î Í groups. T he structure of the copolymer chain f ragment is depicted in scheme (à) below :
Î - Í -.Î
ñ. Î
- Í -.Î
ñ
Î
1
( à)
Y
í -î
Ñ ~
ã Ñ
ä p.,-~. î î -, ñ--.-.î î ' â î m ,î ûí , î (b )
Ñ III
N
A s is seen, the ionogenic ? Ñ copolymers admit the formation of intramolecular hydrogen bonds of the two types: (I) between the acid groups of À À and (Ï ) between the carboxyl group of À À and the ester f rag-
ment of à mesogenic group. In addition, there is à considerable fraction of free carboxyl groups (Ø ). The interaction of ionogenic copolymers with amines was studied by the IR spectroscopy of the blend samples based on the copolymer f raction 3 àï 4 containing 8.7, 14.5, 20.6, and 30 mol % ODA . Figure 5à shows the spectrum of copolymer fraction 3 (curve 1) in compari son with the spectra of anune and the blend containing 8.7 mol % ODA (curve 3). The bands of antisymmetric and symmetric vibrations of the NHz groups (3340 and 3260 cm ', respectively) are present in the spectrum of amine (curve 2), but are mi ssing from the spectrum of blend. The intensity of à broad band at - 3200 cm- ' , attributed to the voÄ vibrations of à hydrogen-bonded carboxyl group, al so drops in the blend spectrum. In the region of the stretching vibrations of carbonyl (vco), the passage f rom polymer to blend leads (Fig. 5b) to à decrease in intensity of both high-frequency and low-f requency wings of the complex band of vco with increasing amine concentration. However, ï î further changes in this region are observed beginning with an amine content of 30%: whereby the spectrum contains à single absorption band due to the vco of the ester group. T hese data are indicative of the formation of an ionic complex —ÑÎ Î
N H , R as à result
of protonation of the NH~ amine groups by carboxyl groups of the ionogenic copolymer. Indeed, in this case PO LY M E R SC I E N C E
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19 9 9
~
PHASE STATE OF IONOGENIC LIQUID-CRYSTALLINE COPOLYMER BLENDS
34 l
the ÷,ù bands must disappear and the bands of ÑÎ Î Í must be replaced by the bands of ÑÎ Î ions observed in the region of 1360- 1450 cm ' (unfortunately, the later bands are masked by the bands of ÑÍ bending vibrations). In order to compare the relative contributions of bound and free carboxyl groups in the blends containing different amounts of amine, we have analyzed the difference spectra with correction for the sample thickness. A s is seen f rom Fig. 6, the intensity of bands belonging to the bound ÑÎ Î Í groups ( 1704 ñï è ') decreases to à greater extent. This implies that the saltlike complexes of the ÑÎ Î N H , R type are more readily f ormed by the ÑÎ Î Í groups bound by the hydrogen bonds. A n additional evidence f or the formation of ionic bonds is gained f rom the comparison of spectra of the blends of ODA with à copolymer containing ÑÂ groups and 30 mol % of À À methyl ether, in which ï î protonation of the NHz groups is possible (Fig. 7). The IR spectra of à blend containing 20 mol % ODA show à signal corresponding to vibrations of the primary amino groups. Thus, the experimental results confi rm the possibility of ionic bond f ormation between the acid group of à comb-shaped ÜÑ copolymer and ODA . T he structure of à blend with incompletely substituted carboxy l groups of the ionogenic copolymer is depicted in scheme (b) above.
F i g . 4 . I R sp ec t r a : ( 1 ) f r ac t i o n 3 o f t h e i o n o g e n i c L C c o p o l y m e r ; ( 2 ) Ñ Â h o m o p o l y m er ; ( 3 ) d i f f er e n c e sp ec tr u m o b t ai n ed b y su b tr ac t i n g c ur v e 2 f r o m cur v e 1.
(à)
+c à î
.é 4 0 Å OS
Thermal Behavi or and Phase State î~ Â1åï éç The blends of polymers and primary amines are usual ly studied on the complexes of equimolar composition, containing one amine molecule per acid group of the polymer. In this work, we have studied the nonstoichiometric mixtures with an ODA content varied within broad limits (from á to 29 mol %, which con esponds, upon recalculation f rom the molar concentration of amine (î that of acid groups in the copolymer, to 0.2—1.0). Study î é Üå samples with diff erent ODA contents shows how the phase behavior and thermal stability of the mesophase can be aff ected by the gradual attachment of additional nonmesogenic molecules of the low-molecular-mass amine (î the comb-shaped macromolecule. Figure 2 shows DSC thermograms of the polymer blends. A s is seen, the curves of all samples show well pronounced peaks of melting, corresponding to various structural transitions. The clarifi cation temperatures of the blends were determined using the method of polarization microscopy, j udging by the vanishing of à fanshaped or homeotropic texture characteristic of the SA-phase. The blends having à nematic structure exhibit à characteristic marble-like texture. The f ormation of the ß,-phase is evidenced by the f ormation of à fanshaped texture and additionally confi rmed by the Õ-ray è ã ë ì è ~ êñ þ ëã ã
Ñ ÐÏ Ð Ñ À
÷à ë
10 0 0
24 20 v x 10- ~. cm '
28
17
16
15 èõ 10 2 ñò - '
F i g . 5 . I R sp ec tr a i n th e r an g e o f ( à ) 2 0 0 0 —3 6 0 0 c m ' a n d ( b ) 15 0 0 - 180 0 c m - ' . ( 1 ) f r ac ti o n 3 o f th e i o n o g en i c 1. Ñ c o p o l y m e r ; ( 2 ) O D A ; ( 3 ) b l e n d o f th e 1î ï î g e n i c Ü Ñ c o p o l y m e r w i t h 8 .7 m o l % O D A .
diff raction data. T he interplanar spacings are as follows: disap = 5.1 + 0.1 À ; ñ/~~, = 29.9 + 0.5 À ; dying = 14.9 ~ 0.3 À . The DSC curves of the samples containing above 24 mol % amine show à low-temperature transition at
BARMATOV et al.
34 2
l 7 .2
18 .0
16 .4
÷ õ 10 ~, ñò ' F i g . 6 . D i f f er e n c e I R sp ec t r a : ( 1 ) i o n o g e n i c 1. Ñ c o p o l y m er ; ( 2 ) b l e n d o f th e i o n o g en i c 1. Ñ c o p o l y m er w i th 14 .5 m o l % O D A .
çî
25
49- 54' Ñ with an enthalpy varying within 8—30 J/g depending on the amine content (Fig. 1, curves 2 and 3). The high enthalpy of melting is indicative of the f ormation of ordered smectic phases in the blends studied. Figure 8 shows schematic Õ-ray diff raction patterns f or the blends of ODA with fractions 1 and 3 of the ionogenic 1. Ñ copolymer. A n analysi s of the diff raction patterns confi rmed the formation of smectic phases of the Sz and Sz types in the blends with the amine content above 24 mol %. The Sz-phase is manifested by à single narrow refl ection corresponding to df fp = 4.16 A , which is observed at large scattering angles and is indicative of à close packing of the side mesogenic groups (f orming à 2D lattice of hexagonal symmetry). The interpl anar spacing was used to estimate the average value of the diameter of side groups à = 4.8 A (Table 2). The Õ-ray diff ractograms contain two refl ections corresponding (î the S~ phase (äö~ = 4.10 A and dz~ = 3.71 À ), which are observed in the region of large scattering angles. The pattern of refl ections in the region of small angles is characteristic of the normal smectic phases. For all the blends f orming ordered phases, the parameters of layer packing of the mesogenic groups remain unchanged to within the accuracy of measurement and correspond to the values reported above for the SÄ-phase. Table 2 gives the parameters of the wideangle refl ections and the packing parameters of the Sz-phase, calculated assuming the orthorhombic packing of the side groups. '?he unit cell parameters à and b agree well with the data published for the Sz-phase f ormed in the blends of PA A with low-molecular-mass long-chain secondary amines [ 18] .
v x 10 ~. ñò F i g. 7. I R spectr a: ( ! ) copo l y m er w i th À À m ethy l ether ; (2) O D A ; (3 ) bl end of the above A A cop o ly m er
w ith 28 mol % ODA .
( à)
Fi g. 8. Schematic di ffractograms: (à) blend of fraction 1 w ith 27 mol % ODA ; (Ü) blend of fraction 3 with 28 mol % ODA .
Eff ect î ~ Ì î 1åñè1àò Ì àçè of l onogeni~c L Ñ Copolymers on the Phase Behavi or of Âlånds L et us consider the effect of the molecular mass of à polymer matrix on the phase state of complexes. Unfortunately, the available literature off ers ï î works devoted to this problem. A ll the experiments were usually perf ormed with polyacids having the same fi xed molecular mass, and the effect of this parameter on the properties of blends was not systematically studied. In [ 18] , the complexes with aliphatic amines were prepared using PAA with à weight-average degree of polymerization 70 (oligomeric range), while in [20] this value was as high as - 3000, corresponding to the region of true polymers. Unfortunately, some works do not specify the molecular masses of polymer matrices used, which hinders analysis of the data reported. Bazuin [ 17] showed for the blends of PA A with primary aliphatic amines that polymers with narrow molecular-mass distribution melt within à narrower temperature interval as compared to that of the samples having à broad molecular-mass distribution. However. this result is quite obvious and sheds ï î additional light on the nature of ionic complexes. Gohy et al. [24] PO L Y M E R SC IE N C E
Series À
×î !. 4 1
No. 3
~÷î î
~
PHA SE STATE OF IONOGENIC LIQUID-CRYSTALLINE COPOLYMER BLENDS assessed the effect of the molecular mass of à polymer on the phase state of ÜÑ ionomers for the blends of PS, containing one or two terminal carboxyl groups per macromolecule, with tertiary ÜÑ amines. I t was demonstrated that increasing the PS fragment length above certain critical value (77 or 154 PS units f or the monoor bifunctional i onomers, respectively) leads to vanishing of the 1. Ñ-phase f rom the blend. A t the same time, à polymer with à molecular mass below the critical value affects neither the phase state nor the transition temperature of the blends. Thus, in order to provide f or an adequate analysis of the effect of the polymer nature on the phase state of its complexes, it is necessary to study à series of samples with narrow molecular-mass distributions in à broad range of the degree of polymerization. A ll the copolymers studied in this work satisfy these requirements, the molecular masses diff ering by à factor of 4 at à rather low polydispersity of the samples ( 1.26—1.53). Figure 9 shows phase diagrams for the copolymer blends of various molecular masses. A s is seen, the introduction of ODA molecules into the complex leads to à drop in the temperature of transition f rom liquid crystal to isotropic melt. The effect increases with the degree of polymerization of the polymer matrix. À dif ference between the melting temperatures of the copolymer and that of à blend having the 1:1 composition (- 30 mol % ODA ) amounts to 48' Ñ for fraction 1 and to 24' Ñ for fraction 3. This fact gives evidence f or the f ormation of à new compound, since à depression î é ëå transition temperature is less pronounced in mechanical mixtures without any additional interaction between the initial components (polymer and à lowmolecular-mass additive) and each component of the mixture melts independently. À remarkable f eature in the phase behavior of the blends is the disappearance of à nematic phase, characteristic of the initial ionogenic copolymer, and the formation of the SA-phase, observed for the ODA concentration of 5—14 mol %. The minimum concentration of the aliphatic amine necessary for the formati on of à smectic phase decreases with increasing molecular mass of the copolymer. This behavior of the complexes is even more unexpected if we take into account that the comb-shaped polymer chain propagates by attachment of the aliphatic tai ls possessing ï î mesogenic properties. M oreover, the f ormation of ionic bonds between ODA and the acid group of copolymer breaks the system of intramolecular hydrogen bonds responsible for the thermal stability î é ëå 1 Ñ phase in the initial copolymer [ 10] , which by ï î means favors the f ormation of ordered phases in the blends studied. Explanation of the unique behavior of complexes should be related to the electrostatic nature of the bonds between acid and primary amine. The acid—amine ionic pairs probably exhibit self-organization to f orm associates (multiplets) [25] comprising two or more groups. The intra- and/oã interchain associates act as the physiÐÎ ! Ó Ì Å É ß [E N C E
Ser ies À
× î 1. 4 1
No. 3
1999
34 Ç
12 0 ~
90
60 ~ ~
~ì å~
100 40 ~-
~Å
þ
(4 i
I
1
!
Ì
N
/ I I
I
~ë G
,
I
~â
[O D A ] , m o l % F i g . 9 . Ph a se d i ag r am s o f t h e b l e n d s o f i o n o g e n i c ?. Ñ c o p o l y m e r w i th O D A : ( à) f r a c t i o n 1; ( Ü) fr ac t i o n 2 ; ( c ) f r ac t i o n 3 .
cal cross-l inks (entanglements), fi xing the polymer chain fragments between the cross-l inks. This, in turn, restricts the mobility of side mesogenic and aliphatic groups and stimulates the appearance of à translational order (layer packing of the side groups). Thus, the smectic order in systems with à low ODA concentration is related for the most part ñî the con clusters decreasing the entropy of the system, rather than to the long side aliphatic chains of amine involved in the comb-shaped polymer growth. This conclusion implies
T a b l e 2 . I n te r p l a n ar sp ac i n g s a n d l at t i c e p a r am e te r s o f th e o r d er e d p h ase s f o r m i x e d f r ac ti o n s 1 a n d 3 o f an L Ñ c o p o l y ò åã b l e n d w i t h O D A ( 2 7 an d 2 9 m o l % O D A , r e sp e c t i v el y )
Sam pl e
Phase type ~À , , A i deas À Ã à, À
F racti on F r ar t i ~ g 3
4 IO ~â
4 1á
3 .7 1
7 .4 2
4 .9 2
~
R A RM A T A V et a l
that induction of the smectic order is due to the þ ï pair f ormation. Following the above notions, the abi lity of blends to f orm the SA-phase is independent of the length of the aliphatic tai l of the primary amine. I n order to verif y this assumption, we have synthesized à blend of f raction 2 of the ionogenic polymer with laurylamine [NHz(CHz) ÄCH, , T = 28' Ñ] , the latter having à 30% shorter aliphatic tail compared to that in ODA . The blend containing 12.6 mol % laurylamine exhibits the following phase behavior: G 36' SÄ 60' N 67' Ñ 1. The melting temperature of the complex is 67' Ñ (- 10' Ñ lower than the value f or the blend with ODA ). This implies that the temperature interval of existence of the ÜÑ phase narrows with decreasing length of the aliphatic tail of amine. However, the main factor is the ability of the sample ñî form the ß,,-phase. Unfortunately, à further decrease in the length of the aliphatic tail of primary amines i s accompanied by à sharp drop of their boiling temperature. This circumstance hinders using these surf actants f or the blend preparation (because the transition temperatures of blends become higher as compared ñî those of the " short" amines). À considerable contribution î é ëå ionic interactions to the phase behavior of the blends was additionally confi rmed by the synthesis of the so-called ionomerscompounds in which à part of the carboxyl groups is neutralized by the ions of metals of groups I or II of the periodic table. In our case, an ÜÑ ionomer was obtained by the reaction of exchange between the carboxyl groups of ionogenic L C copolymer (fraction 1) and sodium acetate. For this purpose, à calculated amount of sodium acetate in ethanol was added to the copolymer solution in T HF. The equilibrium was shifted toward the polymer salt formation by annealing the sample in vacuum at 100—120' Ñ until t ermi nat i on of the acetic acid yield. Study of the phase state of à sample with the degree of sodium þ ï substitution 1.3 mol % showed evidence of the Sz-phase formation, which was indicated by à f an-shaped texture formation and the presence of à small-angle refl ection in the diff ractogram of the ionomer [26] . Thus, the results of investigation of the blends with laurylamine and ÜÑ ionomers confi rms the assumption made above, according to which the smectic phase induction at low ODA concentration is related to the þ ï associate formation. T he role of the al iphatic groups of ODA must be manifested at à high concentration of the surfactant, where the eff ects of the microphase separation on the level of side groups of à comb-shaped polymer become operative. I t was f ound that the relatively high ODA concentrations (exceeding 24 mol %) give rise to the f ormation of ordered phases. The samples having à degree of polymerization Є = 25- 29 f orm the S~-phase, while the samples with Ð,„ = 100 account for the Sz value. A pparently, the ability to form ordered phases is related to long methylene chains of ODA
formi ng à microphase of its own. However, à j oint packing of the ODA molecules and mesogenic groups is also not excluded. In concluding, let us briefl y summarize the results of investigation of the effect of molecular mass of an ÜÑionogenic copolymer on the phase state of the blends with ODA . First, the depression of the temperature of transition f rom an 1. Ñ phase to isotropic melt is more pronounced in à polymer matrix with greater molecular mass. Second, an increase in the molecular mass noticeably decreases the concentration interval of the nematic phase and increases the domain of existence of the SA-phase. Finally, exceeding the critical value of the degree of polymerization (Є ) 59) leads to à trend of f ormation of the structurally ordered phases. Unfortunately, the fractions of polymer with still greater molecular masses (Є > 100) are not available, which hinders f ollowing the effect of the growth in molecular mass on the phase behavior of the blends. W hether the equilibrium state is attained in which the phase behavior of the blend becomes independent of the molecular mass of the polymer matrix. A nswering this question is the sub~ec( of the further investigation. REFER EN CES 1. Pl ate, N .À . and Shi baev, × Ð., Comb-Shaped Polymers àï 4 Li qui d Crystals, New York : Plenum, 1987. 2. Shi baev, × Ð., Frei dzon, Ya.S., àï 4 Kostromin, $.0 ., Li qui d Crystal li ne and M esomorphi c Polymers, Shi baev, V.P. and L am. L ., Eds., New York : Springer, 1996, ð. 77. 3. Kato, Ò. and Frechet, Ì Ç., M acromol ecules, 1989, vol . 22, ï î . 9, ð. 3818. 4. Kato, Ò. and Frechet, Ì ..1., Macromol. Svmp., 1995, vol . 98, ð. 3 11. 5. Wiesemann, À ., Zentel , R., and Pakula, Ò., Polymer, 1992, vol . 33, ð. 53 15. 6. Wiesemann, À . and Zentel, R., Li q. Cryst., 1993, vol . 14, ð. 1925. 7. Kosaka, Y. and Uryu, Ò., Macromolecules, 1995, vol . 28, ï î . 4, ð. 870. 8. Kosaka, Y. and Uryu, Ò., Macromolecules, 1994, vol , 27, ï î . 22, ð. 6286. 9. Barmatov, Å. ., Pebalk, D .À ., Barmatova, Ì .V., and Shibaev, V.P„ Li q. Cryst., 1997, vol . 23, ï î . 3, ð. 447. 10. Barmatov, Å. ., Barmatova, Ì .V., Grokhovskaya, Ò.Å., and Shi baev, V.P., Polymer Sci ence, Ser. À , 1998, vol . 40, ï î . 4, ð. 295. 11. Shi baev, × .P., Barmatov, Å.Â., and Barmatova, Ì .V., Colloi d. Polym. Sci ., 1998, vol . 276, ï î . 8, ð. 662. 12. Paleos, Ñ .Ì . Tsi ourvas, D ., and Photis D ais, Li q. Cryst., 1989, vol . 5, ï î . 6, ð. 1747. 13. Ö éå, S. and Iimura, Ê ., Chem. Å.åè., 1990, ð. 995. 14. Uj i ie, S., Tanaka, Y., and 1èòø ãà, Ê ., M ol. Cryst. Li q Cryst. Sci ., 1993, vol . 225, ð. 339. 15. Bazuin, Ñ.G., Brandys, F.À ., Å÷å, Ò.Ì ., and Plante, Ì ., Macromol. Svmp., 1994, vol. 84, ð. 183. PO L Y M E R SC I E N C E
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