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NEMATIC POLYMERS AND RELATEDSTRUCTURES

F. Cser

To cite this version:F. Cser. NEMATIC POLYMERS AND RELATED STRUCTURES. Journal de Physique Colloques,1979, 40 (C3), pp.C3-459-C3-470. �10.1051/jphyscol:1979392�. �jpa-00218788�

JOURNAL DE PHYSIQUE

MESOMORPHIC

Colloque C3, supplkment au no 4, Tome 40, Avril 1979, page C3-459

POL YMERS.

NEMATIC POLYMERS AND RELATED STRUCTURES

F. CSER

Research Institute for Plastics, Hungaria Krt. 114, H-1950, Budapest, Hungary

RBsumB. - Avec des polymtres A chaine rigide ou structure helicoidale, des proprietts aniso- tropes apparaissent. Si les polymeres sont obtenus par la polymtrisation d'un monomtre chiral, l'examen de leurs solutions montre une structure cholesterique. Dans le cas d'une miscibilitt illimitte du polymere, en examinant les solutions, on peut inferer les propriktes anisotropes du polymere en masse.

En intkgrant dans la chaine de polymeres des segments anisotropes et rigides, il est possible de synthktiser des polymkres ntmatiques en masse. Dans la littkrature, les proprittks mksomorphes de tels polymkres ne sont pas encore dkcrites en dktail.

L'objet du present travail est l'examen du poly-(phknyl-p-acryloyloxybenzoate) et aussi de quatre poly-(p-alcoxy-phenyl-p-acryloylbenzoates). Nous avons utilise les methodes suivantes : d6termina- tion de la texture A I'aide d'un microscope polarisant, de la densite, ainsi que la diffraction de rayons X (A petit et grand angle) et de lumikre laser, mesures de calorimktrie differentielle et de microscopie 6lectronique. Les rtsultats ont kte compares aux resultats de mesures par la chromatographie sur gels des dimensions molkculaires des polymeres plastifies et aux spectres RMN et de diffraction de rayons X en champs magnktiques.

En conclusion, nous avons donne un modele du polymere nkmatique. Ce modele permet de montrer que le polymere nematique ne peut pas dtre isomorphe par rapport a la phase nematique de son monomere. La polymkrisation effectuee dans la phase monomere nkmatique orientke conduit A un polymere orient6 smectique dont la chaine est perpendiculaire au champ magnktique.

Abstract. - With rigid backbones of helical structures, polymers may display anisotropic align- ments. If the monomer is chiral, the polymer/monomer solutions become cholesteric. When the polymer is completely miscible with the monomer, from a study of solutions, one can infer some properties of the bulk polymer.

Inserting anisotropic, rigid segments in the backbone, one can synthetize bulk nematic polymers : their properties have not yet been described in details. Our aim here was to study poly-(phenyl-p- acryloyloxybenzoate) and also four poly-(p-alkoxy-phenyl-p-acryloylbenzoates). We used the follow- ing methods : texture observations under a polarizing microscope, density measurements, small and wide angle X ray s~ t t e r ing , laser light scattering, differential scanning calorimetry, electron micro- scopy. The results were compared to GPC measurements of molecular size, to NMR spectra and to X ray data on samples oriented by a magnetic field.

We present a structural model for the nematic polymer : this explains why the polymer is not isomorphous to the nematic monomer phase. Polymerization in an oriented nematic monomer phase leads to a smectic (oriented) polymer, with the backbone normal to the magnetic field.

1 . Introduction. - The onset of structure investi- gations of polymers is dated to the time when X-ray structure investigations were started. Although, today it is possible to produce polymeric single crystals, and the unit cell and the atomic arrangements of many polymers are well known, the exact structure of macromolecular systems are yet unknown. The structure of amorphous polymers which are always present even in the polymeric single crystals may only be approximated. The polymers applied in a great quantities in the technical field are generally amor- phous.

2. Some characteristics of polymeric structures. - The polymers are built up mostly from chain mole cules. These molecules can be oriented in their amor- phous state by different fields and the orientation of the molecules can be frozen by cooling the substance under its glass temperature. In this form, the polymers show anisotropic properties similar to the mesomor- phic materials, but the polymer of oriented amor- phous state cannot be regarded as mesomorphic material as it is far from the thermodynamic equili- brium. Its anisotropic properties tend to vanish even after several years.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979392

C3-460 F. CSER

The mesomorphic state is a property of compounds over million was calculated to be some thousands of with a highly anisotropic molecular geometry. Most nm-S. This length was more than 100 times greater of the polymers are linear chain molecules built up than the thickness of the lamelle where the chains from periodical or semiperiodical sequences of one or were situated perpendicular to the lamelle surface. several molecular units. Their overall geometric structure can be very anisotropic depending on the rigidity of the macro-molecule.

The molecular weights of the organic compounds with mesomorphic properties are some hundreds. The molecular weights of the substances considered as polymers vary from some ten thousand to some millions.

3. Structural models for semicrystalline polymers. - As the polymers are structurally similar to the meso- morphic materials, we expected to find many poly- mers of mesomorphic state but actually we did not. This may be attributed to the polymeric main chain.

The main chain of the polymers can be either soft or rigid. If the polymer chain is soft (e.g. unsubstitut- ed paraffines, polyoxymethylenes, proteins, etc.) the geometrical anisotropy of the polymer may vanish due to the formation of coils which are isodimensional bodies.

Polymers with anisotropic properties are expected among polymers with rigid main chain or with helical structure.

The first structural model for explaining the always simultaneously observed crystalline and amorphous character of polymers was the socalled fringed micelle [l, 21. It is shown on figure 1. The crystalline parts represented by parallel lines are bound together by the molecular chains of the amorphous parts. The swarm model of nematics [3] shows many simi- larities to the fringed micelle model of polymers.

FIG. 1. - Fringed micelle model for the structure of semicrystal- line polymers.

Keller [4, 51 studied the single crystals of polyole- fines by electron microscopy. He found 10-20 nm thick plate formed single crystals. The length of the extended chain of the polymer with a molecular weight

FIG. 2. - Lamelle model for the structure of flexible chain semi- crystalline polymers.

Figure 2 demonstrates the structure of the lamelle, built up from folded chains. The polymeric chains are folded several times forming parallel chains in the lamelle and forming an amorphous part above and beneath the lamelle. This type of structure is similar to the smectic state of paraffines [6-S]. The X-ray diffractogram obtained from hexagonal polyamides is very similar to that obtained from smectic B substan- ces [9, 101. The main difference between these struc- tures is that, while the molecules in smectic layers of a low molecular weight compound are fixed in the layer by Van der Waals forces, the linear chain segments of the polymer molecules are bound chemically. Thus, there are significant differencies in the mechanical properties of these substances. The plasticity and the polarization optical texture of hexagonal polyethy- lene are similar but not identical to those of low molecular weight smectic substances.

4. The mesomorphic solutions of polymers. - There are a lot of polymers with semirigid or fully rigid chains. Flory [l 1-13] assumed on the basis of his ther- modynamical investigations on the solutions of poly- mers with rigid chains that above a given limit of polymer concentration an anisotropic solution appears which depends on the ratio of the length and diameter of the cylinder shaped polymeric molecules.

The polymeric chain is rigid, when the main chain is built up from rigid segments. Typical examples are the polyaromatic-p-amides [14-201, aromatic poly- esters [21, 221, poly-alkanoates of p,~'-dihydroxy- a,a'-dimethyl-benzalazines [23]. Whenever the solu- tion of these polymers with molecular weights of some ten thousands proved to be nematic by diffe- rent methods, the polymers themself were not nematic as the nematic solutions turned out to be biphasic by increasing concentration of the polymer, where

NEMATIC POLYMERS AND RELATED STRUCTURES C3-461

besides a nematic polymer solution crystalline poly- mer could be identified as a second phase.

The structure of poly-(p-oxy-benzoic acid) was assumed to be a double spiral [22]. This polymer heated above 640 K showed a phase transition where the X-ray diffractogram of the polymer contained only one sharp diffraction peak characteristic for the hexagonal packing of paralell polymeric chains. This diffractogram was very similar to the diffractogram of a smectic B substance with a very thick layer. The anisotropic properties of the polymer were not investigated in detail.

The polymer molecule can also be rigid when a flexible or semiflexible chain forms a helix and the windings of the helix are bound either by hydrogen bonds as in the helices of peptides or by strong Van der Waals forces containing dipole-dipole components. The first polymer solution with anisotropic properties was found in helical polymers [24, 251. Typical other examples are synthetic and natural polypeptides, DNS, etc. [26-321. The solution of p-y-benzamido-l- glutamate was found to be cholesteric by texture analysis and by the orientability of the polymeric helices by electromagnetical fields [28-311. The mis- cibility of the solvent and the polymers were found also to be limited on both sides consequently, the precipitated polymers were not isomorphous with their cholesteric solutions, they were mostly crystal- line.

Theoretical work in this field [33-361 dealt also with mesomorphous polymer solutions. In, this paper we attempted to find nematic state bulky polymers.

5. The definition of nematic state bulk polymers. - We consider a polymer mesomorphic when the aniso- tropic properties of the polymer appears sponta- neously without the effect of any outer fields and the anisotropic state is stable in a given temperature range but the structure has a non reciprocal symmetry at least in one direction of an orthogonal reference coordination system [37, 381. Within this definition we consider the polymer as nematic when the packing of the cylinder shaped polymer molecules have only one structural characteristic, namely, their long axis are approximately parallel each other, consequently, they give an X-ray diffraction pattern without reflec- tions characteristic to reciprocal lattice.

These definitions are based mainly on the super- molecular structure of the polymers. As the mechani- cal properties of polymers result very high relaxation times, we cannot expect the nematic polymers to show relaxation phenomena similar to the well known nematics. The relaxation properties can be improved by forming solutions or plastified systems with nematic structure respectively, but the properties of these bicomponent systems can only be extrapolat- ed to the properties of the bulk polymer when they form full miscible series [39] on the polymer side.

A nematic polymer is a substance with anisotropic

properties. Optical anisotropy can also be found in non homogeneous polymers containing both amor- phous and crystalline phases. If we are to verify the existence of a nematic polymer we have to exclude the inhomogeneities in microscopic scale due to the crystalline-amorphous heterogeneous system.

The nematic polymer consists of rigid and aniso- tropic molecules with approximately cylinder shape, with the centre of gravity of these rigid molecules dispersed in the space statistically. The only exception is one direction of the orthogonal reference space (in the direction parallel to the long axes of the mole- cules) where a direct or pseudotranslation [37] has to be present. The nearer the shape of the pdlymer mole- cule to the cylinder the more will their packing approach that of the hexagonal packing, consequently, the sharper will be the X-ray reflection characteristic for the hexagonal packing.

In nematic state, the translation periods obtained from the diffuse diffraction peaks by X-ray are the measure of the molecular dimensions. Similar mole- cular volume should be obtained by other methods e.g. by GPC in diluted solution.

As the polymers have great viscosities in molten state with respect to the usual nematics, oriented amorphous states of them can be froozen by quenching the samples under their glass temperature. Solid mesomorphous state [40] can be achieved in such a way. The high relaxation times of polymeric systems are the cause of the long time necessary for orienting the polymer molecules as a whole even in solution [28]. A polymer can be regarded as nematic if its molecules can be oriented by electromagnetic field as rigid body. This orientation will perhaps never be complete, we accept the result if the orientation can already be detected (e.g. by NMR or by X-ray diffraction or by the Kerr effect [41-431). If the orientation experi- ments are carried out on plasticized samples the misciblity of the plasticizer and the polymer have to be proved, too.

6. Experiments for preparing polymers of nematic state. - Due to the expected particular properties of nematic polymers great efforts have been made to prepare them. Initially, nematic solutions were pre- pared using a nematic solvent or solute and a mono- mer capable for polymerization [44-501 and a poly- merization was carried out on the monomer. The polymers prepared in such a way did not show meso- morphic properties after precipitation.

Later, monomers with nematic state were poly- merized in their nematic state [40, 43, 50-821. Here the nematogenic groups were the side chain of an atactic [53] carbon backbone. Others tried to build up a polymer chain consisting of mesogen groups [21- 231.

Most of the papers mentioned above demonstrated the mesomorphic state of the polymers prepared, but non of them performed complete investigations on

C3-462 F. CSER

the nature of the mesomorphic state of the polymers. The most used method for identifying the mesomor- phic state was the SAX and the WAX diffraction [56- 59, 61, 74-76, 81, 821. It was stated after de Vries [83] that the smectic state polymers should have an X- ray diffraction peak at the small angle part of the diffractogram with a Bragg periodicity correspond- ing to the length of the rigid groups as the substituent of the vinyl group. Blumstein et al. [52] considered

.their polymer nematic when t$e X-ray reflection at small angles was diffuse. Perplies et al. [74, 811 found a peak in the small angles of the X-ray diffractogram when the polymerization was carried out in the nema- tic state: Later the same group [82] pointed out that the structure of the polymer did not depend on the state where it had been prepared. Similar structure of polymers in a homologous series were found in poly- mers independent of the presence or absence of nema- tic state of the monomer [58].

Many of the authors tried to prepare oriented nema- tic polymers by polymerizing in the oriented nematic state [55, 66, 67, 761. In all cases described oriented smectic polymers were formed, when the orientation of the side groups remained parallel to the direction of the magnetic field. Figure 3 shows the situation and

FIG. 3. -The formation of oriented smectic state polymer from oriented nematic state monomer.

gives a possible explanation of the phenomenon. In this case, the oriented smectic polymer shows many similarities to the oriented nematic state mono- mer. If we keep in mind, that a nematic polymer should have a cylinder shape, it will probably not have an isomorphism between a nematic monomer and a nematic polymer. Actually the investigation on the state diagram of nematic (or cholesteric) state monomer with the polymer formed from it [58, 591 demonstrated that they do not form homogeneous nematic phase with the, structure of the monomer. Hsu [63] presented a DSc trace for proving the homo- geneous nematic phase of the monomer and the polymer but this DSc trace proves the opposite, namely, they had a biphasic system.

The nematic and the cholesteric state were found unfavourable for the polymerization reaction by

many authors [58,59,67,70,71,73] with respect to the rate of polymerization, too.

Tsvetkov et al. [43, 84-89] investigated the hydro- dynamic properties of polymers built up from nema- togenous monomers. They found the polymers to be very rigid and anisotropic. On the base of the Kerr effect measured in the diluted solution of the polymers they stated that the rigid side chains were perpendicu- lar to, the main chain of the polymer. Finally they presented a geometric model of the nematic poly- mer [85] where the side chains appeared to have the same geometric arrangement in,polymeric form as in nematic state of the monomer. They stated, that the structure of the polymer should be nematic, as the monomer had nematic state, too.

We can conclude based on the review of the lite- rature on nematic state polymerization of vinyl monomers, that the nature of the structure of poly- mers seems to be independent of the state and condi- tions where the polyreaction had been carried out, and a polymer with rigid, anisotropic molecular character is formed independently to the fact whether the monomer has or has not a nematic state. None of the authors dealing with nematic state polymerization proved unequivocally that the polymer prepared in such a way was nematic.

7. Recent experiments for identifying the nematic structure of substituted vinyl polymers. - Based on the theoretical work of Flory [ l l , 131 we searched for nematic polymers among polymers with helical struc- ture. It was clear [61,90] that when a rigid bulky group was bound to the polyvinyl chain by a long, flexible group the polymer tended to take up the fish bone geometry resulting smectic polymer. The monomer molecules had smectic besides nematic states if they contained long chain paraffinic substituents in p- position, containing more -than 4 flexible chain atoms. We synthesized polymers on the base of aro- matic esters of the acrylic acid with a p-alkoxy pheny- lene substitution through an ester group. These poly- mers are stable at higher temperatures (above 250 oC). The length of the paraffinic chain was limited at 4 (p-butoxy). So the homologous series of p-alkoxy- phenyl-p-acryloyloxy-benzoate were synthesized and polymers were prepared from the monomers in liquid state radical polymerization. Two of the monomers, the base monomer, the phenyl-p-acryloyloxy- benzoate and its p-methoxy substituted homolog did not show nematic state. The polymers were investigat- ed by SAX, WAX diffraction SEM. Thermomechani- cal, DSc, and light diffraction investigations were carried out on the rigid bulk polymers. Their densities were measured by flotation, the volume of the rigid polymer molecules were estimated by GPC. The orien- tability of the macromolecules were investigated by NMR and X-ray diffraction using p-buthyloxy- phenyl-p-propyonyloxy-benzoate as plasticizer. The densities of the polymers in amorphous, glassy state

NEMATIC POLYMERS AND RELATED STRUCTURES

were estimated by the procedure described by Bondy [91]. The results of the prior experiments will be published elsewhere (HARDY, G., CSER, F., NYITRAI, K., SAMAY, G., J. Cryst. Growth, and CSER, F., POCSIK, I., TOMPA, K., MENCZEL, J., unpu- blished), here only a precis of the results will be displayed.

FIG. 4. - Polarizing microphotograph of poly-(phenyl-p-acryloy- loxy-benzoate). The film was prepared from the chloroform

solution of the polymer (150 X) .

Figure 4 shows polarizing microphotograph of a film obtained by evaporation of the chloroform solu- tion of poly-(phenyl-p-acryloyloxy-benzoate) at room temperature. Schlieren type texture can be seen on the pattern. If we assume, that the director is pointed towards the singularity the optical sign is negative. The change of the nematic director is smaller in this substance than in the usual nematics.

FIG. 6. -The dependence of the densities of poly-(p-alkoxy- phenyl-p-acryloyloxy-benzoates) on the length of the alkoxy substituents. A = p, = measured by flotation, V = p, = esti-

mated by the procedure of Bondy [91], p* = p,/p, = .

Figure 6 displays the change of the measured and estimated density respectively of the polymers as well as the spatial packing coefficients (p*). Here the estimated density is the density of the amorphous, glassy state polymer. As can be seen, the measured values are lower than the estimated. Similar spatial packing coefficient can be calculated for the close packing of parallel cylinders (p* = 0.907).

The wide angle X-ray diffractogram of the polymers are represented on figure 7. A broad halo at the greater

FIG. S. - Polarizing microphotograph of poly-(p-butyloxy- phenyl-p-acryloyloxy-benzoate). The sample was obtained by

cooling the molten powder of the polymer (150 X) .

Figure 5 shows the polarizing microphotograph of the poly-(p-butoxy-phenyl-p-acryloyloxy-ben- , zoate) prepared by cooling the molten powder. The

'-2L- '

texture is not characteristic one, but this type of i o ' 1 2 - 1 L - - 1 6 i s ' 2 n 2 ' 2i ' 2 6 . 2s j o e z e

texture may be obtained from the molten state of the FIG. 7. -X-ray transmission diffractograms of poly-(p-alkoxy- polymers containing rigid substituents. phenyl-p-acryloyloxy-benzoate).

C3-464 F. CSER

angles displays the packing ( d ) of the side chains, the sharper peaks with increasing intensity by increas- ing length 08 the side chains at the small angles show periodicity ( D ) with values proportional with the length of the side chains (see Fig. 8). If we consider

scattering curves were analysed for different shape of inhomogeneities [93]. The measure of the inhomo- geneities are presented in figure 9.

1 .

O @ @ @ @ polymer

FIG. 8. - The dependence of the D(0) and of the d(a) values on the length of the alkyl substituent in poly-(alkoxy-phenyl-p-acryloy-

loxy-benzoates).

the small angle scattering to be due to the scattering from smectic layers, the densities of the polymers would be scattered around 1.5 g/cm3, which are 30 % higher than the measured values. The number of scattering periods calculated from the line broaden- ing by the formula

R KA 2s in8 - 2 K t g e n = - = - x - - - D p cos 8 A P

were found x 3. Here P is the symbol of half width of the reflection peaks at the half intensity, K N 1, 1 is the wavelength of the X-ray, 8 is the scattering angle at the peak maximum. This small number of scattering periods can not be obtained from reci- procal lattices. Therefore, D values will be considered as the diameter of cylinder shaped molecules built up from layers with the thickness of d. The length of the cylinders were measured by the Guinier plot of the X-ray scattering at zero angles [92, 931. The

FIG. 9. - The dependence of the length of the cylinders and the number of monomeric units (m) in the slice of the cylinder with a thickness of d on the length of the alkyl substituents in poly-(p-alk- oxy-phenyl-p-acryloyloxy-benzoates). h,, h, and h, were obtained by the Guinier plot of the small angle X-ray scattering using one, two or three dimensional shapes of inhomogeneities (A, a, V).

0 = calculated from the results obtained by GPC.

The volumes of the rigid molecules were measured in a diluted solution of sym-trichloro-benzene by GPC. The average [l31 volume of the polymers were recalculated to the length of a cylinder with a dia- meter of D and these lengths are also represented on figure 9. The lengths of the molecules assumed to be rigid do not differ significantly in the two independent methods.

The lengths of the cylinder shape molecules are very close to each others in the polymers with diffe- rent lengths of side chains. They decrease with the increasing length of the substituents in the bulky polymers, but reversed in the solution. The number of monomeric units in the slice of the cylinder with the thickness of d represented on the lower part of figure 9 shows increasing packing density within the polymeric molecule by increasing length of the side chains. When the polymers are soluted the helices are rolled out resulting greater length of the helix as found also in the solution of some biopolymers [94].

The measure of inhomogeneities in the polymers were investigated by scanning electron microscopy.

NEMATIC POLYMERS AND RELATED STRUCTURES C3-465

FIG. 10. - Scanning electron micrograph of poly-(phenyl-p-acry- FIG. 11. - Scanning electron micrograph of poly-(p-buthyloxy- loyloxy-benzoate). Magn. : 12 100. phenyl-p-acryloyloxy-benzoate). Magn. : 6 100.

Figure 10 displays the SEM pattern of the poly- (phenyl-p-acryloyloxy-benzoate). Figure 1 1 shows the SEM pattern of the poly-(p-butoxy-phenyl-p- acryloyloxy-benzoate). The patterns show homoge- neous glassy state of a substance. For comparison the SEM pattern of a smectic state polymer (poly- cholesteryl-vinyl-succinate, [71]) is also present-ed (Fig. 12). Here the layered structure of the polymer is well visible.

In the following the investigations on plastified systems of the poly(pheny1-p-acryloyloxy-benzoate) (pFAB) plastified by p-buthyloxy-phenyl-p-propyony- loxy-benzoate (BPPB) are presented.

The BPPB has a nematic state from 86 to 95 oC. Its X-ray pattern in the oriented nematic state oriented by a magnetic field of 1.5 MA/m is shown on figure 13. The pattern is characteristic for a cybotactic nematic [41, 951 state material. The sample was then cooled to room temperature in the magnetic field, when the oriented crystallization was indicated (Fig. 14). The long axes of the BPPB molecules remained parallel to the direction of the magnetic field in the crystalline state. The conclusion of these figures is that the greatest magnetic polariza- bility of the monomeric units are parallel with the long axis of the molecule. .

The state diagram of BPPB and pPAB is shown on

figure 15. The detailed interpretation of this diagram will be presented in the full paper (Cser et al., to be published). What is important for the present investi- gation is that pPAB and the BPPB form a mesomor- phic solution with a full misciblity on the side of the polymer (field C on figure 15). This mesomorphic phase is transformed into a biphasic reaching field B, then a full miscible isotropic phase is formed (A). The nematic state of BPPB is not isomorphous with the mesomorphic state of pPAB. The field C is favou- rable [58, 59, 96, 971 for the further investigations.

The X-ray pattern of the two component system containing 50 W. % of BPPB taken at 130 OC is shown on figure 16. The broad halos at the small as well as the wide angles refere to an ordered structure. The pattern did not change markedly when a magnetic field was applied. After cooling the sample to room temperature under effect of magnetic field, the oriented crystallization of the excess BPPB (see state diagram) is observed as is shown on figure 17. Here the direc- tion of the long axes of the BPPB molecules are per- pendicular to the direction of the magnetic field. When the system was reheated to 85 OC, where the excess BPPB was'resoluted in the polymer, the orientation of the plastified system was observed (Fig. 18). The orientation of the side groups of the polymer were perpendicular to the orientation of the

FIG. 12. - Scanning electron micrograph of poly-(cholesteryl- vinyl-succinate). Magn. : 6 100.

FIG. 13. - X-ray diffraction pattern of p-buthyloxy-phenyl-p propyonyloxy-benzoate at 90 OC with a magnetic field of 1.5 MA/m.

The arrow shows the direction of the field.

monomer like material (BPPB). Consequently, the macromolecule as rigid body has been oriented with the axes of the cylinder parallel to the orienting field. After the magnetic field was interrupted the aniso- tropy of the system disappeared too as is visible on figure 19.

The orientation effect was investigated by NMR on the systems containing 80 % of polymer and 20 % of BPPB. Figure 20 shows the broad line NMR spectra

FIG. 14. - X-ray diffraction pattern of p-buthyloxy-phenyl-p propyonyloxy-benzoate at room temperature cooled from 90 OC under the influence of magnetic field. The arrow indicates the

direction.of the field.

r ~ . 15. - The state diagram of p-buthy?uxy.pkenyl-p-propyuny- loxy-benzoate and poly-(phenyl-p-acryloyloxy-benzoate), obtained by DSc (A D @a + X ) and by polarizing microscopy (A V 0 0). A = T,, D = endothermic transformation begins, C), V = phase transformation in BPPB phase, a, A = melting of the BPPB phase into nematic state, +, 0 = BPPB phase disappears, = endotherm transformation begins, X , = clearing point. $ = mesomorph phase appears upon cooling. A = isotropic phase, $ = isotropic + mesomorphous phases. C = mesomor- phous phase. D = solid mesomorphous phase. From E to I = bipha- sic systems, where one phase is the BPPB, in nematic (E), in crystal- line I (F) and in crystalline 11 (G, H, I), the other phase is a plast5ed polymer in solid mesomorphic (H, I) and in liquid mesomorphic

(E, F, G) states respective.

NEMATIC POLYMERS AND RELATED STRUCTURES C3-467

FIG. 16. -X-ray diffraction pattern of the 1 : 1 mixture of p- 19. diffraction pattern of the sample shown in buthyloxy-phenyl-p-propyonyloxy-benzoate and poly-(phenyl-p- figure 17 without magnetic field at 80 OC.

acryloyloxy-benzoate) at 130 OC.

FIG. 17. - Room temperature X-ray diffraction pattern of 1 : 1 mixture of p-buthyloxy-phenyl-p-propyonyloxy-benzoate and poly- (phenyl-p-acryloyloxy-benzoates). The sample was cooled from 130 OC in a magnetic field of 1.5 MA/m. The arrow indicates the 90 O

direction of the field.

8 3 O

FIG. 20. - NMR proton resonance spectra of p-buthyloxy-phenyl- p-propyonyloxy-benzoate at different temperatures.

F I ~ . - X-ray pattern of the sample shown in of the two side peaks will not be investigated in detail figure 17 after reheating it in magnetic field up to 80 oC. here. The NMR spectra of the plastified polymer

are shown on figure 21. There are no splittings in the resonance peaks in the holten state of the system

of the BPPB at different temperatures. The splitting (above 80 O C ) . The differencies obtained in the NMR of the single, broad line into three sharp peaks is spectra with different matrix indicates the different characteristic for nematic materials consisting of p- orientation of the side chaines of the polymer when phenylene groups. The anisotropy in the intensities they are free or when they are chemically bound.

FIG. 22. - The .model of cylinder shape polymeric molecules with an axial side chain orientation.

FIG. 21. - NMR proton resonance spectra of the system consisted of 20 % of p-buthyloxy-phenyl-p-propyonyloxy-benzoate and of 80 % of poly-(phenyl-p-acryloyloxy-benzoate) at different tempe-

ratures.

The observations presented above rendered possible the construction of a probable molecular model of the helical polymers with nematic structure, which is shown on figure 22. The molecules have an overall shape of cylinder with a diameter of D, where the side chains are located perpendicular to the axes of the cylinder. As the anisotropic molecules sur- round the axes of the cylinder, their highest compo- nents of magnetic susceptibility do not give a torque to the rigid molecule. H Q W ~ V ~ ~ as those components that are parallel to the axis as is shown on figure 23 become summarized resulting a total torque which was detected by X-ray diffraction and by NMR.

The ratio of thglength to the diamFter of the cylin- ders were found to be less then 4, therefore, the meso- morphic state of the polymers can not be deduced from the theory of Flory [ll-131. The pseudohexagonal packing of these cylindres (as it is shown on figure 24) is in a good agreement with the spatial packing den- sity calculated on the base of density measurements.

As a conclusion of the results presented we were able to draw the geometric model of the polymers with nematic structure. These polymers have macro- molecules with a cylinder shape. This shape can be formed from regular or from irregal helical arrange- ments of the bulky monomeric units. This type of structure is very probable in polymers with rigid

FIG. 23. - The spatial orientation of the components of the magnetic susceptibility in the aromatic side chains of a cylinder

shaped rigid polymeric molecule.

FIG. 24. - The semihexagonal packing of polymeric molecules with cylinder shape.

substituents on the vinyl group. If this rigid substi- tuent is bound to -the polyvinyl-chain by flexible segments, they form a more dense structure, where the side chains are parallel to each other thus, form- ing a smectic type double layer. The main difference between the nematic and the smectic states of poly- mers are detectable in the orientability of the macro- molecules by electromagnetic field. The structure, is smectic when the orientation of the side chains is parallel to the orienting field, and the polymer is

NEMATIC POLYMERS AND RELATED STRUCTURES C3-469

nematic when the orientation of the side chains is nematic structure of the polymers - according to perpendicular to the field. The main axes of the rigid the observations [55, 58, 63, 67, 761 - cannot be polymer are to be considered as the director. This isomorphous with the nematic state of their monomer.

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