Influence of alkoxy tail length and unbalanced mesogenic core on phase behavior of mesogen-jacketed...

Influence of Alkoxy Tail Length and Unbalanced MesogenicCore on Phase Behavior of Mesogen-Jacketed LiquidCrystalline Polymers

SI CHEN,1,2 LAN-YING ZHANG,1 LONG-CHENG GAO,1 XIAO-FANG CHEN,1 XING-HE FAN,1

ZHIHAO SHEN,1 QI-FENG ZHOU1

1Department of Polymer Science and Engineering and Key Laboratory of Polymer Chemistry and Physics of Ministry ofEducation, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China

2College of Engineering, Peking University, Beijing 100871, China

Received 19 September 2008; accepted 23 October 2008DOI: 10.1002/pola.23167Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: When the flexible terminal substituent changes from butoxy to hexyloxyor longer, smectic C (SC) liquid crystalline phase was firstly reported to develop froma kind of mesogen-jacketed liquid crystalline polymer (MJLCP) whose mesogenic sidegroups are unbalancedly bonded to the main chain without spacers. A series ofMJLCPs, poly[4,40-bis(4-alkoxyphenyl)-2-vinylbiphenyl(carboxide)] (nC2Vp, n is thenumber of the carbons in the alkoxy groups, n ¼ 2, 4, 6, 8, 10, and 12) were designedand synthesized successfully via free radical polymerization. The molecular weightsof the polymers were characterized with gel permeation chromatography, and the liq-uid crystalline properties were investigated by differential scanning calorimetry,polarized light microscopy experiments, and 1D, 2D wide-angle X-ray diffraction.Comparing with the butoxy analog, the polymer with unbalanced mesogenic core andshorter flexible substituents (n ¼ 2, 4) keeps the same smectic A (SA) phase, butother polymers with longer terminal flexible substituents (n ¼ 6, 8, 10, and 12) candevelop into a well-defined SC phase instead of SA phase. VVC 2008 Wiley Periodicals, Inc.

J Polym Sci Part A: Polym Chem 47: 505–514, 2009

Keywords: functionalization of polymers; liquid-crystalline polymers (LCP);structure

INTRODUCTION

Liquid crystalline polymers (LCPs) have twomain categories: main-chain LCPs with mesogenunits located in the main chain and side-chainLCPs with mesogens as side groups.1 For side-

chain LCPs, based on Finkelmann’s principle,flexible spacers are needed to decouple motionsbetween the main chain and the mesogenic sidegroups.2 Mesogens can be connected to mainchain via either ‘‘terminal’’ or ‘‘lateral’’ attach-ment in side-chain LCPs.3,4 Extensive reports onvarious phase structures of laterally attachedside-chain LCPs by research groups of Finkle-mann and coworkers,5 Pugh and Schrock,6 Grayand Hill,7 Ober and coworkers,8 Percec and Toma-zos,9 Keller et al.,10 and a few others have beenpublished during the past decade, hoping to widenthe potential applications of laterally attached

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 505–514 (2009)VVC 2008 Wiley Periodicals, Inc.

Additional Supporting Information may be found in theonline version of this article.

Correspondence to: X.-H. Fan (E-mail: [email protected]), Z. Shen (E-mail: [email protected]) or Q.-F. Zhou(E-mail: [email protected])

505

side-chain LCPs. Different from Finkelmann’sprinciple, Zhou et al. found out that when gravitycenters of mesogenic units were connected later-ally to the main chain, flexible spacers to decouplethe dynamics of main chain and side groupsseemed not necessary. Liquid crystalline behaviorof the LCPs was also shown with or without shortspacers.11,12 The polymer backbones are forced toadopt a more extended conformation to accommo-date the spatial requirement of the bulky andrigid mesogenic units, which form a ‘‘jacket’’around the main chain. Thus, a new category of‘‘mesogen-jacketed liquid crystalline polymers’’(MJLCPs) was proposed.

In many laterally attached side-chain LCPswith a spacer of a certain length, polymers candevelop into nematic phases,8,13–15 smectic A(SA)

16–19 and smectic C (SC) phases.16,17,20,21 But

when the spacer is replaced by a single carbon–carbon bond linking the backbone and the meso-genic side groups, polymers can only pack into co-lumnar nematic (UN), hexagonal columnar (UH),hexatic columnar nematic (UHN) phases,10,22,23

and SA24,25 phases.

It is possible to alter the phase structure of theMJLCPs by changing several variables, includingchemical structures of mesogens, the length ortype of the terminal flexible substituent(s), natureof the polymer backbone, tacticity, and so on.26 Wetried to change only one variable so as to studythe relationship between a single structural vari-able of the monomer and the change in the phasestructure of MJLCPs. The series of MJLCPs wechose is poly[4,40-bis(4-butoxyphenyloxycarbonyl)-2-vinylbiphenyl],25 with butoxy as the terminalsubstituent and without spacers. We simplychanged the length of the monomer’s terminalflexible substituent, with all others unchanged. Aseries of polymers with different lengths of theterminal alkyl, poly[4,40-bis(4-alkoxyphenyl)-2-vinylbiphenyl(carboxide)] (nC2Vp, n is the num-ber of the carbons in the alkoxy groups, n ¼ 2,4,25 6, 8, 10, and 12) were designed and synthe-sized (Scheme 1). The chemical structures of thepolymers are as follows:

In this article, we described the synthesis ofthe monomers and the polymers and the specificLC phase structures and transitions as well. Forthe polymers without spacers having the samelaterally attached, unbalanced mesogenic coreand terminal flexible substituents shorter thanbutoxy groups, SA phase kept unchanged;whereas the ones with terminal flexible substitu-ents longer than butoxy groups, well-defined SC

phase was observed.

EXPERIMENTAL

Materials

Chlorobenzene was washed with H2SO4, NaHCO3

and distilled water; and then was distilled fromcalcium hydride. Tetrahydrofuran (THF, AR; Bei-jing Chemical Co.) was heated under reflux overcalcium hydride for at least 8 h and distilledbefore use. Dichloromethane (AR. Beijing Che-mical Co.) was dried with magnesium sulfateanhydrous. Azo-bisisobutryonitrile (AIBN) waspurified by recrystallization from ethanol. Methyl4-bromo-3-methylbenzoate (98%, Alfa Aesar), hy-droquinone (AR. Beijing Chemical Co.), triphenyl-phosphine (99%, Alfa Aesar), trimethylborate(AR. Beijing Chemical Co.), 40% formaldehyde(AR. Beijing Yi Li Chemical Co.), N,N0dicyclohexylcarbodiirnide (DCC, 95%, Sinopharm ChemicalReagent Co.), 4-dimethylaminopyridine (DMAP,99%, ACRO), 1-bromohexane (98%, Alfa Aesar), 1-bromooctane (98%, Alfa Aesar), 1-bromodecane(98%, Alfa Aesar), and 1-bromododecane (98%,Alfa Aesar) were used as received without furtherpurification.

Characterization

1H NMR spectroscopy was performed on aBRUKER 400 MHz with tetramethylsilane as theinternal standard at room temperature in CDCl3or DMSO. Elemental analyses were carried outwith an Elementar Vario EL instrument. Massspectrometry spectra were recorded on a Finni-gan-MAT ZAB-HS spectrometer. Gel permeationchromatography measurements were carried outin THF with a Waters 2410 instrument equippedwith a Waters 2410 RI detector and three Watersl-Styragel columns (103, 104, and 105 A). Theflow rate was 1.0 mL/min at 35 �C. The calibra-tion curve was obtained by linear polystyrenestandards.Scheme 1. Chemical structures of the polymers.

506 CHEN ET AL.

Journal of Polymer Science: Part A: Polymer ChemistryDOI 10.1002/pola

The thermogravimetric analysis (TGA) wasperformed on a TA Q600SDT TGA-DTA-DSCinstrument at a heating rate of 20 �C/min in nitro-gen atmosphere. Differential scanning calorime-try (DSC) examination was carried out on a TADSC Q100 calorimeter at a programmed heatingrate under continuous nitrogen flow. The samplesize was about 5 mg and encapsulated in hermeti-cally sealed aluminum pans of constant weights.The temperature and heat flow scale at differentcooling and heating rates were calibrated usingstandard materials such as indium and benzoicacid. Polarized light microscopy (PLM) observa-tion was conducted on a Leitz Laborlux 12 micro-scope with a Leitz 350 hot stage.

One-dimensional (1D) wide-angle X-ray diffrac-tion (WAXD) experiments were performed on aPhilips X’Pert Pro diffractometer with a 3-kW ce-ramic tube as the X-ray source (Cu Ka) and anX’celerator detector. The sample stage was sethorizontally. The reflection peak positions werecalibrated with silicon powder (2y[ 15�) and sil-

ver behenate (2y \ 10�). A temperature controlunit (Paar Physica TCU 100) in conjunction withthe diffractometer was utilized to study the struc-ture evolutions as a function of temperature. Theheating and cooling rates in the WAXD experi-ments were 10 �C/min.

2D WAXD pattern was obtained using aBruker D8Discover diffractometer with GADDSas a 2D detector. Again, the calibration was con-ducted using silicon powder and silver behenate.The 2D diffraction patterns were recorded in atransmission mode at room temperature. The filmsample was heated and annealed at a certain tem-perature for 10 h. It was mounted on the samplestage and the point-focused X-ray beam was par-allel to the film plane. For both the 1D and 2D dif-fractions, the background scattering was recordedand subtracted from the sample patterns.

Synthesis of Monomers

The synthetic route of the monomers of 4,40-bis(4-alkoxyphenyl)-2-vinylbiphenyl(carboxide) (nC2Vm,n is the number of the carbons in the alkoxygroups, n ¼ 2, 4, 6, 8, 10, and 12) is shown in Fig-ure 1. The experimental details of the monomerssynthesis are in accordance with the literature.25

The mass spectrometry, elemental analysis, and1H NMR data of the monomers are provided inthe Supporting Information (Tables S1 and S2).

Polymerization

All polymers (denoted as nC2Vp in Fig. 1) wereobtained by free radical polymerization (seeFig. 1). For example, about 0.2 g (0.2700 mmol)10C2Vm was placed into a 10 mL reaction tubecontaining a magnetic stir bar. Then, 1.0 g ofchlorobenzene solution of AIBN (0.0048 mmol)was introduced with a syringe. After that, thereaction mixture was purged with nitrogen andsubjected to four freeze-pump-thaw cycles toremove any dissolved oxygen and sealed undervacuum. The tube was placed into an oil bath at60 �C for about 30 h. After the polymerizationwas terminated by putting the tube into ice/watermixture, the tube was broken. The product wasdiluted with THF and precipitated into methanol.To completely eliminate the unreacted monomers,the precipitate was redissolved in THF and thenreprecipitated in methanol for three times. Afterpurification, the polymers were dried to a con-stant weight.

Figure 1. Synthetic route of the monomers andpolymers.

PHASE BEHAVIOR OF MJLCPs 507


RESULTS AND DISCUSSION

Synthesis and Characterization of the Monomersand Polymers

As shown in Figure 1, the monomers were synthe-sized mainly in three steps as follows: (i) one sideetherification of hydroquinone with n-alkyl bro-mide (n ¼ 2, 4, 6, 8, 10, and 12) to get 4-alkoxy-phenol (1); (ii) Suzuki coupling reaction of 4-boro-nobenzoic acid (2) and 4-bromo-3-vinylbenzoicacid (3) to synthesize2-vinyl-4,40-bi(phenyl carbox-ylic acid) (4); (iii) esterification of (1) and (4) toform the monomers. The structures of the mono-mers have been confirmed by conventional analy-ses including 1H NMR, elemental analysis, andmass spectrometry.

All the monomers could be easily polymerizedvia free polymerization method. The polymerswere completely soluble in regular organic solventssuch as THF, chlorobenzene, chloroform, and soforth. Table 1 summarized the molecular charac-teristics of the polymers. The thermal stabilities ofthe polymers were investigated with TGA in anitrogen steam. Under nitrogen atmosphere, allthe polymers have good thermal stability, withtemperature at 5.00%weight loss all above 350 �C.

Phase Transitions and Phase Structures

The results of DSC cooling and heating experi-ments of the nC2Vp with shorter flexible terminalsubstituents showed that all the curves duringthe first cooling cycle and second heating cyclegive little information about the LC phase transi-tion. But for the samples with longer flexible ter-minal substituents, a peak caused by the meltingof crystals formed by the long alkoxy flexible ter-minals could be found below 50 �C. The glass

transition temperatures (Tg) of the polymers (listedin Table 1) take place, but no more transition peakshave been observed, which is similar to most otherMJLCPs.27 Polymers with different terminal flexi-ble substituents (n¼ 2, 4, 6, 8, and 10) exhibited sim-ilar thermal transitions. For the 12C2Vp sample, ithad one more peak at around 250 �C. Combiningwith the results of PLM, we know this peak at 250�C is caused by the phase transition from liquid crys-talline phase to isotropic phase.

Birefringence of the polymers was observedwith PLM. The samples were cast from THF solu-tion and slowly dried at room temperature. Theliquid-crystalline birefringence did not developuntil the sample was heated to a temperaturemuch higher than Tg (Fig. 2). Birefringence of2C2Vp, 4C2Vp, 6C2Vp, 8C2Vp, and 10C2Vp keptunchanged even when heated to 270 �C. Whilecooled to room temperature from 270 �C, the bire-fringence of the sample remained unchanged. Itimplies that the ordered structure formed at hightemperature kept unchanged upon cooling. Theseare all similar with other MJLCPs synthesized inour group.27 However, for sample 12C2Vp, thebirefringence disappeared above 250 �C andappeared again when cooled below 250 �C, keep-ing unchanged during cooling to room tempera-ture, indicating that the phase transition to iso-tropic phase took place above 250 �C.

The phase transition of the polymers was fur-ther verified by variable temperature, 1D WAXDexperiments. In such experiments, samples about30 mg were cast from THF solution. Figure 3describes the change of the structurally sensitive1D WAXD patterns of 2C2Vp from 40 to 300 �C.Upon first heating [see Fig. 3(a)], a scatteringhalo at low 2y angle of 4.4� � 3.6� was observedfrom the as-cast amorphous sample. Moreover,

Table 1. Molecular Weights and Thermal Transitions of Polymers

Sample Mn (�10�4)a Mw/Mna Tg (�C)b Td (�C)c LC Phase

2C2Vp 6.4 1.20 150 394 SA

4C2Vpd 8.3 1.19 109 391 SA

6C2Vp 6.3 1.34 118 383 SC

8C2Vp 11.2 1.44 112 350 SC

10C2Vp 9.7 1.48 96 367 SC

12C2Vp 8.0 1.36 86 387 SC

aObtained from GPC, linear PS as standards.bEvaluated by DSC during second heating cycle at a rate of 20 �C/min.c The temperature at which 5% weight loss of the sample was reached from TGA under nitro-

gen atmosphere.dReferenced as [25].

508 CHEN ET AL.


higher orders of the diffractions were visible attemperatures above 260 �C. When the samplewas cooled, the liquid crystalline phase appearedto be stable, as shown by Figure 3(b), with higherorders of the diffractions clearly visible. The ratioof the scattering vectors of the diffraction peakswas 1:2:3, indicating a smectic structure of thesample. Figure 3(c) is the d-spacing correspondingto the halo and peak in the low 2y angle region asa function of temperature. Upon first heating, theglass transition gave the first inflection at around140 �C and the sample turned into liquid crystal-line phase at about 200 �C. At 260 �C, the smecticphase was finally developed and higher orders ofthe diffractions were readily visible. During firstcooling, the d-spacing kept almost unchangedexcept at temperatures near Tg, again indicatingthat the ordered structure formed at high temper-ature kept unchanged upon cooling. The maxi-mum d-spacing value (2.60 nm) of the sample isalmost identical to the calculated length of therigid mesogenic units in monomers (2.59 nm),which means the mesogenic units are perpendicu-lar to the main chain. So, we presume that thestructure of the liquid crystalline phases is SA,the same as the butoxy analog.25

Figure 4 describes the change of the structur-ally sensitive 1D WAXD patterns of 10C2Vp from40 to 270 �C. Upon the first heating [see Fig.4(a)], a scattering halo at low 2y angle of 2.8� �2.2� was observed from the as-cast amorphoussample. Moreover, higher orders of the diffrac-tions were visible at temperatures above 230 �C,indicating possible existence of a smectic liquidcrystalline phase. When the sample was cooled,the smectic phase appeared to be stable, as shownby Figure 4(b). And Figure 4(c) shows partial pat-terns of Figure 4(b) with 2y higher than 3.7� dur-ing cooling, with higher orders of the diffractionsclearly visible. The ratio of the scattering vectorsof the diffraction peaks was 1:2:3:5, indicating asmectic structure of the sample. Figure 4(d) is thed-spacing corresponding to the halo and peak inthe low 2y angle region as a function of tempera-ture. Upon first heating, we can see that the glasstransition gave the first inflection at around 100�C and the sample turned into liquid crystallinephase at about 190 �C. At 230 �C, the smecticphase was finally developed and higher orders ofthe diffractions were readily visible. During firstcooling, the d-spacing kept almost unchangedexcept at temperatures near Tg, again indicatingthat the ordered structure formed at high tempera-ture kept unchanged upon cooling. The maximumd-spacing value (4.0 nm) of the sample is less thanthe calculated length of the mesogenic units inmonomers (4.4 nm, assuming all the n-alkoxy tailshave all-trans conformation). This indicates thatthemesogenic side chain is probably not perpendic-ular to the main chain, which is different from thebutoxy analog.25 All other polymers (nC2Vp, n¼ 6,8, and 12) exhibited similar behavior.

To further confirm the smectic structure of thepolymers, 2D WAXD experiments were carriedout. Films of 2C2V were mechanically sheared at300 �C. Figure 5(a) shows the 2D WAXD patternwith incident beam perpendicular to the sheardirection. Two pairs of strong diffraction arcs canbe found on the equator at 2y ¼ 3.8� and 7.6� (d-spacings are 2.32 and 1.15 nm, respectively,resulting in a ratio of 1:1/2), indicating that thelayer normal of the ordered structure is parallelto the shear direction on a nanometer scale, whichis perfectly consistent with the 1D WAXD results.Meanwhile, two scattering halos in the high 2yangle region are more or less concentrated on themeridian with rather broad azimuthal distribu-tions, revealing the existence of short-range order.The 2D WAXD pattern in Figure 5(a) proves thatthe 2C2Vp forms a typical SA phase.

Figure 2. Representative texture of 10C2Vp. Sam-ple was heated to 270 �C at 10 �C/min, then cooled to30 �C at 10 �C/min and pictured at 30 �C. [Color fig-ure can be viewed in the online issue, which is avail-able at www.interscience.wiley.com.]



During the 2D WAXD experiments of 10C2Vsamples, we found an interesting phenomenon:the samples without alignment could develop dif-fraction arcs instead of ring patterns after heatingand annealing at a certain temperature, indicat-ing orientation of polymer chains by themselves.The conventional method of mechanically shear-ing the films seemed not necessary. Preliminary

results appear to suggest that such an orientationis surface dependent, but the detailed mechanismis still under investigation. Figure 6(b) shows the2D WAXD patterns of the 10C2Vp sample(annealed at 230 �C for 10 h, N2 atmosphere)recorded at room temperature with X-ray incidentbeam parallel to the film plane. Three pairs ofstrong diffraction arcs can be found on the

Figure 3. 1D WAXD patterns of sample 2C2Vp obtained during first heating (a),first cooling (b) of the as-cast film, and the d-spacing data (d ¼ k/2sin y) as a functionof temperature measured during first heating and first cooling in the low 2y anglerange (c). Note that q* is the value of the scattering vector (q) of the first-order dif-fraction peak, and q ¼ 4psin y/k. [Color figure can be viewed in the online issue,which is available at www.interscience.wiley.com.]

510 CHEN ET AL.


Figure 4. 1D WAXD patterns of sample 10C2Vp obtained during first heating (a),first cooling (b), the partial pattern with a 2y range of 3.7�–31.5� during first cooling(c) of the as-cast film, and the d-spacing data (d ¼ k/2sin y) as a function of tempera-ture measured during first heating and first cooling in the low 2y angle range (d).Note that q* is the value of the scattering vector (q) of the first-order diffractionpeak, and q ¼ 4psin y/k. [Color figure can be viewed in the online issue, which isavailable at www.interscience.wiley.com.].

equator at 2y ¼ 2.2�, 4.4�, and 6.3� (d-spacingsare 4.0, 2.0, and 1.4 nm, with a ratio of 1:1/2:1/3),indicating that the ordered structure is developedparallel to each other on the nanometer scale,which is consistent with the 1D WAXD results.Meanwhile, four scattering halos in the high 2yangle tilted a certain angle with rather broad azi-muthal distributions. The tilt angle is about 20�.This is a typical diffraction pattern of SC phase.The 2D WAXD pattern in Figure 6(a) confirmsthat the 10C2Vp forms a SC phase. Similar pat-terns were obtained from different samples ofnC2Vp (n ¼ 6, 8, 10, and 12). The data of 2y, d-spacing, calculated length of the mesogenic units,and tilt angles are provided in the Supporting In-formation (Table S3).

From all these results, we know the polymersof nC2Vp (n ¼ 6, 8, 10, and 12) form a SC phase ata temperature higher than Tg and the mesogenicside chains are parallel to one another and tilt acertain angle from the layer normal, unlike4C2Vp in which the mesogens are parallel to thelayer normal,25 whereas 2C2Vp polymers keep SA

phase unchanged. So we presume the schematicdrawing of the polymers with rigid unbalanced

mesogenic core with longer flexible terminal sub-stituents is shown in Figure 7.

Although smectic phases (SA) have also beenobserved in MJLCPs with almost balanced meso-genic units,24 the unbalanced nature of the

Figure 5. 2D WAXD film pattern of 2C2Vp(a)polymer recorded at room temperature; beam direc-tion (b).

Figure 6. 2D WAXD film pattern of 10C2Vp(a)polymer recorded at room temperature; beam direc-tion (b).

Figure 7. Schematic drawing of the polymers withrigid unbalanced mesogenic core.

512 CHEN ET AL.


mesogens in the polymers in this study could playan important role in leading to LCPs with LCbehavior similar to that of regular laterallyattached side-chain LCPs. In nC2Vp polymers,there are no spacers between the main chain andmesogenic side chains, thus they do not satisfyFinkelmann’s decoupling principle. On the otherhand, the mesogens are not attached to the mainchain through the gravity center of the mesogeniccore, resulting in larger amplitude of perturbationon mesogenic side chains by the motion of themain chain. This could be the reason that thesepolymers do not behave like typical MJLCPs anddo not form columnar phases. However, the sitewhere the mesogenic side chains are attached tothe main chain is still close to the gravity centerof the mesogenic core, and the aforementionedperturbation is limited. Therefore, such type ofpolymers can still be regarded as MJLCPs, lead-ing to the formation of smectic phases. The funda-mental reason still needs to be investigated.

In this series of nC2Vp polymers, when nincreases above 4, the LC phase of MJLCPschanges from SA (for n ¼ 4) to SC (for n ¼ 6, 8, 10,and 12), whereas the LC phase of MJLCPs keepsthe same SA phase when n decreases below 4 (n ¼2). With increasing length of alkoxy tails on themesogens, the flexible terminal substituents areincreasingly immiscible with the rigid core. Inaddition, longer flexible terminals had larger spa-tial requirements in packing. These two factorscould be the reasons that the mesogens were com-pelled to tilt a certain angle to form SC phases.Furthermore, such a trend from SA to SC phaseson increasing alkoxy length is not abnormal.Small-molecule liquid crystals also tend to formSC phases when alkyl or alkoxy tails increases,although a lot of these molecules start to developSC phases even when butyl or butoxy tails areintroduced.28

CONCLUSIONS

Six monomers with rigid unbalanced mesogeniccore and flexible terminals, 4,40-bis(4-alkoxy-phenyl)-2-vinylbiphenyl(carboxide) (nC2Vm, n isthe number of the carbons in the alkoxy groups, n¼ 2, 4, 6, 8, 10, and 12) were synthesized andpolymerized by free radical polymerization. Weobtained the MJLCPs with unbalanced mesogeniccore and different flexible terminals nC2Vp (n isthe number of the carbons in the alkoxy groups,n ¼ 2, 4, 6, 8, 10, and 12) separately. The chemical

structures of the monomers and polymers wereconfirmed by various characterization techniques.Their phase structures and transitions of thepolymers were investigated with DSC, PLM, andWAXD. Well-defined SC phase was identified forthe first time, which was quite unusual compar-ing with other MJLCPs.

The work described in this article was supported by theNational Natural Science Foundation of China (GrantNos.: 20634010, 20574002, 50743042).

REFERENCES AND NOTES

1. Demus, D.; Goodby, J.; Gray, G. W.; Spiess, H. W.;Vill, V. Handbook of Liquid Crystals; Wiley-VCH:Weinheim, 1998; Vol. 1, Chapter II, p 17.

2. Finkelmann, H.; Wendorff, H. J. In Polymeric Liq-uid Crystals; Blumstein, A., Ed.; Plenum Press:New York, 1985; p 295.

3. Donald, A. M.; Windle, A. H. Liquid CrystallinePolymers; Cambridge University Press: Cam-bridge, UK, 1992.

4. McArdle, C. B. Side-Chain Liquid Crystal Poly-mer; Blackie: Glasgow, Scotland, 1989.

5. Hessel, F.; Herr, R. P.; Finkelmann, H. MakromolChem 1987, 188, 1597–1661.

6. (a) Pugh, C.; Schrock, R. R. Macromolecules 1992,25, 6593–6604; (b) Pugh, C.; Liu, H.; Narayanan,R.; Arehart, S. V. Macromol Symp 1995, 98, 293–310.

7. Gray, G. W.; Hill, J. S.; Lacey, D. Mol Cryst LiqCryst 1991, 197, 43–55.

8. Pragliola, S.; Ober, C.; Mather, P. T.; Jeon, H. G.Macromol Chem Phys 1999, 200, 2338–2344.

9. Percec, V.; Tomazos, D. J Mater Chem 1993, 3,643–650.

10. Keller, P.; Hardouin, F.; Mauzac, M.; Achard, M.F. Mol Cryst Liq Cryst 1988, 155, 171–178.

11. Zhou, Q. F.; Zhu, X. L.; Wen, Z. Q. Macromole-cules 1989, 22, 491–493.

12. Zhu, X. L.; Yang, Q. C.; Zhou, Q. F. Chin J PolymSci 1992, 2, 187–194.

13. Li, M. H.; Auroy, P.; Keller, P. Liq Cryst 2000, 27,1497–1502.

14. Gopalan, P.; Ober, C. K. Macromolecules 2001, 34,5120–5124.

15. Gopalan, P.; Zhang, Y.; Li, X.; Wiesner, U.; Ober,C. K. Macromolecules 2003, 36, 3357–3364.

16. Komp, A.; Finkelmann, H. Macromol Rapid Com-mun 2007, 28, 55–62.

17. Arehart, S. V.; Pugh, C. J Am Chem Soc 1997,119, 3027–3037.

18. Kim, G. M.; Pugh, C.; Cheng, S. Z. D. Macromole-cules 2000, 33, 8983–8991.

19. Small, A. C.; Pugh, C. Macromolecules 2002, 35,2105–2115.



20. Pugh, C.; Bae, J. Y.; Dharia, J.; Ge, J. J.; Cheng,S. Z. D. Macromolecules 1998, 31, 5188–5200.

21. Pugh, C.; Dharia, J.; Arehart, S. V. Macromole-cules 1997, 30, 4520–4532.

22. Ye, C.; Zhang, H. L.; Huang, Y.; Chen, E. Q.;Lu, Y.; Shen, D.; Wan, X. H.; Shen, Z.; Cheng,S. Z. D.; Zhou, Q. F. Macromolecules 2004, 37,7188–7196.

23. Tang, H.; Zhu, Z. G.; Wan, X. H.; Chen, X. F.;Zhou, Q. F. Macromolecules 2006, 39, 6887–6897.

24. Chai, C. P.; Zhu, X. Q.; Wang, P.; Ren, M. Q.;Chen, X. F.; Xu, Y. D.; Fan, X. H.; Chun, Y.;

Chen, E. Q.; Zhou, Q. F. Macromolecules 2007, 40,9361–9370.

25. Chen, S.; Gao, L. C.; Zhao, X. D.; Chen, X. F.;Fan, X. H.; Xie, P. Y.; Zhou, Q. F. Macromolecules2007, 40, 5718–5725.

26. Pugh, C.; Kiste, A. L. Prog Polym Sci 1997, 22,601–691.

27. Zhang, D.; Liu, Y. X.; Wan, X. H.; Zhou, Q. F.Macromolecules 1999, 32, 5183–5185.

28. Gray, G. W.; Goodby, J. W. G. Smectic LiquidCrystals: Textures and Structures; Leonard Hill:Glasgow and London, 1984.

514 CHEN ET AL.


Influence of alkoxy tail length and unbalanced mesogenic core on phase behavior of mesogen-jacketed...

Documents

Transcript of Influence of alkoxy tail length and unbalanced mesogenic core on phase behavior of mesogen-jacketed...