PolymerChemistry

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aBeijing National Laboratory for Molecular

and Engineering, Key Laboratory of Polym

Education, College of Chemistry and Mo

Beijing 100871, China. E-mail: fanxh@pku.bSchool of Materials Science and Engineerin

100081, ChinacState Key Laboratory of Polymer Physics an

Science and Materials, Beijing National Labo

Chemistry, Chinese Academy of Science, Bei

† Electronic supplementary informatiomonomer and polymers, NMR spectra ofPMVBPs as well as 1D WAXD patterns10.1039/c3py01755a

Cite this: Polym. Chem., 2014, 5, 4526

Received 22nd December 2013Accepted 8th March 2014

DOI: 10.1039/c3py01755a

www.rsc.org/polymers

4526 | Polym. Chem., 2014, 5, 4526–4

Synthesis and phase behavior of a new 2-vinylbiphenyl-based mesogen-jacketed liquidcrystalline polymer with a high glass transitiontemperature and low threshold molecular weight†

Qi-Kai Zhang,a Hai-Jian Tian,a Chang-Feng Li,ab Yu-Feng Zhu,a Yongri Liang,c

Zhihao Shen*a and Xing-He Fan*a

We have synthesized a new mesogen-jacketed liquid crystalline polymer, poly(40-(methoxy)-2-

vinylbiphenyl-4-methyl ether) (PMVBP) containing a biphenyl core in the side-chain. PMVBP has a

smaller monomer molecular weight (MW), a higher glass transition temperature and a lower threshold

MW for liquid crystalline (LC) formation. PMVBP was obtained via a nitroxide-mediated living radical

polymerization and characterized by gel permeation chromatography, differential scanning calorimetry,

polarized light microscopy, and one- and two-dimensional wide-angle X-ray diffraction (WAXD)

experiments. The number-average MW (Mn) of the polymers ranges from 0.41 � 104 to 1.64 � 104 g

mol�1. A relatively high glass transition temperature is observed, which increases from 173 to 208 �Cwith increasing MW. The LC phase developed at relatively high temperatures is strongly dependent on

the Mn of the polymer. A hexagonal columnar (FH) LC phase is observed above 260 �C when the Mn is

only above 0.53 � 104 g mol�1, a low threshold MW for LC formation. All of the LC phases are retained

during cooling.

Introduction

As one of the most widely used functional materials of somatter, liquid crystalline polymers (LCPs) have received muchattention owing to their various supramolecular self-assembledstructures and phase transitions1–5 as well as their remarkableapplications in organic semiconducting materials, nonlinearoptical devices, engineering plastics, self-assembled nano-materials, and so on.6–9 Mesogen-jacketed liquid crystallinepolymers (MJLCPs), rst reported by Zhou et al. in 1987, havebulky side groups attached laterally to the main chain through acarbon–carbon bond or a very short spacer, and they can act assupramolecular mesogens to form liquid crystalline (LC) pha-ses.10–12 In the past few decades, many MJLCPs have been

Sciences, Department of Polymer Science

er Chemistry and Physics of Ministry of

lecular Engineering, Peking University,

edu.cn; zshen@pku.edu.cn

g, Beijing Institute of Technology, Beijing

d Chemistry, Joint Laboratory of Polymer

ratory for Molecular Sciences, Institute of

jing 100190, China

n (ESI) available: Synthesis of thethe initiator and MBP, TGA curves ofof PMVBP-3 and PMVBP-5. See DOI:

533

designed with novel structures and potential for applications aselectroluminescent materials,13–17 birefringent lms for opticalcompensators,18 surface-modifying agents19 and so on. MJLCPswith side-chain cores based on 2-vinylhydroquinone,11 2-vinyl-1,4-phenylenediamine,20 2-vinylterephthalic acid,21–23 vinyl ter-phenyl,24,25 and vinyl biphenyl26–29 have been synthesized.Various LC phases have been obtained, such as hexagonalcolumnar (FH) phases,30–32 columnar nematic (FN) phases,22,28

hexatic columnar nematic (FHN) phases,22,23 rectangularcolumnar (FR) phases,33 and smectic A (SmA) and smectic C(SmC) phases.14,26,34

However, in our previous studies, control of the thresholdmolecular weight (MW) for the formation of LC phases and theglass transition temperature (Tg) has not been a focus. High Tgvalues and LC states can improve the service conditions andmaintain the physical network of thermoplastic elastomers.Due to the difficulties in obtaining high-MW coil segments inthermoplastic elastomers, the design and synthesis of anMJLCP with a smaller MW monomer, a higher glass transitiontemperature, and a lower threshold MW for LC formation, iscrucial to obtain high-performance thermoplastic elastomersbased on MJLCPs.

The MW of the monomer is determined by its chemicalstructure, and the Tg and the threshold MW for LC formation ofan MJLCP are dramatically inuenced by the chemical structureof the monomer and the degree of polymerization.22,35 For

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MJLCPs with 2-vinylterephthalic acid in the side-chain core,typical poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}(PMPCS) with a monomer (MPCS) MW of 404 g mol�1 has a Tgof about 120 �C, and it becomes liquid crystalline only when thenumber-average MW (Mn) is above 104 g mol�1. Between 1.0 �104 and 1.6 � 104 g mol�1, a FN phase forms. Above 1.6 � 104 gmol�1, a FHN phase is observed.22 However, poly{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) with a monomer(BPCS) MW of 488 g mol�1, has a Tg of about 108 �C because ofits longer alkoxy tails. When Mn is over 3.4 � 104 g mol�1,PBPCS forms an LC phase at high temperatures.23

For MJLCPs with terphenyl in the side-chain core, poly[2,5-bis(40-alkoxyphenyl)styrenes] have been synthesized to investi-gate the inuence of the alkoxy tail length on the LC behavior ofthe polymers.24 Among these samples, when the alkoxy tail is amethoxy group with amonomerMW of 316 gmol�1, Tg is 230 �Cand the threshold MW for LC formation is 3.1 � 104 g mol�1.For MJLCPs with biphenyl in the center of the side-chain coresuch as 4,40-bis(4-butoxyphenyloxycarbonyl)-2-vinylbiphenyl(PBP2VBP) and 4,40-bis(4-butoxyphenyloxycarbonyl)-3-vinyl-biphenyl (PBP3VBP) with monomer MWs of 564 g mol�1, the Tgvalues are 104 and 110 �C, respectively,26 which is possiblycaused by exible ester linkages in the side chains.The threshold MWs of the polymers for LC formation are 2.4 �104 g mol�1.

In this work, we aimed to design and synthesize an MJLCPwith a smaller monomer MW, a higher Tg and a lower thresholdMW for LC formation. For the three systems mentioned above,Tg increases with increasing conjugation and rigidity in theside-chain mesogen of the polymer when the same exible alkylsubstituent is used, while the threshold MW for LC formationincreases with the increasing size of the side chain. Therefore,we should design a monomer with high rigidity, a small MWand a small diameter. Terphenyl is not a suitable side-chaincore to use because the polymer will have a higher monomerMW and a larger column diameter, both of which tend toincrease the threshold MW of the polymer. As a result, wesynthesized an MJLCP containing a biphenyl core in the sidechains. In order to obtain a higher Tg, we chose amethoxy groupas a exible substituent at the side-chain ends. The structure ofthe designed polymer, poly[40-(methoxy)-2-vinylbiphenyl-4-methyl ether] (PMVBP), is shown in Chart 1. The dependence ofthe LC properties on the MW of PMVBP was also investigated.

Experimental sectionMaterials

2-Bromo-5-methoxybenzaldehyde (Sigma-Aldrich, 97%), 4-methoxyphenylboronic acid (J&K, 98%), tetrakis-

Chart 1 Chemical structure of PMVBP.

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(triphenylphosphine)palladium(0) (Pd(PPh3)4, Sigma-Aldrich,99%), methyltriphenylphosphonium bromide (Sigma-Aldrich,98%), and n-butyllithium (J&K, 2.4 M solution in hexanes) wereused as received without further purication. Anisole (BeijingChemical Reagents Co., A.R.) was washed with NaOH anddistilled water and then distilled from calcium hydride. Tetra-hydrofuran (THF, Beijing Chemical Reagents Co., A.R.) wasreuxed over sodium and distilled before use. All other reagentswere commercially available and used as received.

Measurements

The chemical structures of the intermediates and the monomerwere characterized by 1H/13C NMR, high resolution massspectroscopy (HR-MS), and elemental analysis (EA). 1H NMR(400MHz) and 13C NMR (100MHz) spectra were obtained with aBruker ARX400 spectrometer using deuterated chloroform asthe solvent and tetramethylsilane as the internal standard atambient temperature. HR-MS were recorded on a Bruker ApexIV Fourier-transform ion cyclotron resonance mass spectrom-eter by electrospray ionization (ESI). EA was carried out with anElementar Vario EL instrument. Other characterizationmethods, such as gel permeation chromatography (GPC)measurements, thermogravimetric analysis (TGA), differentialscanning calorimetry (DSC), polarized light microscopy (PLM),and one-dimensional wide-angle X-ray diffraction (1D WAXD)experiments were performed according to previously describedprocedures.32,36 Two-dimensional (2D) WAXD measurementswere performed on a Rigaku S/MAX 3000 with MicroMax-007HFsystem equipped with a Cu (l¼ 1.54 A) rotating anode operatedat 40 kV and 30mA and an imaging plate detector (size: 150 mm� 150 mm, Fuji Co.). The 2D WAXD data were calibrated usingsilicon powder (2q ¼ 28.44� at a wavelength of 1.54 A).

Synthesis of the PMVBP polymers

The synthesis route of PMVBP is shown in Scheme 1. Theexperimental details are described in the ESI.†

Results and discussionSynthesis and characterization of the monomer and polymers

As shown in Scheme 1, themonomer containing a biphenyl corein the side chains could be successfully prepared in two efficientsteps. 4,40-Bis(methoxy)biphenyl-2-carbaldehyde (MBP) wassynthesized by a Suzuki cross-coupling reaction between 2-bromo-5-methoxybenzaldehyde and 4-(methoxy)phenylboronicacid in a high yield (91%). The monomer MVBP was then effi-ciently obtained via a typical Wittig reaction.

In an alternative route, we could rstly synthesize theprecursor 2-bromo-5-methoxy-1-vinylbenzene via a Wittig reac-tion, followed by a Suzuki cross-coupling reaction to obtain thetarget monomer. Considering the high reaction temperaturerequired for the Suzuki cross-coupling reaction, the interme-diates or the monomer could possibly undergo thermal poly-merization at such a high temperature. Therefore, the synthesisroute as shown in Scheme 1 was chosen. The chemical

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Scheme 1 Synthetic route of PMVBP.

Fig. 1 1H NMR spectra of the monomer MVBP (top line) and thecorresponding polymer PMVBP with Mn ¼ 1.11 � 104 g mol�1 (bottomline).

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structures of the intermediates and the monomer wereconrmed by 1H NMR, 13C NMR, HR-MS, and EA.

Nitroxide-mediated living radical polymerization (NMP) is acontrolled/living radical polymerization (CLRP) method that isuseful for obtaining well-dened functional polymers.37,38 Aseries of PMVBPs with different Mn values and relatively lowpolydispersity indices (PDIs) were synthesized via NMP in

4528 | Polym. Chem., 2014, 5, 4526–4533

anisole (as shown in Scheme 1). Fig. 1 and S3 (in ESI†) show the1H and 13C NMR spectra of the monomer MVBP, respectively.The 1H NMR spectrum of the corresponding polymer PMVBP inCDCl3 is also shown in Fig. 1, with characteristic resonances ofthe vinyl group in the monomer appearing at d ¼ 5.17–5.20,5.65–5.70, and 6.67–6.74 ppm. Aer polymerization, the signalsrelated to the vinyl group completely disappear and are replacedby the resonance peaks of PMVBP, which are rather broad owingto the slower motion of the protons, indicating successfulpolymerization. The polymers are quite soluble in commonorganic solvents, such as anisole, chloroform, dichloro-methane, chlorobenzene, THF and so on.

The characterization results of the polymers are summarizedin Table 1. A variety of samples were synthesized by changingthe ratio of initiator to monomer. GPC analysis (as shown inFig. 2) of PMVBPs shows that no monomer exists in the polymersamples and that theMn values of the polymers range from 0.41� 104 to 1.64 � 104 g mol�1, with relatively low PDIs (<1.4),which demonstrates the good controllability of the NMPprocess.

Thermal properties and phase behaviors of the polymers

The thermal properties of the polymers were characterized byTGA. The thermogravimetric curves are shown in Fig. S4 of ESI.†As shown in Table 1 and Fig. S4,† all of the polymers exhibitexcellent thermal stabilities under a nitrogen atmosphere,and their 5% weight loss temperature (Td) values are all about370 �C.

The phase transitions of the polymers were characterized byDSC experiments. All of the samples were heated from ambienttemperature to 280 �C at a rate of 20 �C min�1 in order toeliminate any thermal history. The PMVBP polymers were thencooled at a rate of 10 �C min�1 and heated at a rate of 20 �Cmin�1 under a nitrogen atmosphere. All of the DSC thermo-grams only exhibit glass transitions (as shown in Fig. 3), similarto many other previously reported MJLCPs.22,23,28,32,39 A secondheating process was used to obtain the Tg values, with theresults listed in Table 1. Common for polymers includingPMPCS, a typical MJLCP, the Tg value of PMVBP also shows aMW dependence.22,35 PMVBP exhibits a relatively high Tg(173 �C) even at a relatively low Mn of 0.41 � 104 g mol�1. Tgincreases with increasingMn and levels off at about 210 �C whenMn increases to 1.11 � 104 g mol�1. The Tg value of PMVBP ismuch higher than those of most other MJLCPs, such as PMPCS(about 120 �C),22 PBPCS (about 108 �C)23 and so on,27,40 probablydue to the lack of exible linkages such as ester connections inthe side chain.

Liquid crystalline properties and phase structures of thepolymers

Themonomer and the polymers were all white solids at ambienttemperature. No liquid crystallinity was observed for themonomer during the PLM experiments at different tempera-tures. Polymer samples were cast from THF solutions and slowlydried at ambient temperature. Some of the polymers, suchas PMVBP-1, PMVBP-3, and PMVBP-5, showed very weak

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Table 1 Characteristics and thermal properties of PMVBPs

Sample Mna (� 104 g mol�1) PDIa Td

b (�C) Tgc (�C) Liquid crystallinityd

PMVBP-1 0.41 1.36 367 173 NoPMVBP-2 0.53 1.37 365 185 YesPMVBP-3 0.86 1.33 376 191 YesPMVBP-4 1.11 1.29 369 207 YesPMVBP-5 1.64 1.31 375 208 Yes

a Mn and PDI values of the polymers determined by GPC in THF using PS standards. b The temperature at 5% weight loss of each polymer evaluatedby TGA heating experiments under a nitrogen atmosphere at a heating rate of 20 �C min�1. c The glass transition temperature of each polymermeasured under a nitrogen atmosphere by DSC at a scanning rate of 20 �C min�1 during the second heating cycle. d Evaluated using PLM and1D WAXD measurements.

Fig. 2 GPC curves of PMVBPs.

Fig. 3 DSC thermograms of PMVBPs during the second heatingprocess at a rate of 20 �C min�1 under a nitrogen atmosphere. Tgincreases with increasing Mn.

Fig. 4 PLM micrographs of solution-cast films of PMVBP-2 taken at250 �C (a) and PMVBP-3 at 270 �C during cooling after it was heated to310 �C (b).

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birefringence at ambient temperature, possibly caused byorientation of the polymer chains during precipitation.However, such results can not illustrate whether the polymersare liquid crystalline. Upon heating, the polymers showeddifferent properties depending on the MWs. The samplePMVBP-1 with anMn of 0.41 � 104 g mol�1 did not show a largearea of birefringence during heating up to 280 �C. However,PMVBP-2 with an Mn of 0.53 � 104 g mol�1 clearly exhibitedbirefringence during heating up to 240 �C. A Schlieren-liketexture was observed during further heating at 250 �C (as shownin Fig. 4a). The birefringence of PMVBP-2 remained when it wascooled to ambient temperature. Analogously, as shown in

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Fig. 4b, PMVBP-3 also showed a Schlieren-like texture when itwas heated to 310 �C and cooled to 270 �C. With a furtherincrease in MW, the Tg of PMVBP-4 and PMVBP-5 increased to208 �C. These two samples are very rigid, and the temperaturesat which liquid crystalline phases start to develop are higherthan those of the other samples. Birefringence was detected at278 and 290 �C for PMVBP-4 and PMVBP-5, respectively.However, the textures of these two samples were not typicalones, possibly due to the low mobilities of the polymer chains.Therefore, clear birefringence was observed in all of the samplesexcept PMVBP-1 and it remained when the samples were cooleddown to ambient temperature. This phenomenon is similar tothat of other previously reported MJLCPs.21,26,32 Specically,PMVBP starts to show liquid crystallinity at a much lower Mn ofonly 0.5 � 104 g mol�1, compared with most other MJLCPs,such as PMPCS, which forms a FN phase whenMn is in between

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Fig. 5 1DWAXD patterns of PMVBP-1 during the first heating (a) and the subsequent cooling (b) processes under a nitrogen atmosphere and thed-spacing of the low-angle halo as a function of temperature (c) during the first heating and the subsequent cooling processes as shown in (a)and (b).

Fig. 7 1DWAXD patterns of PMVBP-2 after annealing at 260 �C for 0.5h (black line) and subsequent cooling (red line) under a nitrogenatmosphere.

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1.0 � 104 and 1.6 � 104 g mol�1 and a FHN phase with Mn over1.6 � 104 g mol�1.22

Because the textures in the PLM experiments may not beused to determine the exact phase structures, the phasebehavior of the samples were further characterized by variable-temperature 1D WAXD experiments. In these experiments,polymer samples of about 30 mg were cast from THF solutions,and the solvents were then evaporated at ambient temperature.Two sets of 1D WAXD patterns of PMVBP-1 (with an Mn of 0.41� 104 g mol�1) recorded during the rst heating and subse-quent cooling processes are shown in Fig. 5. At low tempera-tures, the proles of the sample only exhibit two scatteringhalos at a low 2q value of 6.75� and a high 2q value of 20.11�,respectively. The intensity of the low-angle scattering haloincreases a little upon the rst heating process, as shown inFig. 5a, but still remains as a broad scattering halo for the wholetemperature range studied, even at 280 �C. Upon cooling, asshown in Fig. 5b, the intensity of the low-angle scattering haloremains the same. Fig. 5c shows the change in the d-spacing ofthe low-angle halo as a function of temperature during the rstheating and subsequent cooling processes for PMVBP-1. The d-spacing does not show any sharp changes at temperaturesabove Tg during heating and cooling, indicating that no liquid

Fig. 6 1DWAXD patterns of PMVBP-2 during the first heating (a) and thed-spacing of the low-angle halo/peak as a function of temperature (c) du(a) and (b).

4530 | Polym. Chem., 2014, 5, 4526–4533

crystalline phase transitions occur when the temperature ischanged. With the combination of PLM results, it can beconcluded that PMVBP-1 with a low Mn of 0.41 � 104 g mol�1 isnot liquid crystalline.

The phase behavior of PMVBP-2 was also examined by vari-able-temperature 1D WAXD experiments. Two sets of 1D WAXD

subsequent cooling (b) processes under a nitrogen atmosphere and thering the first heating and the subsequent cooling processes as shown in

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Fig. 8 1DWAXD patterns of PMVBP-4 during the first heating (a) and the subsequent cooling (b) processes under a nitrogen atmosphere and thed-spacing of the low-angle halo/peak as a function of temperature (c) during the first heating and the subsequent cooling processes as shown in(a) and (b).

Fig. 9 2DWAXD pattern of PMVBP-3 at ambient temperature with theX-ray beam aligned perpendicular to the shear direction (a), theshearing geometry (b) with the X direction as the shear direction andthe integral 1D WAXD pattern (c) obtained from (a).

Fig. 10 Schematic of the phase diagram for PMVBPs.

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patterns of PMVBP-2 (with an Mn of 0.53 � 104 g mol�1)obtained during the rst heating and subsequent coolingprocesses are shown in parts (a) and (b) of Fig. 6, respectively. At

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ambient temperature, the WAXD prole also shows two scat-tering halos at a low 2q value of 6.71� and a high 2q value of19.99�, respectively. Upon the rst heating (as shown in Fig. 6a),a sharp diffraction peak in the low-angle region develops at260 �C, which is higher than the Tg value of the sample. Thepeak slightly shis to a higher angle of 7.20�. The intensity ofthe low-angle peak at high temperatures is much higher thanthat of the halo at ambient temperature and is alsomuch higherthan that of the halo from PMVBP-1 at high temperatures,which indicates the development of an ordered structure.Combined with the PLM results in Fig. 4a, such an orderedstructure is determined to be an LC phase. No higher-orderdiffraction peaks of the low-angle peak are observed in the 1DWAXD experiments, while the high-angle scattering halo movesto lower angles with increasing temperature mainly due tothermal expansion. Upon cooling, as shown in Fig. 6b, theintensity of the low-angle diffraction peak remains the same,indicating that the LC phase of PMVBP-2 is maintained uponcooling.

Fig. 6c summarizes the d-spacing changes of the low-anglescattering halo or diffraction peak as a function of temperatureduring the rst heating and subsequent cooling processes forPMVBP-2. Upon the rst heating process, the d-spacingdecreases a little with increasing temperature before 240 �C,then decreases sharply between 240 and 260 �C until it levels off(the black line). This sharp change indicates a rst-order tran-sition, which is the formation of an LC phase. On the otherhand, the d-spacing decreases gradually during cooling, indi-cating that no phase transition occurs, and the slope of thecooling line (the red line) represents the coefficient of thermalexpansion (CTE) of the structure studied.22 The CTE value isabout 1.7 � 10�4 nm �C�1.

Seeing as no higher-order diffraction peaks of the low-anglepeak were observed in the 1D WAXD experiments, the samplewas further treated by thermal annealing in a vacuum at 260 �Cfor 0.5 h. As shown in Fig. 7, a higher-order diffraction peak wasobserved aer thermal annealing. The 1D WAXD prole of thesample at 260 �C exhibits two diffraction peaks at low 2q valuesof 7.35� and 12.87�. The scattering vectors (q’s) of these twopeaks are 5.23 and 9.14 nm�1, respectively, and the ratio

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between them is 1 : 31/2, indicating that there is hexagonalpacking. Therefore, PMVBP-2 has a FH structure. These twodiffraction peaks remain during the cooling process, with thepeaks slightly shiing to higher angles. Using the d-spacingvalue of 1.17 nm at 40 �C, the hexagonal lattice parameter a,which is the distance between neighboring polymer rods, iscalculated to be 1.35 nm. This value is nearly equal to thesimulated length (1.32 nm) of the side chain of the polymer,indicating that the side chains are aligned almost perpendic-ular to the main chain.

PMVBP-3 shows similar 1D WAXD results (Fig. S5 in theESI†) to PMVBP-2. The difference is that, without thermalannealing, the WAXD prole of PMVBP-3 at 240 �C duringheating shows a second-order diffraction peak of the FH phase,which is retained during cooling.

The results of PMVBP-4 are also similar. The 1D WAXDpatterns are shown in Fig. 8, with a second-order peak clearlyvisible, suggesting that the liquid crystalline structure is moreordered. The scattering vector ratio is also 1 : 31/2, indicating aFH phase. The d-spacing also exhibits a sharp decrease duringheating (Fig. 8c, black line) due to the formation of the LCphase. The CTE value is about 1.6 � 10�4 nm �C�1.

The 1D WAXD results of PMVBP-5 are similar to those ofPMVBP-3 and PMVBP-4. The 1D WAXD patterns are shown inFig. S6 of the ESI.† A FH phase is also formed during heating,and it is retained upon cooling. For PMVBP-2, PMVBP-3,PMVBP-4, and PMVBP-5, the WAXD proles at low tempera-tures aer cooling all have a shoulder halo appearing at thele of the rst-order low-angle diffraction peak. This may becaused by an amorphous phase of low-MW fractions in thepolymers.

Finally, in order to further conrm the liquid crystallinephases of the PMVBP samples, 2D WAXD experiments wereconducted with mechanically sheared samples taking intoconsideration of the dimensionality limit of 1D WAXD experi-ments. Taking PMVBP-3, which was mechanically sheared at280 �C, as an example, Fig. 9a shows its 2D WAXD pattern withthe X-ray beam along Y direction, which is perpendicular to theshear direction (the X direction. The shear geometry is shown inFig. 9b). Two pairs of diffraction arcs in the low-angle region onthe equator can be clearly discerned, which demonstrate theexistence of an ordered structure with lattice planes orientedparallel to the meridian direction, which is the direction of thepolymer main chains upon shearing (in other words, lateralpacking of the polymer chains). An additional higher-orderdiffraction peak appears in the 1D WAXD pattern (Fig. 9c)obtained through integration of the 2D pattern. The scatteringvector ratio of the peaks is 1 : 31/2 : 2, conrming aFH structure,and the peaks can be assigned as (100), (110), and (200)diffractions.

The phase behavior of PMVBP with increasing MW can besummarized in the phase diagram shown in Fig. 10. PMVBPcan form a liquid crystalline phase at relatively low MWs,compared to other MJLCPs. When theMn is higher than 0.53 �104 g mol�1, it can develop into a FH LC phase above 250 �Cupon the rst heating process and the LC phase remainsduring cooling.

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Conclusions

In summary, we have obtained a new series of MJLCPs, PMVBPsbased on a 2-vinylbiphenyl monomer with a smaller monomerMW, a higher glass transition temperature, and a lowerthreshold MW for LC formation. PMVBPs with different Mn

values and relatively low PDIs were synthesized via NMP. TheMn values of these polymers determined by GPC are in the rangeof 0.41 � 104 to 1.64 � 104 g mol�1. Tg increases with increasingMn and levels off at about 210 �C. In addition, the Tg value ofPMVBP is higher than those of most other MJLCPs. PMVBP canform a FH phase at relatively low MWs, compared to otherMJLCPs. When theMn is higher than only 0.53 � 104 g mol�1, itcan develop into a FH liquid crystalline phase above 250 �Cupon heating, and the LC phase is maintained during cooling.Due to its higher glass transition temperature and lowerthreshold MW for LC formation, PMVBP is an excellent candi-date as the hard segment of an ABA-type thermoplastic LCelastomer. To this end, research work is currently in progress.

Acknowledgements

This work was supported by the National Natural ScienceFoundation of China (Grants 21134001 and 20990232) and theNational Basic Research Program of China (973 Program,Project 2011CB606004).

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