Extended Chain Lamella Formation Characteristics of Main-Chain

Mar 29, 2016 - A series of liquid crystal (LC) PB-8/12 copolyesters have been synthesized from 4,4′-biphenol with sebacic acid and tetradecanedioic ...
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Extended Chain Lamella Formation Characteristics of Main-Chain Smectic Liquid Crystalline Copolyesters Comprising Different Length Units Masatoshi Tokita,*,† Astuki Sugimoto,† Chiharu Takahashi,† Shusuke Yoshihara,‡ Renee van de Watering,†,§ and Sungmin Kang† †

Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8552, Japan Frontier Materials Development Laboratories, Kaneka Corporation 5-1-1, Torikai-Nishi, Settsu, Osaka 566-0072, Japan

‡

S Supporting Information *

ABSTRACT: A series of liquid crystal (LC) PB-8/12 copolyesters have been synthesized from 4,4′-biphenol with sebacic acid and tetradecanedioic acid, and their LC structures and morphologies have been examined. The copolyesters formed smectic I (SmI) LCs similarly as to the corresponding PB-8 and PB-12 homopolyesters; however, dissimilarity of the comonomer lengths decreased the smectic layer order while sustaining the hexagonal order in the lateral packing of the chains. The SmI LCs consisted of 100-nm-thick lamellae stacked along the polymer chain direction. The lamella thicknesses are more than two times greater than the thicknesses of the homopolyesters and comparable to or greater than the chain contour lengths, indicating the formation of extended chain lamellae.

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INTRODUCTION Flexible polymers can crystallize into extended conformations through the hexagonal columnar (Colh) mesophase; however, they form folded-chain lamellar crystals, because these metastable crystals have the highest growth rate from the isotropic melt. While polyethylene (PE) crystallizes directly from the isotropic melt at ambient pressure to yield folded-chain lamellae with thicknesses of approximately 10 nm, at pressures above 4 kbar and at small supercooling temperatures, PE crystallizes from the Colh phase to yield extended-chain lamellar crystals.1 This extended-chain crystallization via the Colh mesophase has been observed at ambient pressure for poly(vinylidene fluorideco-trifluoroethylene) (P(VDF/TrFE))2 and 1,4-trans-polybutadiene (1,4-t-PBD).3 In the Colh phase, individual polymer chains or stems form cylindrical columns that are packed in a twodimensional hexagonal lattice and can translate easily along the chain axis by overcoming the low energy barrier to eliminate the folds. The Colh phases in simple polymers such as PE and 1,4-t-PBD are induced by breaking the translation order along the chain axis due to conformational defects such as g+tg− kinks; this translation disorder can be introduced by chemical aperiodicity, as in P(VDF/TrFE). Stable Colh phases have been found in a wide temperature range in main-chain liquid crystal (LC) copolyethers comprising mesogens connected randomly by spacers of two different lengths.4−6 For example, TPP copolyethers synthesized from 1-(4-hydroxy-4′-biphenyl)-2-(4-hydroxyphenyl)propane with 1,7-dibromoheptane and 1,12-dibromododecane formed Colh phases, although the corresponding homopolymers formed © XXXX American Chemical Society

hexatic smectic F (SmF) phases. The Colh phases were induced by the dissimilarity of the comonomer lengths, which destroyed the long-range order in the polymer chain direction (i.e., the smectic layer order) but sustained the hexagonal lateral molecular packing. However, thick extended-chain lamellar morphology has not been reported for these Colh copolyethers. In this study, we prepared PB-8/12-x copolymers to examine the effects of chemical aperiodicity on their layer order and lamellar morphology. The PB-8/12-x copolymer comprises PB-8 and PB-12 units that are composed of 4,4′-biphenol connected to dibasic acids with 8 and 12 methylene units, respectively.7 x is the molar fraction of the PB-8 unit in units of percent.

Similar to a PB-10 homologue,8,9 the PB-8 and PB-12 homopolymers formed hexatic smectic I (SmI) liquid crystals; their morphologies are characterized by lamellae that consist of the SmI and isotropic liquid phases and that stack along the chain axis. The copolymer SmI phases have lower layer orders than the homopolymer phases, while preserving the hexagonal lateral packing of the mesogens; they form lamellae with thicknesses comparable to the chain contour lengths. Received: January 14, 2016 Revised: February 27, 2016

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DOI: 10.1021/acs.macromol.6b00100 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Characterization of PB-8, PB-8/12-x, and PB-12 polyesters sample

Mwa/g mol−1

Mna/g mol−1

Mw/Mna

Tmb/°C

ΔHmb/kJ mol−1

Tib/°C

ΔHib/kJ mol−1

Tmc/°C

ΔHmc/kJ mol−1

Tic/°C

ΔHic/kJ mol−1

PB-8 PB-8/12-75 PB-8/12-50 PB-8/12-25 PB-12

52700 50000 39400 44800 38400

17100 16800 13800 14300 13000

3.08 2.98 2.86 3.13 2.95

212 131 102 136 196

14.8 2.34 2.84 4.93 18.7

281 261 244 235 238

20.3 21.3 22.7 23.1 23.9

194 125 95 128 184

15.6 2.52 3.32 5.54 18.3

265 247 230 221 218

20.3 22.2 22.6 23.2 22.2

a Determined by SEC. bDetermined by the endothermic peak temperature and area in the second-heating DSC thermogram measured at a rate of 10 °C min−1. cDetermined by the exothermic peak temperature and area in the first-cooling DSC thermogram measured at a rate of 10 °C min−1.

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EXPERIMENTAL SECTION

RESULTS AND DISCUSSION The PB-8 and PB-12 homopolyesters and PB-8/12-x copolyesters formed crystal, SmI, and isotropic liquid phases sequentially as the temperature increased. The temperatures (Tm and Ti) and enthalpy changes (ΔHm and ΔHi) of the crystal−SmI and SmI−isotropic phase transitions were determined by the DSC thermogram shown in Figure S1 and are listed in Table 1. For the copolymers, Ti and ΔHi vary linearly with addition of the second comonomers, while Tm and ΔHm are significantly depressed, showing eutectic behavior; this suggests much lower disruption of the SmI phase compared to the crystal phase in the copolyesters.7 The type of the LC phase was elucidated from WAXS patterns. Figure 1a shows a typical WAXS pattern measured for a fibrous PB-12 sample at 210 °C. The fibrous sample with about 0.3-mm-diameter was prepared by elongating the isotropic melt at 250 °C with tweezers and illuminated by X-ray beam perpendicular to the fiber axis. Although one weak equatorial reflection at 2θ = 4.68° (d-spacing of 1.89 nm) remains to be explained, all the other reflections can be explained by the monoclinic unit cell with a = 0.64 nm, b = 0.90 nm, c = 2.60 nm, and β = 127°, similar to the reflections observed for PB-10,8 indicating that the type of the LC phase is SmI (Table 2). Figure 1b shows a WAXS pattern of PB-8 measured for a sheared film by irradiating with an X-ray beam from the velocity direction. The film sample with 0.1 mm thickness was prepared by shearing the isotropic melt at 290 °C, and the edge of the several thicknesses of the film was illuminated by X-ray beam.

Materials. PB-8/12-x polyesters were synthesized from 4,4′-biphenol diacetate with sebacic acid and tetradecanedioic acid via melt condensation.7 The value of x/(1 − x) is assumed to be equal to the charging ratio of sebacic acid to tetradecanedioic acid. PB-8/12-100 and PB-8/12-0 correspond to the PB-8 and PB-12 homopolymers, respectively. The number- and weight-average molecular weights (Mn and Mw) and polydispersity indices (Mw/Mn) of the polymers were estimated using size exclusion chromatography (SEC) (Viscotek HT-GPC with a refractive index detector) in a p-chlorophenol/ toluene (3/8 volume ratio) solution using polystyrene as the standard and based on the universal calibration curve, and are listed in Table 1. Measurements. Differential scanning calorimetry (DSC) was performed using a PerkinElmer DSC7 calorimeter under a flow of dry nitrogen. Wide-angle and small-angle X-ray scattering (WAXS and SAXS) patterns were obtained with Cu Kα radiation using Bruker D8 DISCOVER and NanoSTAR instruments equipped with Vantec-500 and Hi-STAR detectors, respectively. The synchrotron radiation (SR) SAXS measurements were performed at the BL-6A beamline at the Photon Factory, Tsukuba, Japan, using a Dectris PILATUS3 1 M detector with a sample-to-detector length of approximately 2.5 m. The X-ray wavelength (λ) was 0.1488 nm. The scattering intensity was corrected by transmission and subtraction of background scattering and was plotted against the scattering vector q = 4π sin θ/λ, where 2θ is the scattering angle. Scanning electron microscope (SEM) observations were performed using a Hitachi S-4800 microscope operating at a voltage of 2.0 kV. A sample with a flat surface was cut out using a microtome, exposed to RuO4 vapor, and then platinum−palladium sputter-coated.

Figure 1. WAXD pattern for (a) a fibrous PB-12 sample and (b) a film PB-8 sample, measured at 210 and 230 °C, respectively. In part a, the fiber axis is vertical. In part b, the film normal is vertical.

Figure 2. (a) WAXD and (b) SAXS patterns measured for PB-8/12-75 at ambient temperature. The fiber axis is vertical.

Table 2. Comparison of Observed and Calculated d-Spacings of Polyesters PB-12 a = 0.64 nm, b = 0.90 nm, c = 2.60 nm and β = 127°

PB-8 a = 0.64 nm, b = 0.85 nm, c = 1.98 nm, and β = 123°

PB-8/12-75 a = 0.70 nm, b = 0.9 nm,0 c = 2.39 nm, and β = 130°

dobs/nm

dcalc/nm

hkl

dobs/nm

dcalc/nm

hkl

dobs/nm

dcalc/nm

hkl

2.08 0.69 0.52 0.49 0.45 0.26

2.08 0.69 0.52 0.50 0.44 0.26

001 003 11̅ 3 1̅11 110 200

1.66 0.84

1.66 0.83

001 002

1.83

1.83

001

0.45 0.27

0.45 0.27

110 200

0.46 0.27

0.46 0.27

110 200

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Macromolecules

This diffraction pattern reveals that the mesogens lying parallel to the film normal (velocity gradient) are packed laterally in the 2D hexagonal lattice and compose layers with the normal tilted 33° away from the film normal, i.e., the long axes of the mesogens. A similar LC orientation has been observed for films of injection-molded PB-10 polyesters.10 This type of molecular packing can be associated with either a SmF or a SmI phase with C-centered monoclinic unit cells. Although the other reflections disappear because of poor orientation in the film, preventing us from differentiating between the SmF and SmI phases, we assume that PB-8 forms a SmI phase because two of its homologues, PB-10 and PB-12, form SmI phases. Copolymerization of PB-8 and PB-12 units having different unit lengths decreases the layer order in the smectic phase. A typical WAXS pattern measured for fibrous PB-8/12-75 is shown in Figure 2a. The spread of the reflections is similar to that observed for the WAXS pattern of the fibrous PB-12 sample, showing that the smectic structure is well oriented in the fibrous PB-8/12-75 sample; however, the copolyester displayed fewer reflections than both homopolymers because of a decrease in the smectic layer order. The copolyester loses the 002 and 003 reflections in addition to the 11̅ 3 and 11̅ 1 reflections. On the other hand, the copolymers maintained the reflections on the equator, which is attributed to the hexagonal packing of the mesogens. This decrease in layer order was observed for all the PB-8/12-x copolymers. The WAXS intensity profiles were measured for the nonoriented samples of the PB-8 and PB-12 polyesters and the PB-8/12-x copolymers in the liquid crystalline state, and are shown in Figure 3, with the intensity normalized with the 110 reflection intensity. The copolymers, especially PB-8/12-75 and PB-8/12-50, displayed weaker smectic layer reflections than the homopolymers. The PB-8/12-x copolymers displayed scattering maxima in a smaller angle region, which is ascribed to stacks of lamellae with a long period. Figure 2b shows a two-dimensional SAXS pattern measured for the fibrous PB-8/12-75 sample at room temperature. The SAXS pattern includes five scattering maxima at q, with integer ratios showing the existence of lamellae stacking along the fiber axis (i.e., the polymer chain axis) at a spacing of 94.4 nm. The lamellar spacing (d0) of the copolymers is remarkably greater than that of their corresponding homopolymers. Figure 4 shows SAXS profiles measured for the PB-8 and PB-12 polyesters and the PB-8/12-x copolyesters. Here, the sample was cooled from the isotropic liquid phase to room temperature at a rate of 10 °C min−1; the temperature was then increased to a liquid crystalline temperature just moments before X-ray irradiation. To prevent any changes in morphology, such as lamellar thickening, the SAXS data were obtained using 5 min SR X-ray illumination. The copolymers displayed first-order scattering peaks at a smaller q than the homopolymers, although the first order peak was not observed for PB-8/12-50 because of its larger d0; this indicates that the d0 values of the copolymers

Figure 3. WAXD intensity profiles of the PB-8 and PB-12 homopolymers and the PB-8/12-x copolymers, obtained at 230, 210, and 180 °C, respectively.

Figure 4. SR-SAXS intensity profiles (dots) for (a) PB-8, (b) PB-8/ 12-75, (c) PB-8/12-50, (d) PB-8/12-25, and (e) PB-12. The samples were initially prepared by cooling the isotropic melts at a rate of 10 °C min−1 and then heating to LC temperatures of (a) 230, (b) 180, (c) 180, (d) 180, and (e) 210 °C. The solid curves indicate the calculated intensities based on paracrystal theory.

A fiber of PB-8 could not be obtained such as for PB-12 because the isotropic melt transformed to the LC before being elongated due to the high Ti. In the pattern, reflections appear at 2θ = 5.33° and 10.5° (d-spacing: 1.66 and 0.84 nm) in a direction tilted 33° away from the meridional parallel to the normal of the film. On the equator, reflections at 2θ = 19.6° (d-spacing: 0.45 nm) and 33.5° (d-spacing: 0.27 nm) appear.

Table 3. Dimensions of Stacked Lamellae and the Mean Contour Lengths of the Polymer Chains

a

sample

d0a/nm

dLCa/nm

dama/nm

σLCa/nm

σama/nm

dLC/d0

Lb/nm

PB-8 PB-8/12-75 PB-8/12-50 PB-8/12-25 PB-12

55.0 102.8 108.0 66.6 39.0

51.3 100.0 101.7 58.4 32.0

3.7 2.8 6.3 8.2 7.0

5.0 6.0 12.0 3.0 3.0

0.6 3.0 0.05 0.1 3.0

0.933 0.973 0.942 0.877 0.821

96.6 98.5 83.4 88.8 82.7

Estimated by fitting the observed scattering intensity to the intensity calculated by paracrystal theory. bCalculated from Mn. C

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D

The same sample as PB-8/12-75 in Table 1. bDetermined by SEC. cDetermined by the endothermic peak temperature and area in the second-heating DSC thermogram measured at a rate of 10 °C min−1. dDetermined by the exothermic peak temperature and area in the first-cooling DSC thermogram measured at a rate of 10 °C min−1. a

237 240 247 1.94 2.19 2.52 121 122 125 16.8 19.2 21.3 253 255 261 1.51 2.10 2.34 130 128 131 2.25 3.17 2.98 9900 36800 50000 PB-8/12-75-44 PB-8/12-75-116 PB-8/12-75-168a

Mnb/g mol−1 Mwb/g mol−1 sample

Table 4. Characterization of PB-8/12-75-y polyesters

lamellar stacks in the PB-8/12-x copolymers that were cooled from the isotropic phase at a rate of 10 °C min−1. SEM images of the surfaces, cut out using a microtome, display the LC lamellae as either protrusions or grooves. Assuming that edge-on lamellae appear at the smallest spacing, the thicknesses of lamellae in PB-8/12-50 and PB-8/12-25 measure 100 and 60 nm, respectively, as shown by thin lines on the images. Although PB-8/12-75 hardly appeared edge-on lamellae under SEM, the lamellar thickness seems comparable to that in PB-8/12-50. Thus, the values of lamellar thickness are comparable to those estimated by SAXS (Table 3). Interestingly, the dLC values of PB-8/12-75 and PB-8/12-50 are as large as the mean contour lengths of the polymer chains (L). L was calculated from Mn, and the repeat unit lengths are listed in the eighth column of Table 3. Here, the repeat lengths of each unit are assumed to be equal to the c-axis lengths of the SmI monoclinic lattices of PB-8 and PB-12. For the PB-8/12-x copolymers, the molecular weights and lengths of the repeat units are assumed to be the number-average values of each monomer unit. While the d0 values of the PB-8 and PB-12 homopolymers are more than two times smaller than the L values, indicating that the polymer chains are folded to compose the lamellae, the d0 values of the copolymers are comparable to or larger than the L values. For the PB-8/12-75 and PB-8/12-50 copolymers, dLC is larger than L, suggesting

Mw/Mnb

Tmc/°C

Figure 5. Lamellar stack in (a) PB-8/12-50, (b) PB-8/12-75, and (c) PB-8/12-25 copolymers cooled from the isotropic liquid phase at a rate of 10 °C min−1. In parts a and c, thin lines are a guide to the eye. Scale bar: 100 nm.

4400 11600 16800

ΔHmc/kJ mol−1

Tic/°C

ΔHic/kJ mol−1

Tmd/°C

ΔHmd/kJ mol−1

Tid/°C

ΔHid/kJ mol−1

are remarkably larger than those of the homopolymers. The lamellae consisted of smectic LC and isotropic liquid phases, and the thicknesses of the lamella of each phase (dLC and dam) as well as the d0 values were estimated by comparing the observed intensities with scattering profiles numerically calculated using paracrystal theory.9,11−14 The solid curves in Figure 4 represent the best-fitted calculated profiles. The values of d0, dLC, and dam and the standard deviations of each lamellar thickness (σLC and σam) are listed in Table 3. Here, dLC was assumed to be larger than dam because a sufficient number of smectic layers were stacked within each lamella to produce smectic layer reflections in the WAXS patterns. The dLC and d0 values of the copolymers are two times greater than those of the homopolymers, although the volume fractions of LC (dLC/d0) between the polymers are comparable. These thick lamellae were confirmed by SEM observations. Figure 5 shows the

16.5 19.4 22.2

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Table 5. Dimensions of Stacked Lamellae and the Mean Contour Length of Polymer Chains for PB-8/12-y Copolyesters sample

d0b/nm

dLCb/nm

damb/nm

σLCb/nm

σamb/nm

dLC/d0

Lc/nm

PB-8/12-75-44 PB-8/12-75-116 PB-8/12-75-168a

83.5 94.0 102.8

75.0 90.0 100.0

8.5 4.0 2.8

13.0 8.5 6.0

3.3 3.0 3.0

0.898 0.957 0.973

25.8 68.2 98.5

The same sample as PB-8/12-75 in Table 3. bEstimated by fitting observed scattering intensity to the intensity calculated by paracrystal theory. Calculated from Mn.

a c

polymer chains are extended owing to the orientational order of the mesogens incorporated in the backbone, they include chain foldings at thermodynamic equilibrium to recover some part of the entropy lost because of the polymer chain extending along the director, as pointed out by de Gennes15 and Warner16,17 and as observed by small-angle neutron scattering.18,19 Smectic LCs having liquid-like packing of mesogens (e.g., smectic A, smectic C, and smectic CA) can include chain folding at thermodynamic equilibrium. Although the scattering maxima attributed to stacked lamellae were not observed for these smectic LCs, they have been observed for crystals formed upon cooling of the smectic LCs.20,21 The lamellae observed for the crystals are expected to exist already in the foregoing smectic LC because the orientational order is conserved at the LC−crystal transition. The lamellar spacing was increased by annealing in the crystalline state; it recovered its original value by annealing in the smectic LC phase, suggesting that the chains fold at thermodynamic equilibrium in the smectic LC phases with liquid-like lateral chain packing. In contrast to the above smectic LCs, the SmI phase arranges the lateral mesogens in a short-range two-dimensional hexagonal positional order. The SmI phases of PB-n polyesters exhibited SAXS maxima that are ascribed to stacked chainfolded lamellae; the spacing increased with annealing in the SmI phase, suggesting that the SmI LCs tend to eliminate chain folding by chain-sliding diffusion.22 Similar thickened lamellae, composed of almost completely extended polymer chains, have been observed for a TPP polyether annealed in a SmF phase.23 Thus, chain-sliding diffusion and the elimination of folding require two-dimensional hexagonal packing of the lateral chains, as in the SmI and SmF phases. The rate of chain-sliding diffusion can be increased by decreasing the smectic layer order, i.e., the positional order along the chain axis. In hexatic smectic phases with lowered layer orders, polymer chains can be extended rapidly, as in the Colh phase, so that they assemble to form extended chain lamellae.

that the polymer chains are most extended to aggregate into lamellae. Thus, extended-chain lamellae were formed in these copolymers. PB-8/12-75, which has a lower Mn value, exhibited similar d0 and dLC values, irrespective of the smaller L values. The samples are listed in Table 4 and are designated as PB-8/12-75-y, where y corresponds to Mn divided by 100. Thus, the abovementioned PB-8/12-75 is designated here as PB-8/12-75−168. The lamellar dimension parameters were determined from the SAXS profiles in the same way as for the PB-8/12-x polymers (see Figure S3) and are summarized in Table 5. While L decreases from 99 to 26 nm in proportion to Mn, dLC decreases more moderately than L (from 100 to 75 nm), indicating that the LC lamellae in PB-8/12-75−44 and PB-8/ 12-75−116 include the chain ends. This chain end inclusion has been observed for the SmI lamellae in PB-10.9 The chain ends can induce structural defects within the lamellae, as suggested by the dependences of ΔHi and the volume fraction of the LC lamella upon Mn. With decreasing Mn, ΔHi of the SmI LC decreases by 20%, while the volume fraction of the LC lamella, which is equal to dLC/d0, decreases slightly from 0.97 to 0.90. The lamellae can accommodate the chain ends, and their thickness is independent of L. The lamellar thickness may be dependent on the liquid crystallization temperature rather than L. In the DSC thermogram, measured at the same cooling rate (10 °C min−1) used for SAXS sample preparation, PB-8/12-75−168 exhibited the exothermic peak ascribed to the isotropic-SmI transition at Ti = 247 °C, which decreases with decreasing Mn, as found in Figure S2 and Table 4. The three PB-8/12-75-y polyesters exhibit d0 and dLC values that decrease with decreasing Ti. This suggests that d0 and dLC decrease with increasing liquid crystallization rate, although the kinetics of liquid crystal formation remains to be investigated by examining the liquid crystals formed isothermally from the isotropic melt. Extended chain lamella formation in the copolymers can be associated with the disturbed layer order in the copolymers, as revealed by the WAXS patterns. As seen in Figure 3, PB-8/ 12-75 and PB-8/12-50, which formed extended-chain lamellae, displayed weaker 001 reflections than PB-8/12-25 as well as the PB-8 and PB-12 homopolymers, while the 110 reflections are similar between all the polymers. This demonstrates that, in the polymers that form extended-chain lamellae, the positional order of the polymer chains along the chain axis is significantly disturbed, whereas the hexagonal lateral packing of the polymer chains is conserved. This molecular packing resembles that in the Colh phase. The Colh phase produces extended-chain lamellae of some semiflexible polymers, such as PE, P(VDF/TrFE), and 1,4-t-PBD, which form folded-chain lamellae during crystallization directly from the isotropic melt. Extended chain lamellae formation requires a hexagonal order in the lateral chains as well as a lowered positional order along the chain axis. The main-chain LC polymers in the nematic LCs have no positional order along the chain axis. Although the

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CONCLUSIONS Extended chain lamellae were found in main-chain PB-8/12-x copolyester SmI LCs. The dLC values of the PB-8/12-50 and PB-8/12-75 copolymers are 100 nm, comparable to the L values, while the PB-8 and PB-12 homopolymers formed chain-folded lamellae with dLC values of 30 and 50 nm, respectively, which are less than half as long as the L values. The SmI LCs of the PB-8/12 copolyesters are characterized by low smectic layer orders due to dissimilarity of the comonomer lengths, while the short-range hexagonal order in the lateral chain packing is preserved. In these SmI phases, the polymer chains can diffuse along the chain axis with sufficient rapidity to eliminate chain folding upon liquid crystallization during cooling of the isotropic liquid. The LC lamellae can accommodate the chain ends. dLC of PB-8/12-75 decreases moderately from 103 to 84 nm when Mn decreases from 16800 to 4400, while L decreases from 99 to 26 nm in proportion to Mn. This chain E

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Macromolecules end inclusion in the LC lamellae explains why the ΔHi values are smaller than the values expected on the basis of the volume fraction of the LC lamellae.

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main-chain polymer smectic liquid crystals as a result of the inclusion of chain ends. Polymer 2014, 55, 2609−2613. (10) Yoshihara, S.; Ezaki, T.; Nakamura, M.; Watanabe, J.; Matsumoto, K. Enhanced Thermal Conductivity of Thermoplastics by Lamellar Crystal Alignment of Polymer Matrices. Macromol. Chem. Phys. 2012, 213, 2213−2219. (11) Roe, R.-J. Methods of X-ray and Neutron Scattering in Polymer Science; Oxford University Press: 2000. (12) Ishige, R.; Ishii, T.; Tokita, M.; Koga, M.; Kang, S.; Watanabe, J. Well-Ordered Lamellar Microphase-Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle Segment. Macromolecules 2011, 44, 4586− 4588. (13) Koga, M.; Ishige, R.; Sato, K.; Ishii, T.; Kang, S.; Sakajiri, K.; Watanabe, J.; Tokita, M. Well-Ordered Lamellar MicrophaseSeparated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle Segment 2: Influence of Amorphous Segment Molecular Weight. Macromolecules 2012, 45, 9383−9390. (14) Koga, M.; Abe, K.; Sato, K.; Koki, J.; Kang, S.; Sakajiri, K.; Watanabe, J.; Tokita, M. Self-Assembly of Flexible−Semiflexible− Flexible Triblock Copolymers. Macromolecules 2014, 47, 4438−4444. (15) De Gennes, P. G. Mechanical Properties of Nematic Polymers. In Polymer Liquid Crystals; Cifferri, A., Krigbaum, W. R., Mayer, R. B., Eds.; Academic Press: New York, 1982. (16) Wang, X. J.; Warner, M. Theory of nematic backbone polymer phases and conformations. J. Phys. A: Math. Gen. 1986, 19, 2215− 2227. (17) Williams, D. R. M.; Warner, M. Statics and dynamics of hairpins in worm-like main chain nematic polymer liquid crystals. J. Phys. (Paris) 1990, 51, 317−339. (18) Li, M.; Brûlet, A.; Davidson, P.; Keller, P.; Cotton, J. Observation of hairpin defects in a nematic main-chain polyester. Phys. Rev. Lett. 1993, 70, 2297−2300. (19) Li, M. H.; Brûlet, A.; Cotton, J. P.; Davidson, P.; Strazielle, C.; Keller, P. Study of the chain conformation of thermotropic nematic main chain polyesters. J. Phys. II 1994, 4, 1843−1863. (20) Tokita, M.; Takahashi, T.; Hayashi, M.; Inomata, K.; Watanabe, J. Thermotropic Liquid Crystals of Polyesters Having a Mesogenic p, p ‘-Bibenzoate Unit. 7. Chain Folding in the Smectic Phase of BB-6. Macromolecules 1996, 29, 1345−1348. (21) Tokita, M.; Osada, K.; Watanabe, J. Thermotropic liquid crystals in main chain polyesters having a mesogenic 4,4′ -biphenyldicarboxylate unit. 9. Chain folding in solid polyesters crystallized from smectic A. Liq. Cryst. 1997, 23, 453−456. (22) Tokita, M.; Osada, K.; Yamada, M.; Watanabe, J. Chain-Folded Lamellar Structure in the Smectic H Phase of a Main-Chain Polyester. Macromolecules 1998, 31, 8590−8594. (23) Ho, R.-M.; Yoon, Y.; Leland, M.; Cheng, S. Z. D.; Percec, V.; Chu, P. Phase Identification in a Series of Liquid-Crystalline TPP Polyethers and Copolyethers Having Highly Ordered Mesophase Structures. 4. Phase Structures and Order Evolution in TPP(n = 12) Thin Films. Macromolecules 1997, 30, 3349−3353.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b00100. DSC thermograms of polyesters and SR-SAXS intensity profiles and the calculated intensities based on the paracrystal theory for PB-8/12-75-44 and PB-8/12-75-116 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*e-mail: [email protected]. Present Address §

Visiting student of Young Scientist Exchange Program from the Department of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The SR-SAXS measurement has been performed under the approval of the Photon Factory Program Advisory Committee (No. 2013G544 and No. 2015G622).

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DOI: 10.1021/acs.macromol.6b00100 Macromolecules XXXX, XXX, XXX−XXX