Helical Nylons and Polyphthalamides Synthesized ... - ACS Publications

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Helical Nylons and Polyphthalamides Synthesized by Chiral Interfacial Polymerizations between Chiral Nematic Liquid Crystal and Water Layers Jinwoo Park, Munju Goh,† and Kazuo Akagi* Department of Polymer Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan ABSTRACT: Polyamides are one of the most widely used engineering plastics. Aliphatic polyamide represented by nylon has been previously synthesized by an interfacial polymerization reaction between an organic layer of diacyl chloride and a water layer of diamine. However, for more than 75 years, there has been no reported polymerization method that can enable the synthesis of both helical aliphatic polyamide (nylon) and aromatic polyamide (polyphthalamide) and can control their spiral morphologies. In this study, we developed a novel polymerization method based on chiral interfacial polycondensation using a chiral nematic liquid crystal (N*LC) layer and a water layer and, for the first time, succeeded in synthesizing helical nylons and polyphthalamides with onehanded spiral morphologies. The swirling directions in the spiral morphology of the helical polyamides were controlled by selecting the chirality of the chiral dopant used for preparing the N*-LC. The present synthesis method should extend the applicability of asymmetric interfacial polymerizations using N*-LC to various types of polyamides.

1. INTRODUCTION Polyamides are versatile engineering plastics consisting of aliphatic or aromatic main chains, represented by nylons or polyphthalamides, respectively. Nylon-6,6 was invented in the late 1930s by Carothers.1 Since that time, nylons have been widely utilized in industry because of their excellent mechanical properties, including high tensile strength, high elongation, excellent abrasion resistance and high resistance to chemicals. Nylons are typically synthesized by ring-opening polymerization or interfacial polycondensation. In particular, nylon n,m is synthesized by an interfacial polycondensation reaction between a diamine and a diacid. By using a diacyl chloride in the place of the diacid, nylon synthesis at room temperature is more efficient due to the increased reactivity of the diacyl chloride. Interfacial polymerization proceeds in a two-phase system, where the amine is dissolved in water, and the diacyl chloride is dissolved in an organic solvent. Polycondensation occurs at the interface of the aqueous and organic solutions. Polyphthalamide is regarded as “an aromatic nylon” and is prepared from the polycondensation between a diacid, such as terephthalic acid (TPA) or isophthalic acid (IPA), and a diamine. Compared with aliphatic polyamides, aromatic polyamides have superior thermal and mechanical properties including a high melting point (Tm), a high glass transition temperature (Tg), high stiffness, high chemical resistance, and low water absorption.2 Helical polymers have been extensively investigated since the right-handed α-helix of proteins3 and the right-handed and double-stranded helix of DNA4 were discovered by Pauling in © 2014 American Chemical Society

1951 and by Watson and Crick in 1953, respectively. A highly stereoregular isotactic polypropylene with a helical conformation using a Ziegler−Natta catalyst was synthesized by Natta.5 In the 1970s, synthetic helical polymers were developed. An optically active vinyl polymer was synthesized by through a helix sense selective polymerization of an achiral triphenylmethyl methacrylate.6 Green et al. found that polyisocyanates with chiral side chains have helical structures and that the rightand left-handed helical conformations can be separated by rarely occurring helical interconversion.7 They also found that chiral amplification in polyisocyanates occurs via a small chiral bias through covalent or noncovalent bonding interactions with a high cooperativity, giving a large helical sense excess of the polymer chain. Such discoveries have stimulated the development of other types of optically active polymers such as polysilanes8 and polyacetylene derivatives.9 Furthermore, it has been reported that chiral poly(lactic acid) (PLA) has higher crystallinity and tensile strength compared with racemic PLA.10 This suggests that a chiral or helical structure may be useful for achieving high stereoregularity, increased crystallinity and improved mechanical properties in polymers. There have been several approaches for the synthesis of helical polymers; e.g., introduction of a chiral moiety to the polymer side chains,11 addition of chiral compounds to an achiral polymer,12 asymmetric polymerization with a chiral Received: March 10, 2014 Revised: April 3, 2014 Published: April 14, 2014 2784

dx.doi.org/10.1021/ma500515s | Macromolecules 2014, 47, 2784−2795

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Scheme 1. Synthesis Reaction of Helical Nylon 6,10 and Polyphthalamide through Polycondensation between Sebacoyl Chloride or Terephthaloyl Chloride and Hexamethylene Diamine in LC (N-LC or N*-LC)/Liquid (H2O−NaOH) Interface

Scheme 2. Synthetic Routes of PCH506 and BPCH52

catalyst13 or polymerization in a chiral reaction field.14 Among these, the use of a chiral reaction field based on a chiral nematic liquid crystal (N*-LC) can be applied to various polymerization methods, such as interfacial polymerization, chemical polymerization and electrochemical polymerization. Upon the discovery that helical polyacetylene (H-PA) with hierarchical spiral morphology can be synthesized using a N*-LC,14 the use of N*-LCs has been regarded as a promising method for synthesizing helical aromatic conjugated polymers such as poly(bithiophene phenylene) (PBTP)15a and poly(3,4-ethylenedioxythiophene) (PEDOT).15b It has also been found that the helical pitch of the N*-LC can be adjusted by changing the concentration of the chiral dopant or by changing the helical twisting power of the chiral dopant itself.16 To date, it has been shown that binaphthyl derivatives, when used as chiral dopants, not only have good miscibility in N-LCs due to their LC moieties in substituted groups but also have higher helical twisting powers than asymmetric center-containing chiral compounds due to their axial chirality.16 However, for more than 70 years there has been no reported polymerization method that can enable the synthesis of both helical aliphatic polyamide (nylon) and aromatic polyamide (polyphthalamide) and can control their spiral morphologies.

In this work, we developed a novel synthesis method for aliphatic and aromatic polyamides bearing one-handed spiral morphologies. The chiral interfacial polymerizations developed here were achieved in a liquid crystal (N-LC or N*-LC)/liquid (water) interface (Scheme 1 and see Figure 5). The structures, morphologies and thermal properties of the resulting helical aliphatic and aromatic polyamides were investigated through polarizing optical microscope (POM), scanning electron microscope (SEM), X-ray diffraction (XRD) measurements, and thermogravimetric analysis (TGA).

2. RESULTS AND DISCUSSION Synthesis and Preparation of the Asymmetric Reaction Field. Four types of N-LCs [4-(trans-4-npropylcyclohexyl)ethoxybenzene (PCH302), 4-(trans-4-npropylcyclohexyl)butoxybenzene (PCH304), 4-(trans-4-n-pentylcyclohexyl) hexoxybenzene (PCH506) and 4-ethyl-4′-(trans4-pentylcyclohexyl)biphenyl (BPCH52)] were synthesized using the following synthetic methods. PCH302 and PCH304 were synthesized according to a previously described method.14 PCH506 was synthesized through a Williamson etherification reaction between p-(trans-4-n-pentylcyclohexyl)phenol (PCH500) and 6-bromohexane. BPCH52 was synthesized through a Suzuki-Miyaura coupling reaction between 4-(4′2785


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Figure 1. Molecular structures of N-LCs (PCH302, PCH304, PCH506 and BPCH52) and chiral dopants [(R)- and (S)-D1, (R)- and (S)-D2] used for N*-LC, and phase transition temperature of LC mixture (PCH302: PCH304: PCH506: BPCH52 = 100:100:50:50 in mole ratio) in cooling process (K, crystal; N, nematic; I, isotropic).

Table 1. Mixing Ratios of N-LCs and Chiral Dopants (mol %) and Helical Pitches of N*-LCs

conditions of the D1 and D2 synthesis reactions were previously reported.18 The molecular structures of the four N-LCs and the chiral dopants are shown in Figure 1. The host N-LC was prepared by mixing four LCs, PCH302, PCH304, PCH506, and BPCH52, at a molar ratio of 100:100:50:50 and was designated as System 1. The N*-LC was prepared by adding small amounts of the binaphthyl derivatives (D1 or D2) to the host N-LC. The N*-LCs containing 1.6 mol % (R)- and (S)-D1, i.e., PCH302:PCH304:PCH506:BPCH52:D1 = 100:100:50:50:5 (mole ratio), were designated as Systems 2 and 3, respectively. The N*-LCs containing 1.6 mol % (R)- and (S)-D2, PCH302:PCH304:PCH506:BPCH52:D2 = 100:100:50:50:5 (mole ratio), were designated as Systems 4 and 5, respectively. The prepared N-LC and N*-LCs as well as their helical pitches are summarized in Table 1. Helical pitches of 2.4−2.5 μm were observed in the N*-LCs containing D1 (Systems 2 and 3), while pitches of 0.25−0.26

pentylcyclohexyl)phenyl) boronic acid and 1-bromo-4-ethylbenzene. The synthetic routes of PCH506 and BPCH52 are shown in Scheme 2. Axially chiral binaphthyl derivatives were used as chiral dopants because they possess larger helical twisting powers (HTPs) than asymmetric carbon-containing chiral compounds. This property arises from large steric repulsions between hydrogen atoms at the 8 and 8′ positions of binaphthyl rings.17 The disubstituted binaphthyl derivatives [(R)-, (S)-2,2′PCH506-1,1′-binaphthyl, designated as (R)-D1 and (S)-D1, respectively] were synthesized through Williamson etherification reactions between chiroptical (R)- and (S)-1,1-bi-2naphthols and phenylcyclohexyl derivatives (PCH5Br). The tetrasubstituted binaphthyl derivatives [(R)-, (S)-2,2′PCH5012-6,6′-PCH5-1,1′-binaphthyl, designated as (R)-D2 and (S)-D2, respectively] were synthesized by introducing the phenylcyclohexyl moieties without alkyl spacers [PCH5Br] at the 6 and 6′ positions of the binaphthyl rings. The reaction 2786


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Figure 2. Polarizing optical micrographs (POMs) of the N*-LC containing chiral dopants (D1, D2) and sebacoyl chloride. (a) System 2 with sebacoyl chloride. (b) System 3 with sebacoyl chloride. (c) System 4 with sebacoyl chloride. (d) System 5 with sebacoyl chloride. The POMs were measured using two “micro cover glasses”, in which the LC sample was inserted without spacers. The cover glasses used have no alignment treatment.

Figure 3. POMs of the N*-LC containing chiral dopants (D1, D2) and terephthaloyl chloride (a) System 2 with terephthaloyl chloride. (b) System 3 with terephthaloyl chloride. (c) System 4 with terephthaloyl chloride. (d) System 5 with terephthaloyl chloride. The POMs were measured using two “micro cover glasses”, in which the LC sample was inserted without spacers. The cover glasses used have no alignment treatment.

μm were observed in the N*-LCs containing D2 (Systems 4 and 5). The helical twisting powers (βM) of the chiral dopant, or the ability to convert N-LC into N*-LC, was evaluated using the following equation

βM = [(1/p)/c]c → 0,

where p is the helical pitch in micrometers and c is the mole fraction of the chiral dopant in the N*-LC.17,19 The helical 2787


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Table 2. Helical Pitches of N*-LCs with Sebacoyl Chloride or Terephthaloyl Chloride

Figure 4. Experimental setup of traditional interfacial polycondensation (method 1) for synthesis of nylon-6,10 and polyphthalamide.

twisting powers of D1 and D2 were 171 μm−1 and 449 μm−1, respectively. Thus, the helical twisting power of D2 is approximately 2.6 times larger than that of D1. This may be due to a difference in the number of substituents. Namely, the axially twisting torque of D2 is more effectively transferred to environmental nematic LC molecules by virtue of intermolecular interactions between the four PCH substituents of D2 and the PCH moieties of LC molecules, compared with the two PCH substituents in D1.18 Figures 2 and 3 show polarizing optical micrographs (POMs) of the N*-LCs containing chiral dopants (D1, D2) and diacyl chloride (sebacoyl chloride and terephthaloyl chloride). We observed fingerprint textures characteristic of N*-LC (Figures 2c,d and 3c,d).15 The N*-LC containing diacyl chloride showed a stable N*-LC phase at temperatures below 43 °C. This suggests that the N*-LC may be used as an asymmetric solvent for synthesis of helical polyamides. The helical pitch of the N*-LC was determined by measuring the distance of Cano lines appearing on the surface of a wedge type cell.20 When the helical pitch was smaller than the 1 μm resolution of the Cano lines method, it was evaluated using a selective reflection method. The helical pitch (p) was calculated according to p = λ/n, where λ is a wavelength of selectively

reflected light and n is a refractive index of N*-LC (n ≅ 1.5).21 We confirmed that the N*-LCs of Systems 4 and 5 showed selective reflections in the visible region. In addition, the helical pitches of N*-LCs with sebacoyl chloride or terephthaloyl chloride are shown in Table 2. The N*-LCs with diacyl chloride showed larger helical pitches by 10% than the N*-LCs without diacyl chloride, implying a slight decrease in helicity of the former N*-LCs. However, N*-LCs containing diacyl chloride were confirmed to be feasible for the chiral solvent. Synthesis of Helical Nylon-6,10 and Helical Polyphthalamide. In the traditional polymerization of polyamides (method 1), organic solvents such as chloroform or tetrachloromethane were used to dissolve diacyl chloride, resulting in the organic layer below the diamine-containing water layer. The water solution was carefully poured onto the surface of the organic solution. A polyamide film soon formed through polycondensation at the organic-aqueous interface. The film was picked up and pulled out with tweezers to obtain a polyamide fiber. The fiber was then washed with distilled water and organic solvents (Figure 4). In the alternate polymerization method presented here (method 2), liquid crystals were used as an organic layer. Because liquid crystals have a lower density than water, the 2788


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Figure 5. Experimental setup of chiral interfacial polycondensation (method 2) for synthesis of helical nylon-6,10 and helical polyphthalamide.

polymerization interface is above the water layer. Thus, this polymerization can be considered as an inverse interfacial polymerization compared with the traditional interfacial polymerization of polyamides. Here, we designed a new apparatus for the polymerization shown in method 2 and synthesized helical nylon-6,10 (Figure 5). The polymerization temperature was kept constant at room temperature to maintain the N*-LC phase. Water was first added to the reaction container, and the LC solution containing sebacoyl chloride was added dropwise to the water layer using a syringe. The water/LC solution was left to stabilize at the interface for 30 min. Subsequently, the aqueous solution containing hexamethylene diamine was slowly added to the water layer using a funnel without stirring. The polycondensation reaction soon occurred at the interface between the organic layer containing sebacoyl chloride and the water layer containing hexamethylene diamine (sebacoyl chloride: hexamethylene diamine = 1:20 mol ratio). The polymerization was carried out for 1 h. The resulting nylon-6,10 film was washed with an acetone/H2O solution, acetone and then chloroform. The film was dried under vacuum for 24 h. Polyphthalamide was synthesized using the same procedure as that for nylon-6,10. Therein, the LC layer and the water layer contained terephthaloyl chloride and hexamethylene diamine, respectively (terephthaloyl chloride: hexamethylene diamine = 1:20 mol ratio). The synthesized polyphthalamide film was washed and dried using the same procedure as described for the nylon-6,10 film. Morphology of Helical Nylon-6,10. Figure 6 shows scanning an electron microscope (SEM) image of the nylon6,10 fiber synthesized by the traditional polymerization between water and organic solvent (CHCl3) layers. The nylon fiber exhibits a porous and globular morphology. Figures 7 and 8 show SEM images of the nylon-6,10 films synthesized by the present polymerizations between liquid crystal (N-LC, System 1; N*-LC, Systems 2−5) and water layers, respectively. The helical pitches of the N*-LCs with sebacoyl chloride were 2.8 μm (System 2), 2.9 μm (System 3), 262 nm (System 4), and 267 nm (System 5). The fibers of nylon-6,10

Figure 6. Scanning electron microscope (SEM) image of the nylon6,10 film synthesized by the traditional polymerization between water and organic solvent (CHCl3) layers.

Figure 7. SEM image of the nylon-6,10 film synthesized by the present polymerization between N-LC and water layers (System 1).

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Figure 8. SEM images of nylon films synthesized in N*-LCs. The helical pitches of N*-LC used for the polymerization are (a) 2.8 μm [System 2], (b) 2.9 μm [System 3], (c) 0.26 μm [System 4], and (d) 0.27 μm [System 5]. The values of twice distance of fibril bundles shown in Figure 7a−c are close to helical pitches of N*-LCs, Systems 2−4.

Morphology of Helical Polyphthalamide. The morphology of polyphthalamide synthesized in N-LC was examined. Figure 9 shows that the polyphthalamide fibrils are partially

synthesized in the N-LC (System 1) are partially aligned due to the flow of N-LC during the polymerization. The morphology of the nylon fibers reflects the morphology of the N-LC host (Figure 7). The nylon-6,10 films synthesized in the N*-LC containing the disubstituted chiral dopant (D1) showed quite interesting morphologies. Namely, the nylon films synthesized in (R)- and (S)-N*-LCs exhibited screwed fibril morphologies with right- and left-handed directions, respectively. It was found that the screw directions of the fibrils are the same as those of the N*-LCs. Namely, the nylon fibrils are screwed right in the right-handed N*-LC [(R)-System 2] (Figure 8a). Meanwhile, the fibrils are screwed left in the left-handed N*-LC [(S)System 2] (Figure 8b). It is also of interest that twice the distances of the nylon fibril bundles (2.5 and 2.9 μm) are close to the helical pitches of the corresponding N*-LCs with sebacoyl chloride. These results imply that the screw direction of the helical nylon can be controlled by choosing the helicity of the N*-LC. Moreover, it was found that nylon-6,10 containing the tetrasubstituted chiral dopant (D2) has a spiral fibril morphology with a helical pitch of 270 nm which is similar to the helical pitch of the N*-LC. It was difficult to determine the screw directions of the fibrils in the nylons synthesized using Systems 4 and 5.

Figure 9. SEM image of the polyphthalamide film synthesized in NLC (System 1). 2790


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Figure 10. SEM images of the polyphthalamide films synthesized in N*-LCs. The helical pitches of N*-LC used for the polymerization are (a) 2.8 μm [System 2], (b) 2.6 μm [System 3], (c) 0.26 μm [System 4], (d) 0.27 μm [System 5]. The values of twice distance of fibril bundles shown in Figure 9a−d are close to helical pitches of N*-LCs, Systems 2−5.

interfacial polymerization presented here enabled us to synthesize helical nylon-6,10 and polyphthalamide with onehanded spiral morphologies, owing to a spatially chiralregulated polymerization environment. The present approach could be useful for synthesizing other types of helical commodity polymers. Structure of Helical Nylon-6,10. Crystal structures of the nylon films synthesized in N-LC and N*-LCs were examined using X-ray diffraction (XRD) measurements. Figure 11 shows that two XRD peaks are observed at 2θ = 20.6° (4.3 Å) and 2θ = 23.3° (3.8 Å) in all of the nylon films. The former (4.3 Å) and the latter (3.8 Å) correspond to the interchain distance within a sheet of coplanar polymers and the layered intersheet distance, respectively, as described in Figure 12. Hence, the crystal structures of the nylon films can be assigned as an α phase, where the polymer chains both within a sheet and between the layered sheets are linked by amide (CO--NH) type hydrogen bonds.22 It is of interest that the d spacings of the nylon films synthesized in N*-LCs are coincident with those of nylons synthesized in N-LC or in isotropic solvents such as CHCl3 and CCl4. This result suggests that although the chiral interfacial environment affects the higher-order structure of nylon to provide a peculiar spiral morphology, it does not affect the lower-order primary and/or secondary structures.

aligned in the microscopic region corresponding to the domain of the N-LC. Additionally, the morphologies of polyphthalamides synthesized in the N*-LC containing the di-substituted chiral dopant (D1) were investigated as shown in Figure 10. The polyphthalamides synthesized in the N*-LCs containing (R)-D1 [System 2] and (S)-D1 [System 3] exhibited left- and right-handed spiral fibril morphologies with fibril bundles twice the distances of 2.9 and 2.8 μm, respectively. These values are close to those (2.8 and 2.6 μm) of the corresponding N*-LCs with terephthaloyl chloride (Figure 10, parts a and b). Parts c and d of Figure 10 show that polyphthalamides synthesized in the N*-LCs containing (R)-D2 [System 4] and (S)-D2 [System 5] form spiral fibril morphologies with left- and right-handed directions, respectively, and that the degrees of swirling in the spiral morphology are much higher than those of the polyphthalamides synthesized by Systems 2 and 3. Such a difference is attributed to the difference in helical twisting power between the chiral dopants of D1 used in Systems 2 and 3 and D2 used in Systems 4 and 5. It is worth emphasizing that the flexibility and nonrigidity of the main chains in nonconjugated commodity polymers such as polyamides suppress formations of higher-ordered structures, particularly a helical or spiral morphology, so far as isotropic polymerization solvents are employed. However, the chiral 2791


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with a heating rate of 10 °C/min. The above films showed respective melting temperatures of 219.9, 218.5, 217.6, 221.7, and 219.5 °C (Figure 13b). TGA and DTA measurements were also performed on the polyphthalamide films. The polyphthalamide films synthesized in CHCl3 by method 1, in diethyl ether by method 2, in N-LC (System 1) and in N*-LCs (Systems 3 and 5) have thermal decomposition temperatures of 423.1, 421.4, 422.4, 423.1, and 423.5 °C, respectively (Figure 14a). They demonstrated melting temperatures at 371.2, 370.7, 370.5, 371.3, and 371.9 °C, respectively (Figure 14b). Thus, all of the nylon-6,10 films exhibited similar thermal degradation curves and melting temperatures. In particular, the nylon-6,10 films synthesized in N-LC and N*-LC through the interfacial polymerizations have comparable thermal properties to those of nylon-6,10 film synthesized in CHCl3 by traditional interfacial polymerization. This holds true for the thermal properties of the polyphthalamide film as well. It should be noted that traditional polyamides, such a nylon6,10 and polyphthalamide, are synthesized by interfacial polymerization using chloroform as an organic layer, followed by spinning and drawing to provide fibers with high crystallinity and thermal properties.23 The present polyamide films synthesized by interfacial polymerization with LCs exhibit thermal properties comparable to those of traditional polyamides. This is due to the usage of LCs which enables the alignment of the polymers and hence provides the enhancement of crystallinity without the need for drawing.

Figure 11. X-ray diffraction (XRD) profiles of nylon-6,10 films synthesized in CHCl3, N-LC (System 1) and N*-LCs (Systems 2−5).

Thermal Properties of Helical Nylon-6,10 and Helical Polyphthalamide. Thermogravimetric analysis (TGA) profiles show that the nylon-6,10 film synthesized in CHCl3 by method 1, in diethyl ether by method 2, in N-LC (System 1) and in N*-LCs (Systems 3 and 5) have thermal decomposition temperatures in nitrogen of 419.9 °C, 420.8 °C, 420.6 °C, 421.7 °C, and 424.7 °C, respectively (Figure 13a). Differential thermal analysis (DTA) measurements were carried out by heating nylon-6,10 films from room temperature to 800 °C

Figure 12. α-Crystal structure of nylon-6,10. The interchain distance within a sheet and the intersheet distance are 4.3 and 3.8 Å, respectively. 2792


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Figure 13. (a) Thermogravimetric analysis (TGA) and (b) differential thermal analysis (DTA) profiles of nylon-6,10 films synthesized in CHCl3 by method 1, and nylon-6,10 films synthesized in diethyl ether, N-LC (System 1), and N*-LCs (Systems 3 and 5) by method 2. Heating rate was 10 °C/min in N2 gas.

Figure 14. (a) TGA and (b) DTA profiles of polyphthalamide films synthesized in CHCl3 by method 1, and polyphthalamide films synthesized in diethyl ether, N-LC (System 1), and N*-LCs (Systems 3 and 5) by method 2. Heating rate was 10 °C/min in N2 gas. [PCH300], 4-(trans-4-n-pentylcyclohexyl)phenol [PCH500] and 4(trans-4-n-pentylcyclohexyl) bromobenzene [PCH5Br], were purchased from Kanto Chemical Ltd. Dibromine, 18-crown-6-ether, 1bromo-4-ethylbenzene, tetrakis(triphenylphosphine)palladium (0) (Pd(TPP)4), diethylazodicarboxylate (DEAD), bromoethane, 1bromobuthane, 1-bromohexane, 6-bromo-1-hexanol, 12-bromo-1dodecanol, trimethoxy borate, and (4-(4-pentylcyclohexyl)phenyl)boronic acid were purchased from Tokyo Kasei Co. Ltd. The compounds, acetone, chloroform, n-hexane, tetrahydrofuran (THF), ethyl acetoacetate, ethanol, diethyl ether, dichloromethane, acetic acid, n-butyllithium (nBuLi), hydrochloric acid (HCl), sodium (Na), sodium chloride (NaCl), sodium hydride (NaH), sodium hydrogen carbonate (NaHCO3), sodium sulfate (Na2SO4), and triphenylphosphine (TPP) were purchased from Nacalai Tesque, Inc. Bromine (Br2), magnesium (Mg), and potassium carbonate (K2CO3) were purchased from Wako Pure Chemical Industries, Ltd. 4.2. Methods. Proton (1H) nuclear magnetic resonance (NMR) spectra were measured in chloroform-d using either JEOL JNM EX400 400 MHz or Bruker AVANCE-600 600 MHz NMR spectrometer. Chemical shifts are represented in parts per million downfield from tetramethylsilane (TMS) as an internal standard. Elemental analysis was measured using a PerkinElmer 2400 CHN Elemental Analyzer. The microscope observation was carried out under crossed nicols using a Nikon ECLIPSE E400 POL POM equipped with a Nikon COOLPIX 950 digital camera and a Linkam TH600PM and L600 heating and cooling stage with temperature control. The samples for

3. CONCLUSIONS Novel synthesis methods for helical aliphatic and aromatic polyamides were developed by using chiral nematic LCs (N*LCs) in interfacial polymerization. Helical nylon-6,10 and polyphthalamide with one-handed spiral morphologies were synthesized for the first time. The swirling directions in the spiral morphology of the helical polyamides were controlled by selecting the chirality of the chiral dopant used for preparing the N*-LC. The present synthesis method has the potential to extend the applicability of asymmetric interfacial polymerizations using N*-LC to various types of polyamides. It is expected that helical polyamides would have superior and/or more peculiar physical and mechanical properties than traditional nonhelical polyamides. 4. EXPERIMENTAL SECTION 4.1. Materials. All experiments were performed under argon atmosphere. Tetrahydrofuran (THF) and dichloromethane (CH2Cl2) were distilled prior to use. Williamson etherification and Suzuki coupling reactions were used to obtain the chiral dopant. The chemical compounds, (R)- and (S)-2,2-dihydroxy-1,1-binaphthyl (optical purity, 0.99), were purchased from commercially available sources. The mesogenic compounds, 4-(trans-4-n-propylcyclohexyl)phenol 2793


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observations with POM were sandwiched between two cover glasses. Thermal behavior of the polymers was investigated in a heating run at a heating rate of 10 °C/min in flowing nitrogen gas, using thermogravimetry differential thermal analysis (TG-DTA) apparatus (TG-DTA6200, Seiko). The accelerating voltage of field emission (FE) -SEM (JSM-7500F, JEOL) was 2−10 kV. The nylon and polyphthalamide films were coated with Pt or Pt−Pd alloy using an ion coater with type of S6 JFC1600 (JEOL) before measurements of SEM. The coating thickness was evaluated to be ca. 5 nm. The distance between the fibril bundles of the helical nylon and polyphthalamide films was estimated from SEM images. XRD diffraction (XRD) measurements of the polymers were performed with a Rigaku ultra X18 diffractometer. XRD patterns were recorded with an X-ray generator with Nickel filtered CuKα radiation (40 kV/300 mA: λ = 0.154 nm) and a flat plate camera (RINT2500, Rigaku). The diffraction pattern was recorded on an imaging plate and scanned by a R-AXIS DS3A imaging plate reader at 100 μm resolution. 4.3. Syntheses of LCs. The syntheses of the PCH 506 and BPCH52 are written below: Synthesis of 4-(trans-4-n-Pentylcyclohexyl)hexoxybenzene [PCH506]. p-(trans-4-n-Pentylcyclohexyl)phenol (PCH500), (20.0 g, 81.2 mmol), 1-bromohexane (11.3 mL, 81.2 mmol), K2CO3 (33.7 g, 243.7 mmol), and a catalytic amount of 18-crown-6-ether were dissolved in acetone (150 mL). The mixture was stirred for 3days at 60 °C. The mixture was extracted with H2O and CHCl3. The organic layer was washed with brine and dried over Na2SO4. The organic solvent removed by rotary evaporation. The organic layer was subjected to chromatography on silica gel using CHCl3:n-hexane = 1:1 as an eluent to give a white powder (23.8 g, 89%). Anal. Found for C23H38O: C,83.48; H,11.73. 1 H NMR (400 MHz, CDCl3, from TMS, ppm) = 0.85−1.86 (m, 31H, CH, CH2, CH3), 2.39−2.40 (m, 1H, Ph−CH), 3.90−3.94 (t, J = 6.6, 2H, O−CH2), 6.80−6.82 (d, J = 8.8, 2H, phenyl), 7.09−7.11 (d, J = 8.5, 2H, phenyl). Synthesis of 4-Ethyl-4′-(trans-4-Pentylcyclohexyl)biphenyl [BPCH52]. (4-(4-Pentylcyclohexyl)phenyl)boronic acid. 1-Bromo-4(4-pentylcyclohexyl)benzene (PCH5Br) (10 g, 32.33 mmol) and Mg (1.57g, 64.66 mmol) were dissolved in dried THF (40 mL) and stirred for 3 h at room temperature. Trimethylborate (7.21 mL, 64.66 mmol) was added dropwise to the reaction mixture at 78 °C. The reaction mixture was stirred for 24 h at room temperature. The mixture was extracted and washed several times with water and CHCl3. The organic layer was subjected to chromatography on silica gel using CHCl3 and ethyl acetate in a sequence as an eluent to give a white powder (6.2 g, 70%). Anal. Found for C17H27BO2: C, 74.46; H, 9.92; B, 3.94; O, 11.67. 1 H NMR (400 MHz, CDCl3, from TMS, ppm) = 0.85−1.86 (m, 22H, CH, CH2, CH3), 2.70−2.73 (m, 1H, Ph−CH), 6.80−6.82 (d, J = 8.8, 2H, phenyl), 7.09−7.11 (d, J = 8.5, 2H, phenyl). (Usually, boronic acid cannot be detected in the mass spectrum by the EI method.) 4-Ethyl-4′-(trans-4-pentylcyclohexyl)biphenyl [BPCH52]. (4-(4Pentylcyclohexyl)phenyl)boronic acid (4 g, 10.2 mmol), 1-bromo-4ethylbenzene (1 mL, 6.9 mmol), NaHCO3 (2 g, 20.3 mmol), and a catalytic amount of Pd(PPh3)4 were added to the reaction mixture. The mixture was refluxed in H2O (20 mL) and THF (20 mL) for overnight at 70 °C, and then it was cooled down and washed several times with H2O and CHCl3. The organic layer was washed with brine and dried over Na2SO4. The organic solvent removed by rotary evaporation. The organic layer was subjected to chromatography on silica gel using n-hexane/CHCl3 = 1 as an eluent to give a white powder (1.9 g, 84%). Anal. Found for C25H34: C, 89.76; H, 10.26. 1 H NMR (400 MHz, CDCl3, from TMS, ppm) = 0.85−1.86 (m, 25H, CH, CH2, CH3), 2,58−2.62 (q, 3H, Ph−CH3), 2.70−2.73 (m, 1H, Ph−CH), 7.35−7.40 (d, J = 8.8, 8H, phenyl). HRMS (EI, m/z): [M]+ found for C25H34, 334.2658.

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AUTHOR INFORMATION

Corresponding Author

*(K.A.) E-mail: [email protected]. Present Address †

Institute of Advanced Composite Materials, Korea Institute of Science and Technology Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Grants-in-Aid for Science Research (A) (No. 25246002) and (No. 25620098) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

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