Polymorph Control of Calcium Carbonate Films in a Poly(acrylic acid)-Chitosan System Akiko Kotachi, Takashi Miura, and Hiroaki Imai* Department of Applied Chemistry, Faculty of Science and Technology, Keio UniVersity, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan
CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 7 1636-1641
ReceiVed October 7, 2005; ReVised Manuscript ReceiVed April 10, 2006
ABSTRACT: We successfully controlled the crystal structure of calcium carbonate films grown on a 260 °C-baked chitosan using a single chemical species of poly(acrylic acid) (PAA) as a soluble agent. The planar morphology of the calcium carbonate films was basically ascribed to the guided growth by PAA molecules anchored to chitosan on a glass substrate. Selective production of a particular crystal structure, such as calcite, aragonite, or vaterite, was achieved by variation of the molecular weight of PAA and the temperature of the solution. The control of the polymorphs was ascribed to a templating effect due to the arrangement of PAA molecules anchored on the surface of chitosan. Introduction Life skillfully produces fascinating architectures of inorganic materials on a wide range of nano- and macro-scales. Generally, the architecture, including the components, polymorphism, orientation, and morphology of biominerals, is strictly controlled by various kinds of organic matrices and soluble agents in cells.1-4 Recently, the morphological control of calcium carbonate, which is one of the typical biominerals observed in mollusks, has been developed rapidly using a biomimetic artificial system. Planar films and porous architectures mimicking biominerals were produced in a supersaturated solution containing various kinds of additives.5-14 The formation of planar films was induced on a specific substrate of insoluble polyalcohols with the assistance of a soluble agent of polymeric anions.5,6,9-13 The crystal structures of calcium carbonate, such as calcite, aragonite, and vaterite, are influenced by the condition of precipitation and the addition of impurities in an aqueous solution. Whereas calcite is the thermodynamically stable form in the ambient condition, an increase in the degree of supersaturation in an aquatic system promotes the formation of metastable aragonite and vaterite. The substitution of Ca2+ by Mg2+ or Co2+ in the carbonate structure has been reported to be effective in the selective formation of aragonite.15,16 In recent years, the selective formation of the metastable polymorphs using organic agents has been studied to develop artificial biomimetic systems.17-19 The calcium carbonate grown on a porphyrin monolayer in a system containing poly(acrylic acid) (PAA) as a soluble agent was calcite.17 Aragonite and vaterite films were achieved on a poly(vinyl alcohol) (PVA) substrate with PAA and poly(glutamic acid) (PGlu), respectively.18 A natural template of an eggshell membrane was reported to induce the formation of aragonite and vaterite films in the presence of PGlu and poly(aspartic acid) (PAsp), respectively.19 However, the selectivity of the polymorphism has been insufficient compared to the morphological control. Moreover, on the formation of calcium carbonate films using chitin or its derivatives and PAA as a substrate and a soluble agent, respectively, the polymorphism was different in each case.8-10,13 Therefore, the crystal structure was not strictly controlled by organic agents, although aragonite films were selectively produced by the addition of Mg2+ to the chitosan-PAA system.9 Moreover, the * Fax: +81 45 566 1551. Tel: +81 45 566 1556. E-mail: hiroaki@ applc.keio.ac.jp.
polymorphism was reported to be sensitive to temperature.15,20 The presence of a transient amorphous calcium carbonate prior to the formation of stable crystalline phases has been reported.21-23 The morphological control of calcite was achieved using preliminary deposition of the transient amorphous phase.17 Nevertheless, the essence of the comprehensive control of the polymorphism of calcium carbonate by regulation with organic molecules has not been clarified. Recently, we successfully produced planar films consisting of orientated crystal grains of calcite on a glass substrate using a binary PAA system.24 In this case, calcite was purely obtained in the presence of PAA. On the other hand, the existence of a chitosan substrate complicated the polymorphism of the deposited calcium carbonate. In the present work, the polymorphism was successfully controlled in a simple system including a chitosan substrate and PAA by variations of the molecular weight of the polymeric species and the temperature of the solution. Our experimental results suggested that the arrangement of PAA molecules on a chitosan surface was essential for the control of the crystal structure of calcium carbonate films grown on the substrate. Experimental Section Precipitation of calcium carbonate was performed in a 10 mM calcium chloride solution supersaturated by the introduction of carbon dioxide generated by the decomposition of ammonium carbonate. We added 2.4 × 10-3 wt % PAA with different average molecular weights (2000 (2k) Sigma-Aldrich, 90 000 (90k) Polyscience, and 250 000 (250k) Sigma-Aldrich) as coexisting electrolytes and immersed a substrate for heterogeneous nucleation into the precursor solution before the introduction of carbon dioxide. The molar concentration of carboxy groups on PAA chains was 0.33 mM. Chitosan-coated glass slides used as a substrate were prepared by spin-coating an acetic acid solution of chitosan (Wako Pure Chemical) and neutralizing it in diluted ammonia water. The substrates were then baked at 100 and 260 °C on a hot plate for 1 min in air. We set the substrates upright in a vessel to prevent deposition of precipitates formed through homogeneous nucleation. Vessels containing 150 cm3 of aqueous solution of calcium chloride and the coexisting electrolytes were covered with a polymer film having several pinholes and then placed in a 1.2 dm3 closed plastic container with 2.0 g of ammonium carbonate. The temperature of the container was strictly controlled in a range of 10-35 °C in a thermostatic oven. After 24 h, calcium carbonate films obtained on the chitosan substrate were removed from the solution, washed with water, and dried at room temperature. The morphology of deposited films was observed by an optical microscope and a Hitachi S-4700 field-emission scanning microscope
10.1021/cg050528l CCC: $33.50 © 2006 American Chemical Society Published on Web 05/26/2006
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Figure 1. A typical appearance of the calcium carbonate on a chitosan surface in the presence of PAA. (FE-SEM). The crystal structure of calcium carbonate in the deposited films was basically evaluated by a Rigaku RAD-C X-ray diffraction (XRD) system using Cu KR radiation. However, it was difficult to determine the crystal structure accurately in the deposited films because small crystalline grains produced weak diffraction signals for characterization. Moreover, a mixture of the polymorphs was frequently observed on the substrate. Recently, highly oriented calcite crystals were grown epitaxially on the underlying thin films of polycrystalline calcium carbonate.25 We found that the crystal structure and crystallographic orientation of the basal films were inherited by the daughter crystals grown through the overgrowth.26 The crystal structure of each film was basically evaluated using a microdiffraction system (Rigaku RINT-RAPID). Then we successfully determined the polymorphism using the development of the particular morphological habits depending on the crystal structure, such as rhombohedral calcite, spicular aragonite, and petaline vaterite, and an increase in the diffraction signals from the daughter crystal grains.
Results and Discussion In general, the formation of thin films with calcium carbonate required the presence of soluble polymeric anions, such as PAA, PGlu, PAsp,5-10,12,13 and silicates,11 and a substrate of insoluble polyalcohol. On the other hand, we found that a high-molecularweight PAA promoted the formation of calcite films on a glass substrate without the polyalcohol substrate in our previous work.24 In the current study, we mainly investigated the morphology and the crystal structure of obtained films of calcium carbonate on chitosan baked at 100 and 260 °C in the presence of PAA having different molecular weights at various temperatures. A typical appearance of the calcium carbonate crystals grown with PAA on a chitosan substrate is shown in Figure 1. Granular particles were occasionally observed with the films. The planar and circular appearance of the films was fundamentally the same for the deposits obtained under all the conditions regardless of the crystal structure. Generally, the diameter of circular films on 260 °C-baked chitosan was relatively larger than that of films on 100 °Cbaked chitosan (Figure 2). The promotion of the lateral growth of the films suggests a high affinity of calcium carbonate for the surface of the annealed chitosan. In contrast to the similarity of the morphology, the crystal structure of the films was varied with the conditions. Figure 3 shows XRD patterns of the films deposited on 260 °C-baked chitosan in the presence of PAA2k and -250k at various temperatures. Diffraction peaks due to calcite seem to be dominant in all the XRD patterns for the products except for PAA250k at a temperature above 25 °C. Weak diffractions assigned to vaterite were also observed except for PAA2k at 10 °C. The formation of aragonite was confirmed in the products at 35 °C. As shown in Figures 1 and 2, the products on the substrate were commonly obtained as a mixture of various sizes of planar films and granular particles. Therefore, it is difficult to determine
Figure 2. Optical micrographs of calcium carbonate grown at 10 °C with 2.4 × 10-3 wt % PAA250k on 100 °C- (a) and 260 °C-baked (b) chitosan. Arrows indicate planar films. Black shadows are granular particles.
the crystal structure of the planar films using the XRD patterns. Since the rhombohedral habits of particles found around the planar films were attributed to the calcite structure, the intense signals of calcite in the XRD chart (signals marked (C) in Figure 3) are mainly ascribed to the diffraction from the particles. Consequently, we could not determine the crystal structure of each film from the conventional XRD patterns. For the exact characterization of the various films grown at various conditions, we performed subsequent overgrowth of calcium carbonate in a supersaturated solution without any additives.26 The planar films were developed by the overgrowth to an array of grains having a particular habit, which depended on the crystal structure. The crystal structure of each film was initially evaluated using a microdiffraction system (Rigaku RINT-RAPID). Then, we confirmed that the polymorph and the crystallographic orientation of the basal crystals were fundamentally inherited by the overgrown micrograins. As shown in Figure 4, rhombohedral grains, thin plates standing upright, and spicular needles were grown on the basal films of calcite, vaterite, and aragonite, respectively. The subsequent overgrowth technique successfully visualized the polymorphism of the CaCO3 films. On the basis of the habits of the daughter grains, we determined the crystal structure of the films depending on the preparation conditions. The polymorph was reported to be influenced by the PAA concentration.10 In our study, however, the crystal structure of the films was independent of the PAA concentration between 0.16 and 3.3 mM. The specific structure of the planar films was obvious grown on 260 °C-baked chitosan, whereas the influence of the baking temperature of chitosan as a substrate on the crystal structure was negligible. Thus, hereinafter, the polymorphism depending on the preparation conditions is mainly discussed using the results of the products grown on 260 °Cbaked chitosan. Table 1 shows the crystal structures of the films grown on a glass slide or a 260 °C-baked chitosan substrate determined by the SEM observation of the morphology of the micrograins after the subsequent overgrowth. Small circular films of calcite were formed in the presence of low-molecular-weight PAA (PAA2k). However, relatively large films of vaterite were grown with
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Figure 3. XRD patterns of calcium carbonate grown on 260 °C-baked chitosan in the presence of PAA at various temperatures (C, calcite; A, aragonite; V, vaterite).
high-molecular-weight PAAs (PAA90k and -250k) at the same temperature. An increase in the temperature of the solution containing PAA2k also induced the formation of vaterite. Since the petaline plates of vaterite were perpendicularly arranged (Figure 4b), the crystallographic orientation was regulated by the substrate. An intense diffraction signal due to (110) of vaterite indicates that the c-axis was parallel to the surface (Figure 5). We found that aragonite films were grown at relatively high temperatures (25-35 °C). Especially, aragonite films were dominantly produced (>90%) with high-molecular-
Kotachi et al.
weight PAAs (PAA90k and -250k) at 35 °C. On the other hand, pure calcite films were always observed on a bare glass substrate with high-molecular-weight PAA (PAA90k and -250k). Vaterite and aragonite were prepared on a PVA substrate by using PAA and PGlu, respectively, as soluble species.18 The essence of the control of the polymorphs was ascribed to the lattice matching between the ab planes of PVA and the crystal structures. In the previous report, however, the role of the soluble species was not clarified. In the present work, we found that the polymorphs were varied by the chain length of a single soluble species, PAA, and temperature of the solution. The adsorption of the soluble polymeric molecules onto insoluble polymer substrates, such as chitosan and cellulose, was confirmed by ellipsometry and infrared spectra.6,10 The films were not obtained on the chitosan surface in the absence of PAA, whereas the presence of high-molecular-weight PAA induced the film formation independently. These facts also indicate that the film formation was induced by PAA molecules attached on the chitosan surface. On the other hand, the variation of the polymorphs is not ascribed to pH or viscosity of the solutions because those values were hardly influenced by the molecular weight of PAA in the diluted systems. Consequently, we assume that a particular arrangement of PAA molecules adsorbed to the chitosan surface selectively promoted the nucleation and lateral growth of a specific crystal structure, such as calcite, aragonite, or vaterite. Alcoholic hydroxyl groups of chitosan are more effective for the adsorption of negatively charged PAA molecules than a glass surface, which is negatively charged under a neutral or basic condition. The formation of calcium carbonate through heterogeneous nucleation would be influenced by the arrangement of carboxy groups of PAA chains anchored to the chitosan surface. Since the crystal structure depended on the molecular weight of PAA and the temperature, the arrangement of PAA was modulated by the chain length and mobility of the polymeric molecules. Metastable amorphous calcium carbonate (ACC) has been reported to be previously deposited and then transformed into a crystalline phase.25,27-29 Although the previous formation of metastable ACC was not detected in this work, the transient amorphous phase may be produced as a precursor of the crystalline films. In that case, the surface of the substrate would promote the transition of ACC into a specific crystalline phase. Anyway, the crystallization process was controlled by the template effect of the arrangement of PAA anchored on the surface. Rhombohedral calcite and spherical vaterite were deposited on the chitosan surface in a supersaturated solution without PAA. The addition of PAA inhibited the formation of vaterite, and the high-molecular-weight molecules (PAA90k and -250k) promoted the formation of planar films consisting of small calcite grains on a glass substrate.24 Thus, the presence of PAA was fundamentally suitable for the formation of calcite regardless of molecular weight. The distance of carboxy groups of PAA chains (5.02 Å) is relatively close to that of carbonate ions on the {104} and {110} faces of calcite (4.99 Å). Hence, the adsorption of the polymeric molecules stabilizes the calcite form. Furthermore, high-molecular-weight PAA adsorbed on a glass surface induced the nucleation of calcite and promoted the lateral growth of the crystal along the substrate. The capping effect of PAA molecules suppressed the upward growth of carbonate crystals, and then planar films of calcite were formed on the substrate. However, aragonite and vaterite were formed with PAA by the existence of chitosan as substrates. As described above, many reports suggested that PAA molecules anchored to the specific surface induce the formation of the
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Figure 4. Typical SEM images of the development of the planar films into microarrays by the subsequent overgrowth without any additives for visual determination of the polymorphs: (a, b) calcite; (c, d) vaterite; (e, f) aragonite. Table 1. Dependence of the Crystal Structures of Calcium Carbonate Films on the Substrate, Molecular Weight of PAA, and Temperaturea temperature (°C) PAA/substrate
10
15
25
35
2k/chitosan 90k/chitosan 250k/chitosan 90kb/glass
C V V -
V(C) V V -
V(C) A,V Cc
A,V A(V)d A(V) -
a A, aragonite; C, calcite; V, vaterite; -, no data; (), a minor component. CPAA90k ) 7.2 × 10-2 wt %. c The temperature of the solutions was not strictly controlled. d The proportion of aragonite in the whole crystals was estimated to be >90% from the SEM observation of the morphology of the micrograins after the subsequent overgrowth.
b
Figure 5. An X-ray diffraction pattern of the vaterite film and the standard (JCPDS#33-268).
planar films. Therefore, the arrangement of carboxy groups of PAA molecules adsorbed on the substrate would be guided by the lattice of hydroxyl groups on the chitosan surface, and then the nucleation of calcium carbonate crystals would be influenced by the arrangement (directly in the solution or through the transition from ACC). The crystal structure was also influenced by the temperature of the system containing PAA and chitosan. However, calcite was always obtained with PAA at temperatures ranging from 10 to 35 °C in the absent of chitosan. This result indicates that the direct influence of the temperature on the polymorphism is negligible in this narrow range. Consequently, the dependence of the polymorphs suggests that the arrangement of PAA molecules anchored to the chitosan surface is affected by
temperature of the solution. Moreover, the chain length of the polymeric molecules influences the arrangement because the polymorph depended on the molecular weight of PAA. The lattice of the crystal planes of chitosan was basically reflected in the arrangement of PAA molecules adsorbed on the substrate. Since microcrystals of chitosan disperse in the polymer substrate, the specific planes of crystalline chitosan could appear partially on the surface. As shown in Table 1, the combination of highmolecular-weight PAAs and the ordered lattice of crystalline chitosan could promote the nucleation of aragonite and vaterite. Since the diameter of circular films on 260 °C-baked chitosan was relatively larger than that on the 100 °C-baked one, specific crystal growth of calcium carbonate was promoted by baking of chitosan. The crystallinity of chitosan was improved by baking at a high temperature. Moreover, anhydrous chitosan could be formed in the polymer films by baking above 240 °C.30-32 Figure 6 shows the arrangement of hydroxyl groups on bc and ac planes of chitosan and anhydrous chitosan. The distinct rectangular lattices of hydroxy groups of chitosan and anhydrous chitosan are suitable for the nucleation of orthorhombic aragonite rather than trigonal calcite. Aragonite films were produced at a high temperature with high-molecular-weight PAAs. The adequate arrangement of carboxy groups of highmolecular-weight PAAs is achieved through the strong interaction between the anchored long-chain molecules and the substrate. The arrangement of the PAA molecules could be smoothly adjusted on the chitosan surface by “annealing” at a high temperature. On the other hand, the regularity of the arrangement of carboxy groups is degraded by a decrease in the chain length due to the weakening of the interaction of the anchored molecules and the chitosan surface. Moreover, the adjustment of the arrangement of PAA molecules on the chitosan surface occurs slowly at a relatively low temperature. Consequently, the formation of calcite was preferred with lowmolecular-weight PAA at a low temperature because the ordered array of hydroxyl groups on the chitosan surface was hardly reflected in the adsorbed molecules under those conditions. On the other hand, vaterite was obtained under intermediate conditions with high-molecular-weight PAAs at a low temperature or with low-molecular-weight PAA at a high temperature. In these cases, the c axis of vaterite grown on the chitosan substrate was parallel to the surface. Since the rectangle array of the {1-10} planes of vaterite is roughly similar to the lattices of chitosan and anhydrous chitosan crystals, the lateral growth,
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Figure 6. Structure of chitosan (a) and anhydrous chitosan (b).30-32
in which the c axis of vaterite is parallel to the chitosan surface, could be induced by loosely arranged PAA molecules on chitosan and anhydrous chitosan. The unit cell of vaterite (c ) 8.56 Å) is close to the array of hydroxyl groups of anhydrous chitosan (a ) 8.50 and b ) 8.62 Å) rather than that of chitosan (a ) 8.95 Å). Thus, the growth of vaterite films was promoted on 260 °C-baked substrates containing anhydrous chitosan. Unfortunately, the crystallinity and the orientation of the crystal lattice of chitosan and anhydrous chitosan were not directly evaluated because the X-ray diffraction signals were extremely weak. Further investigation is required to clarify the arrangement of PAA molecules on the surface of crystalline chitosan. DiMasi et al. reported that a Langmuir monolayer had no epitaxial relation to CaCO3 planes from the results of in-situ synchrotron X-ray scattering analysis.33 The lattice matching between the monolayer and the crystal planes, which is required for epitaxial growth, could not be strictly achieved in that system. On the other hand, our experimental results indicated that PAA molecules anchored on a crystalline chitosan surface worked as a template for the crystal growth of CaCO3. We assume that the flexibility of the lattice matching due to the presence of the intermediate PAA molecules is essential for the performance as a template. Conclusions We found that the polymorphism of calcium carbonate films grown on a 260 °C-baked chitosan substrate depends on the molecular weight of poly(acrylic acid) as a coexisting electrolyte and temperature. Although calcite films were basically produced on a glass substrate in the presence of high-molecular-weight PAA, the selective production of metastable phases, such as
aragonite and vaterite, was achieved by the arrangement of PAA anchored to the chitosan surface. The strict control of the structure with high-molecular-weight PAAs on a 260 °C-baked chitosan at a relatively high temperature promoted the formation of aragonite. Weak guidance with low-molecular-weight PAA or a relatively low-temperature induced the lateral growth of vaterite. This knowledge is useful for a biomimetic approach to the comprehensive control of the architecture of inorganic crystals using an organic molecular system. Acknowledgment. We thank Rigaku Corporation for the measurement of the XRD pattern using a RINT-RAPID microdiffraction system. This work was supported by Grant-inAid for Scientific Research (No. 15560587) and the 21st Century COE program “KEIO Life Conjugate Chemistry” from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. References (1) Simkiss, K.; Wilbur, K. M. Biomineralization; Academic Press: San Diego, CA, 1989. (2) Lowenstam, H. A.; Weiner, S. On Biomineralization; Oxford University Press: Oxford, U.K., 1989. (3) Addadi, L.; Weiner, S. Angew. Chem., Int. Ed. Engl. 1992, 31, 153169. (4) Mann, S. Biomineralization, Oxford University Press: Oxford, U.K., 2001. (5) Kato, T.; Suzuki, T.; Amamiya, T.; Irie, T. Supramol. Sci. 1998, 5, 411-415. (6) Zhang, S.; Gonsalves, K. E. Langmuir 1998, 14, 6761-6766. (7) Gower, L. A.; Tirrell, D. A. J. Cryst. Growth 1998, 191, 153-160. (8) Kato, T.; Amamiya, T. Chem. Lett. 1999, 28, 199-200. (9) Sugawara A.; Kato, T. Chem. Commun. 2000, 487-488. (10) Hosoda N.; Kato T. Chem. Mater. 2001, 13, 688-693.
Biomimetic Control of the Polymorphs of CaCO3 (11) Kotachi, A.; Miura, T.; Imai, H. Chem. Lett. 2003, 32, 820-821. (12) Kotachi, A.; Miura, T.; Imai, H. Trans. Mater. Res. Soc. Jpn. 2004, 29, 2257-2259. (13) Wada, N.; Suda, S.; Kanamura, K.; Umegaki, T. J. Colloid Interface Sci. 2004, 279, 167-174. (14) Imai, H.; Terada, T.; Miura, T.; Yamabi, S. J. Cryst. Growth 2002, 244, 200-205. (15) Kitano, Y. Bull. Chem. Soc. Jpn. 1962, 35, 1980-1985. (16) Jyonosono, K.; Kato, A. Inorg. Mater. 1995, 2, 259, 492-497. (17) Xu, G.; Yao, N.; Aksay, I. A.; Groves, J. T. J. Am. Chem. Soc. 1998, 120, 11977-11985. (18) Hosoda, N.; Sugawara, A.; Kato, T. Macromolecules 2003, 36, 64496452. (19) Ajikumar, P. K.; Lakshminarayanan, R.; Valiyaveettil, S. Cryst. Growth Des. 2004, 4, 331-335. (20) Ku¨ther, J.; Tremel, W. Chem. Commun. 1997, 2029-2030. Ku¨ther, J.; Seshadri, R.; Knoll, W.; Tremel, W. J. Mater. Chem. 1998, 8, 641-650. (21) Aizenberg, J.; Lambert, G.; Addadi, L.; Weiner, S. AdV. Mater. 1996, 8, 222-226. (22) Aizenberg, J.; Lambert, G.; Weiner, S.; Addadi, L. J. Am Chem. Soc. 2002, 124, 32-39.
Crystal Growth & Design, Vol. 6, No. 7, 2006 1641 (23) Gower, L. B.; Odom, D. J. J. Cryst. Growth 2000, 210, 719-734. (24) Kotachi, A.; Miura, T.; Imai, H. Chem. Mater. 2004, 16, 31913196. (25) Volkmer, D.; Harms, M.; Gower, L.; Zigler, A. Angew. Chem., Int. Ed. 2005, 44, 639-644. (26) Kotachi, A.; Imai, H. Chem. Lett. 2006, 35, 204-205. (27) Loste, E.; Park, R. J.; Warren, J.; Meldrum, F. C. AdV. Funct. Mater. 2004, 14, 1211-1220. (28) Loste, E.; Meldrum, F. C. Chem. Commun. 2001, 901-902. (29) Rieger, J.; Thieme, J.; Schmidt, C. Langmuir 2000, 16, 83008305. (30) Okuyama, K.; Noguchi, K.; Miyazawa, T.; Yui, T.; Ogawa, K. Macromolecules 1997, 30, 5849-5855. (31) Yui, T.; Imada, K.; Okuyama, K.; Obata, Y.; Suzuki, K.; Ogawa, K.; Macromolecules 1994, 27, 7601-7605. (32) Ogawa, K.; Hirano, S.; Miyanishi, T.; Yui. T.; Watanabe, T. Macromolecules 1984, 17, 973-975. (33) DiMasi, E.; Olszta, M. J.; Patel, V. M.; Gower, L. B. CrystEngComm 2003, 5, 346-350.
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