Layer-by-Layer Assembly of Partially Sulfonated Isotactic Polystyrene

Mar 6, 2012 - The stereoregular synthetic polymer isotactic polystyrene bearing partially sulfonated groups (SiPS) was used as a layer-by-layer assemb...
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Layer-by-Layer Assembly of Partially Sulfonated Isotactic Polystyrene with Poly(vinylamine) Hiroharu Ajiro,†,‡ Klaus Beckerle,§ Jun Okuda,§ and Mitsuru Akashi*,†,‡ †

The Center for Advanced Medical Engineering and Informatics, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan § Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen, Germany ‡

S Supporting Information *

ABSTRACT: The stereoregular synthetic polymer isotactic polystyrene bearing partially sulfonated groups (SiPS) was used as a layer-by-layer assembled thin film for the first time. When a low molecular weight compound was employed as the pair for the alternative layer-by-layer (LbL) assembly, the frequency shift was very small using quartz crystal microbalance (QCM) analysis, whereas poly(vinylamine) (PVAm) formed an effective pair for the construction of LbL films with SiPS. When it was neutralized, SiPS was not assembled, probably due to the loss of effective polymer−polymer interactions. The ionic strength conditions revealed a slight difference of the assembly behavior on the isotactic polymer as compared to the atactic one. The assembled LbL film showed the same peaks over the range from 1141 to 1227 cm−1 and 700 cm−1 in the FT-IR/ATR spectra as the bulk complex of SiPS/PVAm, and the thickness on one side was calculated at 76 nm by QCM analysis. The surface roughness of the film was also observed by AFM.

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INTRODUCTION When the surface of a material can be selectively controlled and metamorphosed, while maintaining its bulk characteristics, the potential applications for this material can be dramatically expanded because the surface is the part that is in contact with the external environment. The alternative layer-by-layer (LbL) technique1 has received much attention for decades as a facile approach to construct thin films on a solid substrate. As the substrate is alternatively dipped into two kinds of polymer solutions, the polymers were adsorbed onto the substrate at each step through polymer−polymer interactions, such as electrostatic interactions,2 hydrogen bond interactions,3 and hydrophobic interactions.4 Recently, various chemical interactions have been applied for LbL assemblies, such as supramolecular assembly,5 specific protein interactions,6 dipole interactions,7 metal coordination interactions,8 covalent bond formation,9 and van der Waals interactions.10 The variety of chemical interactions available for fabrication of LbL assembled film contributes to the development of the material. For example, the physical characteristics of material surfaces are easily improved, such as its wettability,11 conductivity,12 and refractive index.13 An LbL assembly method was also employed for producing novel functional materials with stimuli responsivity,14 biocompatibility,15 and molecular selectivity16 as well as important nanotechnologies including nanopatterning,17 nanocapsules,18 and nanohybrids.19 Among the large number of studies on LbL assembly, only few reports on stereoregular synthetic polymers exist.10,20−22 © 2012 American Chemical Society

Furthermore, they are limited to poly(methyl methacrylate) (PMMA) derivatives, especially isotactic PMMA and syndiotactic PMMA. They are not composed of a single stereoregular polymer but require other complementary stereoregularity. For, a stereocomplex formation based on van der Waals interactions was utilized as the driving force, and a stereoregular nanoporous film was successfully prepared by replacing syndiotactic PMMA with syndiotactic poly(methacrylic acid), which can be removed from the LbL film due to the different solubility.21 This regulated nanospace has resulted in highly stereospecific template polymerization.22 In a series of studies on LbL assembly with stereoregular PMMAs and their derivatives, we were motivated to evolve them into other systems using stereoregular synthetic polymers because the stereoregularity of the polymer main chain would stabilize the regular conformation as crystallization on the substrate. In other words, a mechanically strong or thermally stable surface could be easily constructed because stereoregularity of the synthetic polymers usually improve their physical and chemical characteristics. Furthermore, a molecularly regulated structure at the nanometer level could be created if a stereoregular synthetic polymer can be applied to LbL assembled film, which various functional groups could be introduced. Received: February 13, 2012 Revised: March 6, 2012 Published: March 6, 2012 5372

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Layer-by-Layer Assembly. A QCM electrode was used as the substrate and was cleaned three times with a piranha solution (H2SO4/ 40% H2O2 aqueous solution = 3/1 by volume) for 1 min each time, followed by rinsing with ultrapure water and drying with nitrogen gas. The cleaned substrate was immersed into a polystyrene derivative solution for 5 min at 25 °C. The substrate was then taken out and rinsed thoroughly with each washing solvent as mentioned above. The substrate was again immersed into a PVAm solution for 5 in at 25 °C. This procedure was then repeated to fabricate complexes on the substrate. This alternating deposition cycle was repeated for 16 steps. Measurement. An AT-cut QCM with a parent frequency of 9 MHz was obtained from USI (Japan). The frequency was monitored by an Iwatsu frequency counter (model 53131A). The quartz crystal (9 mm diameter) was coated on both sides with mirrorlike polished gold electrodes (4.5 mm in diameter). The alternating immersion process was performed with QCM substrates. Using the multilayered thin films on QCM substrate, FT-IR/attenuated total reflection (ATR) spectra of the fhin films were then obtained with a Spectrum 100FTIR spectrometer (Perkin-Elmer). The interferograms were coadded 64 times and Fourier-transformed at a resolution of 4 cm−1. Atomic force microscopy (AFM) images were obtained with a JSPM-5400 (JEOL, Japan) that was operated in the tapping mode in air at ambient temperature. Scanning was performed using silicon cantilevers (NSC35, μ-mesch, resonance frequency aroud 150 kHz, spring constant 4.5 N/m) within an area of 1 × 1 μm2 or 10 × 10 μm2 with a 512 scan line and a scan speed of 2.0 μm/s.

Isotactic polystyrene (iPS) is a well-known stereoregular synthetic polymer and is synthesized by specific organometallic catalysts23,24 as is syndiotactic polystyrene (sPS).25 Recently, iPS with narrow polydispersity index (PDI) has become accessible by living coordinate polymerization using postmetallocene titanium complexes.26 The crystal structure of iPS was found to consist of 31 helices,27 whereas sPS adopts a 21 helical form including regularly dispersed solvent molecules.28 The structural properties of iPS have been established with their Fourier transform infrared (FT-IR) spectra,29 gelation mechanism,30 and higher order structures in solution.31 Moreover, it is easy to introduce various substituents on the phenyl rings of iPS and sPS, and therefore we focused on polystyrene as the backbone for the stereoregular synthetic polymer. The sulfonation of polystyrene has been studied for a long time,32 and sulfonated polystyrenes have been employed for many applications due to their electrostatic interactions for separation and molecular template effects.33 It is not surprising that sulfonated polystyrene has been employed for the LbL technique,34 but they have always been atactic polystyrene (aPS) derivatives, although some stereoregular effects in solution have been reported about 50 years ago.35 In this study, we investigated the interactions between partially sulfonated isotactic polystyrene (SiPS) and poly(vinylamine) (PVAm) on quartz crystal microbalance (QCM) substrates in order to achieve the creation of LbL assembled thin films with a single stereoregular synthetic polymer, as well as PDI effect of iPS, which was also related with the regularity of polymer main chain structure. The alternating layered behavior was monitored by QCM analysis, and the stereoregularity effect, molecular weight effect, and salt concentration effects were discussed.

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RESULTS AND DISCUSSION The synthesis of iPS has been described in the literature.24 The number-average molecular weight (Mn) of the obtained iPS was 117 000, and its PDI was 6.82 (Supporting Information, Figure S1). The iPS and aPS were sulfonated using anhydrous acetic acid and sulfonic acid in 1,1,2-trichloroethane.32 The 1H NMR spectra are shown in Figure 1. The sulfonated iPS and aPS

EXPERIMENTAL METHODS

Materials. Syrene (Tokyo Chemical Industry Co. Ltd.) was distilled with calcium hydride before use. 1.0 mol/L of triethylaluminum in hexane (Tokyo Chemical Industry Co. Ltd.), 1.0 mol/L titanium(IV) chloride solution in dichloromethane (Aldrich Co. Ltd.), sulfuric acid (Tokyo Chemical Industry Co. Ltd.), 1,1,2-trichloroethane (Tokyo Chemical Industry Co. Ltd.), 1-chlorodecane (Tokyo Chemical Industry Co. Ltd.), acetonitrile (Tokyo Chemical Industry Co. Ltd.), and poly(vinylamine) hydrochloride (Polyscience, Inc.) were used as received. Polystyrene standard for SEC analysis was used as aPS with narrow PDI (F-40, Tosoh Corp., Ltd.). iPS was synthesized by the previously reported literature,23,26 and the sulfonation of the polymers was achieved by the reported methods32 (Supporting Information). Polymer Solution Preparation. The solvent and concentration were screened for the almost saturated conditions of each polymer, and the polymer solutions were filtered (Millex LG 0.20 μm, 0.20 μm mesh, Millipore) before QCM analysis. A chloroform/1-chlorodecane/ethanol (1/1/1, v/v/v) mixed solvent at 1 mg/mL was selected as the SiPS and SaPS solvent. PVAm was dissolved in 1 wt % ammonium hydroxide solution at 3 mg/mL for 0.54 M ionic strength. 0.1 wt % ammonium hydroxide solution/0.12 M NaCl(aq) (1/1, v/v), 0.1 wt % ammonium hydroxide solution, and ultrapure water were employed for the 0.20, 0.09, and 0.03 M ionic strength PVAm solutions at 3 mg/mL. 4VP was dissolved in ultrapure water to 3 mg/ mL. SiPSNa was dissolved in 0.01 M NaOH(aq)/acetonitrile (1/1, v/ v) to 1 mg/mL. At the washing stages of the QCM surface after each immersion step, the proper solvents were also selected for the nitrogen purge procedure. Chloroform/ethanol (1/1, v/v) was used for the SiPS and SaPS washing process, and 0.01 M NaOH(aq)/acetonitrile (1/1, v/v) was used for SiPSNa. Ultrapure water was used for the PVAm and 4VP washing processes.

Figure 1. 1H NMR spectra of iPS before the reaction (a) and after the reaction with iPS (b) and with aPS (c) (in MeOH/CDCl3 = 1/1, at rt, 400 MHz).

became insoluble in chloroform, and thus they were measured in a MeOH/CDCl3 (1/1, v/v) mixed solvent. The introduction ratio of the sulfonic groups was calculated from the aromatic region of the 1H NMR spectra to be 30% and 24% for SiPS and sulfonated aPS (SaPS), respectively. When the sulfonic groups were perfectly introduced into the polystyrene, it would be easy to have a random conformation by electrostatic repulsion, and hence the above-mentioned partially sulfonated polystyrenes were selected for this study. They were also neutralized by NaOH powder in MeOH/ CHCl3 at 60 °C for 24 h. The neutralized SiPS (SiPSNa) was precipitated in a MeOH/CHCl3 (1/1, v/v) mixed solvent, but 5373

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solution for SiPS, and then a CHCl3/1-chlorodecane/EtOH (1/1/1, v/v/v) mixed solvent was selected as the assembly solvent in this study. Similarly, 1 wt % ammonium hydroxide solution was chosen for the PVAm solvent. When the 1 mg/mL SiPS solution in CHCl3/1-chlorodecane/EtOH (1/1/1, v/v/v) was combined with 3 mg/mL PVAm solution in 1 wt % ammonium hydroxide solution, white precipitates appeared on the interface of the two liquid layers (Supporting Information, Figure S3), suggesting the formation of a SiPS/PVAm complex. Next, each solution was used for LbL assembly on the QCM substrate. Figure 2 shows the QCM analyses of the LbL for SiPS/ PVAm and SaPS/PVAm in various ionic strengths. In both cases, the final values of the frequency shift after 16 steps decreased when the ionic strength decreased, suggesting that the polymer−polymer interaction was not the only electrostatic interaction and included other interactions such as hydrogen bonding and hydrophobic interactions in water. It is interesting that this decreasing trend was gradual for the SaPS/PVAm series (Figure 2a−d) but converged in the case of the SiPS/ PVAm series at higher ionic strengths (Figure 2e−h). Such a slight difference could be based on the stereoregularity and different crystallizability. Figure 3 summarizes the LbL assembly behavior of polystyrene derivatives. Sequential changes were observed for SiPS/PVAm and SaPS/PVAm, and LbL film formation on the QCM substrate was confirmed, but the stereoregularity effect of the polystyrene backbone was not detected to a significant degree, using SiPS (Mn = 117K, PDI = 6.82) (Figure 3d) and SaPS (Mn = 16K, PDI = 2.34) (Figure 3c). The layered amount also showed no significant difference in stereoregularity, even when the narrow PDI polymers were employed with SiPS (Mn = 310K, PDI = 1.44) (Figure 3a) and SaPS (Mn = 430K, PDI = 1.02) (Figure 3b), whereas the total amounts showed the larger values (3958 ± 39 and 3619 ± 132 Hz) in both cases of SiPS (Mn = 310K, PDI = 1.44) (Figure 3a) and SaPS (Mn = 430K, PDI = 1.02) (Figure 3b) than those of the broad PDI samples (2272 ± 46 and 2593 ± 25 Hz) with SiPS (Mn = 117K, PDI = 6.82) (Figure 3d) and SaPS (Mn = 16K, PDI = 2.34) (Figure 3c). We suggest that the low molecular weight polymers in the broad PDI samples were not adsorbed on the surface sufficiently. This was supported by the results in LbL assemblies with different Mn with narrow PDI. Three different

they were soluble in water/MeOH. These observations on the solubility changes support a neutralizing process. Next, three kinds of polymers (SiPS, SaPS, and SiPSNa) were ground finely (Supporting Information, Figure S2) and filtered these solutions for the characteristics and QCM analyses. The partial crystallization of the stereoregular synthetic polymer sometimes gives a structural construction approach.36 The strategy for the LbL assembly of SiPS is shown in Scheme 1. The polymer backbone of SiPS would be easily crystallized Scheme 1. (a) Chemical Structure for LbL Assembly in This Study; (b) Schematic Illustration of the Strategy of LbL Film with SiPS and PVAm Using Crystallization Ability of iPS and Polymer−Polymer Interaction of SiPS and PVAm

when the thermal motion was suppressed on the substrate by the LbL assembly approach, and the polymer−polymer interactions between the SiPS and PVAm could cover the SiPS surface next to construct the LbL assembly. 1-Chlorodecane, decalin, and trans- or cis-decalins are known as theta solvents for polystyrene,29,30 and thus the proper solvent was explored for SiPS using theta solvents. The addition of chloroform and ethanol (EtOH) resulted in a transparent

Figure 2. QCM analyses of alternative LbL assembly with SaPS (Mn = 16K, PDI = 2.34) and PVAm. Ionic strength = 0.54 (a), 0.20 (b), 0.09 (c), and 0.03 M (d). Alternative LbL assembly with SiPS (Mn = 117K, PDI = 6.82) and PVAm. Ionic strength = 0.54 (e), 0.20 (f), 0.09 (g), and 0.03 M (h). 5374

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Figure 3. QCM analyses of alternative layer by layer assembly with SiPS (Mn = 310K, PDI = 1.44) and PVAm (a), SaPS (Mn = 430K, PDI = 1.02) and PVAm (b), SaPS (Mn = 16K, PDI = 2.34) and PVAm (c), SiPS (Mn = 117K, PDI = 6.82) and PVAm (d), SiPS (Mn = 117K, PDI = 6.82) and 4VP (e), SiPSNa (Mn = 117K, PDI = 6.82) and PVAm (f), SiPS (Mn = 310K, PDI = 1.44) and PVAm (g), SiPS (Mn = 150K, PDI = 1.21) and PVAm (h), and SiPS (Mn = 61K, PDI = 1.02) and PVAm (i) (n = 3).

SiPSs (Mn = 310K, PDI = 1.44; Mn = 150K, PDI = 1.21; Mn = 61K, PDI = 1.02) were tested for LbL assemblies with PVAm, reaching similar frequency shifts after 16 steps in the order of Mn values (Figure 3g−i). Although a slight decrease in weight was recognized at both PVAm steps, the frequency shifts reached 2272 and 2592 Hz for SaPS/PVAm and SiPS/PVAm after 16 steps, respectively (n = 3). The partial peeling off might occur at SiPS or SaPS steps if the PVAm would join LbL assembly. Assuming that the polymer density was 1 g/cm3, the film thicknesses corresponded to 76 and 87 nm on the QCM substrate (diameter = 0.45 cm, area = 0.159 cm2) because the 1 Hz shift of the QCM system translates into 1.07 ng weight change. After the fabrication of LbL films of SiPS/PVAm, the film on the QCM substrate dipped into 1 M HCl(aq) for the purpose of confirming the LbL film stability revealed that there was no frequency shift, suggesting that both SiPS and PVAm remained in the complex film. In order to examine the LbL assembly in detail, the PVAm solution was replaced with 4VP in ultrapure water to 3 mg/mL. When the low molecular weight compound 4VP was used for LbL assembly, the assembly behavior was uncertain (n = 3), and it showed a much lower amount than PVAm (Figure 3e). This result implies that a polymer pair with polymer−polymer interactions (PVAm) was necessary to fabricate the nanofilm, supporting the alternative LbL assemblies. On the other hand, when the SiPS solution was replaced with SiPSNa in 0.01 M NaOH(aq)/acetonitrile (1/1, v/v) to 1 mg/mL, the neutralized SiPSNa did not form a LbL film with PVAm either, suggesting that the improved solubility of SiPSNa made the polymer− polymer interaction difficult (Figure 3f). Therefore, the complementary polymer, which possessed polymer−polymer interactions, was required for the LbL assembled film of polystyrene derivatives, whereas almost no difference was observed between the two kinds of stereoregularities. The FT-IR/ATR of the bulk complex SiPS and PVAm were measured as shown in Figure 4. The spectrum of PVAm possessed the characteristic broad peaks over the range of 1141 to 1227 cm−1 and from 1462 to 1651 cm−1 (Figure 4a), whereas SiPS showed peaks at 700, 1131, and 1181 cm−1. The bulk complex of SiPS/PVAm obtained by mixing both solutions (Supporting Information, Figure S3) showed all of the characteristic peaks.

Figure 4. FT-IR/ATR spectra of PVAm (a), SiPS (Mn = 117K, PDI = 6.82) (b), and PVAm/SiPS bulk complex, which was prepared by mixing SiPS solution and PVAm solution (c).

The LbL film on the QCM substrate of SaPS/PVAm and SiPS/PVAm was similarly measured as shown in Figures 5 and 6. The spectral pattern of SaPS/PVAm (Figure 5) did not resemble that of the bulk sample (Figure 4) and lacked the intensity balances between the peaks at 700 cm−1 and over the range from 1141 to 1227 cm−1. Meanwhile, the results from the

Figure 5. FT-IR/ATR spectra of PVAm (a), SaPS (Mn = 16K, PDI = 2.34) (b), and PVAm/SaPS complex, which was fabricated on QCM substrate by alternative LbL assembly with 16 steps (c). 5375

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or the PVAm was replaced with a low molecular weight compound, it became difficult to prepare the LbL film. The amount of layered SiPS was not affected by the stereoregularity, as evidenced by the LbL results from SaPS/PVAm. However, the strong ionic strength and the narrow PDI accelerated the LbL film formation behavior, suggesting that stereoregular SiPS showed additional interaction for building up the LbL film. The composition of the LbL film of SiPS/PVAm was same as that of the bulk SiPS/PVAm complex of several dozen nanometers thickness.

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ASSOCIATED CONTENT

S Supporting Information *

Experimental procedures, 1H NMR and 13C NMR spectra of polystyrene derivatives in this study, solubility test of SiPS, SaPS, and SiPSNa, photos of powder and solutions of SiPS, SaPS, and SiPSNa. This material is available free of charge via the Internet at http://pubs.acs.org.

Figure 6. FT-IR/ATR spectra of PVAm (a), SiPS (Mn = 117K, PDI = 6.82) (b), and PVAm/SiPS complex, which was fabricated on QCM substrate by alternative LbL assembly with 16 steps (c).

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SiPS/PVAm LbL film (Figure 6) showed a similar intensity ratio to the bulk complex (Figure 4), suggesting that the SiPS/ PVAm LbL assembly proceeded ideally to the same composition as the bulk state. Finally, the SiPS/PVAm film was analyzed by AFM as shown in Figure 7. The surface roughness of SiPS/PVAm increased

AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; phone +81-6-68797356; Fax +81-6-6879-7359. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by Tokuyama Science Foundation and by the Deutsche Forschungsgemeinschaft through the International Research Training Group SeleCa. We thank Drs. T. Kida, M. Matsusaki, and T. Akagi for their helpful discussions.

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(1) (a) Lvov, Y.; Decher, G.; Moehwald, H. Assembly, Structural Characterization, and Thermal Behavior of Layer-by-Layer Deposited Ultrathin Films of Poly(vinyl sulfate) and Poly(allylamine). Langmuir 1993, 9, 481−486. (b) Decher, G.; Lvov, Y.; Schmitt, J. Proof of Multilayer Structural Organization in Self-Assembled Polycation− Polyanion Molecular Films. Thin Solid Films 1994, 244, 772−777. (c) Decher, G. Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites. Science 1997, 277, 1232−1237. (d) Bertrand, P.; Jonas, A.; Laschenwsky, A.; Legras, R. Ultrathin Polymer Coatings by Complexation of Polyelectrolytes at Interfaces: Suitable Materials, Structure and Properties. Macromol. Rapid Commun. 2000, 21, 319− 348. (2) (a) Ariga, K.; Lvov, Y.; Kunitake, T. Assembling Alternate DyePolyion Molecular Films by Electrostatic Layer-by-Layer Adsorption. J. Am. Chem. Soc. 1997, 119, 2224−2231. (b) Hodak, J.; Etchenique, R.; Calvo, E. J.; Singhal, K.; Bartlett, P. N. Layer-by-Layer Self-Assembly of Glucose Oxidase with a Poly(allylamine)ferrocene Redox Mediator. Langmuir 1997, 13, 2708−2716. (c) Krasemann, L.; Tieke, B. Selective Ion Transport Across Self-Assembled Alternating Multilayers of Cationic and Anionic Polyelectrolytes. Langmuir 2000, 16, 287−290. (d) He, J.; Samuelson, L.; Li, L.; Kumar, J.; Tripathy, S. K. Oriented Bacteriorhodopsin/Polycation Multilayers by Electrostatic Layer-byLayer Assembly. Langmuir 1998, 14, 1674−1679. (e) Rouse, J. H.; Lillehei, P. T. Electrostatic Assembly of Polymer/Single Walled Carbon Nanotube Mulilayer Films. Nano Lett. 2003, 3, 59−62. (f) Pei, R.; Cui, X.; Yang, X.; Wang, E. Assembly of Alternating Polycation and DNA Mutilayer Films by Electrostatic Layer-by-Layer Adsorption. Biomacromolecules 2001, 2, 463−468. (g) Shi, X.; Cassagneau, T.; Caruso, F. Electrostatic Interactions between Polyelectrolytes and a Titania Precursor: Thin Film and Solution Studies. Langmuir 2002, 18, 904−910. (h) Li, C.; Mitamura, K.; Imae, T. Electrostatic Layer-by-

Figure 7. AFM images of SiPS (Mn = 117K, PDI = 6.82)/PVAm LbL film with 10 μm × 10 μm (a) and 1 μm × 1 μm (b). QCM bare surface with 10 μm × 10 μm (c) and 1 μm × 1 μm (d).

after 16 steps (Figure 7a,b), to which about 2 μg of the polymer was attached, as compared as the QCM substrate surface (Figure 7c,d). The roughness was uniformly spread across wide area (Figure 7a) in spite of the partial agglomerations (Figure 7b). The SiPS/PVAm LbL film kept its asperity to within about 100 nm. The mean-square roughness (Ra) of the LbL assembled film showed a value of 15.4 nm (Figure 7a), while that of the QCM substrate was 3.8 nm (Figure 7c). When the value was compared to the sole example as the stereoregular synthetic polymer, it lied midway between isotactic-PMMA/ syndiotactic-poly(methyl methacrylate) stereocomoplex film (Ra = 7.2 nm) and the resultant single isotactic-PMMA film after removal of st-PMAA (Ra = 39 nm),37 suggesting that the roughness was reasonable to form the polymer−polymer interaction in the alternative LbL assembled film.

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REFERENCES

CONCLUSION

We demonstrated for the first time that the LbL fabrication of a single stereoregular synthetic polymer with polymer−polymer interactions. The conditions for SiPS/PVAm LbL assembly on the substrate were investigated. When the SiPS was neutralized 5376

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