Substitution and Condensation Reactions with Poly(anilineboronic

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Substitution and Condensation Reactions with Poly(anilineboronic acid): Reactivity and Characterization of Thin Films Carmen L. Recksiedler, Bhavana A. Deore, and Michael S. Freund* Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2 Received November 15, 2004. In Final Form: January 31, 2005 Poly(anilineboronic acid) thin films are treated under various conditions to achieve substitution or condensation reactions involving the boronic acid moiety. These reactions are studied with polarization modulated infrared reflection absorption spectroscopy, cyclic voltammetry, and UV-vis spectroscopy. The results suggest the single-step formation of substituted polyanilines, such as poly(hydroxyaniline), halogenated polyanilines, and mercury chloride-substituted polyaniline. A condensation reaction of poly(anilineboronic acid) with cis-diol compounds in aqueous solution, as well as with phenylenebisboronic acid and salycilamide in THF, indicates the formation of boronic esters. The latter reactions appear to be a good entry point for the formation of complex or supramolecular polymer structures.

Introduction Boronic acids such as aryl or aromatic boronic acids have become an extremely important class of organic compounds. They have been employed in a variety of biological and medical applications, such as carbohydrate recognition,1 protease enzyme inhibition,2 neutron capture therapy3 for cancer treatment, and transmembrane transport.4 They also provide a versatile chemical precursor to impart a wide range of functional groups.5 For example, aromatic boronic acid groups can be used for a variety of transformations via ipso-hydroxylation,5a ipso-halogenation,5b-d and ipso-nitration5k under mild conditions. In these particular cases, a boron activation/electrophilic displacement mechanism giving ipso-substitution with isolated yields typically greater than 90% has been proposed. In recent years, boronic acids have also gained tremendous popularity as substrates and building blocks in * Author to whom correspondence should be addressed. E-mail: [email protected]. (1) For reviews, see: (a) Wulff. G. Pure Appl. Chem. 1982, 54, 20932102. (b) James, T. D.; Sandanayake, S.; Shinkai, S. Angew. Chem., Int. Ed. Engl. 1996, 35, 1911-1922. (2) For examples, see: (a) Kettner, C. A,; Shenvi, A. B. J. Biol. Chem. 1984, 259, 15106-15114. (b) Zhong, S.; Haghjoo, K.; Kettener, C.; Jordan, F. J. Am. Chem. Soc. 1995, 117, 7048-7055. (c) Priestley, E. S.; Decicco, C. P. Org. Lett. 2000, 2, 3095-3097. (3) For reviews, see: (a) Barth, R. F.; Soloway, R. G.; Fairchild, R. G. Sci. Am. 1990, 263, 100-103. (b) Hawhorne, M. Angew. Chem., Int. Ed. Engl. 1993, 32, 950-984. (c) Soloway, A. H.; Tjarks, W.; Bamum, B. A.; Rong. F. G.; Barth, R. F.; Codogni, I. M.; Wilson, J. G. Chem. Rev. 1998, 98, 1515-1562. (4) For example, see: Smith, B. D.; Gardiner, S. J. Adv. Supramol. Chem. 1999, 5, 157-202 and references therein. (5) For examples of possible reactions, see: (a) Simon, J.; Salzbrunn, S.; Prakash, G. K. S.; Petasis, N. A.; Olah, G. A. J. Org. Chem. 2001, 66, 633-634. (b) Nesmeyanov, A. N.; Sazonova, W. A.; Drozd, V. N. Chem. Ber. 1960, 93, 2717. (c) Kuivila, H. G.; Hendrickson, A. R. J. Am. Chem. Soc. 1952, 74, 5068-5070. (d) Kuivila, H. G.; Williams, R. M. J. Am. Chem. Soc. 1954, 76, 2679-2682. (e) Herradura, P. S.; Pendola, K. A.; Guy, R. K. Org. Lett. 2000, 2, 2019-2022. (f) Michaelis, A.; Becker, P. Ber. Dtsch. Chem. Ges. 1882, 15, 180. (g) Savarin, C.; Srogl, J.; Liebeskind, L. S. Org. Lett. 2001, 3, 91-13. (h) Savarin, C.; Srogl, J.; Liebeskind, L. S. Org. Lett. 2000, 2, 3229-3231. (i) Suzuki, A. Pure Appl. Chem. 1991, 63, 419. Badone, D.; Baroni, M.; Cardamone, R.; Ilemini, A.; Guzzi, U. J. Org. Chem. 1997, 62, 7170-7173. (j) Vogels, C. M.; Wellwood, H. L.; Biradha, K.; Zaworotko, M. J.; Westcott, S. A. Can. J. Chem. 1999, 77, 1196-1207. (k) Salzbrunn, S.; Simon, J.; Prakash, G. K. S.; Petasis, N. A.; Olah, G. A. Synlett 2000, 1485-1487.

organic synthesis and combinatorial chemistry. For example, the utilization of boron compounds as building blocks for the construction of macrocyclic two- and threedimensional assemblies is an emerging topic in supramolecular chemistry.6 The formation of boronate macrocycles via condensation reactions lead to the construction of highly ordered molecular or supramolecular assemblies directly and spontaneously.7 In addition, boronic acids are known to undergo facile condensation reactions with various diols to form boronic esters.8 Recently, it has been demonstrated that boronic acidsubstituted polyaniline can be electrochemically polymerized from 3-aminophenylboronic acid in the presence of fluoride.9-11 The resulting polymer exhibits conductivity and redox behavior similar to those of polyaniline. In addition, the boronic acid groups remain reactive11 and in turn provide a chemical handle for further transformations such as formation of substituted polyanilines.12 Substituted polyanilines have received much interest recently, as the processability and properties of conducting polymers greatly impact potential applications in rapidly evolving areas including sensing, batteries, light emitting diodes, and electrochemical devices.11,13 As a result, there has been considerable interest in developing new synthetic approaches for their production. Typically, the substituted polymer can be generated via oxidative polymerization of the corresponding monomer.14 However, in many cases, the desired moiety is either too difficult to oxidize or (6) For reviews, see: (a) Hopfl, H. Struct. Bonding 2002, 103, 1-56. (b) Ma, K.; Scheibitz, M.; Scholz, S.; Wagner, M. J. Organomet. Chem. 2002, 652, 11-19. (7) Lehn, J. M. Supramolecular Chemistry; VCH Publishers: Germany, 1995. (8) Springsteen, G.; Wang, B. Tetrahedron, 2002, 58, 5291-5300. (9) Nicolas, M.; Fabre, B.; Marchand, G.; Simonet, J. Eur. J. Org. Chem. 2000, 9, 1703-1710. (10) Shoji, E.; Freund, M. S. J. Am. Chem. Soc. 2001, 123, 33833384. (11) Shoji, E.; Freund, M. S. J. Am. Chem. Soc. 2001, 123, 1248612493. (12) Shoji, E.; Freund, M. S. Langmuir 2001 17, 7183-7185. (13) For examples see: (a) Wei, X.-L.; Wang, Y. Z.; Long, S. M.; Bobeczko, C.; Epstein, A. J. J. Am. Chem. Soc. 1996, 118, 2545-2555. (b) Chan, H. S. O.; Ng, S.-C.; Wong, P. M. L.; Neuendorf, A. J.; Young, D. J. Chem. Commun. 1998, 1327-1328. (c) Liu, B.; Yu, W.-L.; Lai, Y.-H.; Huang, W. Chem. Mater. 2001, 13, 1984-1991. (d) Liu, J.; Kadnikova, E. N.; Liu, Y.; McGehee, M. D.; Frechet, J. M. J. Am. Chem. Soc. 2004, 126, 9486-9487.

10.1021/la047195z CCC: $30.25 © 2005 American Chemical Society Published on Web 03/15/2005

Reactions with Poly(anilineboronic acid) Scheme 1

sensitive to oxidative or acidic conditions. Recently, we reported a novel strategy for preparing a wide range of substituted polyanilines from a single precursor poly(anilineboronic acid) (PABA).12 In addition to these substitution reactions, there are many other possible reactions accessible through the boronic acid group present in PABA, as shown in Scheme 1. For example, synthesis of mercury chloride-substituted polyaniline will be of great interest because this polymer could play an important role in the synthesis of diblock copolymers and fungicidal organomercurials. Also, the substitution of mercury chloride into a polyaniline network is potentially beneficial since the mercury metal ion might give access to physical and chemical properties that are not present in pure and other substituted polyanilines. Taking advantage of the reactive nature of the PABA polymer, the synthesis of supramolecular polymer architectures should be possible via condensation reactions. Supramolecular conducting polymers are expected to have a number of potential advantages in terms of processability and thermal stability compared to their linear analogues.15 Herein, we present the reactions of PABA accessible through the boronic acid group, including substitution with mercury chloride, condensation with cis-diols in aqueous solution, and condensation with phenylenebisboronic acid and salicylamide in nonaqueous solutions at 65 °C. All reactions were carried out on thin films of PABA and characterized using polarization modulated infrared reflectance absorption spectroscopy (PM-IRRAS), UV-vis spectroscopy, and cyclic voltammetry. An important aspect of this work is that, although reactions with boronic acid are known, very little work has been done with conducting polymers or within thin films. PMIRRAS in conjunction with UV-vis and electrochemistry provides a means for investigating these reactions within conducting polymer thin films. (14) For example, see: Pringsheim, E.; Terpetschnig, E.; Wolfbeis, O. S. Anal. Chim. Acta 1997, 357, 247-252. (15) Ward, R. E., Meyer, T. Y. Macromolecules 2003, 36, 4368-4373. Dufour, B.; Rannou, P.; Djurado, D.; Janeczek, H.; Zagorska, M.; Geyer, A.; Travers, J.; Pron, A. Chem. Mater. 2003, 15, 1587-1592. Dufour, B.; Rannou, P.; Djurado, D.; Zagorska, M.; Kulszewicz-Bajer, I.; Pron, A. Synth. Met. 2003, 135-136, 63-68.

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Experimental Section Instrumental Setup. Indium-doped tin oxide (ITO, 6 ( 2 Ω/square) glass slides were purchased from Delta Technologies, Ltd. Cyclic voltammetric (CV) measurements were performed using a CH Instrument CHI 660 workstation. In the voltammetric experiments, a three-electrode configuration was used including a platinum wire (0.2 mm diameter) counter electrode, Ag/AgCl reference electrode, and ITO glass slides as a working electrode. PM-IRRAS spectra of polymer films on ITO glass slides were recorded at a resolution of 8 cm-1 using a Nexus 870 spectrometer (Thermo Nicolet Corporation). A grazing angle of 67° was used to collect 300 interferograms for each spectrum. UV-vis spectra of thin films on ITO glass slides were obtained using an Agilent 8453 spectrophotometer. Electropolymerization of PABA. PABA was deposited electrochemically onto ITO-coated glass slides (1 × 2 cm2). The monomer solution was prepared using 40 mM 3-aminophenylboronic acid and 200 mM sodium fluoride in 0.5 M hydrochloric acid solution. The potential was cycled between -0.1 and +1.1 V vs Ag/AgCl at a scan rate of 100 mV/s for 25 cycles. The thickness of the films was around 300 nm. The film that was obtained was washed with water and placed in a 0.5 M HCl solution to verify its redox behavior with CV. The potential window for CV measurements was -0.1 to 1.1 V. The final scan was stopped at a potential of 0.8 V. After verifying that the redox response was stable, the oxidized PABA films were used for further reactions, as shown in Scheme 1. Substitution Reactions of PABA (Scheme 1a-d). The substitution reaction conditions used (see Scheme 1a-c) were the same as those previously reported.12 For reaction 1d, a PABA film was exposed to 100 mM HgCl2 in 83% (v/v) acetone/water solution and stirred under nitrogen until reaction was complete. Calcium carbonate was added in a molar ratio of 1:6 with mercury chloride. Addition of calcium carbonate accelerated the reaction by removing HCl that was formed as a byproduct of the reaction.16 For all substitution reactions, the change in the redox activity of polymer films was monitored frequently throughout the course of the transformation with CV in 0.5 M HCl by scanning within potential window of -0.3 to 1.0 V vs Ag/AgCl at a scan rate of 100 mV/sec. The final scan was stopped at a potential of 0.8 V. After careful washing with pure water, the films were used for UV-vis and PM-IRRAS spectroscopic characterization. Complexation Reactions of PABA in Aqueous Solution (Scheme 1e-g). PABA films were soaked in pH 7.4 phosphatebuffered solution overnight before complexation reactions were performed. Further, these PABA films were placed in 20 mL of 100 mM D-fructose, catechol, or cis-1,2-cyclopentanediol solution in phosphate-buffered solution for 10 min. After reaction, the films were rinsed in pure water before measurements were made to ensure that uncomplexed reagent was removed from the film. Complexation Reactions of PABA in Nonaqueous Solution (Scheme 1h and i). PABA films were placed in 100 mM 1,4-phenylenebisboronic acid or 1 M salicylamide in 20 mL THF at ∼65 °C. The reaction was complete at 1 and 6.5 h for 1,4phenylenebisboronic acid and salicylamide, respectively. After reaction, the films were rinsed with neat THF to remove uncomplexed reagent from the film before any measurements were made.

Results and Discussion The PABA thin films, prepared on ITO glass and transformed to poly(hydroxyaniline) and halogenated polyaniline as previously described,12 were characterized with PM-IRRAS and UV-vis spectroscopy. PM-IRRAS spectra of PABA before and after the substitution reaction are shown in Figure 1. Vibrations characteristic of polyaniline are observed at 1603, 1510, and 1160 cm-1 and correspond to quinoid, benzenoid, and C-N stretching ring modes, respectively (Figure 1a).17 In aromatic boronic (16) Matteson, D. S.; Waldbillig, J. O. J. Am. Chem. Soc. 1964, 86, 3778-3781. (17) Epstein, A. J.; McCall, R. P.; Ginder, J. M.; MacDiarmid, A. G. Spectroscopy of Advanced Materials; John Wiley and Sons: New York, 1991.

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Figure 2. UV-vis spectra of PABA film (a) before and (b) after exposure to H2O2, (c) after iodination, and (d) after bromination conditions.

Figure 1. PM-IRRAS spectra of PABA film (a) before and (b) after exposure to H2O2, (c) after iodination, and (d) after bromination conditions.

acids, B-OH bending modes are observed at 986 and 1115 cm-1, while the vibrations attributed to asymmetric B-O stretching and B-F stretching mode lie at 1330 and 888 cm-1, respectively.17,18 The ratio of the relative intensities of quinoid to benzenoid ring modes (I1603/I1510) is ∼ 1.5, which suggests that the percentage of imine units is higher than that of amine units. These results and the presence of B-F stretching vibration indicate that PABA is in its oxidized self-doped form. In Figure 1b-c, a decrease in intensity is seen for the vibrations at 1115 and 986 cm-1 after each of the three substitution reactions, suggesting the loss of the B-OH moiety. However, the characteristic peaks of polyaniline are present in all cases. The loss of the intensity of the B-O stretching vibration at 1330 cm-1 suggests that the boronic acid group is no longer present. Aside from the disappearance of the boronic acid vibrations, reaction with peroxide (Figure 1b) results in a decrease in the peak intensity at 1603 cm-1 and the appearance of a broad peak at around 1287 cm-1. The peak at 1287 cm-1, assigned to C-O stretching and O-H in-plane and out-of-plane deformation vibrations, indicates the formation of phenol.18,19 The reaction of PABA with iodine results in the appearance of the broad peak at 1141 cm-1 and the shoulder at 1347 cm-1, as shown in Figure 1c. These vibrations are attributed to phenyl-I stretching and C-I stretching, respectively.18,20 In the case of the reaction of PABA film with bromine (Figure 1d), a sharp vibration is observed at 1250 cm-1 together with a shoulder around 1047 cm-1 due to C-Br and phenyl-Br stretching modes.18,20 Also, the red shift in the intensities of quinoid and benzenoid ring modes and a decrease in their relative intensity ratio is observed. The decrease in the relative intensity ratio of quinoid to benzenoid ring modes indicates that the polymer is less oxidized after hydroxyl and halogen substitution reactions (Figure 1b-d). This is likely due to conversion of the initial polymer from the oxidized self-doped form (see Scheme 1) to the neutral base form. IR results are consistent with the UV-vis spectroscopic results obtained on the same films. For example, Figure (18) Socrates, G. Infrared Characteristic Group Frequencies; John Wiley and Sons: New York, 1994. (19) Mecke, R.; Rossmy, G. Z. Elektrochem. Angew. Phys. Chem. 1955, 59, 866. (20) Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy; Academic Press, New York, 1975.

2 shows the UV-vis spectra of a PABA film before and after performing the substitution reaction. The spectrum of a PABA film (Figure 2a) exhibits absorption bands similar to those of unsubstituted polyaniline at ∼ 340, 440, and 800 nm associated with π-π*, polaron, and bipolaron band transitions, respectively.21 With transformation to substituted polyanilines (Figure 2b-d), the polaron band at ∼440 nm nearly disappears while the bipolaron band at ∼800 nm shows a significant reduction in intensity with respect to the 340 nm peak and also exhibits a blue shift. The disappearance of the former suggests the absence of the exciton in the polaron lattice that is formed upon doping.21a The blue shift and decrease in the absorbance of the latter suggests that the number of species undergoing bipolaron band transition, i.e., the ratio of quinoid to benzenoid group, has decreased. However, after exposure of substituted polyaniline films to HCl vapor, films exhibit optical properties similar to polyanilines21,22 reported previously. Figure 3 shows PM-IRRAS spectra of the mercury chloride substitution of PABA as a function of time. Previous reports indicate that mercury coordinates to aryl boronic acids and then undergoes an electrophilic displacement of the boronic acid.16 In comparison with other substitution reactions involving PABA, mercury chloride substitution to PABA is relatively slow. Initially, the dramatic decrease in the intensity of characteristic boronic acid vibrations (in Figure 3a at 1115 and 986 cm-1) is observed, as shown in Figure 3b. In addition, new vibrations due to the reaction appear at 1456, 1372, and 1208 cm-1 together with an increase in intensity of vibrations at 1330 and 880 cm-1. Further, with time, the intensity of these vibrations increases, as seen in Figure 3c-e. The vibrations at 1456, 1372, and 1330 cm-1 likely arise from phenyl-metal ring stretching vibrations.17 The vibrations at 1208 and 880 cm-1 are consistent with phenyl-Hg sigma bond stretching. These results are further supported by X-ray photoelectron spectroscopy, which suggests approximately 60% substitution of mercury chloride (see Figure 1 in the Supporting Information). The cyclic voltammogram of the HgCl2-substituted polyaniline film is similar to that of the previously reported iodine- and bromine-substituted polyaniline.12 Boronic acids are capable of reversible formation of covalent bonds with the diol functionalities of carbohydrates resulting in the generation of cyclic esters, to an (21) (a) Stafstrom, S.; Breda, J. L.; Epstein, A. J.; Woo, H. S.; Tanner, D. B.; Huang, W. S.; MacDiarmid, A. G. Phys. Rev. Lett. 1987, 59, 14641467. (b) Wudl, F.; Angus, R. O.; Lu, F. L.; Allemand, P. M.; Vachon, D. J.; Nowak, M.; Liu, Z. X.; Heeger, A. J. J. Am. Chem. Soc. 1987, 109, 3677-3684. (22) Athawale, A. A.; Patil, S. F.; Deore, B. A.; Patil, R. C.; Vijayamohanan, K. Polym. J. 1997, 29, 787-794.

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Figure 5. PM-IRRAS spectra of PABA film after being reacted with (a) 1,4-phenylenebisboronic acid and (b) salicylamide in THF.

Figure 3. PM-IRRAS spectra of PABA film (a) and after being reacted with HgCl2 as a function of time; (b) 6 h, (c) 18 h, (d) 25 h, and (e) 40 h.

Figure 4. PM-IRRAS spectra of PABA film after complexation with (a) D-fructose, (b) catechol, and (c) cis-cyclopentane diol.

extent dependent upon the pH of the solution.23 These reactions have been used with PABA for the detection of saccharides in open circuit potential measurements.11 PMIRRAS is ideal for following this reaction within polymer thin films. For example, Figure 4 shows the formation of boronate esters by the complexation of D-fructose, catechol, and cis-1,2-cyclopentanediol with PABA. The disappearance of the 888 cm-1 band, after stabilization of PABA film in pH 7.4 phosphate-buffered solution suggests the removal of fluoride due to the ion exchange reaction. In Figure 4a-c, after complexation, the intensity of 1115 and 986 cm-1 vibrations (see Figure 1a) decrease and the 1330 cm-1 vibration increases. This is consistent with the loss of the free B-OH group which occurs concomitantly with an increase in asymmetric B-O bond formation, consistent with the formation of boronate ester. The presence of a new band at 1064 cm-1 in Figure 4a is attributed to C-O stretching and bending modes in the D-fructose moiety. The new band observed at 1490 cm-1 in Figure 4b corresponds to C-C stretching and C-H (23) (a) Eggert, H.; Frederiksen, J.; Morin, C.; Norrild, C. J. Org. Chem. 1999, 64, 3846 and references therein. (b) Paugam, M. F.; Valencia, L. S.; Boggess, B.; Smith, B. D. J. Am. Chem. Soc. 1994, 116, 11203-11204 and references therein. (c) Pizer, R.; Ricatto, P. J. Inorg. Chem. 1994, 33, 2402-2406 and references therein.

in-plane bending vibrations of the benzene ring in catechol.24 The intensity of vibrations at 1244 and 1115 cm-1 also increase and correspond to asymmetric C-O and symmetric B-O stretching, respectively, due to formation of boronate ester.14,25 Similarly, in the case of complexation of PABA with cis-1,2-cyclopentanediol (Figure 4c), the band at 1411 cm-1 appears as a new vibration due to C-H stretching in cyclopentane. A shoulder is also seen in the spectrum at 1225 and 1064 cm-1, and can be assigned to asymmetric C-O and symmetric B-O stretching. These results suggest that boronate ester formation results in strong covalent interactions while maintaining an extended conjugated state of polyaniline. PM-IRRAS spectra of PABA films after reaction with phenylenebisboronic acid and salicylamide in THF are shown in Figure 5. There is no significant change observed in the spectra of PABA films reacted in blank THF under identical reaction conditions, except the decrease in the relative intensity ratio of quinoid to benzenoid ring modes due to reduction of polymer films. The reaction with phenylenebisboronic acid yields small relative changes from the PABA spectrum (Figure 5a). There is an increase in asymmetric B-O stretching observed at 1330 cm-1 due to complexation, as shown in Scheme 1h. The intensity of the B-OH stretching (1115 and 986 cm-1) remains constant as some B-OH is likely added upon the ester formation with phenylenebisboronic acid. The presence of the B-F stretching mode at 888 cm-1 and the high relative intensity ratio of quinoid to benzenoid ring modes suggest that the PABA remains in the conducting form after complexation with phenylenebisboronic acid. These conclusions are consistent with UV-vis spectroscopy results. UV-vis spectra of PABA films after reaction without and with phenylenebisboronic acid in THF at around 65 °C are shown in Figure 6. In the absence of phenylenebisboronic, the conducting salt form is converted to the insulating base form of PABA (see Figure 6a), as indicated by the loss of the polaron band (420 nm) and more than a 100 nm blue shift in the bipolaron band. In contrast, Figure 6b shows that, in the presence of phenylenebisboronic acid, the PABA film remains in the conducting state. These results suggest that the condensation reaction between PABA and phenylenebisboronic acid results in the formation of boronate ester while maintaining the conducting state of the polymer through self-doping (Scheme 1h). Following the reaction with phenylenebisboronic acid, the polymer becomes soluble in methanol, suggesting that this may be facile means for manipulating solubility. (24) Scherer, J. R. Spectrochim. Acta 1965, 21, 321-39. (25) Chen, X.; Liang, G.; Whitemire, D.; Bowen, J. P. J. Phys. Org. Chem. 1998, 11, 378-386.

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Figure 6. UV-vis spectra of PABA film in THF at high temperture without (a) and with 1,4-phenylenebisboronic acid (b).

The condensation reaction of PABA with salicylamide results in many changes in the PM-IRRAS spectrum of PABA that are consistent with the formation of boronate macrocycle, as is shown in Figure 5b. New vibrations are observed corresponding to carbonyl of amide (1657), B-N stretching (1498), benzene ring stretching of salicylamide (1471), N-H bending (1427), phenyl-CO-NH stretching (1256 and 1124), C-O and B-O symmetric stretching (1030), and C-H stretching (936) in boronate macrocycle shown in Scheme 1i.18,26 UV-vis spectrum of PABA film reacted with salicylamide in THF (see Figure 3 in the Supporting Information) suggest that the polymer remains in an insulating state after complexation in contrast to phenylenebisboronic acid (see Figure 6b). (26) Palomar, J.; De Paz, J. L. G.; Catala, J. Chem. Phys. 1999, 246, 167-208.

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Conclusions The boronic acid groups present in PABA are ideal chemical handles for producing functionalized polyaniline and cross-linked and supramolecular conducting polymer architectures. PM-IRRAS is an excellent method in conjunction with UV-vis to investigate the reactivity of PABA in a wide range of reactions. For example, the optical and PM-IRRAS spectra of hydroxyl and halogen-substituted polyaniline suggest that the chemical and electronic properties of the polymer in a thin film are chemically and electronically similar to those in the bulk. A new reaction involving PABA has resulted in the formation of a previously unreported mercury chloride-substituted polyaniline. This new form of polyaniline is expected to be a useful reactive precursor for new synthetic strategies involving polyaniline. Finally, condensation reactions with phenylenebisboronic acid and salicylamide have been explored. Macrostructured polymers produced using these reactions are anticipated to enhance mechanical and physical properties of the polymer and are currently being investigated. Acknowledgment. Financial support from the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canada Foundation for Innovation (CFI), the Manitoba Foundation for Innovation and the University of Manitoba are gratefully acknowledged. This research was undertaken, in part, thanks to funding from the Canada Research Chairs Program. Supporting Information Available: Survey scan and UV-vis spectra of reacted and unreacted PABA film. This material is available free of charge via the Internet at http://pubs.acs.org. LA047195Z