Synthesis of N-Alkyl Methacrylate Polymers with Pendant Carbazole Moieties and Their Derivatives

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Synthesis of n-Alkyl Methacrylate Polymers with Pendant Carbazole Moieties and Their Derivatives

Yuriy Bandera,1,2 Tucker M. McFarlane,1,2,3 Mary K. Burdette,1,2 Marek Jurca,1,2 Oleksandr Klep,1,2 Stephen H. Foulger 1,2,4 1Center for Optical Materials Science and Engineering Technologies, Advanced Materials Research Laboratories, Clemson University, 91 Technology Drive, Anderson, South Carolina 29625 2Department of Materials Science and Engineering, Clemson University, Clemson, South Carolina 29634 3Sonoco Institute of Packaging Design and Graphics at Clemson University, Clemson University, Clemson, South Carolina 29634 4Department of Bioengineering, Clemson University, Clemson, South Carolina 29634 Correspondence to: S. H. Foulger (E-mail: [email protected])

Received 3 October 2018; Accepted 6 November 2018; published online 3 December 2018 DOI: 10.1002/pola.29285

ABSTRACT: New methacrylate monomers with carbazole moie- their effect on the energy proﬁle, thermal, dielectric, and ties as pendant groups were synthesized by multistep synthe- photophysical properties when compared to the parent poly- ses starting from carbazoles with biphenyl substituents in the mer poly(2-(9H-carbazol-9-yl)ethyl methacrylate). According to aromatic ring. The corresponding polymers were prepared the obtained results, these compounds may be well suited for using a free-radical polymerization. The novel polymers memory resistor devices. © 2018 Wiley Periodicals, Inc. contain N-alkylated carbazoles mono- or bi-substituted with J. Polym. Sci., Part A: Polym. Chem. 2019, 57,70–76 biphenyl groups in the aromatic ring. N-alkyl chains in polymers vary by length and structure. All new polymers were KEYWORDS: dielectric properties; radical polymerization; struc- synthesized to evaluate the structural changes in terms of ture-property relations

INTRODUCTION A widely studied semiconducting polymer is exhibit multiple types of switching behavior.14,15,28 Polymers poly(N-vinyl carbazole) (PVK), which has seen uses in a wide with pendant carbazole groups require proper face-to-face variety of organic electronic devices including organic light alignment of the carbazole moieties for efficient charge trans- – – emitting diodes (OLEDs),1 9 photovoltaics,10 13 and memory fer, and due to the steric hindrance of the carbazole groups 14–20 devices. PVK was found to utilize pendant carbazole caused by their proximity to the backbone of the polymer, groups as the main charge carrier and has been shown to have PVK has been shown to have a single conductivity state as the 21,22 high hole mobility. It initially found prominence as a highly carbazole groups have a frustrated realignment.15 However, photosensitive organic conductor and was extensively studied changes to the flexibility of the carbazole groups through by the Xerox Corporation primarily due to its role in electro- modifications of the chain length that separate the electroni- photography leading to further understanding of the charge cally active group from the polymer backbone enhances the transport properties and excimer formation.23–27 The charge freedom of the carbazole group and allows for conformational transport of PVK is based on the pendant carbazole groups, changes under electric fields resulting in multiple resistivity thus their alignment and spatial proximity is key for efficient states.15 2-(9H-carbazol-9-yl)ethyl methacrylate (PEMA) charge mobility. The importance of the carbazole spacing was (cf. Fig. 1 C2) is one such polymer that offers sufficient flexi- demonstrated by chemically altering the polymer to adjust the alignment of the carbazole groups resulting in varied electrical bility to the carbazole groups such that they are capable of fi properties.24 Therefore, conformational changes in the undergoing realignment under an electric eld and transition- carbazole groups allow for the alteration of conductivity in the ing from a low conductivity OFF state to a high conductivity 15 polymer leading to the development of resistive memory appli- ON state. Due to its low volatility and propensity to remain cations using pendant carbazole groups.14–16 in the ON state when exposed to a reverse bias, as well as over large time scales, this material is used to create write- With this in mind, acrylate polymers have been developed, once-read-many devices which limits its possible applications. which are based on PVK that have pendant carbazoles and However, this approach to enhancing conformational Additional supporting information may be found in the online version of this article.

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O O

O O O O

O O O O O O 7 9 7 N N N N N

C2 8a 8b9 15

FIGURE 1 Monomers synthesized in the effort: (C2) 2-(9H-carbazol-9-yl)ethyl methacrylate (8a) 9-(3-([1,10-biphenyl]-4-yl)-9H-carbazol-9-yl) nonyl methacrylate (8b) 11-(3-([1,10-biphenyl]-4-yl)-9H-carbazol-9-yl)undecyl methacrylate (9) 9-(3,6-di([1,10-biphenyl]-4-yl)-9H-carbazol- 9-yl)nonyl methacrylate (15) 2-(2-(2-(3-([1,10-Biphenyl]-4-yl)-9H-carbazol-9-yl)ethoxy)ethoxy)ethyl methacrylate.

flexibility has shown promise in creating polymers with multi- polymerization with AIBN in chlorobenzene at 60–65 C with ple conductive states.14 yields ranging from 28% to 66% (cf. Supporting Information for details). Lengthening or oxygenating the n-alkyl chain and The current effort explores the role that linkage length and adding one or more biphenyl groups to the carbazole pendant pendant “bulkiness” has on the thermophysical and electrical group on the parent polymer were investigated.33 Structure– properties of four polymers with pendant carbazole moieties property relationships, such as glass transition temperature relative to PEMA. These polymers are developed through a (Tg), decomposition temperature, activation energy, electronic synthetic approach utilizing previously reported routes.29–32 band gap, absorbance, and photoluminescence were studied Specifically, carbazole derivatized n-alkyl methacrylate poly- to interpret the full effect of these manipulations when com- mers are synthesized and studied with side chain lengths pared to the properties of C2, poly(9-(9H-carbazol-9-yl)nonyl ranging from n =2ton = 11 and coupled with mono- or dual- methacrylate) (PNMA, the unsubstituted version of 10a and substituted biphenyl groups on the pendant carbazole group 11), and poly(9-(9H-carbazol-9-yl)undecyl methacrylate) with molar volumes of the derivatized carbazole moieties (PUMA, the unsubstituted version of 10b).14 ranging from 266.5 or 391.1 cm3. Thermal Properties Perhaps the most drastic change observed when lengthening RESULTS AND DISCUSSION or oxygenating the n-alkyl chain as well as adding one or Figure 1 presents poly(2-(9H-carbazol-9-yl)ethyl methacry- more biphenyl groups to the carbazole moiety occurred in the late) (C2) and the monomers synthesized in the current study. thermal properties of the polymer when compared to C2. The Monomers were synthesized with a multistep route utilizing glass transition temperatures (and molecular weights) for modified Suzuki coupling reactions followed by a variety of polymers 10a,b, 11, and 16 are shown in Table 1. When nucleophilic substitution reactions.29–32 Polymers with vari- increasing the length of the chain from 9 methylene bridges ous molecular weights were obtained through free-radical (10a) to 11 methylene bridges (10b), the Tg is lowered by

TABLE 1 Molecular Weight, Glass Transition, and Decomposition Temperature Characterization

a b c d Compound Mn (g/mol) Tg ( C) Tdecomp ( C) Change in Structure from C2

10a 11,900 73 405 Alkyl chain increased by 7 CH2 groups and biphenyl group attached to carbazole moiety

10b 11,456 59 386 Alkyl chain increased by 9 CH2 groups and biphenyl group attached to carbazole moiety

11 21,489 95 445 Alkyl chain increased by 7 CH2 groups and double biphenyl group attached to carbazole moiety 16 16,231 78 398 Oxygenation of alkyl chain and biphenyl group attached to carbazole moiety C2 – 125 306 – a c Molecular weight (Mn) was characterized by gel permeation chromatog- Decomposition temperature (Tdecomp) was found via thermogravimetric raphy (GPC) with chloroform as the eluent. analysis (TGA). b d Glass transition temperature (Tg) was found via differential scanning Tabulated structural changes in monomer when compared to C2. calorimetry (DSC).

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14 C due to the extra ﬂexibility of the chain that the addi- motion of the end group, a beta (β) transition associated with tional methylene bridges provide. The longer n-alkyl chain the motion of the side chains, and an alpha (α) transition asso- allows the carbazole moiety more freedom of movement with ciated with the motion of the entire polymer occurring near

a negligible increase to the free volume. However, when Tg of the glass transition temperature. However, previous work has PNMA is compared to its counterpart (10a), the Tg of PNMA shown that the alpha transition merges with the beta transi- is much greater (14 C) than that of 10a (73 C) due to the tion at high temperature and/or when the side chain becomes addition of the bulky biphenyl group to the carbazole moi- longer in n-alkyl methacrylate polymers.34 Therefore, these 14 ety. Similarly, the Tg of PUMA is much greater than that of polymers only exhibit a high temperature β transition and a 10b, again, due to the addition of the biphenyl group.14 As low temperature γ transition denoted by peaks in the tan(δ). expected, increasing the number of biphenyl substituents on The response of 10a observed in Figure 2 was representative the carbazole moiety from one (10a) to two (11) greatly of the other polymers presented in this work (cf. Supporting

increases the Tg due to the added bulkiness of the polymer Information). At low temperatures, the gamma (γ) transition provided by the extra biphenyl group, illustrated by the molar can be observed from approximately −135 to −70 C indi- volume of the derivatized carbazole moieties. When compared cated by a small bump in the tan(δ) and a minute change in to 10a, with a molar volume of 266.5 cm3, as calculated with the capacitance. At high temperatures, the beta (β) transition Advanced Chemistry Development (ACD/Labs), the molar vol- can be observed from approximately 95 to 150 C indicated ume increases by 67% when adding an additional biphenyl by a sharp increase in both the capacitance and tan(δ) of the

group (11), leading to a 22% increase in Tg. As expected, the material. Figure 2(c) represents an alternate view of the tan Tg of 11 is much greater than the non-substituted version, (δ) where individual frequencies have been shown with PNMA. When compared to 10a, introducing oxygen atoms into labeled γ and β transitions. Figure 2(d) presents the apparent

the n-alkyl chain (16) leads to a slight increase in the Tg activation energies that were calculated from the slope of the because the length of the overall side chain is decreased. The logfmax versus 1/T plot, where fmax is the frequency at the Tg of all newly synthesized polymers is lower than that of C2 maximum in tan(δ). (Tg = 125 C) due to the shorter n-alkyl chain in C2 inhibiting the movement of the polymer. It appears that, while the As was previously reported with similar carbazole systems, biphenyl groups do impart rigidity to the polymer, the stiff- the γ transition is a thermally activated relaxation and was lin-

ness of a two methylene bridge linkage overrides the ear in a log fmax 01/T plot. The β transition was also a ther- increased free volume term of Tg of polymers 10a,b, 11, and mally activated relaxation; however, it had curvature in the 16. By adding the biphenyl groups, 10a,b, 11, and 16 cannot Arrhenius plot, possibly from the merging of the α and β tran- stack as closely as C2 due to steric hindrance, thus, leaving sitions (cf. Fig. 2).35,36 The γ transitions were relatively consis- more room for the carbazole to move. The decomposition tent for all polymers falling between 33.14 and 37.01 kJ/mol,

temperature (Tdecomp) for all polymers ranges from 386 to which is consistent with previously reported polymers with 445 C with 11 and 10b decomposing at the highest and low- similar compositions that utilize a long chain length attached est temperature, respectively. Two biphenyl groups on 11 to the carbazole; for comparison, PNMA and PUMA have a γ yield more advantageous thermal stability due to the transition at about 38 kJ/mol.14 However, the β transitions increased probability of π-π stacking of the aromatic groups were more varied with 10b having the lowest at when compared to the polymers with the single biphenyl 184.72 kJ/mol and 16 having the highest at 347.57 kJ/mol, group, while the extra methylene bridges in the n-alkyl chain the former of which is similar to previous studies on a num- decrease the thermal stability of the polymer. As predicted, ber of poly(n-alkyl methacrylate)s.37–39 Previous work with the decomposition of C2 is lower than that of 10a,b, 11, and similar polymers has shown a correlation between the glass 16 due to the enhanced cohesive inﬂuence the biphenyl sub- transition temperature and the temperature at which these stituents impart to the novel polymers. It appears that molec- transitions occur.14,37 At the β transition, this is observed with

ular weight does not have a large impact on the Tg of these the highest Tg polymer (16) transitioning at the highest tem- polymers (cf. Table 1). perature and the lowest Tg polymer (10b) transitioning at the lowest temperature. This appears to shift slightly during the γ Dielectric Spectroscopy transition as 16 transitions at a lower temperature relative to To fully understand the electrical response of the material, the other polymers in this work. This is likely due to the size dielectric spectroscopy was used to probe the materials of the biphenyl groups that have a large effect on the free vol- frequency/temperature dependence. Due to the structural ume (molar volume up to 292% more than that of C2) and similarities of the polymers presented in this work with other allow the γ transition to occur at a lower temperature. This n-alkyl methacrylate polymers that have been previously stud- shift in the free volume does not appear to affect other transi- ied, they are expected to have similar dielectric properties tions that occur at higher temperatures in relation to the with obvious perturbations from the pendant dipolar other polymers investigated in this work. N-heterocyclic ring.14 Figure 2(a,b) presents the tan(δ) and the capacitance response over a temperature range of −150 Photophysical Characterization to 150C and a frequency range of 1,000,000−1Hzof10a. The absorbance and photoluminescence characteristics are Traditionally, methacrylate based polymers with pendant similar for all polymers presented. For polymers 10a, 10b, groups exhibit a gamma (γ) transition associated with the and 16, the maximum absorbance occurs at 301 nm with a

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FIGURE 2 (a) The tan(δ) and the (b) capacitance of 10a over a range of temperatures and frequencies. (c) The tan(δ)of10a showing the response at frequencies of 1 × 106 Hz (), 1.86 × 105 Hz, 4.84 × 104 Hz, 1.26 × 104 Hz, 3.28 × 103 Hz, 854 Hz, 222 Hz, and 57.8 Hz (○). (d) The activation energies for 10a (■), 16 (×), 11 (○), and 10b (△). [Color figure can be viewed at wileyonlinelibrary.com] secondary absorbance peak occurring at 242 nm, while the to C2, PNMA, and PUMA. Additionally, C2, PNMA, and PUMA photoluminescence of these polymers has a peak at 392 nm have two significant, distinct absorbance peaks at 262 and with a shoulder at about 371–379 nm. Polymer 16 does have 294 nm as well as two smaller peaks and a small broad shoul- a broader, less defined shoulder than polymers 10a,b, which der at 330, 344, and 312–323 nm, respectively, while 10a,b, is likely due to the oxygenated side chain of the polymer, 11, and 16 show two very broad peaks.14 Similarly, the emis- which contains more delocalized electrons than either poly- sion of C2, PNMA, and PUMA clearly show a doublet peak mer 10a or 10b. Even though the n-alkyl chain of 11 does not with peak maxima at 347 and 362 nm. The emission peaks of have oxygen atoms, it does exhibit a red-shifted absorbance 10a,b, 11, and 16 appear as a much less defined, broader, and emission characteristics when compared to the other red-shifted doublet peak. The blending of the peaks is due to polymers; the maximum absorbance of 11 occurs at 308 nm the delocalization of the extended electron cloud and an with a secondary peak occurring at 267 nm, and the maxi- increase in conjugation length. mum emission occurring at 401 nm with an indistinct shoulder from about 382 to 387 nm. The bathochromic shift Electrochemical and Optical Band Gap Analysis suggests that introducing two biphenyl groups to the carba- Voltammograms were analyzed in order to derive the onset zole pendant group of the polymer lengthens the overall π-π potential (Eonset). This process was not reversible and only conjugation length resulting in a redshift from the expected allowed for the observation of the oxidation peak, so for full absorbance and emission (cf. Fig. 3).40 examination of the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and While the absorbance and emission characteristics of the band gap, the band gap was calculated from the experimen- above polymers are similar, their profiles are quite different tally observed electronic absorbance band edge. LUMO could 33 14 from C2, PNMA, and PUMA. Both the absorbance and then be calculated through the equation ΔE = ELUMO - EHOMO. photoluminescence profile of 10a,b, 11, and 16 are greatly The addition of the conjugated bonds by introducing the red-shifted, and peak broadening is observed when compared biphenyl substituents appears to affect the state of the

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value of 3.51, which is more than the band gap of 10a, 11, and 16, suggesting that the extended conjugation length of these polymers result in a lower band gap. PUMA also exhibits a higher band gap value than 10b also due to the extended conjugation length of 10b. C2

CONCLUSION

Adding biphenyl groups to the carbazole pendant group T 10a greatly increases the g of the polymers due to the bulkiness of the biphenyl groups, while the addition of methylene brid-

ges in the n-alkyl chain greatly decreases the Tg by allowing carbazole group to move more freely. Increasing the conjugation length, through the addition of biphenyl groups, of these 10b methacrylate based polymers with carbazole moieties causes a bathochromic shift in the absorbance and emission of the

normalized absorbance (a.u) polymers when compared to C2, PNMA, and PUMA due to the extended conjugation length in the heterocyclic portion of normalized photoluminescence (a.u.) the monomers. While the overall band gap for the compounds 11 described in this paper are very similar, the band gaps are slightly smaller than that of C2, PNMA, and PUMA. These materials have applications in memory resistor (“memristor”) technologies as memristor devices have been made from PNMA and PUMA.14 16

250 300 350 400 450 500 550 EXPERIMENTAL wavelength (nm) Chemical Characterization FIGURE 3 Absorbance (solid lines) and photoluminescence All chemicals and solvents used for preparation of monomers (dashed lines) of polymers C2 (pink), 10a (black), 11 (red), 10b and polymers were purchased from commercial suppliers, (blue), and 16 (green). Excitation at 295 nm for all polymers. such as Alfa Aesar and TCI America and were used without Both absorbance and photoluminescence were obtained in further purification. All solvents used for reactions were dis- μ tetrahydrofuran at a concentration of 10 and 1 g/mL, tilled under nitrogen after drying over an appropriate drying fi respectively (shifted for clarity). [Color gure can be viewed at reagent. All synthetic procedures are described in detail wileyonlinelibrary.com] in Supporting Information. 1H and 13C NMR spectra were electrons in the carbazole system by decreasing the band gap recorded on a JEOL ECX300 spectrometer. Chemical shifts for when compared to C2.33 However, the addition of two biphe- protons are reported in parts per million downfield from tet- nyl groups to the carbazole (11) moiety and the addition of ramethylsilane and are referenced to residual protium in the oxygen into the side chain (16) does not appear to have a sig- NMR solvent (CDCl3: δ 7.26 ppm, DMSO-d6: δ 2.50 ppm). nificant effect beyond the initial change observed when one Chemical shifts for carbons are reported in parts per million biphenyl substituent was added to the carbazole moiety downfield from tetramethylsilane and are referenced to the (10a,b) (cf. Table 2). Additionally, PNMA exhibits a band gap carbon resonances of the solvent (CDCl3: δ 77.16 ppm). Data are presented as follows: chemical shift, multiplicity (s = sin- TABLE 2 Electronic Characteristics of Methacrylate Polymers glet, d = doublet, t = triplet, m = multiplet, and/or multiple Measured through Cyclic Voltammetry and UV–vis resonances), coupling constant in hertz (Hz), and signal area Spectroscopy; All Energies are Relative to the Vacuum Level integration in natural numbers. Carbon and proton NMR spec-

a b c tra for compounds are provided in Supporting Information. Compound ΔEop HOMO LUMOop Melting points were determined on an EZ-Melt automated 10a 3.33 −5.64 −2.31 melting point apparatus. Matrix-assisted laser desorption/ion- 10b 3.33 −5.56 −2.23 ization mass analyses were prepared using a Voyager DE spectrometer. All manipulations involving air- and/or 11 3.35 −5.49 −2.14 moisture-sensitive compounds were performed with standard 16 3.39 −5.39 −2.00 Schlenk techniques under nitrogen. Analytical thin-layer chro- C2 3.54 −5.52 −1.98 matography was performed on glass plates coated with – ﬂ a Optical band gap taken from electronic absorbance band edge. 0.25-mm 230 400 mesh silica gel containing a uorescent b ¼ − − : indicator. Column chromatography was performed using silica EHOMO EOðÞonset 4 4. c ΔE = ELUMOop - EHOMO. gel (Grade 60A, particle size 63–210 μm).

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Optical Characterization ACKNOWLEDGMENTS Absorbance spectra were collected using a Perkin-Elmer The authors thank the Gregg-Graniteville Foundation and the Lambda 950 UV/VIS/NIR spectrophotometer. Photolumines- National Science Foundation (OIA-1632881 and DMR- cence spectra were collected using a Jobin-Yvon Fluorolog 1507266) for ﬁnancial support. 3–222 Tau spectrometer.

REFERENCES AND NOTES Electrochemical Characterization The electrochemical characteristics of the materials were 1 B. Luszczynska, E. Dobruchowska, I. Glowacki, A. Danel, investigated through cyclic voltammetry (CV) to estimate their J. Ulanski, J. Lumin. 2009, 129, 1215. corresponding HOMO energy levels. This was performed by 2 B. H. Tong, Q. B. Mei, S. J. Wang, Y. Fang, Y. Z. Meng, using an ITO-coated glass slide as the working electrode, which B. Wang, J. Mater. Chem. 2008, 18, 1636. had a thin film of the polymer of interest deposited on it, an 3 C. F. Huebner, J. B. Carroll, D. D. Evanoff, Y. R. Ying, Ag/AgCl reference electrode, and a platinum wire as a counter B. J. Stevenson, J. R. Lawrence, J. M. Houchins, A. L. Foguth, J. Sperry, S. H. Foulger, J. Mater. Chem. 2008, 18, 4942. electrode. CV measurements were conducted in a 0.1 M LiClO 4 4 E. Dobruchowska, I. Glowacki, J. Ulanski, J. Sanetra, acetonitrile solution at room temperature with a scan rate of J. Pielichowski, Chem. Phys. 2008, 348, 249. 50 mV s−1; the electrochemical cell was calibrated against fer- 5 F. C. Chen, Y. Yang, M. E. Thompson, J. Kido, Appl. Phys. Lett. rocene and the half-wave potential was estimated to be 2002, 80, 2308. 415 mV against an Ag/AgCl reference. The LUMO energies 6 F. Pschenitzka, J. C. Sturm, Appl. Phys. Lett. 2001, 79, 4354. were based on the difference of the measured oxidation poten- 7 J. Kido, K. Hongawa, K. Okuyama, K. Nagai, Appl. Phys. Lett. tial (HOMO), and the energy at the experimentally observed 1994, 64, 815. 41 electronic absorption band edge. 8 P. D’Angelo, M. Barra, A. Cassinese, M. G. Maglione, P. Vacca, C. Minarini, A. Rubino, Solid-State Electron. 2007, 51, 123. Thermal Characterization 9 Y. Kawamura, S. Yanagida, S. R. Forrest, J. Appl. Phys. 2002, Differential scanning calorimetry (DSC) was performed on all 92, 87. polymers using a heat/cool/heat method at a heating rate of 10 G. M. Wang, S. X. Qian, J. H. Xu, W. J. Wang, X. Liu, X. Z. Lu, 10 C/min and a cooling rate of 5 C/min in a nitrogen atmo- F. M. Li, Physica B 2000, 279, 116. sphere. Thermogravimetric analysis (TGA) was performed 11 H. S. Kim, C. H. Kim, C. S. Ha, J. K. Lee, Synth. Met. 2001, before DSC to determine decomposition temperatures. Each 117, 289. TGA was performed at a ramp rate of 10 C/min in a nitrogen 12 M. C. Tria, K. S. Liao, N. Alley, S. Curran, R. Advincula, atmosphere. The TGA furnace was purged with nitrogen for J. Mater. Chem. 2011, 21, 10261. 15 min prior to the start of the TGA run. 13 N. Ikeda, T. Miyasaka, Chem. Commun. 2005, 1886. 14 T. M. McFarlane, B. Zdyrko, Y. Bandera, D. Worley, O. Klep, Molecular Weight Analysis M. Jurca, C. Tonkin, S. H. Foulger, J. Vilcakova, P. Saha, fl Molecular weights of the polymers were analyzed with gel J. P eger, J. Mater. Chem. C 2018, 6, 2533. permeation chromatography (GPC) using an eluent of chlo- 15 S. L. Lim, Q. D. Ling, E. Y. H. Teo, C. X. Zhu, D. S. H. Chan, E. T. Kang, K. G. Neoh, Chem. Mater. 2007, 19, 5148. roform and a pump rate of 1 mL/min. Before the GPC analysis, the samples were dissolved in chloroform for 12 h and 16 E. Y. H. Teo, Q. D. Ling, Y. Song, Y. P. Tan, W. Wang, E. T. Kang, D. S. H. Chan, C. X. Zhu, Org. Electron. 2006, 7, 173. were subsequently filtered through a 0.45 μm syringe filter 17 L. H. Xie, Q. D. Ling, X. Y. Hou, W. Huang, J. Am. Chem. Soc. before being injected into the column. The fractions were 2008, 130, 2120. analyzed with a UV/vis detector (Waters 2489) and a 18 S. Park, K. Kim, J. C. Kim, W. Kwon, D. M. Kim, M. Ree, Poly- refractive index detector (Waters 2414). Molecular weight mer 2011, 52, 2170. fractions from samples were compared against polystyrene 19 X. D. Zhuang, Y. Chen, G. Liu, B. Zhang, K. G. Neoh, standards. E. T. Kang, C. X. Zhu, Y. X. Li, L. J. Niu, Adv. Funct. Mater. 2010, 20, 2916. Dielectric Spectroscopy 20 G. Liu, B. Zhang, Y. Chen, C. X. Zhu, L. J. Zeng, D. S. H. Chan, Dielectric spectroscopy was performed on a Novocontrol K. G. Neoh, J. N. Chen, E. T. Kang, J. Mater. Chem. 2011, 21, Broadband Dielectric/Impedance Alpha-A Quatro Series 6027. Spectrometer. Samples were sandwiched between an upper 21 W. D. Gill, J. Appl. Phys. 1972, 43, 5033. and lower electrode that was 10 mm in diameter. The poly- 22 W. Klopffer, J. Chem. Phys. 1969, 50, 2337. mer, as a powder, was placed between the electrodes under 23 P. R. Sundararajan, Macromolecules 1980, 13, 512. a slight load. The assembly was then placed into the spec- 24 D. J. Williams, W. W. Limburg, J. M. Pearson, A. O. Goedde, trometer, and the sample was heated past the glass transi- J. F. Yanus, J. Chem. Phys. 1975, 62, 1501. tion temperature; this resulted in a film thickness of about 25 G. E. Johnson, J. Chem. Phys. 1975, 63, 4047. 100–200 μm. The sample was then cooled to −150 Cand 26 G. E. Johnson, J. Phys. Chem. 1974, 78, 1512. equilibrated for 3 min. The sample was then heated at a 27 G. E. Johnson, T. A. Good, Macromolecules 1982, 15, 409. rate of 2–3 C/min under a nitrogen purge, while being 28 Y. K. Fang, C. L. Liu, W. C. Chen, J. Mater. Chem. 2011, 21, exposed to an AC 1-V signal that varied from 0.001 Hz to 4778. 1 × 106 Hz. 29 C. S. Callam, T. L. Lowary, J. Chem. Educ. 2001, 78, 947.

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30 K. Kawamura, Y. Aotani, H. Tomioka, J. Phys. Chem. B 2003, 35 F. Garwe, A. Schonhals, H. Lockwenz, M. Beiner, K. Schroter, 107, 4579. E. Donth, Macromolecules 1996, 29, 247. 31 N. M. Carballeira, N. Montano, L. F. Padilla, Chem. Phys. 36 D. J. Bergman, Y. Imry, Phys. Rev. Lett. 1977, 39, 1222. Lipids 2007, 145, 37. 37 T. Tetsutani, M. Kakizaki, T. Hideshima, Polym. J. 1982, 32 S. W. Baldwin, J. D. Wilson, J. Aube, J. Org. Chem. 1985, 50, 14, 305. 4432. 38 T. Tetsutani, M. Kakizaki, T. Hideshima, Polym. J. 1982, 33 C. F. Huebner, V. Tsyalkovsky, Y. Bandera, M. K. Burdette, 14, 471. J. A. Shetzline, C. Tonkin, S. E. Creager, S. H. Foulger, Nano- 39 J. D. Ferry, S. Strella, J. Colloid Sci. 1958, 13, 459. scale 2015, 7, 1270. 40 J. Autschbach, J. Chem. Educ. 2007, 84, 1840. 34 H. Sasabe, S. Saito, J. Polym. Sci. Part A-2: Polym. Phys. 41 M. Skompska, L. M. Peter, J. Electroanal. Chem. 1995, Ther. 1968, 6, 1401. 383, 43.

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