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Transcending the Trade-off in Refractive Index and Abbe Number for Highly Refractive Polymers: Synergistic Effect of Polarizable Skeletons and Robust Hydrogen Bonds

  • Seigo Watanabe
    Seigo Watanabe
    Department of Applied Chemistry and Research Institute for Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
  • Teru Takayama
    Teru Takayama
    Department of Applied Chemistry and Research Institute for Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
  • , and 
  • Kenichi Oyaizu*
    Kenichi Oyaizu
    Department of Applied Chemistry and Research Institute for Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
    *Email: [email protected]
Cite this: ACS Polym. Au 2022, 2, 6, 458–466
Publication Date (Web):August 18, 2022
https://doi.org/10.1021/acspolymersau.2c00030

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Abstract

High-refractive-index polymers (HRIPs) are attractive materials for the development of optical devices with high performances. However, because practical components and structures for HRIPs are limited from the viewpoint of synthetic techniques, it has proved difficult using traditional strategies to enhance the refractive index (RI) of HRIPs to more than a certain degree (over 1.8) while maintaining their visible transparency. Here, we found that poly(phenylene sulfide) (PPS) derivatives featuring both methylthio and hydroxy groups can simultaneously exhibit balanced properties of an ultrahigh RI of nD = 1.85 and Abbe number of νD = 20 owing to the synergistic effect of high molar refraction and dense intermolecular hydrogen bonds (H-bonds). This brand new strategy is anticipated to contribute to the development of HRIPs displaying ultrahigh RI with adequate Abbe numbers beyond the empirical nD–νD threshold, which has not been achieved to date.

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Introduction

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High-refractive-index polymers (HRIPs) have attracted worldwide attention in the field of optical devices from the viewpoint of enhancing performance and flexibility. (1−4) To date, numerous HRIPs bearing highly polarizable groups with a small volume (e.g., aromatics (5−7) and heteroatoms (8−14)) have been reported to display high refractive indices greater than 1.7. The desired refractive index (RI, n) values of optical polymers have been increased alongside the rapid development of photonic technologies; for example, transparent materials with RI values exceeding 1.8 are required for use as LED encapsulants in order to enhance the light extraction efficiency. (1) However, HRIPs displaying both ultrahigh RI values of over 1.8 and amorphous features have seldom been reported among optical polymers for visible-light usage. This can be ascribed to the relatively low polarity of the components of most organic polymers. Thianthrene-containing poly(phenylene sulfide) (PPS) (15) and triazine-bearing polymers (16) are among the few reported examples of HRIPs with RI values above 1.8 in the visible-light region. Selenium- or tellurium-containing polymers (17−19) and sulfur-rich polymers (20,21) have also been found to exhibit ultrahigh RI values exceeding 1.8 owing to their very high molar refraction ([R]). However, these polymers also displayed strong absorption bands in the near-UV–visible region, which led to coloration or low Abbe numbers (i.e., large chromatic aberration and low transparency) of the resulting films and limited their applications in this wavelength region. HRIPs with balanced properties (ultrahigh RI, thermostability, and adequate Abbe number) are required for outstanding optical materials.
As a solution to this problem, polymers with large numbers of short polysulfide chains synthesized by sulfur chemical vapor deposition of elemental sulfur using comonomers containing multiple vinyl groups were recently reported. (22,23) These polymers exhibited superior transparency and much higher RI values (up to nD = 1.982, where D denotes the sodium D line at 589.3 nm) (23) compared to those of previously reported HRIPs, although the versatility of the synthetic route was limited by the need for vapor deposition. Therefore, the development of facile and versatile preparation methods for HRIPs with ultrahigh RI values, adequate Abbe numbers, and film formability has become a critical issue in the field.
We recently reported that the simultaneous incorporation of a backbone with a moderately high [R] value and substituents with hydrogen bonding (H-bonding) capability effectively afforded polymers with ultrahigh RI values without serious decline of Abbe numbers and transparency. (24) In particular, hydroxy-substituted PPS (OHPPS) exhibited an ultrahigh RI (nD = 1.80) with an Abbe number of νD = 20. Our detailed examination revealed that these superior properties originated from the effects of H-bonds between the side chains. Specifically, this unprecedented example was ascribed to the densely packed yet amorphous bulk polymer structure, affording a high RI with high molar refraction and low molecular volume (V). (24)
In this study, we further expand this proof-of-concept work toward a rational strategy for designing ultrahigh RI polymers, which enables breaking through the traditional empirical RI threshold as well as overcoming the typical trade-off between RI and Abbe number among organic polymers.
First, methylthio-substituted PPS (SMePPS) with a high sulfur content (42 wt %) was prepared as an ultrahigh-RI polymer (nD = 1.81) with high polarizability (Figure 1a). Moreover, by introducing H-bonding scaffolds into the highly polarizable PPS chain through copolymerization with OHPPS (Figure 1b), the RI was further enhanced to nD = 1.85 with an Abbe number of νD = 20. To the best of our knowledge, this is the first reported example of HRIPs simultaneously displaying such an ultrahigh RI and adequate Abbe number, which exceeded the empirical nD–νD threshold. The synergistic effect of high polarizability and intermolecular H-bonds was revealed to be effective for maximizing the RI by increasing the [R]/V values, which was also quantitatively demonstrated by investigation of the bulk structure and properties.

Figure 1

Figure 1. Concept of this study. (a) Synthesis of SMePPS through oxidative polymerization. (b) Further RI enhancement strategy enabled by the copolymerization with the H-bonding scaffold OHPPS leading to higher [R]/V values.

Results and Discussion

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Oxidative Polymerization of Bis(2-methylthiophenyl) Disulfide

First, methylthio-substituted PPS (SMePPS) was synthesized through the oxidative polymerization of bis(2-methylthiophenyl) disulfide (SMeDPS). The SMeDPS monomer was prepared via Grignard reaction of 1-bromo-2-thioanisole and subsequent oxidation of the thiol, affording yellow needle-like crystals. The structure of SMeDPS was confirmed by 1H NMR, 13C NMR, and FAB-MS spectra (see the experimental procedure and Figure S1). Owing to the oxidation feasibility of SMeDPS, as confirmed by the presence of an irreversible oxidation peak at 1.56 V vs Ag/AgCl in the cyclic voltammogram (Figure S2), the oxidative polymerization of SMeDPS proceeded with either oxygen with the VO(acac)2–H+ redox catalyst (25) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (26) as the oxidant. The reaction behavior and polymer structure were investigated through various spectroscopic measurements and density functional theory (DFT) calculations. The linear structure with two carbon–sulfur bonds per one unit was confirmed from the 1H NMR spectrum, in which the signals corresponding to the aromatic and methylthio protons were detected with the same integrals (Figure 2a). From the IR spectrum of the polymer, the presence of 1,2,4-substituted phenylene moieties was verified from not only the absorption bands at 750 and 850 cm–1, which were derived from the terminal 1,2-substituted phenylene, but also the newly observed bands at 810 and 890 cm–1 after the polymerization (Figure 2b). Therefore, in the oxidative polymerization of SMeDPS, the chain-growth reaction (i.e., the electrophilic substitution of the sulfonium electrophile and the sulfide monomer/oligomer) dominantly proceeded at the 4- or 5-position to the carbon–sulfur bonds on the benzene ring. The 13C and 13C-DEPT NMR spectra of the polymer revealed six kinds of aromatic carbons, three of which were assigned as carbons with C–H bonds, indicating the obtained polymer was composed of a single structure with trisubstituted aromatic rings (Figure 2c). Because of the similar electromagnetic features of the aromatic protons and carbons adjacent to the methylthio-substituted carbons and the arylene sulfide-substituted carbons, these signals were indistinguishable in the 1H and 13C NMR spectra. Therefore, we further converted only the methylthio substituents to S═O moieties by mCPBA oxidation to separate the two peaks. In the 1H–1H COSY spectrum of the sulfoxide-labeled polymer, a 1H–1H correlation was observed between the aromatic proton signals at 7.9 and 7.6 ppm, indicating that this pair of adjacent aromatic protons was located just next to the labeled sulfoxide (Figure 2d), and therefore, the structure of SMePPS was finally determined as that of poly(2-methylthio-1,5-phenylenesulfide). The DFT calculation results for SMeDPS also demonstrated Friedel–Crafts reactivity of the carbon at the 5-position higher than that at the 4-position, as confirmed by the presence of both a more distributed HOMO and more negative Mulliken charge of the carbon at the 5-position (Figure S3).

Figure 2

Figure 2. Synthesis of SMePPS. (a) 1H NMR spectrum of SMePPS in chloroform-d. (b) IR spectra of SMeDPS and SMePPS. (c) (i) 13C and (ii) 13C-DEPT 135 NMR spectra of SMePPS in chloroform-d. (d) 1H–1H COSY spectrum of the sulfoxide-labeled SMePPS. The repeating structure was determined to be 2-methylthio-1,5-thiophenylene (structure circled by red square) owing to the correlation signals observed between the aromatic protons at the lowest field.

The molecular weight of SMePPS remained relatively low (up to Mw = 2.3 × 103) according to size exclusion chromatography (SEC) measurements (Table S1). Owing to the relatively low oxidation potential of SMeDPS among PPS derivatives, the monomer was instantly oxidized in the early stage of the reaction, and the subsequent electrophilic substitution (corresponding to chain propagation) can be defined as the rate-determining step. Indeed, the polymerization proceeded better in a low-donor-number solvent at low concentration but remained with small Mw values, suggesting that the low molecular weight of the polymers was ascribed to not the solubility of the polymers but the lower Friedel–Crafts reactivity of SMeDPS compared to that of other DPS monomers. (27) The rigidity and high steric hindrance of the 1,5-disubstituted oligomeric structure during the electrophilic attack ultimately affected low reactivity, which finally resulted in low molecular weight for SMePPS.

Thermal and Optical Properties of SMePPS

Next, the outstanding thermal and optical performances of SMePPS were confirmed from various measurements. The differential scanning calorimetry (DSC) thermogram of SMePPS revealed high thermal stability with single glass-transition behavior in a suitable temperature window (up to Tg = 103 °C) (Figure S5a inset). The X-ray diffraction (XRD) profile also revealed no crystalline peaks derived from pristine PPS, indicating the completely amorphous nature of SMePPS owing to the steric effects associated with the bulky methylthio substituents (Figure S5a). Thermogravimetric analysis (TGA) of SMePPS indicated a high thermal degradation temperature of Td5 = 319 °C, which is similar to the reported values for other PPS and its derivatives obtained by oxidative polymerization (Figure S5b). (14,27) On the basis of these superior properties as an optical material with high processability and good solubility, thin films of SMePPS were fabricated on glass and Si substrates to investigate the optical properties. The SMePPS films showed visible transparency with a transmittance of >74%T for a thickness of 5.4 μm (normalized transmittance: > 94%T for 1 μm thickness) (Figure 3a). This was ascribed to the dispersed nature of the sulfur atoms as sulfide bonds rather than polysulfides, (22) which may cause film coloration (Figure 3a), although the transparency was lower than that for OHPPS with a similar RI (nD = 1.80). (24) This decrease in transparency was also confirmed by the larger extinction coefficient of SMePPS compared to that with other alkyl-, alkoxy-, or hydroxy-substituted PPS in the near-UV region owing to its abundance of highly polarizable sulfur atoms (42 wt %) (Figure S6). Furthermore, SMePPS exhibited an ultrahigh RI of nD = 1.81 and an Abbe number of νD = 19, the former of which especially represents the highest among the PPS-derived homopolymers to the best of our knowledge (Figure 3b). Increasing [R] through the introduction of short sulfide side chains, which also served as a source for steric effects affording amorphous bulk film, was thus demonstrated to be an effective strategy for enhancing the RI of PPS derivatives while maintaining an adequate Abbe number.

Figure 3

Figure 3. Optical properties of SMePPS. (a) UV–vis transmittance spectrum of an SMePPS thin film (inset: photograph of the film on a glass substrate). (b) Refractive index of SMePPS in the visible-light region. See Figure S6 for the detailed spectrum including extinction coefficient in the wider wavelength range.

Synthesis of Hydroxy- and Methylthio-Substituted Copolymers (P2)

Next, we anticipated that the RI of SMePPS could be further enhanced by decreasing the free volume through the introduction of hydroxy-substituted PPS (OHPPS) moieties as a copolymerization unit, which can contribute to realizing higher [R]/V values. (24) First, copolymers composed of SMePPS and OMePPS units (P1) were synthesized through the oxidative polymerization of SMeDPS and OMeDPS to serve as precursors for yielding copolymers with SMePPS and OHPPS units (P2) (Figure 1b). Three kinds of P1 with different composition ratios were prepared to investigate the effect of introducing the methoxy and hydroxy groups into the polymer sequence on the RI values (Table S4). The DOSY NMR spectra of P1 confirmed the presence of copolymerized products, as demonstrated by the same diffusion coefficient for all the signals corresponding to each unit (Figure S7). The IR spectra of P1 also revealed the presence of 1,2,4-substituted benzene rings (δC–H (Ar): 810 and 900 cm–1) and terminal 1,2-substituted benzene rings (δC–H (Ar): 750 and 840 cm–1), indicating that each unit was successfully incorporated as in the case of OMePPS (27) and SMePPS (vide supra) (Figure S8). We also checked the copolymerization kinetics in the system containing the same number of equivalents of fed monomers (Figure S9). The molecular weight of the product increased drastically over the first hour before increasing more gradually (Figure S9a,b). Therefore, the copolymerization proceeded according to a step-growth mechanism in the early stage of the reaction, whereas disulfide exchange and coupling reactions of the oligomeric products appeared to be the major reactions in the middle and latter stages. The reactivity of each monomer was almost identical from the perspective of oxidation potential (Eox = 1.56 V for SMeDPS and 1.58 V for OMeDPS), (27) resulting in an almost constant composition ratio x with values close to the theoretical ones (xtheo = 0.5) during the polymerization progress (Figure S9e). Consequently, a series of P1 were afforded as nearly ideal random copolymers. On the other hand, OMePPSPPS copolymers obtained by oxidative polymerization were gradient-like polymers, which was confirmed from the larger introduction rate of OMePPS unit (see black dots on Figure S9e for the DDQ oxidant system, and see our previous report (24) for the O2/VO(acac)2-H+ system). Due to the randomly incorporated sequence during the copolymerization for P1 synthesis, the oligomers of P1 were highly soluble until the later stage of polymerization and the termination of polymerization was also prevented. Although the molecular weight of P1 still remained in small values of Mw ∼ 103, higher Friedel–Crafts reactivity and p-selectivity of the OMeDPS counterpart prolonged the polymerization and resulted in higher Mw values than SMePPS.
Finally, the target copolymers consisting of OHPPS and SMePPS units (P2) were prepared via postpolymerization modification of P1, according to the same strategy described in our previous report. (24) First, the disulfide bonds in the main chain of P1 were functionalized to obtain methyl-terminated P1 (Me-P1) beforehand for preventing the simultaneous occurrence of disulfide cleavage and demethylation of methoxy groups (Table S5). (24) Although the 1H NMR signal corresponding to the terminal methyl group was observed in the same region as those of the methylthio substituents and could not be detected independently, the progress of the end-functionalization was confirmed from the increased integral ratio of the broad peak near 2.4 ppm in the spectra of Me-P1 with respect to that of P1 (Figure S10). No newly observed peaks were detected in the IR spectra after end-functionalization and Me-P1 contained no structural defects (Figure S11). The degree of end-functionalization was greater than 88%, determined by comparison of the Mn values from the NMR and SEC measurements. The lower Mn and Mw values of Me-P1 compared with P1 indicated that the disulfide bonds of P1 were located not only at the terminus but also within the polymer chains. The subsequent demethylation of Me-P1 also proceeded efficiently with high conversions (≥93%), as monitored through the corresponding peak changes in the 1H NMR and IR spectra (Figure 4a,b and Figures S12 and S13). P2 was finally obtained without any degradation, as confirmed by the similar Mn values before and after the demethylation (Table S6). However, the bulk properties of the PPS derivatives, i.e., molecular weight, mechanical properties, and melt processability, should be further improved for practical applications. We have currently been focusing on these remaining issues by means of engineering the reactive disulfide bond in the PPS chains, which can be accomplished through the end-functionalization using multiarm modification agents, disulfide metathesis, or other transformation reactions (e.g., click reactions) as chain-extension techniques. (28−30)

Figure 4

Figure 4. Synthesis and properties of P2. (a) 1H NMR spectra of Me-P1 (run 2′) and P2 (run 2″) in DMSO-d6. (b) IR spectra of Me-P1 (run 2′) and P2 (run 2″). (c) UV–vis spectra of Me-P1 and P2 thin films (thickness was normalized to 1 μm). Inset: thin films of Me-P1 (run 2′) and P2 (run 2″). (d) Refractive indices of Me-P1 and P2.

Crystalline and Thermal Properties of Copolymers

The amorphous natures of Me-P1 and P2 were revealed from their XRD profiles, irrespective of the x values and the presence/absence of hydroxy groups (Figure S14). Even after the introduction of the H-bonds, the random sequence of each unit and the efficiency of plausible intermolecular interactions other than H-bonds between hydroxy groups (e.g., H-bonds involving methylthio groups as acceptors, S−π interactions of the aromatic rings and methylthio groups, and π–π interactions between the aromatic rings) contributed to the amorphous nature of P2. In addition, the bulkiness of the 1,5-substituted phenylene units compared with 1,4-substituted units presumably assisted with the amorphous structures of Me-P1 and P2.
According to the DSC thermograms, a single glass transition for P1, Me-P1, and P2, which was same as the case for OHPPS-PPS copolymers, suggested a homogeneous bulk structure in a molecular level. The Tg values of P1 were increased according to larger x values owing to the higher Tg of OMePPS (Tg = 105–132 °C) (27) compared with SMePPS; this trend of Tg versus x was retained for the series of Me-P1 (Figure S15a). However, the Tg values of P2 were slightly lower than those of the corresponding Me-P1, contrary to the expected effect of H-bonds described above. This trend was similar to that observed for the demethylation of OMePPSPPS copolymers but distinct from that for OMePPS, which makes Tg higher. (24) The random sequence of P2 was the key to decreasing Tg owing to its lower rotational barrier than Me-P1, whose effect exceeded the binding effect of polymer chains through H-bonds.

Optical Properties of Copolymers

Finally, the influence of the sulfur and hydroxy contents on the optical properties was investigated. Me-P1 and P2 were more transparent in the visible region (over 96%T for 1 μm thickness) than SMePPS owing to their lower contents of highly polarizable sulfur atoms, preventing excessive interactions involving sulfide moieties in the bulk state (Tables 1 and S7). Additionally, higher transparency of P2 than OHPPS-PPS copolymers (24) held the difference of microstructures in the bulk state, suggesting that P2 had more homogeneous structure with less clustering of particular segments and optical scattering would have been prevented. The smaller solution absorptivity of P2 compared with SMePPS also contributed to the higher transparency of the polymers mainly derived from their inherent structures (Figure S19), which was ascribed to the small number of lone pairs and polarizable atoms adjacent to the aromatic rings. (14) Focusing on the properties through the demethylation, the transparency of P2 was slightly decreased in the bulk state but increased in diluted solution (Figure 4c and Figures S20 and S21), which was a different trend from those of Me-OMePPS and OHPPS. (24) Therefore, plausible intermolecular interactions involving methylthio groups as acceptors, such as H-bonds and S−π interactions, apparently occurred in the bulk films of SMePPS and P2, leading to their low visible transparency. The RI values of SMePPS, P1, and Me-P1 decreased upon the introduction of methoxy groups in accordance with the decreased average molar refraction per repeating unit (black lines in Figures 4d and S23). After the demethylation, P2 displayed RI values larger than those of the corresponding Me-P1 owing to the more compact skeleton (red lines in Figures 4d and S23). Furthermore, the differences in nD were small (∼0.02) in the low-x region (run 1″) but larger (∼0.08) in the large-x region (runs 2″ and 3′′), although the Abbe numbers (νD) were maintained with values of approximately 20 irrespective of the x values (Figure 5a). This difference was attributable to the number of H-bonds, whose effect on lowering the free volume was exerted only in the bulk state with the densely incorporated H-bonds. Furthermore, the relationship between the x and nD values of P2 was anomalous: the change in RI was not proportional to x and the maximum nD of 1.85 was observed at the intermediate composition (x = 0.53, run 2″) (Figure 5a and Table 1). In general, the RI values of bicomponent copolymers change monotonically following additivity rules and decrease as the composition ratio of the unit with small [R] increases, similar to that in the previous report; (31) the nD values of Me-P1 changed with x according to this trend. However, this empirical rule was not applicable to the P2 system owing to the unusual bulk structure derived from the H-bonding effect induced by the OHPPS units.
Table 1. Optical Properties and Density of P2
runpolymerxa (−)%Tb at 400 nmnDc (−)νDc (−)densityd (g cm–3)
 SMePPS0941.81191.39
1″P20.27971.80161.39
2″P20.53971.85201.48
3″P20.77961.83171.47
 OHPPS1.0097e1.80e20e1.50e
a

Determined by 1H NMR.

b

Determined by UV–vis spectroscopy (normalized values for a thickness of 1 μm).

c

Determined by spectroscopic ellipsometry.

d

Determined by a dry density meter (the values were density for powder samples).

e

Values from ref (24).

Figure 5

Figure 5. RI changes for Me-P1, P2, and homopolymers depending on the methoxy/hydroxy content. Values for OMePPS (Me-P1 with x = 1.00) and OHPPS (P2 with x = 1.00) were referred from the previous reports (refs (27) and (24), respectively). (a) Relationship between composition ratio and experimental nD for Me-P1 (black squares) and P2 (red triangles) (before and after demethylation). (b) Experimental nD (line graph) and density (bar charts) for SMePPS, OHPPS, and P2. The error bars indicate the standard deviation of the density measurements (average of five times). (c) Estimated (blue open triangles) and experimental (red circles) nD values for SMePPS, OHPPS, and P2 at each composition ratio. The error bars indicate the standard deviation of the estimated RI values, which were in accordance with the deviation of the density measurements. (d) Schematic comparison of H-bond distribution, [R] values, and nD values for SMePPS, OHPPSPPS copolymer, (24) and P2. The blue and red circles represent high-[R] moieties and H-bonding moieties, respectively, and the dotted lines represent intermolecular H-bonds. The color depth of the blue circles represents the magnitude of the [R] values.

Synergistic Effect of Molar Refractivity and Intermolecular Interactions

To elucidate the mechanism underlying the anomalous relationship between the RI and composition ratio of P2, the bulk properties of P2 were further investigated. First, the density of P2 was measured for each x value to examine the H-bonding effect, for the density of a polymer is directly related to its free volume.
P2 with a small x value (run 1″, x = 0.27) exhibited almost the same density as SMePPS, whereas the density of P2 with larger x values (run 2″, x = 0.53, and run 3″, x = 0.77) displayed remarkably high densities similar to that of OHPPS (1.50 g cm3) (Figure 5b). (24) This trend was in accordance with the sharp enhancement of RI in the case of P2 from run 1″ to run 2′′. These results suggested that the introduced H-bonds markedly lowered the free volume in the case of P2 with moderate to high hydroxy contents, which led to the synchronized RI enhancement in this system. To estimate the precise RI values taking the contributions of the [R] and V changes into account, we also estimated nD values for each x through the LorentzLorenz equation, by adopting measured densities and calculated molar refractions (Figure 5c). The estimated nD values (blue data points in Figure 5c) followed the same trend as the experimental values (red data points in Figure 5c) with increasing number of hydroxy groups, suggesting that the experimental RI values varied in accordance with the change in [R]/V values. The deviations of the estimated RI values from the experimental ones were ascribed to the more densely packed structure of the polymers in the bulk (film) states compared with the powder states (the density of powder samples was adopted as an alternative to that of films in this study, owing to the difficulty associated with preparing free-standing films). Because the polymer chains were less densely packed in the powder state than in the bulk state on account of the higher concentration of voids and boundaries, which resulted in a smaller number of neighboring polymer chains, (32) the P2 films would be expected to display higher densities than the powder samples, implying higher experimental RI values in the bulk system. By comparing the IR spectra of P2 before and after film fabrication, the O–H stretching vibrations involving H-bonds were found to shift to lower wavenumbers (Figure S24), indicating the presence of H-bond networks with a more dense and homogeneous distribution in the P2 bulk films.
In our previous study, (24) we reported that copolymers composed of OHPPS and unsubstituted PPS (termed OHPPSPPS copolymers hereafter) exhibited lower RI values than OHPPS; however, in this study, P2 showed RI values higher than those of both OHPPS and SMePPS. This difference suggests that the RI values of OHPPS and its copolymers are strongly dependent on the sequence, the [R] values of each component, and the content of hydroxy-substituted moieties (Figure 5d). Although OHPPSPPS copolymers were obtained with gradient-like sequences and therefore the hydroxy groups were randomly and sparsely incorporated, P2 were random copolymers with homogeneous distributions of hydroxy groups. In particular, the randomness of the P2 sequence was the highest for the composition ratio of x ∼ 0.5 owing to the approximately equivalent incorporation of each unit in the copolymer. The above difference in the unit distribution depends on the reactivity of the monomers toward disulfide oxidation and Friedel–Crafts substitution, both of which are defined as elementary reactions during the oxidative polymerization. (26) Because the introduction of electron-donating groups to a DPS monomer is effective for both lowering the oxidation potential (Eox) and enhancing the electrophilic substitution of the sulfonium cation, the oxidative copolymerization of OMeDPS with another DPS monomer having a similar oxidation potential is effective for obtaining nearly random copolymers with homogeneously distributed H-bonding sites. Furthermore, the higher [R] values of the SMePPS unit compared with the PPS unit partially resulted in different RI changing trends in the system. Taking this hypothesis into account, the synergistic effect of high [R] and H-bonds would lead to an RI enhancement in the case of copolymers composed of OHPPS and another PPS unit if the latter unit satisfies the following conditions: (1) a higher [R] value than the OHPPS unit (contributing to higher unit refractivity) and (2) an Eox value of the corresponding DPS monomer close to that of OMeDPS (affording random sequences). The preparation of OHPPS-incorporated PPS copolymers (OHPPSPPS copolymers, P2, etc.) possessing various sequences, which would be enabled by the development of a precisely controlled oxidative polymerization strategy, and investigation of their optical properties will be among the key objectives for our future work to expand this RI enhancement strategy.

Conclusion

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A series of ultrahigh-refractive-index PPS derivatives bearing both hydroxy and methylthio groups were synthesized by means of postpolymerization modification of the methyl-protected precursors. These copolymers exhibited higher RI values (up to nD = 1.85) than the corresponding homopolymers while maintaining adequate Abbe numbers (νD ∼ 20), owing to the synergistic effect of highly polarizable groups and densely incorporated robust H-bonds. This mechanism was also elucidated from a classical perspective using the Lorentz–Lorenz equation, revealing that the dual incorporation of methylthio and hydroxy groups enhanced the [R]/V values of the polymer on the macroscopic scale, leading to higher refractivity. Practically, these superior optical properties are notable among the previously reported polymers including other PPS derivatives (Figure S25). To the best of our knowledge, this copolymer system is the first example that enhances RI through the copolymerization of each component. This novel strategy is expected to be applicable to the design of not only PPS derivatives but also various other promising HRIP candidates to realize ultrahigh RI values with adequate Abbe numbers beyond the empirical nD–νD threshold.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acspolymersau.2c00030.

  • Synthetic and experimental procedures, data for oxidative polymerization and postpolymerization modification, additional thermal/optical properties, calculation details for the RI estimation (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Seigo Watanabe - Department of Applied Chemistry and Research Institute for Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, JapanOrcidhttps://orcid.org/0000-0002-0498-8330
    • Teru Takayama - Department of Applied Chemistry and Research Institute for Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
  • Author Contributions

    S.W., T.T., and K.O. conceived and designed the experiments. S.W. and T.T. performed the experiments and calculations. S.W. and K.O. wrote the manuscript. K.O. supervised the project. All authors analyzed the data, discussed on the results and the written manuscript, and have given approval to the final version of the manuscript. S.W. and T.T. contributed equally to this work.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was partially supported by Grants-in-Aid for Scientific Research (Nos. 18H05515 (K.O.), 21H04695 (K.O.), and 22J11820 (S.W.)) of MEXT, Japan. S.W. acknowledges the support by Waseda Research Institute for Science and Engineering, Grant-in-Aid for Young Scientists (Early Bird). A part of this work was supported by Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM) of MEXT and was also the result using research equipment (ECX-500, AVANCE III 600, JMS-GCMATE II, RINT-UltimaIII, and TG8120: Material Characterization Central Laboratory) shared in MEXT Project for promoting public utilization of advanced research infrastructure (program for supporting construction of core facilities) Grant No. JPMXS0440500021. The authors thank Dr. Kan Hatakeyama-Sato (Waseda Univ.) for assistance with DFT calculations.

References

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This article references 32 other publications.

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    Liu, J. G.; Ueda, M. High Refractive Index Polymers: Fundamental Research and Practical Applications. J. Mater. Chem. 2009, 19 (47), 89078919,  DOI: 10.1039/b909690f
  2. 2
    Higashihara, T.; Ueda, M. Recent Progress in High Refractive Index Polymers. Macromolecules 2015, 48 (7), 19151929,  DOI: 10.1021/ma502569r
  3. 3
    Kleine, T. S.; Glass, R. S.; Lichtenberger, D. L.; Mackay, M. E.; Char, K.; Norwood, R. A.; Pyun, J. 100th Anniversary of Macromolecular Science Viewpoint: High Refractive Index Polymers from Elemental Sulfur for Infrared Thermal Imaging and Optics. ACS Macro Lett. 2020, 9 (2), 245259,  DOI: 10.1021/acsmacrolett.9b00948
  4. 4
    Lee, T.; Dirlam, P. T.; Njardarson, J. T.; Glass, R. S.; Pyun, J. Polymerizations with Elemental Sulfur: From Petroleum Refining to Polymeric Materials. J. Am. Chem. Soc. 2022, 144 (1), 522,  DOI: 10.1021/jacs.1c09329
  5. 5
    Liu, J.-G.; Nakamura, Y.; Shibasaki, Y.; Ando, S.; Ueda, M. Synthesis and Characterization of Highly Refractive Polyimides from 4,4′-Thiobis[(p-Phenylenesulfanyl)Aniline] and Various Aromatic Tetracarboxylic Dianhydrides. J. Polym. Sci. Part A Polym. Chem. 2007, 45 (23), 56065617,  DOI: 10.1002/pola.22308
  6. 6
    Terraza, C. A.; Liu, J.-G.; Nakamura, Y.; Shibasaki, Y.; Ando, S.; Ueda, M. Synthesis and Properties of Highly Refractive Polyimides Derived from Fluorene-Bridged Sulfur-Containing Dianhydrides and Diamines. J. Polym. Sci. Part A Polym. Chem. 2008, 46 (4), 15101520,  DOI: 10.1002/pola.22492
  7. 7
    Nakagawa, Y.; Suzuki, Y.; Higashihara, T.; Ando, S.; Ueda, M. Synthesis of Highly Refractive Poly(Phenylene Thioether)s Containing a Binaphthyl or Diphenylfluorene Unit. Polym. Chem. 2012, 3 (9), 2531,  DOI: 10.1039/c2py20325a
  8. 8
    Nakano, K.; Tatsumi, G.; Nozaki, K. Synthesis of Sulfur-Rich Polymers: Copolymerization of Episulfide with Carbon Disulfide by Using [PPN]Cl/(Salph)Cr(III)Cl System. J. Am. Chem. Soc. 2007, 129 (49), 1511615117,  DOI: 10.1021/ja076056b
  9. 9
    You, N.-H.; Suzuki, Y.; Yorifuji, D.; Ando, S.; Ueda, M. Synthesis of High Refractive Index Polyimides Derived from 1,6-Bis(p-Aminophenylsulfanyl)-3,4,8,9-Tetrahydro-2,5,7,10-Tetrathiaanthracene and Aromatic Dianhydrides. Macromolecules 2008, 41 (17), 63616366,  DOI: 10.1021/ma800982x
  10. 10
    Fukuzaki, N.; Higashihara, T.; Ando, S.; Ueda, M. Synthesis and Characterization of Highly Refractive Polyimides Derived from Thiophene-Containing Aromatic Diamines and Aromatic Dianhydrides. Macromolecules 2010, 43 (4), 18361843,  DOI: 10.1021/ma902013y
  11. 11
    Fu, M.-C.; Murakami, Y.; Ueda, M.; Ando, S.; Higashihara, T. Synthesis and Characterization of Alkaline-Soluble Triazine-Based Poly(Phenylene Sulfide)s with High Refractive Index and Low Birefringence. J. Polym. Sci. Part A Polym. Chem. 2018, 56 (7), 724731,  DOI: 10.1002/pola.28945
  12. 12
    Wang, X.; Li, B.; Peng, J.; Wang, B.; Qin, A.; Tang, B. Z. Multicomponent Polymerization of Alkynes, Isocyanides, and Isocyanates toward Heterocyclic Polymers. Macromolecules 2021, 54 (14), 67536761,  DOI: 10.1021/acs.macromol.1c00556
  13. 13
    Fang, L.; Sun, J.; Chen, X.; Tao, Y.; Zhou, J.; Wang, C.; Fang, Q. Phosphorus- and Sulfur-Containing High-Refractive-Index Polymers with High Tg and Transparency Derived from a Bio-Based Aldehyde. Macromolecules 2020, 53 (1), 125131,  DOI: 10.1021/acs.macromol.9b01770
  14. 14
    Watanabe, S.; Takayama, T.; Nishio, H.; Matsushima, K.; Tanaka, Y.; Saito, S.; Sun, Y.; Oyaizu, K. Synthesis of Colorless and High-Refractive-Index Sulfoxide-Containing Polymers by the Oxidation of Poly(Phenylene Sulfide) Derivatives. Polym. Chem. 2022, 13 (12), 17051711,  DOI: 10.1039/D1PY01654G
  15. 15
    Suzuki, Y.; Murakami, K.; Ando, S.; Higashihara, T.; Ueda, M. Synthesis and Characterization of Thianthrene-Based Poly(Phenylene Sulfide)s with High Refractive Index over 1.8. J. Mater. Chem. 2011, 21 (39), 15727,  DOI: 10.1039/c1jm12402a
  16. 16
    Kotaki, T.; Nishimura, N.; Ozawa, M.; Fujimori, A.; Muraoka, H.; Ogawa, S.; Korenaga, T.; Suzuki, E.; Oishi, Y.; Shibasaki, Y. Synthesis of Highly Refractive and Highly Fluorescent Rigid Cyanuryl Polyimines with Polycyclic Aromatic Hydrocarbon Pendants. Polym. Chem. 2016, 7 (6), 12971308,  DOI: 10.1039/C5PY01920F
  17. 17
    Kim, H.; Ku, B.-C.; Goh, M.; Ko, H. C.; Ando, S.; You, N.-H. Synergistic Effect of Sulfur and Chalcogen Atoms on the Enhanced Refractive Indices of Polyimides in the Visible and Near-Infrared Regions. Macromolecules 2019, 52 (3), 827834,  DOI: 10.1021/acs.macromol.8b02139
  18. 18
    Gao, Q.; Xiong, L. H.; Han, T.; Qiu, Z.; He, X.; Sung, H. H. Y.; Kwok, R. T. K.; Williams, I. D.; Lam, J. W. Y.; Tang, B. Z. Three-Component Regio- And Stereoselective Polymerizations toward Functional Chalcogen-Rich Polymers with AIE-Activities. J. Am. Chem. Soc. 2019, 141 (37), 1471214719,  DOI: 10.1021/jacs.9b06493
  19. 19
    Wu, X.; He, J.; Hu, R.; Tang, B. Z. Room-Temperature Metal-Free Multicomponent Polymerizations of Elemental Selenium toward Stable Alicyclic Poly(Oxaselenolane)s with High Refractive Index. J. Am. Chem. Soc. 2021, 143 (38), 1572315731,  DOI: 10.1021/jacs.1c06732
  20. 20
    Griebel, J. J.; Namnabat, S.; Kim, E. T.; Himmelhuber, R.; Moronta, D. H.; Chung, W. J.; Simmonds, A. G.; Kim, K. J.; Van Der Laan, J.; Nguyen, N. A.; Dereniak, E. L.; MacKay, M. E.; Char, K.; Glass, R. S.; Norwood, R. A.; Pyun, J. New Infrared Transmitting Material via Inverse Vulcanization of Elemental Sulfur to Prepare High Refractive Index Polymers. Adv. Mater. 2014, 26 (19), 30143018,  DOI: 10.1002/adma.201305607
  21. 21
    Kleine, T. S.; Nguyen, N. A.; Anderson, L. E.; Namnabat, S.; Lavilla, E. A.; Showghi, S. A.; Dirlam, P. T.; Arrington, C. B.; Manchester, M. S.; Schwiegerling, J.; Glass, R. S.; Char, K.; Norwood, R. A.; Mackay, M. E.; Pyun, J. High Refractive Index Copolymers with Improved Thermomechanical Properties via the Inverse Vulcanization of Sulfur and 1,3,5-Triisopropenylbenzene. ACS Macro Lett. 2016, 5 (10), 11521156,  DOI: 10.1021/acsmacrolett.6b00602
  22. 22
    Kim, D. H.; Jang, W.; Choi, K.; Choi, J. S.; Pyun, J.; Lim, J.; Char, K.; Im, S. G. One-Step Vapor-Phase Synthesis of Transparent High Refractive Index Sulfur-Containing Polymers. Sci. Adv. 2020, 6 (28), eabb5320  DOI: 10.1126/sciadv.abb5320
  23. 23
    Jang, W.; Choi, K.; Choi, J. S.; Kim, D. H.; Char, K.; Lim, J.; Im, S. G. Transparent, Ultrahigh-Refractive Index Polymer Film (n ∼ 1.97) with Minimal Birefringence (Δn < 0.0010). ACS Appl. Mater. Interfaces 2021, 13 (51), 6162961637,  DOI: 10.1021/acsami.1c17398
  24. 24
    Watanabe, S.; Oyaizu, K. Designing Ultrahigh-Refractive-Index Amorphous Poly(Phenylene Sulfide)s Based on Dense Intermolecular Hydrogen-Bond Networks. Macromolecules 2022, 55 (6), 22522259,  DOI: 10.1021/acs.macromol.1c02412
  25. 25
    Yamamoto, K.; Tsuchida, E.; Nishide, H.; Jikei, M.; Oyaizu, K. Oxovanadium-Catalyzed Oxidative Polymerization of Diphenyl Disulfides with Oxygen. Macromolecules 1993, 26 (13), 34323437,  DOI: 10.1021/ma00065a029
  26. 26
    Yamamoto, K.; Jikei, M.; Katoh, J.; Nishide, H.; Tsuchida, E. Synthesis of Poly(Arylene Sulfide)s by Cationic Oxidative Polymerization of Diaryl Disulfides. Macromolecules 1992, 25 (10), 26982704,  DOI: 10.1021/ma00036a021
  27. 27
    Watanabe, S.; Oyaizu, K. Methoxy-Substituted Phenylenesulfide Polymer with Excellent Dispersivity of TiO2 Nanoparticles for Optical Application. Bull. Chem. Soc. Jpn. 2020, 93 (11), 12871292,  DOI: 10.1246/bcsj.20200170
  28. 28
    Otsuka, H.; Nagano, S.; Kobashi, Y.; Maeda, T.; Takahara, A. A Dynamic Covalent Polymer Driven by Disulfidemetathesis under Photoirradiation. Chem. Commun. 2010, 46 (7), 11501152,  DOI: 10.1039/B916128G
  29. 29
    Nakai, Y.; Takahashi, A.; Goseki, R.; Otsuka, H. Facile Modification and Fixation of Diaryl Disulphide-Containing Dynamic Covalent Polyesters by Iodine-Catalysed Insertion-like Addition Reactions of Styrene Derivatives to Disulphide Units. Polym. Chem. 2016, 7 (28), 46614666,  DOI: 10.1039/C6PY00963H
  30. 30
    Watanabe, S.; Oyaizu, K. Catechol End-Capped Poly(Arylene Sulfide) as a High-Refractive-Index “TiO2/ZrO2-Nanodispersible” Polymer. ACS Appl. Polym. Mater. 2021, 3 (9), 44954503,  DOI: 10.1021/acsapm.1c00536
  31. 31
    Sato, Y.; Sobu, S.; Nakabayashi, K.; Samitsu, S.; Mori, H. Highly Transparent Benzothiazole-Based Block and Random Copolymers with High Refractive Indices by RAFT Polymerization. ACS Appl. Polym. Mater. 2020, 2 (8), 32053214,  DOI: 10.1021/acsapm.0c00365
  32. 32
    Nambu, Y.; Yoshitake, Y.; Yanagi, S.; Mineyama, K.; Tsurui, K.; Kuwata, S.; Takata, T.; Nishikubo, T.; Ishikawa, K. Dinaphtho[2,1-b :1′,2′-d]Thiophenes as High Refractive Index Materials Exploiting the Potential Characteristics of “Dynamic Thiahelicenes.. J. Mater. Chem. C 2022, 10 (2), 726733,  DOI: 10.1039/D1TC03685H

Cited By

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This article is cited by 2 publications.

  1. Seigo Watanabe, Yoshino Tsunekawa, Teru Takayama, Kenichi Oyaizu. Diverse Side-Chain Transformation of High Refractive Index Methylthio-Substituted Poly(phenylene sulfide)s. Macromolecules 2024, 57 (6) , 2897-2904. https://doi.org/10.1021/acs.macromol.4c00054
  2. Seigo Watanabe, Hiromichi Nishio, Teru Takayama, Kenichi Oyaizu. Supramolecular Cross-Linking of Thiophenylene Polymers via Multiple Hydrogen Bonds toward High Refractive Index. ACS Applied Polymer Materials 2023, 5 (4) , 2307-2311. https://doi.org/10.1021/acsapm.3c00391
  • Abstract

    Figure 1

    Figure 1. Concept of this study. (a) Synthesis of SMePPS through oxidative polymerization. (b) Further RI enhancement strategy enabled by the copolymerization with the H-bonding scaffold OHPPS leading to higher [R]/V values.

    Figure 2

    Figure 2. Synthesis of SMePPS. (a) 1H NMR spectrum of SMePPS in chloroform-d. (b) IR spectra of SMeDPS and SMePPS. (c) (i) 13C and (ii) 13C-DEPT 135 NMR spectra of SMePPS in chloroform-d. (d) 1H–1H COSY spectrum of the sulfoxide-labeled SMePPS. The repeating structure was determined to be 2-methylthio-1,5-thiophenylene (structure circled by red square) owing to the correlation signals observed between the aromatic protons at the lowest field.

    Figure 3

    Figure 3. Optical properties of SMePPS. (a) UV–vis transmittance spectrum of an SMePPS thin film (inset: photograph of the film on a glass substrate). (b) Refractive index of SMePPS in the visible-light region. See Figure S6 for the detailed spectrum including extinction coefficient in the wider wavelength range.

    Figure 4

    Figure 4. Synthesis and properties of P2. (a) 1H NMR spectra of Me-P1 (run 2′) and P2 (run 2″) in DMSO-d6. (b) IR spectra of Me-P1 (run 2′) and P2 (run 2″). (c) UV–vis spectra of Me-P1 and P2 thin films (thickness was normalized to 1 μm). Inset: thin films of Me-P1 (run 2′) and P2 (run 2″). (d) Refractive indices of Me-P1 and P2.

    Figure 5

    Figure 5. RI changes for Me-P1, P2, and homopolymers depending on the methoxy/hydroxy content. Values for OMePPS (Me-P1 with x = 1.00) and OHPPS (P2 with x = 1.00) were referred from the previous reports (refs (27) and (24), respectively). (a) Relationship between composition ratio and experimental nD for Me-P1 (black squares) and P2 (red triangles) (before and after demethylation). (b) Experimental nD (line graph) and density (bar charts) for SMePPS, OHPPS, and P2. The error bars indicate the standard deviation of the density measurements (average of five times). (c) Estimated (blue open triangles) and experimental (red circles) nD values for SMePPS, OHPPS, and P2 at each composition ratio. The error bars indicate the standard deviation of the estimated RI values, which were in accordance with the deviation of the density measurements. (d) Schematic comparison of H-bond distribution, [R] values, and nD values for SMePPS, OHPPSPPS copolymer, (24) and P2. The blue and red circles represent high-[R] moieties and H-bonding moieties, respectively, and the dotted lines represent intermolecular H-bonds. The color depth of the blue circles represents the magnitude of the [R] values.

  • References

    ARTICLE SECTIONS
    Jump To

    This article references 32 other publications.

    1. 1
      Liu, J. G.; Ueda, M. High Refractive Index Polymers: Fundamental Research and Practical Applications. J. Mater. Chem. 2009, 19 (47), 89078919,  DOI: 10.1039/b909690f
    2. 2
      Higashihara, T.; Ueda, M. Recent Progress in High Refractive Index Polymers. Macromolecules 2015, 48 (7), 19151929,  DOI: 10.1021/ma502569r
    3. 3
      Kleine, T. S.; Glass, R. S.; Lichtenberger, D. L.; Mackay, M. E.; Char, K.; Norwood, R. A.; Pyun, J. 100th Anniversary of Macromolecular Science Viewpoint: High Refractive Index Polymers from Elemental Sulfur for Infrared Thermal Imaging and Optics. ACS Macro Lett. 2020, 9 (2), 245259,  DOI: 10.1021/acsmacrolett.9b00948
    4. 4
      Lee, T.; Dirlam, P. T.; Njardarson, J. T.; Glass, R. S.; Pyun, J. Polymerizations with Elemental Sulfur: From Petroleum Refining to Polymeric Materials. J. Am. Chem. Soc. 2022, 144 (1), 522,  DOI: 10.1021/jacs.1c09329
    5. 5
      Liu, J.-G.; Nakamura, Y.; Shibasaki, Y.; Ando, S.; Ueda, M. Synthesis and Characterization of Highly Refractive Polyimides from 4,4′-Thiobis[(p-Phenylenesulfanyl)Aniline] and Various Aromatic Tetracarboxylic Dianhydrides. J. Polym. Sci. Part A Polym. Chem. 2007, 45 (23), 56065617,  DOI: 10.1002/pola.22308
    6. 6
      Terraza, C. A.; Liu, J.-G.; Nakamura, Y.; Shibasaki, Y.; Ando, S.; Ueda, M. Synthesis and Properties of Highly Refractive Polyimides Derived from Fluorene-Bridged Sulfur-Containing Dianhydrides and Diamines. J. Polym. Sci. Part A Polym. Chem. 2008, 46 (4), 15101520,  DOI: 10.1002/pola.22492
    7. 7
      Nakagawa, Y.; Suzuki, Y.; Higashihara, T.; Ando, S.; Ueda, M. Synthesis of Highly Refractive Poly(Phenylene Thioether)s Containing a Binaphthyl or Diphenylfluorene Unit. Polym. Chem. 2012, 3 (9), 2531,  DOI: 10.1039/c2py20325a
    8. 8
      Nakano, K.; Tatsumi, G.; Nozaki, K. Synthesis of Sulfur-Rich Polymers: Copolymerization of Episulfide with Carbon Disulfide by Using [PPN]Cl/(Salph)Cr(III)Cl System. J. Am. Chem. Soc. 2007, 129 (49), 1511615117,  DOI: 10.1021/ja076056b
    9. 9
      You, N.-H.; Suzuki, Y.; Yorifuji, D.; Ando, S.; Ueda, M. Synthesis of High Refractive Index Polyimides Derived from 1,6-Bis(p-Aminophenylsulfanyl)-3,4,8,9-Tetrahydro-2,5,7,10-Tetrathiaanthracene and Aromatic Dianhydrides. Macromolecules 2008, 41 (17), 63616366,  DOI: 10.1021/ma800982x
    10. 10
      Fukuzaki, N.; Higashihara, T.; Ando, S.; Ueda, M. Synthesis and Characterization of Highly Refractive Polyimides Derived from Thiophene-Containing Aromatic Diamines and Aromatic Dianhydrides. Macromolecules 2010, 43 (4), 18361843,  DOI: 10.1021/ma902013y
    11. 11
      Fu, M.-C.; Murakami, Y.; Ueda, M.; Ando, S.; Higashihara, T. Synthesis and Characterization of Alkaline-Soluble Triazine-Based Poly(Phenylene Sulfide)s with High Refractive Index and Low Birefringence. J. Polym. Sci. Part A Polym. Chem. 2018, 56 (7), 724731,  DOI: 10.1002/pola.28945
    12. 12
      Wang, X.; Li, B.; Peng, J.; Wang, B.; Qin, A.; Tang, B. Z. Multicomponent Polymerization of Alkynes, Isocyanides, and Isocyanates toward Heterocyclic Polymers. Macromolecules 2021, 54 (14), 67536761,  DOI: 10.1021/acs.macromol.1c00556
    13. 13
      Fang, L.; Sun, J.; Chen, X.; Tao, Y.; Zhou, J.; Wang, C.; Fang, Q. Phosphorus- and Sulfur-Containing High-Refractive-Index Polymers with High Tg and Transparency Derived from a Bio-Based Aldehyde. Macromolecules 2020, 53 (1), 125131,  DOI: 10.1021/acs.macromol.9b01770
    14. 14
      Watanabe, S.; Takayama, T.; Nishio, H.; Matsushima, K.; Tanaka, Y.; Saito, S.; Sun, Y.; Oyaizu, K. Synthesis of Colorless and High-Refractive-Index Sulfoxide-Containing Polymers by the Oxidation of Poly(Phenylene Sulfide) Derivatives. Polym. Chem. 2022, 13 (12), 17051711,  DOI: 10.1039/D1PY01654G
    15. 15
      Suzuki, Y.; Murakami, K.; Ando, S.; Higashihara, T.; Ueda, M. Synthesis and Characterization of Thianthrene-Based Poly(Phenylene Sulfide)s with High Refractive Index over 1.8. J. Mater. Chem. 2011, 21 (39), 15727,  DOI: 10.1039/c1jm12402a
    16. 16
      Kotaki, T.; Nishimura, N.; Ozawa, M.; Fujimori, A.; Muraoka, H.; Ogawa, S.; Korenaga, T.; Suzuki, E.; Oishi, Y.; Shibasaki, Y. Synthesis of Highly Refractive and Highly Fluorescent Rigid Cyanuryl Polyimines with Polycyclic Aromatic Hydrocarbon Pendants. Polym. Chem. 2016, 7 (6), 12971308,  DOI: 10.1039/C5PY01920F
    17. 17
      Kim, H.; Ku, B.-C.; Goh, M.; Ko, H. C.; Ando, S.; You, N.-H. Synergistic Effect of Sulfur and Chalcogen Atoms on the Enhanced Refractive Indices of Polyimides in the Visible and Near-Infrared Regions. Macromolecules 2019, 52 (3), 827834,  DOI: 10.1021/acs.macromol.8b02139
    18. 18
      Gao, Q.; Xiong, L. H.; Han, T.; Qiu, Z.; He, X.; Sung, H. H. Y.; Kwok, R. T. K.; Williams, I. D.; Lam, J. W. Y.; Tang, B. Z. Three-Component Regio- And Stereoselective Polymerizations toward Functional Chalcogen-Rich Polymers with AIE-Activities. J. Am. Chem. Soc. 2019, 141 (37), 1471214719,  DOI: 10.1021/jacs.9b06493
    19. 19
      Wu, X.; He, J.; Hu, R.; Tang, B. Z. Room-Temperature Metal-Free Multicomponent Polymerizations of Elemental Selenium toward Stable Alicyclic Poly(Oxaselenolane)s with High Refractive Index. J. Am. Chem. Soc. 2021, 143 (38), 1572315731,  DOI: 10.1021/jacs.1c06732
    20. 20
      Griebel, J. J.; Namnabat, S.; Kim, E. T.; Himmelhuber, R.; Moronta, D. H.; Chung, W. J.; Simmonds, A. G.; Kim, K. J.; Van Der Laan, J.; Nguyen, N. A.; Dereniak, E. L.; MacKay, M. E.; Char, K.; Glass, R. S.; Norwood, R. A.; Pyun, J. New Infrared Transmitting Material via Inverse Vulcanization of Elemental Sulfur to Prepare High Refractive Index Polymers. Adv. Mater. 2014, 26 (19), 30143018,  DOI: 10.1002/adma.201305607
    21. 21
      Kleine, T. S.; Nguyen, N. A.; Anderson, L. E.; Namnabat, S.; Lavilla, E. A.; Showghi, S. A.; Dirlam, P. T.; Arrington, C. B.; Manchester, M. S.; Schwiegerling, J.; Glass, R. S.; Char, K.; Norwood, R. A.; Mackay, M. E.; Pyun, J. High Refractive Index Copolymers with Improved Thermomechanical Properties via the Inverse Vulcanization of Sulfur and 1,3,5-Triisopropenylbenzene. ACS Macro Lett. 2016, 5 (10), 11521156,  DOI: 10.1021/acsmacrolett.6b00602
    22. 22
      Kim, D. H.; Jang, W.; Choi, K.; Choi, J. S.; Pyun, J.; Lim, J.; Char, K.; Im, S. G. One-Step Vapor-Phase Synthesis of Transparent High Refractive Index Sulfur-Containing Polymers. Sci. Adv. 2020, 6 (28), eabb5320  DOI: 10.1126/sciadv.abb5320
    23. 23
      Jang, W.; Choi, K.; Choi, J. S.; Kim, D. H.; Char, K.; Lim, J.; Im, S. G. Transparent, Ultrahigh-Refractive Index Polymer Film (n ∼ 1.97) with Minimal Birefringence (Δn < 0.0010). ACS Appl. Mater. Interfaces 2021, 13 (51), 6162961637,  DOI: 10.1021/acsami.1c17398
    24. 24
      Watanabe, S.; Oyaizu, K. Designing Ultrahigh-Refractive-Index Amorphous Poly(Phenylene Sulfide)s Based on Dense Intermolecular Hydrogen-Bond Networks. Macromolecules 2022, 55 (6), 22522259,  DOI: 10.1021/acs.macromol.1c02412
    25. 25
      Yamamoto, K.; Tsuchida, E.; Nishide, H.; Jikei, M.; Oyaizu, K. Oxovanadium-Catalyzed Oxidative Polymerization of Diphenyl Disulfides with Oxygen. Macromolecules 1993, 26 (13), 34323437,  DOI: 10.1021/ma00065a029
    26. 26
      Yamamoto, K.; Jikei, M.; Katoh, J.; Nishide, H.; Tsuchida, E. Synthesis of Poly(Arylene Sulfide)s by Cationic Oxidative Polymerization of Diaryl Disulfides. Macromolecules 1992, 25 (10), 26982704,  DOI: 10.1021/ma00036a021
    27. 27
      Watanabe, S.; Oyaizu, K. Methoxy-Substituted Phenylenesulfide Polymer with Excellent Dispersivity of TiO2 Nanoparticles for Optical Application. Bull. Chem. Soc. Jpn. 2020, 93 (11), 12871292,  DOI: 10.1246/bcsj.20200170
    28. 28
      Otsuka, H.; Nagano, S.; Kobashi, Y.; Maeda, T.; Takahara, A. A Dynamic Covalent Polymer Driven by Disulfidemetathesis under Photoirradiation. Chem. Commun. 2010, 46 (7), 11501152,  DOI: 10.1039/B916128G
    29. 29
      Nakai, Y.; Takahashi, A.; Goseki, R.; Otsuka, H. Facile Modification and Fixation of Diaryl Disulphide-Containing Dynamic Covalent Polyesters by Iodine-Catalysed Insertion-like Addition Reactions of Styrene Derivatives to Disulphide Units. Polym. Chem. 2016, 7 (28), 46614666,  DOI: 10.1039/C6PY00963H
    30. 30
      Watanabe, S.; Oyaizu, K. Catechol End-Capped Poly(Arylene Sulfide) as a High-Refractive-Index “TiO2/ZrO2-Nanodispersible” Polymer. ACS Appl. Polym. Mater. 2021, 3 (9), 44954503,  DOI: 10.1021/acsapm.1c00536
    31. 31
      Sato, Y.; Sobu, S.; Nakabayashi, K.; Samitsu, S.; Mori, H. Highly Transparent Benzothiazole-Based Block and Random Copolymers with High Refractive Indices by RAFT Polymerization. ACS Appl. Polym. Mater. 2020, 2 (8), 32053214,  DOI: 10.1021/acsapm.0c00365
    32. 32
      Nambu, Y.; Yoshitake, Y.; Yanagi, S.; Mineyama, K.; Tsurui, K.; Kuwata, S.; Takata, T.; Nishikubo, T.; Ishikawa, K. Dinaphtho[2,1-b :1′,2′-d]Thiophenes as High Refractive Index Materials Exploiting the Potential Characteristics of “Dynamic Thiahelicenes.. J. Mater. Chem. C 2022, 10 (2), 726733,  DOI: 10.1039/D1TC03685H
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    • Synthetic and experimental procedures, data for oxidative polymerization and postpolymerization modification, additional thermal/optical properties, calculation details for the RI estimation (PDF)


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