Unusual Emission of Polystyrene-Based Alternating Copolymers Incorporating Aminobutyl Maleimide Fluorophore-Containing Polyhedral Oligomeric Silsesquioxane Nanoparticles

In this study, we synthesized an unusual 2-aminobutyl maleimide isobutyl polyhedral oligomeric silsesquioxane (MIPOSS-NHBu) monomer lacking conventional fluorescent groups. We then prepared poly(styrene-alt-2-aminobutyl maleimide isobutyl POSS) [poly(S-alt-MIPOSS-NHBu)] and poly(4-acetoxystyrene-alt-2-aminobutyl maleimide isobutyl POSS) [poly(AS-alt-MIPOSS-NHBu)] copolymers through facile free radical copolymerizations using azobisisobutyronitrile as the initiator and tetrahydrofuran as the solvent. A poly(4-hydroxystyrene-alt-2-aminobutyl maleimide isobutyl POSS) [poly(HS-alt-MIPOSS-NHBu)] copolymer was prepared through acetoxyl hydrazinolysis of poly(AS-alt-MIPOSS-NHBu). We employed 1H, 13C, and 29Si nuclear magnetic resonance spectroscopy; Fourier transform infrared spectroscopy; differential scanning calorimetry; and photoluminescence spectroscopy to investigate the structures and the thermal and optical properties of the monomers and novel POSS-containing alternating copolymers. Intramolecular hydrogen bonding between the amino and dihydrofuran-2,5-dione group and clustering of the locked C=O groups from the POSS nanoparticles in the MIPOSS-NHBu units restricted the intramolecular motion of the polymer chain, causing it to exhibit strong light emission. As a result, the MIPOSS-NHBu monomer and the poly(AS-alt-MIPOSS-NHBu) copolymer both have potential applicability in the detection of metal ions with good selectivity.


Introduction
In recent years, fluorescent materials and polymers have attracted much attention in academic and industrial fields for their potential applications in optoelectronic devices, organic light emitting diodes, bio-imaging, chemical sensors, biosensors, drug delivery, DNA probing, and protein sensors [1][2][3][4][5][6][7][8][9][10][11]. Most fluorescent organic molecules exhibit a strong emission in dilute solution, but become non-luminescent or weakly emissive in their condensed or aggregated state, a phenomenon known as aggregation-caused quenching [12][13][14][15]. Therefore, synthesized organic luminescent Subsequently, we prepared a poly(HS-alt-MIPOSS-NHBu) alternating copolymer through acetoxyl hydrazinolysis of poly(AS-alt-MIPOSS-NHBu) in the presence of hydrazine monohydrate in 1,4-dioxane at room temperature (Scheme 2). We used 1 H-, 13 C-, and 29 Si-NMR spectroscopy and Fourier transform infrared (FTIR) spectroscopy to confirm the structures of the monomers and polymers. Furthermore, we used differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to examine the glass transition temperatures, thermal degradation temperatures, and char yields of the POSS-containing alternating copolymers. In addition, we used wide-angle X-ray diffraction (WAXD) and photoluminescence (PL) spectroscopy to determine the crystallinity and optical properties of these monomers and POSS-containing alternating polymers. PL spectroscopy also revealed the potential applications of MIPOSS-NHBu and poly(AS-alt-MIPOSS-NHBu) as sensors for metal ions in solution.
Subsequently, we prepared a poly(HS-alt-MIPOSS-NHBu) alternating copolymer through acetoxyl hydrazinolysis of poly(AS-alt-MIPOSS-NHBu) in the presence of hydrazine monohydrate in 1,4-dioxane at room temperature (Scheme 2). We used 1 H-, 13 C-, and 29 Si-NMR spectroscopy and Fourier transform infrared (FTIR) spectroscopy to confirm the structures of the monomers and polymers. Furthermore, we used differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to examine the glass transition temperatures, thermal degradation temperatures, and char yields of the POSS-containing alternating copolymers. In addition, we used wide-angle X-ray diffraction (WAXD) and photoluminescence (PL) spectroscopy to determine the crystallinity and optical properties of these monomers and POSS-containing alternating polymers. PL spectroscopy also revealed the potential applications of MIPOSS-NHBu and poly(AS-alt-MIPOSS-NHBu) as sensors for metal ions in solution.
2,3-Dibromosuccinimide Isobutyl POSS (MIPOSS-2Br) [57]. Br 2 solution (0.65 g, 4.01 mmol) diluted in CHCl 3 (5 mL) was added dropwise to a solution of maleimide isobutyl POSS (MIPOSS; 3.00 g, 3.15 mmol) in dry CHCl 3 (20 mL) in an ice-bath under a N 2 atmosphere. The mixture was then stirred for 24 h at room temperature. The solvent was evaporated under vacuum and the solid residue was extracted with DCM three times. The product was purified through column chromatography [SiO 2 ; hexane/EA, 1:1 (v/v)] to obtain a white powder. 1 [57]. Et 3 N (0.150 g, 1.43 mmol) was added dropwise over 20 min to a solution of MIPOSS-2Br (1.50 g, 1.35 mmol) in dry THF (20 mL) in an ice bath under a N 2 atmosphere. The mixture was then stirred for 72 h. The precipitate was filtered off and the solution concentrated (rotary evaporator) to afford a yellow solid. The crude product was purified through column chromatography (hexane:EA, 1:1) to obtain a yellow powder. 1  2-(Butylamino)-Maleimide Isobutyl POSS (MIPOSS-NHBu). n-Butylamine (0.037 g, 0.50 mmol) was added to a solution of MIPOSS-Br (0.500 g, 0.484 mmol) in dry THF (20 mL) in an ice bath and then the mixture was stirred for 10 min. Et 3 N (0.052 g, 0.51 mmol) was added dropwise to the cooled reaction mixture (ice bath) and then the mixture was stirred for 24 h at room temperature. The solvent was evaporated under vacuum and the solid residue was extracted three times in with DCM (40 mL), water (20 mL), and aqueous NaCl (30 mL) and then dried over MgSO 4 . The crude mixture was purified through column chromatography (SiO 2 ; hexane/EA, 1:1) to yield a yellow powder. 1 Table 1 summarizes the number-average molecular weight (M n ), the molecular weight distribution, and the thermal properties of these alternating copolymers.

Characterization
1 H-and 13 C-NMR spectra were recorded using an INOVA 500 spectrometer (McKinley Scientific, Sparta, NJ, USA), CDCl 3 as the solvent, and tetramethylsilane (TMS) as the internal reference. A Bruker Tensor-27 FTIR spectrometer (Billerica, MA, USA) was used to quantitatively characterize the chemical structures of the alternating copolymers, which were cast from THF solutions onto KBr crystal plates. The spectra were collected from 32 scans at a resolution of 4 cm −1 at room temperature. The molecular weights and polydispersities of the synthesized alternating copolymers were determined using a Waters 510 gel permeation chromatography (GPC, Waters, Taipei, Taiwan) system equipped with a refractive index detector and three Ultrastyragel columns (100, 500, and 1000 Å) connected in series. DMF was the eluent, at a flow rate of 1 mL/min, at 40 • C. DSC measurements were performed using a TA Q-20 system (TA Instrument, New Castle, DE, USA), under N 2 as a purge gas (50 mL/min), and at a heating rate of 20 • C/min. The sample (ca. 5-7 mg) was placed in a sealed aluminum sample pan. The thermal stabilities of the homopolymers and alternating copolymers were investigated using a TA Q-50 thermogravimetric analyzer (TA Instrument, New Castle, DE, USA), under N 2 as a purge gas (60 mL/min), and at a heating rate of 20 • C/min from 30 to 800 • C. UV-vis spectra were recorded using a Shimadzu mini 1240 spectrophotometer (Shimadzu, Taipei, Taiwan). PL spectra were recorded at room temperature using a monochromatized Xe light source, solutions of polymers in THF at a concentration of 10 −4 M, and an excitation wavelength of 330 nm. The quantum efficiencies (Φ f ) in solution and in the solid state were measured using an integrated sphere (Ocean Optics). WAXD profiles were measured using the wiggler beamline BL17A1 of the National Synchrotron Radiation Research Center (NSRRC) of Hsinchu, Taiwan. A triangular bent Si (111) single crystal was used to obtain a monochromated beam having a wavelength (λ) of 1.32 Å. The samples were annealed prior to WAXD measurements.

Synthesis of MIPOSS-2Br, MIPOSS-Br, and MIPOSS-NHBu
In this study, observed unusually strong emissions from polymers containing butylamine maleimide isobutyl POSS NPs in the solid state and in solution and also investigated their application as metal ion sensors. First, we prepared MIPOSS-2Br through the reaction of MIPOSS with Br 2 in dry CHCl 3 at room temperature (Scheme 1b). A subsequent elimination reaction of MIPOSS-2Br with Et 3 N in dry THF afforded MIPOSS-Br (Scheme 1c), thereafter used as a raw material for the high-yield synthesis of MIPOSS-NHBu (Scheme 1d). The chemical structures of all of the monomers synthesized in this study were confirmed using 1 H-and 13 C-NMR and FTIR spectroscopies. Figure 1 displays the 1 H-NMR spectra of MIPOSS-Br and MIPOSS-NHBu in CDCl 3 . The characteristic resonance of the CH=C units appeared as a signal at 6.69 ppm for both MIPOSS-Br and MIPOSS-NHBu. The signal at 3.54 ppm corresponded to the two protons of the NCH 2 CH 2 unit, while the signal at 0.87 ppm corresponded to the two protons of the SiCH 2 CH 2 CH 2 linkage between the maleimide ring and the POSS core. We assign the signals at 3.95 and 1.28 ppm to the NHCH 2 CH 2 and NHCH 2 CH 2 units, respectively, of MIPOSS-NHBu ( Figure 1b). Figure 2 presents the 13 C-NMR spectra of MIPOSS-Br and MIPOSS-NHBu. The signal for the maleimide C=O groups appeared at 169.03 and 166.72 ppm. For all of the maleimide isobutyl POSS monomers, the signals of the CH=C group were centered at 132.25 and 134.67 ppm, while those at 46.07 and 9.46 ppm represented the resonances of the SiCH 2 CH 2 CH 2 N methylene unit and the SiCH 2 CH(CH 3 ) 2 methine unit, respectively, of the POSS core. The significant downfield shift for the signal of the CH=C group from 134.67 ppm MIPOSS-Br to 149.79 ppm for MIPOSS-NHBu confirmed the success of the substitution reaction. Figure 3 presents the FTIR spectra of MIPOSS, MIPOSS-Br, and MIPOSS-NHBu. The characteristic absorption bands of the POSS core and the maleimide ring appeared at 2956-2878 cm −1 (aliphatic CH stretching); 1768 and 1714 cm −1 (asymmetric and symmetric imide C=O stretching); 1636 cm −1 (C=C stretching); 1238 cm −1 (C-N bending); and 1110 cm −1 (Si-O-Si stretching of POSS core); with a signal at 3445 cm −1 for N-H stretching of MIPOSS-NHBu appearing in Figure 3c. The NMR and FTIR spectra data indicated that we had successfully incorporated the alkyl chain in the maleimide isobutyl POSS NP unit.

Synthesis of MIPOSS-2Br, MIPOSS-Br, and MIPOSS-NHBu
In this study, observed unusually strong emissions from polymers containing butylamine maleimide isobutyl POSS NPs in the solid state and in solution and also investigated their application as metal ion sensors. First, we prepared MIPOSS-2Br through the reaction of MIPOSS with Br2 in dry CHCl3 at room temperature (Scheme 1b). A subsequent elimination reaction of MIPOSS-2Br with Et3N in dry THF afforded MIPOSS-Br (Scheme 1c), thereafter used as a raw material for the highyield synthesis of MIPOSS-NHBu (Scheme 1d). The chemical structures of all of the monomers synthesized in this study were confirmed using 1 H-and 13 C-NMR and FTIR spectroscopies.
Polymers 2017, 9, 103 9 of 20 9.01 ppm corresponding to the C=O groups, aromatic moieties, SiCH2CH2CH2N methylene units, and SiCH2CH(CH3)2 methine units, respectively. In Figure 5d, the signal from the aromatic rings at 155.87 (PhOH, peak u) had shifted from 149.3 (Ph-OCOCH3) and 115.60 ppm (peak t) in Figure 5c; the absence of the signal for the Ph-OCOCH3 group at 31.20 ppm confirmed the successful hydrolysis of poly(HS-alt-MIPOSS-NHBu). Other peak assignment was also summarized in Scheme 2. We also recorded 29 Si-NMR spectra of poly(S-alt-MIPOSS-Br), poly(S-alt-MIPOSS-NHBu), poly(AS-alt-MIPOSS-NHBu), and poly(HS-alt-MIPOSS-NHBu) to confirm the presence of their POSS cores and that no cage cleavage had occurred during the free radical copolymerizations of these alternating copolymers ( Figure 6). Indeed, the 29 Si-NMR spectra revealed signals at −54.03 (peak a) and −54.25 (peak b) ppm representing their OSiCH2CH2CH2N and OSiCH2CH(CH3)2 units, respectively.  Figure S3 displays the FTIR spectra of these alternating copolymers. Typical characteristic absorption bands for isobutyl CH stretching and Si-O-Si stretching of the maleimide isobutyl POSS structure in alternating copolymers appeared at 2920-2847 and 1105 cm −1 , respectively, with the signal for the C=C bond at 1634 cm −1 disappearing, consistent with the occurrence of free radical copolymerization. The spectrum of poly(AS-alt-MIPOSS-NHBu) ( Figure S3c) features a typical absorption band at 1768 cm −1 for C=O stretching of the acetyl groups in the AS units. This signal was absent in the spectrum of poly(HS-alt-MIPOSS-NHBu) ( Figure S3d); instead, it displayed an absorption band at 3312 cm −1 for OH stretching in the HS units, confirming the successful hydrolysis of poly(HS-alt-MIPOSS-NHBu). The GPC profiles ( Figure S4) of these new alternating copolymers displayed unimodal curves which were prepared via free radical polymerization process; Table 1 summarizes the data obtained for these alternating copolymers.  Figure S3 displays the FTIR spectra of these alternating copolymers. Typical characteristic absorption bands for isobutyl CH stretching and Si-O-Si stretching of the maleimide isobutyl POSS structure in alternating copolymers appeared at 2920-2847 and 1105 cm −1 , respectively, with the signal for the C=C bond at 1634 cm −1 disappearing, consistent with the occurrence of free radical copolymerization. The spectrum of poly(AS-alt-MIPOSS-NHBu) ( Figure S3c) features a typical absorption band at 1768 cm −1 for C=O stretching of the acetyl groups in the AS units. This signal was absent in the spectrum of poly(HS-alt-MIPOSS-NHBu) ( Figure S3d); instead, it displayed an absorption band at 3312 cm −1 for OH stretching in the HS units, confirming the successful hydrolysis of poly(HS-alt-MIPOSS-NHBu). The GPC profiles ( Figure S4) of these new alternating copolymers displayed unimodal curves which were prepared via free radical polymerization process; Table 1 summarizes the data obtained for these alternating copolymers.

Thermal Properties of Monomers and Alternating Copolymers
We employed DSC under a N2 atmosphere to investigate the thermal properties of the monomers and alternating copolymers. Figure S5

Thermal Properties of Monomers and Alternating Copolymers
We employed DSC under a N 2 atmosphere to investigate the thermal properties of the monomers and alternating copolymers. Figure S5   We used TGA under a N2 atmosphere to determine the decomposition temperatures and char yields of these alternating copolymers ( Figure S6). The degradation temperatures and char yields of poly(S-alt-MIPOSS-Br) and poly(S-alt-MIPOSS-NHBu) were higher than those of the standard PS homopolymer (337 °C and 0%, respectively) because of the steric bulk of the rigid-cage MIPOSS units and the readier pyrolysis of the PS main chain [51,52]. The degradation temperature and char yield of alkylamine-functionalized poly(S-alt-MIPOSS-NHBu) (355 °C and 6.9%, respectively) were lower than those of the bromine-functionalized poly(S-alt-MIPOSS-Br) (364 °C and 12.2%, respectively); this behavior was expected because an alkyl chain possesses thermal stability lower than that of a bromide group. To examine the crystalline properties of the synthesized maleimide POSS derivatives and the amorphous characteristics of the alternating copolymers, we performed WAXD analyses at room temperature ( Figure 8). The WAXD spectrum in Figure 8a (Figure 8b-d). The spectra of all the alternating copolymers exhibited two major sharp diffraction peaks at values of 2θ of 4.85° and 9.6°, representing d-spacing of 1.59 and 0.80 nm, respectively [55]; the first peak is consistent with the average distance between the POSS cages in the MIPOSS segment, while the other is due to the average distance between the maleimide groups of the MI-POSS segments [55]. The formed d-spacing is larger than that found for the pure PMAPOSS segment (d = 1.0 and 0.49 nm) [58], presumably because the functional NHBu groups on the main chain and inserted styrene-based segments into the MIPOSS-NHBu units expanded the d-spacing of these alternating copolymers, as displayed in inset scheme of Figure 8. Herein, we also observed that the full-width at half maximum of these two peaks did not change, indicating that the particle size of POSS did not change after incorporation after introduction of S, AS, and HS units into MIPOSS-NHBu segment. Thus, the maleimide monomer and the alternating copolymers possessed crystalline and amorphous structures, respectively, consistent with the results of the DSC analyses in Figure 7. We used TGA under a N 2 atmosphere to determine the decomposition temperatures and char yields of these alternating copolymers ( Figure S6). The degradation temperatures and char yields of poly(S-alt-MIPOSS-Br) and poly(S-alt-MIPOSS-NHBu) were higher than those of the standard PS homopolymer (337 • C and 0%, respectively) because of the steric bulk of the rigid-cage MIPOSS units and the readier pyrolysis of the PS main chain [51,52]. The degradation temperature and char yield of alkylamine-functionalized poly(S-alt-MIPOSS-NHBu) (355 • C and 6.9%, respectively) were lower than those of the bromine-functionalized poly(S-alt-MIPOSS-Br) (364 • C and 12.2%, respectively); this behavior was expected because an alkyl chain possesses thermal stability lower than that of a bromide group. To examine the crystalline properties of the synthesized maleimide POSS derivatives and the amorphous characteristics of the alternating copolymers, we performed WAXD analyses at room temperature ( Figure 8). The WAXD spectrum in Figure 8a (Figure 8b-d). The spectra of all the alternating copolymers exhibited two major sharp diffraction peaks at values of 2θ of 4.85 • and 9.6 • , representing d-spacing of 1.59 and 0.80 nm, respectively [55]; the first peak is consistent with the average distance between the POSS cages in the MIPOSS segment, while the other is due to the average distance between the maleimide groups of the MI-POSS segments [55]. The formed d-spacing is larger than that found for the pure PMAPOSS segment (d = 1.0 and 0.49 nm) [58], presumably because the functional NHBu groups on the main chain and inserted styrene-based segments into the MIPOSS-NHBu units expanded the d-spacing of these alternating copolymers, as displayed in inset scheme of Figure 8. Herein, we also observed that the full-width at half maximum of these two peaks did not change, indicating that the particle size of POSS did not change after incorporation after introduction of S, AS, and HS units into MIPOSS-NHBu segment. Thus, the maleimide monomer and the alternating copolymers possessed crystalline and amorphous structures, respectively, consistent with the results of the DSC analyses in Figure 7.

Optical Properties
Next, we studied the relationship between the molecular structure and photophysical properties in solid state and solution state for the series of maleimide and succinimide isobutyl POSS derivatives containing 2-butylamino units. Figure S8 shows the UV-vis spectra of MIPOSS, MIPOSS-2Br, MIPOSS-Br and MIPOSS-NHBu in dichloromethane solution (10 −4 M). These monomers exhibited absorptions peaks at 234, 235, 245 and 236 nm, respectively which can be attributed to a π-π* transitions. Figure 9 displays the PL spectra of maleimide and succinimide isobutyl POSS in the solid state. Interestingly, MIPOSS-NHBu display an unusual fluorescence, with a strong emission peak near 506.6 nm, resulting from the spatial separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), based on density functional theory calculations as reported in previous literature [34]. In contrast, MIPOSS-2Br and MIPOSS-Br did not show any emission peak, presumably because of the internal heavy atom effects of their bromine atoms. Figure S10  These alternating copolymers showed absorption peaks at 259, 258, 257 and 243, 264 nm, respectively which can be due to a π-π* and n-π* transitions.

Optical Properties
Next, we studied the relationship between the molecular structure and photophysical properties in solid state and solution state for the series of maleimide and succinimide isobutyl POSS derivatives containing 2-butylamino units. Figure S8 shows the UV-vis spectra of MIPOSS, MIPOSS-2Br, MIPOSS-Br and MIPOSS-NHBu in dichloromethane solution (10 −4 M). These monomers exhibited absorptions peaks at 234, 235, 245 and 236 nm, respectively which can be attributed to a π-π* transitions. Figure 9 displays the PL spectra of maleimide and succinimide isobutyl POSS in the solid state. Interestingly, MIPOSS-NHBu display an unusual fluorescence, with a strong emission peak near 506.6 nm, resulting from the spatial separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), based on density functional theory calculations as reported in previous literature [34]. In contrast, MIPOSS-2Br and MIPOSS-Br did not show any emission peak, presumably because of the internal heavy atom effects of their bromine atoms. Figure S10  These alternating copolymers showed absorption peaks at 259, 258, 257 and 243, 264 nm, respectively which can be due to a π-π* and n-π* transitions. in the solid state, relative to those of the other alternating copolymers, was presumably caused by: (i) strong dipole-dipole interactions between AS···AS and MIPOSS···MIPOSS units; and (ii) strong intermolecular hydrogen bonding between the NH groups from the MIPOSS-NHBu segments and the C=O groups from the AS segments; together, these effects hindered the free rotation of the copolymer chains about the C-C single bonds and, thereby, enhanced the emission of poly(AS-alt-MIPOSS-NHBu).             The PL intensities of poly(S-alt-MIPOSS-NHBu) and poly(AS-alt-MIPOSS-NHBu) increased upon increasing the H2O content from 40% to 50%. We assign the decreases in the emission intensities of MIPOSS-NHBu, poly(S-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) to the high polarity of H2O; this behavior generally occurs in donor-acceptor luminogens. Therefore, MIPOSS-NHBu, poly(S-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) displayed weak AIEE activity in solution. We also measured the quantum efficiencies (Фf) of maleimide, succinimide isobutyl POSS, and the novel alternating copolymers in the solid state and in solution; Table S1 summarizes the values. Furthermore, we used dynamic light scattering (DLS) to measure the sizes of the particles of MIPOSS-NHBu, poly(S-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) in the THF/H2O mixtures (Figures S12 and S13). Upon increasing the H2O content from 40% to 50% to 60%, the sizes The PL intensities of poly(S-alt-MIPOSS-NHBu) and poly(AS-alt-MIPOSS-NHBu) increased upon increasing the H 2 O content from 40% to 50%. We assign the decreases in the emission intensities of MIPOSS-NHBu, poly(S-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) to the high polarity of H 2 O; this behavior generally occurs in donor-acceptor luminogens. Therefore, MIPOSS-NHBu, poly(S-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) displayed weak AIEE activity in solution. We also measured the quantum efficiencies (Φ f ) of maleimide, succinimide isobutyl POSS, and the novel alternating copolymers in the solid state and in solution; Table S1 summarizes the values. Furthermore, we used dynamic light scattering (DLS) to measure the sizes of the particles of MIPOSS-NHBu, poly(S-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) in the THF/H 2 O mixtures ( Figures S12 and S13). Upon increasing the H 2 O content from 40% to 50% to 60%, the sizes of nanoaggregate structures formed from MIPOSS-NHBu decreased from 273 to 161 to 57 nm ( Figure S12). Upon increasing the H 2 O content from 40, 50, 60 and 80, the sizes of NPs for poly(S-alt-MIPOSS-NHBu) were 886, 423, 303 and 187 nm, respectively, while for poly(AS-alt-MIPOSS-NHBu) they were 1102, 808, 724 and 255 nm, respectively ( Figure 13).

Fluorescence Responses of MIPOSS-NHBu and Poly(AS-alt-MIPOSS-NHBu) toward Metal Ions
We examined the selectivity response of solutions of MIPOSS-NHBu and poly(AS-alt-MIPOSS-NHBu) in THF (10 −3 M) to five different metal cations: Zn 2+ , Fe 3+ , Cu 2+ , Al 3+ , and In 3+ . For MIPOSS-NHBu, the PL emission intensity decreased slightly upon the addition Zn 2+ , Al 3+ , and In 3+ , relative to the original state, but it decreased significantly upon the addition of Fe 3+ and Cu 2+ (Figure 14). Poly(AS-alt-MIPOSS-NHBu) ( Figure 15) exhibited similar phenomena, presumably because of the formation of strong Fe 3+ and Cu 2+ complexes with the C=O groups in the imide units and with the NH groups, through metal-ligand interactions.

Conclusions
We have synthesized the monomer MIPOSS-NHBu and the alternating copolymers poly(S-alt-MIPOSS-NHBu), poly(AS-alt-MIPOSS-NHBu), and poly(AS-alt-MIPOSS-NHBu) through free radical copolymerizations, with their structures confirmed using NMR and FTIR spectroscopy. Thermal analyses revealed that the thermal stabilities and char yields of the POSS-containing alternating copolymers improved after incorporating the inorganic MIPOSS units. WAXD analyses indicated that these POSS-containing alternating polymers were amorphous. Because of intramolecular hydrogen bonding between the amino and dihydrofuran-2,5-dione groups and the clustering of locked C=O groups from the POSS NPs of the MIPOSS-NHBu units, the intramolecular motion of the polymer chain was restricted, thereby resulting in stronger light emission than that from the MIPOSS unit. These novel luminescent copolymers displayed good selectivity responses for the detection of metal ions.