Synthesis and properties of a second‐order nonlinear optical side‐chain polyimide

A thermal stable aromatic polyimide (PI) with side‐chain second‐order nonlinear optical (NLO) chromophores has been developed. The PI was prepared by the ring‐opening polyaddition of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride with a new diamine having two N‐ethyl‐N‐[4‐[(6‐chlorobenzothiazol‐2‐yl)diazenyl]phenyl]‐2‐aminoethanol units as the NLO chromophore, followed by poling during or after the thermal imidization process. The resulting PI had number and weight‐average molecular weights (M_n, M_w) of 25,000 and 80,000, respectively, and a relatively high glass transition temperature of 180°C. The second harmonic coefficient (d₃₃) of PI at the wavelength of 1.064 μm was 138 pm/V (329.6 × 10⁻⁹ esu) and remained unchanged at elevated temperatures. The corona poling process of the NLO‐substituted poly(amic acid) to the PI was also studied in detail by measuring the second harmonic generation (SHG) from the polymer films. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1321–1329, 1999     

Synthesis of comb‐like polystyrene with poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as macroinitiator

The copolymerization of N‐phenyl maleimide and p‐chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′‐bipyridine, well‐defined comb‐like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006     

Synthesis and polymerization of N‐(4‐tetrahydropyranyl‐oxyphenyl)maleimide

N‐(4‐Tetrahydropyranyl‐oxy‐phenyl)maleimide (THPMI) was prepared and polymerized by radical or anionic initiators. THPMI could be polymerized by 2,2′‐azobis(isobutyronitrile) (AIBN) and potassium tert‐butoxide. Radical polymers (poly(THPMI)r) were obtained in 15–50% yields for AIBN in THF at 65°C after 2–5 h. The yield of anionic polymers (poly(THPMI)a) obtained from potassium tert‐butoxide in THF at 0°C after 20 h was 91%. The molecular weights of poly(THPMI)r and poly(THPMI)a were M_n = 2750–3300 (M_w/M_n = 1.2–3.3) and M_n = 11300 (M_w/M_n = 6.0), respectively. The difference in molecular weights of the polymers was due to the differences in the termination mechanism of polymerization and the solubility of these polymers in THF. The thermal decomposition temperatures were 205 and 365°C. The first decomposition step was based on elimination of the tetrahydropyranyl group from the poly(THPMI). Positive image patterns were obtained by chemical amplification of positive photoresist composed of poly(THPMI) and 4‐morpholinophenyl diazonium trifluoromethanesulfonate used as an acid generator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 341–347, 1999     

Preparation and phase behavior of side‐chain cholesteric liquid‐crystalline elastomers

A series of new side‐chain cholesteric elastomers derived from cholesteryl 4‐(10‐undecylen‐1‐yloxy)‐4′‐ethoxybenzoate and phenyl 4,4′‐bis(10‐undecylen‐1‐yloxybenzoyloxy‐p‐ethoxybenzoate) was synthesized. The chemical structures of the monomers were confirmed by elemental analyses, Fourier transform infrared, and ¹H NMR and ¹³C NMR spectra. The mesomorphic properties of elastomers were investigated with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the content of the crosslinking unit on the phase behavior of the elastomers was examined. Monomer M₁ showed a cholesteric phase, and M₂ displayed smectic and nematic phases. The elastomers containing <15 mol % of the crosslinking units revealed reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3315–3323, 2005     

Synthesis and characterization of indenofluorene‐based copolymers containing 2,5‐bis(2‐thienyl)‐N‐arylpyrrole for bulk heterojunction solar cells and polymer light‐emitting diodes

Two novel alternating π‐conjugated copolymers, poly[2,8‐(6,6′,12,12′‐tetraoctyl‐6,12‐dihydroindeno‐[1,2b]fluorene‐ alt‐5(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole) ( P1 ) and poly[2,8‐(6,6′,12,12′‐tetraoctyl‐6,12‐dihydroindeno‐[1,2b]fluorene‐ alt‐5(1‐(p‐octylphenyl)‐2,5‐di(2‐thienyl)pyrrole) ( P2 ), were synthesized via the Suzuki coupling method and their optoelectronic properties were investigated. The resulting polymers P1 and P2 were completely soluble in various common organic solvents and their weight‐average molecular weights (M_w) were 5.66 × 10⁴ (polydispersity: 1.97) and 2.13× 10⁴ (polydispersity: 1.54), respectively. Bulk heterojunction (BHJ) solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM(1:5)/TiO_x/Al configurations. The BHJ solar cell with P1 :PC₇₀BM (1:5) has a power conversion efficiency (PCE) of 1.12% (J_sc= 3.39 mA/cm², V_oc= 0.67 V, FF = 49.31%), measured using AM 1.5 G solar simulator at 100 mW/cm² light illumination. We fabricated polymer light‐emitting diodes (PLEDs) in ITO/PEDOT:PSS/emitting polymer:polyethylene glycol (PEG)/Ba/Al configurations. The electroluminescence (EL) maxima of the fabricated PLEDs varied from 526 nm to 556 nm depending on the ratio of the polymer to PEG. The turn‐on voltages of the PLEDs were in the range of 3–8 V depending on the ratio of the polymer to PEG, and the maximum brightness and luminance efficiency were 2103 cd/m² and 0.37 cd/A at 12 V, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3169–3177, 2010     

Synthesis and characterization of thiazolothiazole‐based polymers and their applications in polymer solar cells

A novel series of thiazolothiazole (Tz)‐based copolymers, poly[9,9‐didecylfluorene‐2,7‐diyl‐alt‐2,5‐bis‐(3‐hexylthiophene‐2‐yl)thiazolo[5,4‐d]thiazole] (P1), poly[9,9‐dioctyldibenzosilole‐2,7‐diyl‐alt‐2,5‐bis‐(3‐hexylthiophene‐2‐yl)thiazolo[5,4‐d]thiazole] (P2), and poly[4,4′‐bis(2‐ethylhexyl)‐dithieno[3,2‐b:2′,3′‐d]silole‐alt‐2,5‐bis‐(3‐hexylthiophene‐2‐yl)thiazolo[5,4‐d]thiazole] (P3), were synthesized for the use as donor materials in polymer solar cells (PSCs). The field‐effect carrier mobilities and the optical, electrochemical, and photovoltaic properties of the copolymers were investigated. The results suggest that the donor units in the copolymers significantly influenced the band gap, electronic energy levels, carrier mobilities, and photovoltaic properties of the copolymers. The band gaps of the copolymers were in the range of 1.80–2.14 eV. Under optimized conditions, the Tz‐based polymers showed power conversion efficiencies (PCEs) for the PSCs in the range of 2.23–2.75% under AM 1.5 illumination (100 mW/cm²). Among the three copolymers, P1, which contained a fluorene donor unit, showed a PCE of 2.75% with a short‐circuit current of 8.12 mA/cm², open circuit voltage of 0.86 V, and a fill factor (FF) of 0.39, under AM 1.5 illumination (100 mW/cm²). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Nonlinear optical (NLO) polymers. IV. Second‐order optical nonlinearity of NLO polyurea and copolyurea with NLO dipole moments aligned transverse to the main backbone

This article presents the molecular orientation and second‐order optical nonlinearity of newly prepared polyureas and copolyurea with dipole moments aligned transverse to the main backbone. Nonlinear optical (NLO) polyureas, TPU and TPU2, were prepared from 2,4‐diamino‐4′‐nitroazobenzene (2R‐DIAMINE) with 4,4′‐diphenylmethane diisocyanate (DMDI) and tolylene 2,4‐diisocyanate, respectively. NLO copolyurea was prepared from DMDI with 2R‐DIAMINE and m‐phenylene diamine. TPU and TPU2 gave d₃₃ values of 12.5 and 9.8 pm/V, respectively, under optimum poling conditions. A time‐dependent decay curve of second‐order nonlinear susceptibility was fitted well with a Kohlrausch–Williams–Watts stretched exponential function. The relaxation time of TPU2 was 4.2 × 10⁸ s at 100 °C. Copolyurea was uniaxially drawn in ratios of 1.5 and 2.0. The average molecular angles Φ_X , Φ_Y , and Φ_Z in three laboratory frames were evaluated from the refractive indices. Φ_Y decreased and Φ_X and Φ_Z increased with an increasing draw ratio. The dependence of the second‐order harmonic intensity on the incidence angle, that is, the Maker fringe pattern, was fitted with two independent tensor components, d₃₃ and d₃₁, for undrawn film and five independent tensor components, d₃₃, d₃₂, d₃₁, d₁₅, and d₂₄, for drawn films. For drawn films, Kleinman symmetry was not satisfied: d₃₁ ≠ d₁₅ and d₃₂ ≠ d₂₄. An increase in the draw ratio gave rise to a large increase in the tensor component d₃₃. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 247–255, 2001     

Synthesis and properties of phenothiazylene vinylene‐based polymers: New organic semiconductors for field‐effect transistors and solar cells

A series of new phenothiazylene vinylene‐based semiconducting polymers, poly[3,7‐(4′‐dodecyloxyphenyl)phenothiazylene vinylene] ( P1 ), poly[3,7‐(4′‐dodecyloxyphenyl)phenothiazylene vinylene‐alt‐1,4‐phenylene vinylene] ( P2 ), and poly[3,7‐(4′‐dodecyloxyphenyl)phenothiazylene vinylene‐alt‐2,5‐thienylene vinylene] ( P3 ), have been synthesized via a Horner‐Emmons reaction. FTIR and ¹H NMR spectroscopies confirmed that the configurations of the vinylene groups in the polymers were all‐trans (E). The weight‐averaged molecular weights (M_w) of P1 , P2 , and P3 were found to be 27,000, 22,000, and 29,000, with polydispersity indices of 1.91, 2.05, and 2.25, respectively. The thermograms for P1 , P2 , and P3 each contained only a broad glass transition, at 129, 167, and 155 °C, respectively, without the observation of melting features. UV–visible absorption spectra of the polymers showed two strong absorption bands in the ranges 315–370 nm and 450–500 nm, which arose from absorptions of the phenothiazine segments and the conjugated main chains. Solution‐processed field‐effect transistors fabricated from these polymers showed p‐type organic thin‐film transistor characteristics. The field‐effect mobilities of P1 , P2 , and P3 were measured to be 1.0 × 10^?4, 3.6 × 10^?5, and 1.0 × 10^?3 cm² V^?1 s^?1, respectively, and the on/off ratios were in the order of 10² for P1 and P2 , and 10³ for P3 . Atomic force microscopy and X‐ray diffraction analysis of thin films of the polymers show that they have amorphous structures. A photovoltaic device in which a P3 /PC₇₁BM (1/5) blend film was used as the active layer exhibited an open‐circuit voltage (V_OC) of 0.42 V, a short circuit current (J_SC) of 5.17 mA cm^?2, a fill factor of 0.35, and a power conversion efficiency of 0.76% under AM 1.5 G (100 mW cm^?2) illumination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 635–646, 2010     

Synthesis of tetrazole‐containing azo polymers with properties of photo‐induced birefringence and surface‐relief‐gratings via RAFT polymerization

A novel optically active monomer, 6‐{4‐[4‐(1‐phenyl‐1H‐tetrazol‐5‐yloxy)‐phenylazo] ‐phenoxy}‐hexyl methacrylate (PTPPHMA) bearing tetrazole and azobenzol moieties, was synthesized and polymerized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) as the RAFT agent and 2, 2′‐azobis(isobutyronitrile) (AIBN) as the initiator. Well‐defined optically active photochromic polyPTPPHMA(PPTPPHMA) was obtained. “Living”/controlled characteristics were observed in the polymerization: well‐controlled molecular weights (M_ns), narrow molecular weight distributions (M_w/M_n) of the polymers and successful chain‐extension of PPTPPHMA with styrene (St) as the second monomer. The photochemical interconversion between trans and cis isomers of PPTPPHMA in N,N′‐dimethyl formamide (DMF) solution was explored under irradiation of ultraviolet light. The photoinduced birefringence on the thin films of PPTPPHMA was investigated. A maximum birefringence of 0.1 was obtained, and no significant change of profiles of the birefringence after several cycles of writing/erasing/rewriting sequences was observed. The surface‐relief‐gratings (SRGs) were induced on the polymer films by interference of Kr⁺ laser beams at 413.1 nm with 35 mW/cm² intensity, the diffraction efficiencies from SRGs were measured to be in the range of 2.0–2.5%. The atomic force microscopy (AFM) results showed the gratings produced on the surfaces of the polymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 682–691, 2008     

Cationic,water‐soluble,fluorene‐containing poly(arylene ethynylene)s: Effects of water solubility on aggregation,photoluminescence efficiency,and amplified fluorescence quenching in aqueous solutions

Three novel fluorene‐containing poly(arylene ethynylene)s with amino‐functionalized side groups were synthesized through the Sonogashira reaction. They were poly{9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene}‐alt‐co‐{2,5‐bis[3′‐(N,N‐diethylamino)‐1′‐oxapropyl]‐1,4‐phenylene} ( P1 ), poly{9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene} ( P2 ), and poly({9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene}‐alt‐co‐(1,4‐phenylene)) ( P3 ). Through the postquaternization treatment of P1 – P3 with methyl iodide, we obtained their cationic water‐soluble conjugated polyelectrolytes (WSCPs): P1′ – P3′ . The water solubility was gradually improved from P3′ to P1′ with increasing contents of hydrophilic side chains. After examining the ultraviolet–visible absorption and photoluminescence (PL) spectra, fluorescence lifetimes, and dynamic light scattering data, we propose that with the reduction of the water solubility from P1′ to P3′ , they exhibited a gradually increased degree of aggregation in H₂O. The PL quantum yields of P1′ – P3′ in H₂O displayed a decreasing tendency consistent with the increased degree of aggregation, suggesting that the pronounced degree of aggregation was an important reason for the low PL quantum yields of WSCPs in H₂O. Two structurally analogous water‐soluble trimers of P2′ and P3′ , model compounds 2,7‐bis(9″,9″‐bis{6‴‐[(N,N‐diethyl)‐N‐methylammonium] hexyl}‐2″‐fluorenylethynyl)‐9,9‐bis{6′‐[(N,N‐diethyl)‐N‐methylammonium]hexyl}fluorene hexaiodide and 1,4‐bis(9′,9′‐bis{6″‐[(N,N‐diethyl)‐N‐methylammonium]hexyl}‐2′‐fluorenylethynyl)benzene tetraiodide, were synthesized. The amplified fluorescence quenching of these WSCPs by Fe(CN)₆⁴⁻ in H₂O was studied by comparison with a corresponding analogous trimer. The effects of aggregation on the fluorescence quenching may be two‐edged in these cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5778–5794, 2006     

Thermally stable nonlinear optical polyurea functionalized by multiple charge‐transfer chromophore

A novel high glass‐transition temperature (272 °C) polyurea functionalized by a multiple charge‐transfer chromophore, 2‐{4‐[4,5‐bis(4‐nitrophenyl)imidazolyl]phenyl}‐4,5‐bis(4‐aminophenyl)imidazole, was synthesized. Simultaneous poling and polymerization and the in situ second‐harmonic generation (SHG) measurement technique was carried out to evaluate the thermal stability of the poling‐induced orientation. The nonlinear optical coefficient d₃₃ of poled polyurea film was 24 pm/V at 1064 nm fundamental wavelength. The SHG signal of the poled polymer film was quite stable below 200 °C and still remained 80% of its initial value after heating at 250 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4297–4301, 2002     

Synthesis of bio‐based poly(N‐phenylitaconimide) by atom transfer radical polymerization

Poly(N‐phenylitaconimide) (polyPhII) was prepared using initiators for continuous activator regeneration atom transfer radical polymerization of PhII using FeBr₃ complexes as catalysts. Conversion reached 69% in 24 h, yielding polyPhII with a number average molecular weight M_n = 11,900 and a molecular weight distribution M_w/M_n = 1.52. Copolymerizations of PhII with styrene at various molar ratios were performed providing a range of polyPhII‐copolySt polymers. When the copolymerization was carried out with higher [St]₀ > [PhII]₀ ratio, a one‐pot synthesis of poly(St‐alt‐PhII)‐b‐polySt was achieved. The thermal properties of the obtained copolymers were studied by differential scanning calorimetry. PolyPhII prepared by ATRP showed high glass transition temperature (T_g) of 216 °C and the poly(St‐alt‐PhII)‐b‐polySt exhibited two T_gs, at 162 and 104 °C, corresponding to a poly(St‐alt‐PhII) and polySt segments, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 822–827     

Significantly improved photovoltaic performances of the dithiophene‐benzothiadiazole‐alt‐fluorene copolymers by incorporating carbazole units in fluorene moiety

To exploit an effective way to improve polymeric photovoltaic performance, a series of dithiophene‐benzothiadiazole‐alt‐fluorene copolymers containing carbazole groups at C‐9 positions of the alternating fluorene units (PFO‐FCz‐DBT) were synthesized and characterized. The effect of the carbazole groups on the optophysical, electrochemical, and photovoltaic properties of these copolymers was investigated. By comparison, this type of copolymers with carbazole units exhibited significantly improved photovoltaic properties than poly(2,7‐(9,9‐dioctyl‐fluorene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PFO‐DBT) in the bulk heterojunction solar cells. A maximum power‐conversion efficiency (PCE) of 2.41% and a highest short‐circuit current density (J_sc) of 9.68 mA cm^?2 were obtained for the PFO‐FCz‐DBT30, which are about two times higher than the corresponding levels for the PFO‐DBT30. This work demonstrated that introducing a hole‐transporting carbazole unit into copolymer is a simple and effective method to improve the J_sc and PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Piezoelectric and dielectric properties of siloxane elastomers filled with bariumtitanate

Piezoelectric elastomers were prepared from suspensions of bariumtitanate (BaTiO₃) particles in a telechelic polydimethylsiloxane (t-PDMS) by crosslinking the t-PDMS under an electric field. Crosslinking reaction was monitored by measurement of complex dielectric constant ε′ − iε″. Dielectric constant ε′ increased with increasing BaTiO₃ content, and agreed approximately with the theoretical ε′ calculated with the Maxwell–Wagner theory. Piezoelectric constant d₃₃ of the poled elastomers was measured by application of compressions in the direction of the poling field. It was found that d₃₃ was of the order of 10⁻¹¹ C/N and increased steeply with increasing content of BaTiO₃ but became almost independent of composition in the range of BaTiO₃ content from 3 to 14 vol %. To examine the effect of electric field on the aggregation structure of the particles, we observed light scattering of the suspension under an electric field, and found that the scattering pattern became anisotropic. This indicated that the particles are connected like a pearl necklace and are stretched in the direction of the poling field. The dependence of d₃₃ on the volume fraction of BaTiO₃ was explained by a model proposed by Banno. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3065–3070, 1999     

NLO‐active maleimide copolymers with ­high glass transition temperatures

We synthesized some novel rigid NLO‐active maleimide copolymers bearing DR‐1 moieties ( PMPD , PHSD and PHND ). All copolymers exhibited high T_g's (190～197 °C), good solubilities for common solvents and excellent film‐forming properties. Dependence of film thickness on the d₃₃ value for the poled copolymer films induced by corona poling was investigated and it was demonstrated that in less than thickness of 0.3 µm decrease of the thickness gives rise to remarkable increase in the d₃₃ value. The poled copolymer films exhibited large d₃₃ values (270 × 10^?9 esu (film thickness 0.13 µm) for PMPD , 290 × 10^?9 esu (0.12 µm) for PHSD and 350 × 10^?9 esu (0.08 µm) for PHND ) as well as large r₃₃ values (51.0 pmV^?1 for PMPD and 60.4 pmV^?1 for PHND ) which are significantly large compared to the value of LiNbO₃ (31 pmV^?1) as a typical EO material. The d₃₃ values of the poled copolymers were kept constant even after standing 1000h at 80 °C, although a small decrease was observed at an initial stage. Further, the d₃₃ values did not change up to ca. 123 °C upon heating at the rate of 10 °C/min in all cases. Copyright © 2002 John Wiley & Sons, Ltd.     

Syntheses and characterization of carbazole based new low‐band gap copolymers containing highly soluble benzimidazole derivatives for solar cell application

Newly designed 2H‐benzimidazole derivatives which have solubility groups at 2‐position have been synthesized and incorporated into two highly soluble carbazole based alternating copolymers, poly[2,7‐(9‐(1′‐octylnonyl)‐9H‐carbazole)‐alt‐5,5‐(4′,7′‐di(thien‐2‐yl)‐2H‐benzimidazole‐2′‐spirocyclohexane)] (PCDTCHBI) and poly[2,7‐(9‐(1′‐octylnonyl)‐9H‐carbazole)‐alt‐5,5‐(4′,7′‐di(thien‐2‐yl)‐2H‐benzimidazole‐2′‐spiro‐4′′‐((2′′′‐ethylhexyl)oxy)‐cyclohexane)] (PCDTEHOCHBI) for photovoltaic application. These alternating copolymers show low‐band gap properties caused by internal charge transfer from an electron‐rich unit to an electron‐deficient moiety. HOMO and LUMO levels are –5.53 and –3.86 eV for PCDTCHBI, and –5.49 and –3.84 eV for PCDTEHOCHBI, respectively. Optical band gaps of PCDTCHBI and PCDTEHOCHBI are 1.67 and 1.65 eV, respectively. The new carbazole based the 2H‐benzimidazole polymers show 0.11–0.13 eV lower values of band gaps as compared to that of carbazole based benzothiadiazole polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), while keeping nearly the same deep HOMO levels. The power conversion efficiencies of PCDTCHBI and PCDTEHOCHBI blended with [6,6]phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) are 1.03 and 1.15%, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Low‐bandgap quinoxaline‐based D–A‐type copolymers: Synthesis,characterization, and photovoltaic properties

Three classes of quinoxaline (Qx)‐based donor–acceptor (D–A)‐type copolymers, poly[thiophene‐2,5‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diyl] P(T‐Qx), poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diy} P(BDT‐Qx), and poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(5′,8′‐di‐2‐thienyl‐2,3‐bis(4‐octyloxyl)phenyl)‐quinoxaline‐5,5‐diyl} P(BDT‐DTQx), were synthesized via a Stille coupling reaction. The Qx unit was functionalized at the 2‐ and 3‐positions with 4‐(octyloxy)phenyl to provide good solubility and to reduce the steric hindrance. The absorption spectra of the Qx‐containing copolymers could be tuned by incorporating three different electron‐donating moieties. Among these, P(T‐Qx) acted as an electron donor and yielded a high‐performance solar cell by assuming a rigid planar structure, confirmed by differential scanning calorimetry, UV–vis spectrophotometer, and density functional theory study. In contrast, the P(BDT‐Qx)‐based solar cell displayed a lower power conversion efficiency (PCE) with a large torsional angle (34.7°) between the BDT and Qx units. The BDT unit in the P(BDT‐DTQx) backbone acted as a linker and interfered with the formation of charge complexes or quinoidal electronic conformations in a polymer chain. The PCEs of the polymer solar cells based on these copolymers, in combination with [6,6]‐phenyl C70 butyric acid methyl ester (PC₇₁BM), were 3.3% [P(T‐Qx)], 1.9% [P(BDT‐Qx)], and 2.3% [P(BDT‐DTQx)], respectively, under AM 1.5G illumination (100 mW cm^?2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Influence of nitroxide structure on the 2,5‐ and 2,6‐spirodicyclohexyl substituted cyclic nitroxide‐mediated free‐radical polymerization of styrene

The 2,6‐spirodicyclohexyl substituted nitroxide, cyclohexane‐1‐spiro‐2′‐(3′,5′‐dioxo‐4′‐benzylpiperazine‐1′‐oxyl)‐6′‐spiro‐1″‐cyclohexane (BODAZ), was investigated as a mediator for controlled/living free‐radical polymerization of styrene. The values of the number‐average molecular weight increased linearly with conversion, but the polydispersities were higher than for the corresponding 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) mediated systems at approximately 2.2 and 1.6 at 100 and 120 °C, respectively. These results were reflected in the rate coefficients obtained by electron spin resonance spectroscopy; at 120 °C, the values of the rate coefficients for polystyrene‐BODAZ alkoxyamine dissociation (k_d), combination of BODAZ and propagating radicals (k_c), and the equilibrium constant (K) were 1.60 × 10^?5 s^?1, 5.19 × 10⁶ M^?1 s^?1, and 3.08 × 10^?12 M, respectively. The value of k_d was approximately one and two orders of magnitude lower, and that of K was approximately 20 and 7 times lower than for the NO88Bn and TEMPO adducts. These results are explained in terms of X‐ray crystal structures of BODAZ and NO88Bn; the six‐membered ring of BODAZ deviates significantly from planarity as compared to the planar five‐membered ring of NO88Bn and possesses a benzyl substituent oriented away from the nitroxyl group leading to a seemingly more exposed oxyl group, which resulted in a higher k_c and a lower k_d than NO88Bn. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3892–3900, 2003     

Preparation of ABC miktoarm star terpolymer containing poly(ethylene glycol), polystyrene,and poly(tert‐butylacrylate) arms by combining diels–alder reaction,atom transfer radical,and stable free radical polymerization routes

The ABC type miktoarm star terpolymer was prepared utilizing “core‐in” and “core‐out” methods via combination of Diels–Alder reaction (DA), stable free radical polymerization (SFRP), and atom transfer radical polymerization (ATRP). First, in DA reaction, poly(ethylene glycol)‐maleimide (PEG‐maleimide) precursor was reacted with succinic acid anthracen‐9‐ylmethyl ester 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxy‐carbonyl]‐propyl ester, 8 , to give DA adduct, 9 , which has appropriate functional groups for SFRP and ATRP. Second, a previously obtained 9 was used as a macroinitiator for SFRP of styrene at 125 °C. As a third step, this PEG‐polystyrene (PEG‐PSt) precursor with a bromine functionality in the core was employed as a macroinitiator for ATRP of tert‐butylacrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C to give ABC type miktoarm star terpolymer (PEG‐PSt‐PtBA) with controlled molecular weight and low polydispersity (M_w/M_n < 1.27). The obtained polymers were characterized by gel permeation chromatography and ¹H NMR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 499–509, 2006     

Synthesis of poly(p‐phenylene) macromonomers and multiblock copolymers

Rigid‐rod poly(4′‐methyl‐2,5‐benzophenone) macromonomers were synthesized by Ni(0) catalytic coupling of 2,5‐dichloro‐4′‐methylbenzophenone and end‐capping agent 4‐chloro‐4′‐fluorobenzophenone. The macromonomers produced were labile to nucleophilic aromatic substitution. The molecular weight of poly(4′‐methyl‐2,5‐benzophenone) was controlled by varying the amount of the end‐capping agent in the reaction mixture. Glass‐transition temperatures of the macromonomers increased with increasing molecular weight and ranged from 117 to 213 °C. Substitution of the macromonomer end groups was determined to be nearly quantitative by ¹H NMR and gel permeation chromatography. The polymerization of a poly(4′‐methyl‐2,5‐benzophenone) macromonomer [number‐average molecular weight (M_n) = 1.90 × 10³ g/mol; polydispersity (M_w)/M_n = 2.04] with hydroxy end‐capped bisphenol A polyaryletherketone (M_n = 4.50 × 10³ g/mol; M_w/M_n = 1.92) afforded an alternating multiblock copolymer (M_n = 1.95 × 10⁴ g/mol; M_w/M_n = 6.02) that formed flexible, transparent films that could be creased without cracking. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3505–3512, 2001