Benzooxadiazaole‐based D–A–D co‐oligomers: Synthesis and electropolymerization

Four D–A–D type co‐oligomers have been synthesized by Stille condensation between monostannyl derivatives of furan/thiophene/selenophene/3,4‐ethylenedioxythiophene (EDOT) and 4,7‐dibromo‐benzo[1,2,5]oxadiazole. All these co‐oligomers were successfully electrochemically polymerized in dichloromethane and characterized by spectroelectrochemistry. All four polymers possess narrow optical band gap. Spectroelectrochemical studies of polymer films on indium tin oxide revealed that the replacement of donor EDOT with furan/thiophene/selenophene has affected the low‐energy charge‐carrier (bipolaron) formation significantly. Kinetic studies based on chronoamperometry show that the polymer P5 (EDOT‐capped benzo[1,2,5]oxadiazole system) possess better electrochromic property with high transmittance (66%) in visible region than the other copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

End‐functionalization of semiconducting species with dendronized terpyridine–Ru(II)–terpyridine complexes

Semiconducting oligomers and polymers decorated with two or one dendronized tpy‐Ru(II)‐tpy metallocomplexes are presented. Initially, free terpyridine end‐functionalized semiconducting oligomers (distyrylanthracene, quinquephenylene, mono‐ and trifluorenes) were prepared while in a second approach, atom transfer radical polymerization was employed for the preparation of side‐chain oligomeric and polymeric (oxadiazole)s using a terpyridine initiator. These terpyridine‐bearing oligomers and polymers were complexated with a Percec‐type first‐generation (G1) dendronized terpyridine–Ru(III)Cl₃ monocomplex, having two dodecyloxy groups. All oligomeric and polymeric metallocomplexes were characterized via NMR spectroscopies for their structural perfection and via UV‐Vis and PL spectroscopies for their optical properties. The existence of the organic semiconducting blocks in combination with the terpyridine–Ru(II)–terpyridine groups afforded hybrid metallo‐semiconducting species presenting the optical features of both their components. Moreover, their thin‐film morphologies were investigated through atomic force microscopy, revealing, in some cases, an organization tendency in the nanometer scale. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1939–1952, 2009     

Synthesis of polymers with isolated thiophene–arylidene–thiophene chromophores for enhanced and specific electron/hole transport

The synthesis of nine new polymers intended for future use in light‐emitting diodes is described. The polymers consist of alternating units of thiophene–arylidene–thiophene chromophores and saturated silicon‐containing spacers. The arylidene moieties include benzene‐1,4‐, 2,5‐dimethoxybenzene‐1,4‐, naphthalene‐1,4‐, anthracene‐9,10‐, pyridine‐2,5‐, pyridine‐2,6‐, N‐methylcarbazole‐3,6‐, 1,3,4‐oxadiazole‐2,5‐, and 4,4′‐dimethyl‐2,2′‐bithiazole‐5,5′‐. The syntheses involved dibromination of the central arene followed by Suzuki or Kumada cross‐coupling reactions with two thiophene units. Subsequent dilithiation and reaction with dihalosilylalkanes provided the polymers. Their optical properties, including ultraviolet–visible absorption and emission in solution, were comparable to those of the parent monomer units, and they possessed the physical characteristics of macromolecules. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 872–879, 2001     

New p-n diblock and triblock oligomers: effective tuning of HOMO/LUMO energy levels

A new series of oligomers consisting of thiophene as p-type unit and oxadiazole as n-type unit were synthesized, and their photophysical and electrochemical properties were evaluated. Cyclic voltammography studies demonstrated that the electronic properties of the p-n diblock oligomers could be modulated by changing the number of thiophene and oxadiazole rings. The molecular regiochemical effect to the electrochemical and optical properties was also investigated.     

Synthesis and characterization of poly(fluorene‐co‐alt‐phenylene) containing 1,3,4‐oxadiazole dendritic pendants

A series of poly(fluorene‐co‐alt‐phenylene)s containing various generations of dendritic oxadiazole (OXD) pendent wedges were synthesized by the Suzuki polycondensation of OXD‐functionalized 1,4‐dibromophenylene with 9,9‐dihexylfluorene‐2,7‐diboronic ester. The obtained polymers possessed excellent solubility in common solvents and good thermal stability. Photophysical studies showed that the dendronized polymers appended with higher generations of OXD dendrons exhibited enhanced photoluminescence efficiencies and narrower values of the full width at half‐maximum. This was attributed to the shielding effect induced by the bulky dendritic OXD side chains, which prevented self‐quenching and suppressed the formation of aggregates/excimers. The energy transfer from the OXD dendrons to the polymer backbones was very efficient when excitation of the peripheral OXD dendrons resulted mainly in the polymer backbone emission alone. In particular, the photoluminescence emission intensities by the sensitized excitations of OXD dendrons in solid films of the polymers were all stronger than those by the direct excitations of their polymer conjugated backbones. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6765–6774, 2006     

Electroluminescent block copolymers containing oxadiazole and thiophene via ATRP

Block copolymers containing thiophene units in one block and oxadiazole (OXD) units in the other were prepared. Atom transfer radical polymerization method was used to obtain the thiophene‐containing mesogen‐jacketed polymers, and the kinetic study indicated that the polymerization was controllable and the polymers could be used to initiate the polymerization of the OXD‐containing monomers. Photoluminescent spectra indicated that the fluorescence quantum yields of the polymers increased with increasing content of OXD. And, more OXD domains, that is, more interfaces between the hole‐transport parts and electron‐transport parts, resulting in the higher probability of exciplex formation. The electroluminescent devices containing the block copolymer with 64 mol % OXD as the emissive layer had a maximum brightness of 127 cd/m² and an extremely low onset voltage of 7.7 V, which indicated that the injection and transport of charge carriers were facilitated and the number of charge carriers was sufficiently high in early time after the voltage was turned on. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and photovoltaic properties of copolymers based on benzo[1,2‐b:4,5‐b′]dithiophene and thiophene with electron‐withdrawing side chains

Six alternating conjugated copolymers ( PL1 – PL6 ) of benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thiophene, containing electron‐withdrawing oxadiazole (OXD), ester, or alkyl as side chains, were synthesized by Stille coupling reaction. The structures of the polymers were confirmed, and their thermal, optical, electrochemical, and photovoltaic properties were investigated. The introduction of conjugated electron‐withdrawing OXD or formate ester side chain benefits to decrease the bandgaps of the polymers and improve the photovoltaic performance due to the low steric hindrance of BDT. Bulk heterojunction polymer solar cells (PSCs) were fabricated based on the blend of the as‐synthesized polymers and the fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 2.06% was obtained for PL5 ‐based PSC under the illumination of AM 1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Comparison of ground and excited state polarizabilities of thiophene,cyclopentadiene, and fulvene oligomers and their cyano substituted derivatives—Ab initio study

Ab Initio study of the ground and excited state polarizabilities of thiophene, fulvene, and cyclopentadiene based conducting oligomers and their cyano derivatives have been performed using the restricted Hartree–Fock (RHF) and the configuration interaction singles (CIS) approaches, respectively, with 3‐21G* basis set. For comparison purposes, for some small oligomers (monomers and dimers), higher basis sets (6‐31G*, 6‐31+G*, aug‐cc‐pVTZ) were also employed in the computations of polarizabilities. The trends in polarizability as a function of oligomer length were investigated. For all systems, the RHF polarizability increases as n^1.2–1.3 as n gets larger and the CIS polarizability increases as n^1.4–1.6 for n less than seven or eight rings and then increases approximately linearly with n for larger n. For the thiophene based systems the dependence of the polarizability on bond length alternation (BLA) along the backbone of the oligomers was also investigated using the RHF, density functional (DFT), and CIS theories (with 3‐21G* basis set). For thiophene dimer, we also performed RHF/aug‐cc‐pVTZ calculations of polarizabilities versus BLA. We found that the polarizability is largest when BLA is near zero (for both ground and excited states), which correlates with the lowest excitation energy. Comparison with experimental results has been made where possible. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1983–1995, 2007     

Synthesis and photovoltaic properties of poly(p‐phenylenevinylene) derivatives containing oxadiazole

A novel poly(p‐phenylenevinylene) PPV‐based copolymer (3C‐OXD‐PPV) with electron‐deficient oxadiazole segments as the side chain has been successfully synthesized through the Gilch polymerization. The obtained copolymer is soluble in common organic solvents such as chloroform, tetrahydronfuran, and 1,1,2,2‐tetrachloroethane. The copolymer was characterized by ¹H NMR, elemental analysis and GPC. TGA measurement of the copolymer shows it has good thermal stability with decomposition temperature higher than 350 °C. The absorption, electrochemical properties of the 3C‐OXD‐PPV were investigated and also compared with the properties of MEH‐PPV. The HOMO and LUMO levels of 3C‐OXD‐PPV were estimated from the electrochemical cyclic voltammograms. Bulk‐heterojunction PVCs were fabricated by using 3C‐OXD‐PPV blended PCBM as an active layer. The PCE of the PVC is 1.60% under 100 mW cm^?2 AM 1.5 illumination, which indicates that 3C‐OXD‐PPV is a potential candidate for the application of polymer PVC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1003–1012, 2009     

Synthesis and characterization of luminescent polyethers with 2,5‐distyrylthiophene and aromatic oxadiazole chromophores

Two new luminescent copolyethers ( P1 and P2 ) with isolated 2,5‐distyrylthiophene‐emitting segments and electron‐transporting 2,5‐diphenyl‐1,3,4‐oxadiazole chromophores were successfully synthesized by the Horner–Wadworth–Emmons reaction. The solubility, optical, and electrochemical properties of the polymers were investigated and correlated with nonlinear thiophene and 1,3,4‐oxadiazole groups. P2 with pendant 1,3,4‐oxadiazole was soluble in common organic solvents such as chloroform, tetrahydrofuran, and C₂H₂Cl₄. Thermogravimetric analysis and differential scanning calorimetry showed that the copolyethers were thermally stable below 345 °C, with glass‐transition temperatures higher than 110 °C. They were yellow‐greenish emitting materials with a band gap of 2.57–2.58 eV estimated from the onset absorption. Incorporating the thiophene moiety narrowed the band gaps of the copolyethers. The photophysical and electronic properties of the polymer and the preliminary electroluminescent device made from the polymer demonstrate that the polymer may be a potential candidate material for the fabrication of polymeric light‐emitting devices. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2927–2936, 2002     

Synthesis and characterization of poly(fluorene)‐based copolymers containing various 1,3,4‐oxadiazole pendants

A series of soluble alternating poly(fluorene)‐based copolymers containing electron‐transporting 1,3,4‐oxadiazole (OXD) and hole‐transporting carbazole pendants attached to the C‐9 position of fluorene units by long alkyl spacers were synthesized. These copolymers possess mesogenic and nonmesogenic pendants attached to a rigid mesogenic poly(fluorene) (PF) backbone. All these polymers exhibit glass‐forming liquid crystalline properties, including the nematic and smectic A (SmA) phases, and reveal much wider mesophasic temperature ranges than that of PF. The thermal properties and mesomorphism of these conjugated polymers are mainly affected by the nature of these pendants, and thus the mesophasic temperature ranges and glass‐forming properties are greatly enhanced by introducing the OXD pendants. In addition, the tendencies of crystallization and aggregation of PF are also suppressed by introducing the OXD pendants. A single layer device with P4 as an emitter shows a turn‐on voltage of 5 V and a bright luminescence of 2694 cd/m² at 11 V with a power efficiency of 1.28 cd/A at 100 mA/cm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2700–2711, 2005     

Synthesis and optoelectronic properties of alternating benzofuran/terfluorene copolymer with stable blue emission

The solution processable alternating benzofuran/terfluorene copolymer bearing side oxadiazole groups ( PBF‐OXD ) was synthesized and its optoelectronic properties and color stability were investigated. Electron‐deficient and stereohindered oxadiazole units were used as pendent groups to compensate for the poor electron‐transporting ability of a p‐type polymer backbone, to depress the intermolecular π‐stacking, and to improve solubility while retaining polymer blue emission. PBF‐OXD showed a glass transition at 135 °C and an onset decomposition temperature of ～345 °C. A simple EL device, with the configuration of ITO/PEDOT:PSS/ PBF‐OXD /Ba/Al, displayed a stable blue emission (λ_max = 434 nm), good color purity (full width half‐maximum = 59 nm), maximum brightness of 1400 cd/m², and a maximum luminance efficiency of 0.95 cd/A. The PL and EL spectra changed slightly on annealing and on increasing the applied voltage. These results show that the as‐synthesized copolymer PBF‐OXD had integrated respective functions of its different building blocks and exhibited good thermal and color stability with improved EL performance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5488–5497, 2009     

Synthesis and optical properties of green‐light‐emitting copolymers containing side‐chain oxadiazole units

Atom transfer radical polymerization was used to prepare well‐defined vinyl polyoxadiazole homomacromonomers with a properly modified α‐dicarboxylic acid methyl ester as the initiator. Macromonomers of various molecular weights with narrow polydispersities in some cases were obtained, as proved by gel permeation chromatography (GPC). The structures of the obtained macromonomers were then identified with ¹H NMR spectroscopy. These macromonomers were subsequently copolymerized with a dihydroxy anthracene based monomer by a polycondensation technique, and this resulted in polymacromonomers. Coil–rod–coil copolymers containing side‐chain anthracene and oxadiazole units were also synthesized by atom transfer radical polymerization. The resulting copolymers combined an anthracene derivative as the rigid block with a random copolymer of the desired anthracene‐ and/or oxadiazole‐based monomers as the flexible block. These copolymers were primarily characterized with GPC and ¹H NMR techniques. Additionally, the optical properties of all these copolymers were investigated in detail, and they suggested energy transfer from the oxadiazole to the anthracene chromophores, which became much more efficient in the solid state. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1049–1061, 2005     

Small band gap conjugated polymers based on thiophene–thienopyrazine copolymers

In this study, five small band gap thiophene ( TH )–thienopyrazine ( TP ) conjugated copolymers were synthesized by Stille‐coupling reaction. The polymer structures consisted of one to four thiophene rings with the TP of different side groups provided a systematical investigation on the structure–electronic property relationship. The absorption maxima of the polymer films decreased from 850 to 590 nm as the thiophene moieties increased from thiophene to quaterthiophene. The optical and electrochemical band gaps of the studied poly[2,3‐didodecyl‐5‐(thiophen‐2‐yl)thieno[3,4‐b]pyrazine] ( PTHTP‐C12 ) were 0.97 and 0.78 eV, respectively, indicating a significant intramolecular charge transfer. The theoretical geometry and electronic properties of the TH ‐ TP copolymers by the density functional theory at the B3LYP level and 6‐31G(d) basis set suggested that the bond length alternation enlarged with enhancing the thiophene content and resulted in the variation on the polymer band gap. The relatively small theoretical effective mass of poly( TH ‐alt‐ TP ) also indicated its potential applications for field transistor applications. Our study demonstrates the tunable electronic properties of small band gap copolymers by the thiophene content and the resulted geometry variation. Such polymers could be potentially used for near‐infrared electronic and optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5872–5883, 2007     

Comparison of Thiophene–Pyrrole Oligomers with Oligothiophenes: A Joint Experimental and Theoretical Investigation of Their Structural and Spectroscopic Properties

We have prepared a new series of mixed thiophene–pyrrole oligomers to investigate the electronic benefits arising from the combination of these two heterocycles. The oligomers are functionalized with several hexyl and aryl groups to improve both processability and chemical robustness. An analysis of their spectroscopic (absorption and emission), photophysical, electrochemical, solid state, and vibrational properties is performed in combination with quantum‐chemical calculations. This analysis provides relevant information regarding the use of these materials as organic semiconductors. The balance between the high aromatic character of pyrrole and the moderate aromaticity of thiophene allows us to address the impact of the coupling of these heterocycles in conjugated systems. The data are interpreted on the basis of the aromaticity, molecular conformations, ground and excited electronic state structures, frontier orbital topologies and energies, oxidative states, and quinoidal versus aromatic competition.     

Two novel oligomers based on fluorene and pyridine: Correlation between the structures and optoelectronic properties

To investigate the fine optoelectronic difference of the target oligomers with or without peripheral fluorene moieties, two dumbbell‐shaped oligomers ( F0 and F1 ) were designed and convergently prepared via Suzuki coupling reaction. The molecular structures of the oligomers were fully characterized by ¹H NMR, ¹³C NMR, and MALDI‐TOF mass spectra, respectively. The absorption, photoluminescent behavior, and energy band gaps of the oligomers were examined through UV–vis, photoluminescent spectra and cyclic voltammetry. The experimental results demonstrate that the absorption and photoluminescent properties are little affected by molecular architecture, while the absolute photoluminescence quantum efficiency of films and energy band gaps derived from cyclic voltammetry in solution are strongly correlated with the molecular frameworks. The observed energy band gaps of oligomers are further validated by the different molecular orbital contours of the HOMO energy levels from theoretical calculations. Preliminary electroluminescent investigations for F1 have also been conducted and discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1548–1558, 2008     

Luminescent copoly(aryl ether)s with new electron‐transporting bis(3‐(trifluoromethyl)phenyl)‐1,3,4‐oxadiazole or bis(3‐(trifluoromethyl)phenyl)‐4‐(4‐hexyloxyphenyl)‐4H‐1,2,4‐triazole segments

To investigate the effect of trifluoromethyl groups in enhancing electron affinity of aromatic oxadiazole and triazole chromophores, we prepared four new copoly(aryl ether)s ( P1 – P4 ) consisting of bis(3‐(trifluoromethyl) phenyl)‐1,3,4‐oxadiazole (ETO) or bis(3‐(trifluoromethyl)phenyl)‐4‐(4‐hexyloxyphenyl)‐4H‐1,2,4‐triazole (ETT) segments and hole‐transporting segments [2,5‐distyrylbenzene (HTB) or bis(styryl)fluorine (HTF)]. Molecular spectra (absorption and photoluminescence) and cyclic voltammetry were used to investigate their optical and electrochemical properties. The emissions of P1 – P4 are dominated by the hole‐transporting fluorophores with longer emissive wavelengths around 442–453 nm via efficient excitation energy transfer. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of P1 – P4 , estimated from electrochemical data, are ?5.15, ?5.18, ?5.30, ?5.27, ?3.39, ?3.49, ?3.36, and ?3.48 eV, respectively. The LUMO levels of ETO and ETT segments are significantly reduced to ?3.39～?3.36 eV and ?3.48～?3.49 eV, respectively, as compared with ?2.45 eV of P5 containing a 2,5‐diphenyl‐1,3,4‐oxadiazole segment. Moreover, electron and hole affinity can be enhanced simultaneously by introducing isolated hole‐ and electron‐transporting segments in the backbone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5900–5910, 2004     

Photophysical characteristics of soluble oligo(p‐phenylenevinylene)–fullerene dyad

The fact that C₆₀ is a good acceptor has stimulated interest in covalently linked complexes, including polymers and oligomers. Photoinduced charge transfer in these systems has great potential for use in photovoltaic devices. In this study, an alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene, with pendant C₆₀ moieties, (PPV‐AFCAR) was prepared and characterized. The excited‐state properties of PPV–AFCAR were investigated with steady‐state spectroscopy and lifetime measurements. After photoexcitation, photoinduced energy transfer from the oligomer chain to the pendant moiety occurred in great proportion, but a charge‐separation process did not. Whether the energy‐transfer process was measurable or not depended on the system temperature. At 77 K, a quantum yield of more than 50% for energy transfer was found by the fitting of a linear combination of the excitation spectra of the precursor oligomer, the alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene PPV–ACAR, and the absorption spectra of C₆₀. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3981–3988, 2001     

Synthesis and characterization of a polyfluorene containing carbazole and oxadiazole dipolar pendent groups and its application to electroluminescent devices

We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007     

Synthesis and optoelectronic properties of luminescent poly(p‐phenylenevinylene) derivatives containing electron‐transporting 1,3,4‐oxadiazole groups

Three random copolymers ( P1–P3 ) comprising phenylenevinylene and electron‐transporting aromatic 1,3,4‐oxadiazole segments (11, 18, 28 mol %, respectively) were prepared by Gilch polymerization to investigate the influence of oxadiazole content on their photophysical, electrochemical, and electroluminescent properties. For comparative study, homopolymer poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐p‐phenylenevinylene] ( P0 ) was also prepared by the same process. The polymers ( P0–P3 ) are soluble in common organic solvents and thermally stable up to 410 °C under a nitrogen atmosphere. Their optical properties were investigated by absorption and photoluminescence spectroscopy. The optical results reveal that the aromatic 1,3,4‐oxadiazole chromophores in P1–P3 suppress the intermolecular interactions. The HOMO and LUMO levels of these polymers were estimated from their cyclic voltammograms. The HOMO levels of P0–P3 are very similar (?5.02 to ?5.03 eV), whereas their LUMO levels decrease readily with increasing oxadiazole content (?2.7, ?3.08, ?3.11, and ?3.19 eV, respectively). Therefore, the electron affinity of the poly(p‐phenylenevinylene) chain can be gradually enhanced by incorporating 1,3,4‐oxadiazole segments. Among the polymers, P1 (11 mol % 1,3,4‐oxadiazole) shows the best EL performance (maximal luminance: 3490 cd/m², maximal current efficiency: 0.1 cd/A). Further increase in oxadiazole content results in micro‐phase separation that leads to performance deterioration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4377–4388, 2007