White electroluminescent single‐polymer achieved by incorporating three polyfluorene blue arms into a star‐shaped orange core

A series of star‐like dopant/host single‐polymer systems with a D‐A type star‐shaped orange core and three blue polyfluorene arms were designed and synthesized. Through tuning the doping concentration of the orange core and thermal annealing treatment of white polymer light‐emitting diodes based on them, highly efficient white electroluminescence has been achieved. A typical single‐layer device (ITO/PEDOT:PSS/polymer/Ca/Al) realized pure white emission with a luminous efficiency of 16.62 cd A^?1, an external quantum efficiency of 6.28% and CIE coordinates of (0.33, 0.36) for S‐WP‐002TPB3 containing 0.02 mol % orange core. The high efficiency of the devices could be mainly attributed to the suppressed concentration quenching of the dopant units, more efficient energy transfer from polymer host to orange dopant and thermal annealing‐induced α‐phase polyfluorene (PF) self‐dopant in amorphous PF host. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Phenothiazine‐S,S‐dioxide‐ and fluorene‐based light‐emitting polymers: Introduction of e−‐deficient S,S‐dioxide into e−‐rich phenothiazine

A novel series of poly(10‐hexyl‐phenothiazine‐S,S‐dioxide‐3,7‐diyl) and poly(9,9′‐dioctyl‐fluorene‐2,7‐diyl‐alt‐10‐hexyl‐3,7‐phenothiazine‐S,S‐dioxide) (PFPTZ‐SS) compounds were synthesized through Ni(0)‐mediated Yamamoto polymerization and Pd(II)‐catalyzed Suzuki polymerization. The synthesized polymers were characterized by ¹H NMR spectroscopy and elemental analysis and showed higher glass transition temperatures than that of pristine polyfluorene. In terms of photoluminescence (PL), the PFPTZ‐SS compounds were highly fluorescent with bright blue emissions in the solid state. Light‐emitting devices were fabricated with these polymers in an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration. The electroluminescence (EL) of the copolymers differed from the PL characteristics: the EL device exhibited a redshifted greenish‐blue emission in contrast to the blue emission observed in the PL. Additionally, this unique phenothiazine‐S,S‐dioxide property, triggered by the introduction of an electron‐deficient SO₂ unit into the electron‐rich phenothiazine, gave rise to improvements in the brightness, maximum luminescence intensity, and quantum efficiency of the EL devices fabricated with PFPTZ‐SS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1236–1246, 2007     

Synthesis of linear and star‐like poly(ε‐caprolactone)‐b‐poly{γ‐2‐[2‐(2‐methoxy‐ethoxy)ethoxy]ethoxy‐ε‐caprolactone} amphiphilic block copolymers using zinc undecylenate

Linear and star‐like amphiphilic diblock copolymers were synthesized by the ring‐opening polymerization of ε‐caprolactone and γ‐2‐[2‐(2‐methoxyethoxy)ethoxy]ethoxy‐ε‐caprolactone monomers using zinc undecylenate as a catalyst. These polymers have potential applications as micellar drug delivery vehicles, therefore the properties of the linear and 4‐arm star‐like structures were examined in terms of their molecular weight, viscosity, thermodynamic stability, size, morphology, and drug loading capacity. Both the star‐like and linear block copolymers showed good thermodynamic stability and degradability. However, the star‐like polymers were shown to have increased stability at lower concentrations with a critical micelle concentration (CMC) of 5.62 × 10^?4 g L^?1, which is less than half the concentration of linear polymer needed to form micelles. The star‐like polymeric micelles showed smaller sizes when compared with their linear counterparts and a higher drug loading capacity of doxorubicin, making them better suited for drug delivery purposes. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3601–3608     

π‐Extended Star‐Shaped Polycyclic Aromatic Hydrocarbons based on Fused Truxenes: Synthesis,Self‐Assembly,and Facilely Tunable Emission Properties

A new set of star‐shaped polycyclic aromatic hydrocarbons (PAHs) based on naphthalene‐fused truxenes, TrNaCn (n=1–4), were synthesized and characterized. The synthesis involved a microwave‐assisted six‐fold Suzuki coupling reaction, followed by oxidative cyclodehydrogenation. Multiple dehydrocyclization products could be effectively isolated in a single reaction, thus suggesting that the oxidative cyclodehydrogenation reaction involved a stepwise ring‐closing process. The thermal, optical, and electrochemical properties and the self‐assembly behavior of the resulting oxidized samples were investigated to understand the impact of the ring‐fusing process on the properties of the star‐shaped PAHs. Distinct bathochromic shift of the absorption maxima (λ_max) revealed that the molecular conjugation extended with the stepwise ring‐closing reactions. The optical band‐gap energy of these PAHs varied significantly on increasing the number of fused rings, thereby resulting in readily tunable emissive properties of the resultant star‐shaped PAHs. Interestingly, the generation of rigid “arms” by using perylene analogues caused TrNaC2 and TrNaC3 to show significantly enhanced photoluminescence quantum yields (PLQYs) in solution (η=0.65 and 0.66, respectively) in comparison with those of TrNa and TrNaC1 (η=0.08 and 0.16, respectively). Owing to strong intermolecular interactions, the TrNa precursor was able to self‐assemble into rod‐like microcrystals, which could be facilely identified by the naked eye, whilst TrNaC1 self‐assembled into nanosheets once the naphthalene rings had fused. This study offers a unique platform to gain further insight into—and a better understanding of—the photophysical and self‐assembly properties of π‐extended star‐shaped PAHs.     

Synthesis of pyridoxine‐based eagle‐shaped asymmetric star polymers through seATRP

The vitamin B₆‐based macroinitiator was prepared for the first time by the transesterification reaction of pyridoxine with 2‐bromoisobutyryl bromide. A pyridoxine‐based star‐shaped block copolymer with a hydrophilic pyridoxine core and a dual hydrophilic poly(2‐(dimethylamino)ethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) arms was synthesized for the first time via a simplified electrochemically mediated atom transfer radical polymerization, utilizing only 20 ppm of catalyst complex. The rate of the polymerizations was controlled by applying appropriate potential/current values during electrolysis to prevent the possibility of intermolecular coupling of the polymer stars. The asymmetric star polymers showed narrow molecular weight distribution (?  = 1.09–1.13). ¹H NMR spectral results confirm the formation of star‐like block (co)polymers. These new vitamin B₆‐based eagle‐shaped star (co)polymers may find biomedical and biosensor applications as pH‐sensitive and thermo‐sensitive drug delivery systems. Copyright © 2017 John Wiley & Sons, Ltd.     

Norbornene‐functionalized PEO‐b‐PCL: A versatile platform for mikto‐arm star,umbrella‐like,and comb‐like graft copolymers

Well‐defined in‐chain norbornene‐functionalized poly(ethylene oxide)‐b‐poly(?‐caprolactone) copolymers (NB‐PEO‐b‐PCL) were synthesized from a dual clickable containing both hydroxyl‐ and alkyne‐reactive groups, namely heterofunctional norbornene 3‐exo‐(2‐exo‐(hydroxymethyl)norborn‐5‐enyl)methyl hexynoate. A range of NB‐PEO‐b‐PCL copolymers were obtained using a combination of orthogonal organocatalyzed ring‐opening polymerization (ROP) and click copper‐catalyzed azide–alkyne cycloaddition (CuAAC). Ring‐opening metathesis polymerization (ROMP) of NB‐PEO‐b‐PCL macromonomers using ruthenium‐based Grubbs’ catalysts provides comb‐like and umbrella‐like graft copolymers bearing both PEO and PCL grafts on each monomer unit. Mikto‐arm star A₂B₂ copolymers were obtained through a new strategy based on thiol–norbornene photoinitiated click chemistry between 1,3‐propanedithiol and NB‐PEO‐b‐PCL. The results demonstrate that in‐chain NB‐PEO‐b‐PCL copolymers can be used as a platform to prepare mikto‐arm star, umbrella‐, and comb‐like graft copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 4051–4061     

New series of highly phenyl‐substituted polyfluorene derivatives for polymer light‐emitting diodes

A new series of highly phenyl‐substituted polyfluorene derivatives were synthesized and characterized. The resulting polymers were amorphous and showed excellent solubility in common organic solvents, such as chloroform, tetrahydrofuran, xylene, toluene, chlorobenzene, and so forth. All possessed satisfied thermal stability with glass‐transition temperatures (T_g's) in the range of 79–115 °C. They emitted blue light with photoluminescent (PL) maximum peaks at about 408–412 nm in thin films. The PL efficiencies of the polymer films were measured around 30–33%. The highly phenylated pendants improved the T_g of polyfluorene without forming defects in the polymers and reduced their tendency to form aggregate/excimers. Polymer light‐emitting diodes were fabricated from these polymers with the configuration of indium tin oxide/polyethylenedioxythiophene:polystyrene sulfonic acid/polymer/Ba/Al, which emitted bright blue light with maximum peaks at 418–420 nm. The maximum external quantum efficiencies of these devices were 0.41–0.6%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2985–2993, 2004     

Star‐like PAA‐g‐PPO well‐defined amphiphilic graft copolymer synthesized by ATNRC and SET‐NRC reaction

A series of well‐defined amphiphilic star graft copolymers consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic poly(propylene oxide) side chains were synthesized by the sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization and atom transfer nitroxide radical coupling (ATNRC) or single electron transfer‐nitroxide radical coupling (SET‐NRC) reaction followed by the selective hydrolysis of poly(tert‐butyl acrylate) backbone. A Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromopropanoyloxy)methyl)acrylate, was first homopolymerized via RAFT polymerization using a new star‐like chain‐transfer agent with four arms in a controlled way to give a well‐defined star‐like backbone with a narrow molecular weight distribution (M_w/M_n = 1.23). The grafting‐onto strategy was used to synthesize the well‐defined PtBA‐g‐PPO star graft copolymers with narrow molecular weight distributions (M_w/M_n = 1.14–1.25) via ATNRC or SET‐NRC reaction between the Br‐containing PtBA‐based star‐like backbone and poly(propylene oxide) with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl end group using CuBr/PMDETA or Cu/PMDETA as catalytic system. PAA‐g‐PPO amphiphilic star graft copolymers were obtained by the selective acidic hydrolysis of star‐like PtBA‐based backbone in acidic environment without affecting the side chains. The critical micelle concentrations in aqueous media and brine were determined by the fluorescence probe technique. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2084–2097, 2010     

New π‐Conjugated Polymers Containing 1,3,5‐Triazine Units in the Main Chain: Synthesis and Optical and Electrochemical Properties of the Polymers

Summary: Three new soluble π‐conjugated polymers containing 1,3,5‐triazine units in the main chain, Pa–Pc, were synthesized. The polymers showed optical properties in solution that were mainly dependant on the properties of the substituting R groups, on the triazine ring. Hence, Pa and Pb (R = H and  OCH₃, respectively) showed blue photoluminescent (PL) emission with high quantum yields (QY) even in polar solvents, whereas Pc (R = N,N‐dimethylamino) gave green‐blue PL emission with very low QY. The PL spectra of the polymers in solution were concentration and polarity dependent, which suggested the formation of an exciplex.

The three new soluble π‐conjugated polymers containing 1,3,5‐triazine units in the main chain synthesized here.     

Synthesis and micellization of star‐like hyperbranched polymer with poly(ethylene oxide) and poly(ε‐caprolactone) arms

Novel star‐like hyperbranched polymers with amphiphilic arms were synthesized via three steps. Hyperbranched poly(amido amine)s containing secondary amine and hydroxyl groups were successfully synthesized via Michael addition polymerization of triacrylamide (TT) and 3‐amino‐1,2‐propanediol (APD) with feed molar ratio of 1:2. ¹H, ¹³C, and HSQC NMR techniques were used to clarify polymerization mechanism and the structures of the resultant hyperbranched polymers. Methoxyl poly(ethylene oxide) acrylate (A‐MPEO) and carboxylic acid‐terminated poly(ε‐caprolactone) (PCL) were sequentially reacted with secondary amine and hydroxyl group, and the core–shell structures with poly(1TT‐2APD) as core and two distinguishing polymer chains, PEO and PCL, as shell were constructed. The star‐like hyperbranched polymers have different sizes in dimethyl sulfonate, chloroform, and deionized water, which were characterized by DLS and ¹H NMR. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1388–1401, 2008     

Luminescence properties of soluble 2,2′,7,7′‐Tetrakis(2‐(9‐hexyl‐9H‐carbazol‐3‐yl)‐vinyl)‐9,9′‐spirobifluorene‐labeled dendrimers: Photoluminescence and electroluminescence

New light emitting dendrimers were synthesized by reacting 3,5‐bis‐(3,5‐bis‐benzyloxy‐benzyloxy)‐benzoic acid or 3,5‐bis‐[3,5‐bis‐(3,5‐bis‐benzyloxy‐benzyloxy)‐benzyloxy]‐benzoic acid with a carbazolyl vinyl spirobifluorene moiety. A blue‐emitting core dye was encapsulated by multibenzyloxy dendrons, and two dendrimers having different densities of dendrons were prepared. Photoluminescence (PL) studies of the dendrimers demonstrated that at the higher density of benzyloxy dendrons, the featureless vibronic transitions were improved, causing lesser excimer emission. The similarity of the solution and solid emission spectra of the larger dendrimer, 10 , revealed the suppression of molecular aggregation in the solid film, which is attributed to the presence of the bulky benzyloxy dendrons. The electroluminescence spectra of multilayered devices made using 10 predominantly exhibited blue emissions; similar emission was observed in the PL spectra of its thin film. The multilayered devices made using 3 , 9 , and 10 showed luminances of 1021 cd m^?2 at 5 V, 916 cd m^?2 at 6 V, and 851 cd m^?2 at 6.5 V, respectively. The largest dendrimer, 10 , bearing a greater number of benzyloxy dendrons, exhibited a blue‐like emission with CIE 1931 chromaticity coordinates of x = 0.16 and y = 0.13, which is due to the influence of a higher shielding effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 501–514, 2008     

Hyperbranched polymers as scaffolds for multifunctional reversible addition–fragmentation chain‐transfer agents: A route to polystyrene‐core‐polyesters and polystyrene‐block‐poly(butyl acrylate)‐core‐polyesters

Polydisperse hyperbranched polyesters were modified for use as novel multifunctional reversible addition–fragmentation chain‐transfer (RAFT) agents. The polyester‐core‐based RAFT agents were subsequently employed to synthesize star polymers of n‐butyl acrylate and styrene with low polydispersity (polydispersity index < 1.3) in a living free‐radical process. Although the polyester‐core‐based RAFT agent mediated polymerization of n‐butyl acrylate displayed a linear evolution of the number‐average molecular weight (M_n) up to high monomer conversions (>70%) and molecular weights [M_n > 140,000 g mol^?1, linear poly(methyl methacrylate) equivalents)], the corresponding styrene‐based system reached a maximum molecular weight at low conversions (≈30%, M_n = 45,500 g mol^?1, linear polystyrene equivalents). The resulting star polymers were subsequently used as platforms for the preparation of star block copolymers of styrene and n‐butyl acrylate with a polyester core with low polydispersities (polydispersity index < 1.25). The generated polystyrene‐based star polymers were successfully cast into highly regular honeycomb‐structured microarrays. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3847–3861, 2003     

Synthesis,self‐assembly and recognition properties of biomimetic star‐shaped poly(ε‐caprolactone)‐b‐glycopolymer block copolymers

Biomimetic star‐shaped poly(ε‐caprolactone)‐b‐poly(gluconamidoethyl methacrylate) block copolymers (SPCL‐PGAMA) were synthesized from the atom transfer radical polymerization (ATRP) of unprotected GAMA glycomonomer using a tetra(2‐bromo‐2‐methylpropionyl)‐terminated star‐shaped poly(ε‐caprolactone) (SPCL‐Br) as a macroinitiator in NMP solution at room temperature. The block length of PGAMA glycopolymer within as‐synthesized SPCL‐PGAMA copolymers could be adjusted linearly by controlling the molar ratio of GAMA glycomonomer to SPCL‐Br macroinitiator, and the molecular weight distribution was reasonably narrow. The degree of crystallization of PCL block within copolymers decreased with the increasing block length ratio of outer PGAMA to inner PCL. Moreover, the self‐assembly properties of the SPCL‐PGAMA copolymers were investigated by NMR, UV‐vis, DLS, and TEM, respectively. The self‐assembled glucose‐installed aggregates changed from spherical micelles to worm‐like aggregates, then to vesicles with the decreasing weight fraction of hydrophilic PGAMA block. Furthermore, the biomolecular binding of SPCL‐PGAMA with Concanavalin A (Con A) was studied by means of UV‐vis, fluorescence spectroscopy, and DLS, which demonstrated that these SPCL‐PGAMA copolymers had specific recognition with Con A. Consequently, this will not only provide biomimetic star‐shaped SPCL‐PGAMA block copolymers for targeted drug delivery, but also improve the compatibility and drug release properties of PCL‐based biomaterials for hydrophilic peptide drugs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 817–829, 2008     

Synthesis and self‐assembly of well‐defined cyclodextrin‐centered amphiphilic A14B7 multimiktoarm star copolymers based on poly(ε‐caprolactone) and poly(acrylic acid)

Novel amphiphilic A₁₄B₇ multimiktoarm star copolymers composed of 14 poly(ε‐caprolactone) (PCL) arms and 7 poly(acrylic acid) (PAA) arms with β‐cyclodextrin (β‐CD) as core moiety were synthesized by the combination of controlled ring‐opening polymerization (CROP) and atom transfer radical polymerization (ATRP). 14‐Arm star PCL homopolymers (CDSi‐SPCL) were first synthesized by the CROP of CL using per‐6‐(tert‐butyldimethylsilyl)‐β‐CD as the multifunctional initiator in the presence of Sn(Oct)₂ at 125 °C. Subsequently, the hydroxyl end groups of CDSi‐SPCL were blocked by acetyl chloride. After desilylation of the tert‐butyldimethylsilyl ether groups from the β‐CD core, 7 ATRP initiating sites were introduced by treating with 2‐bromoisobutyryl bromide, which further initiated ATRP of tert‐butyl acrylate (tBA) to prepare well‐defined A₁₄B₇ multimiktoarm star copolymers [CDS(PCL‐PtBA)]. Their molecular structures and physical properties were in detail characterized by ¹H NMR, SEC‐MALLS, and DSC. The selective hydrolysis of tert‐butyl ester groups of the PtBA block gave the amphiphilic A₁₄B₇ multimiktoarm star copolymers [CDS(PCL‐PAA)]. These amphiphilic copolymers could self‐assemble into multimorphological aggregates in aqueous solution, which were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2961–2974, 2010     

Polyfluorenes minimally doped with 1,4‐bis(2‐thienyl‐2‐cyanovinyl)benzene chromophore: Their synthesis,characterization, and application to white‐light‐emitting materials

Copolyfluorenes ( PFR1 and PFR2 ), chemically doped with 0.1 and 0.025 mol % 2,5‐dihexyloxy‐1,4‐bis(2‐thienyl‐2‐cyanovinyl)benzene (MR chromophere) were synthesized by the Suzuki coupling reaction. The PFR s were used to fabricate white‐light‐emitting devices through incomplete energy transfer. Because of the low content of the MR chromophore, the optical, thermal, and electrochemical properties of the PFR s were almost identical to those of polyfluorene, except for their photoluminescent (PL) and electroluminescent (EL) properties. The copolymer films showed PL peaks at about 428 and 570 nm originating from fluorene segments and MR chromophores, respectively. Compared with the model compound ( MR ), the polymer chains extended the conjugation length of the MR chromophores and exhibited a 20–48 nm red‐shift in the emission band. In addition, the lower LUMO level of the MR (?3.27 eV) was expected to improve the electron injection. The EL devices [ITO/PEDOT:PSS/ PFR s/Ca (50 nm)/Al (100 nm)] showed a broad emission band, covering the entire visible region, with chromaticity coordinates of (0.36, 0.35) and (0.32, 0.30) for PFR1 and PFR2 devices, respectively. The emission color of the PFR2 device was very similar to that of a pure white light (0.33, 0.33); and the maximal brightness and current efficiency were 3011 cd/m² and 1.98 cd/A, respectively, which surpass those found for polyfluorene devices (1005 cd/m², 0.28 cd/A). A). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3703–3713, 2008     

Enhanced efficiency of polyfluorene derivatives: Organic–inorganic hybrid polymer light‐emitting diodes

Two novel organic–inorganic hybrid polyfluorene derivatives, poly{(9,9′‐dioctyl‐2,7‐fluorene)‐co‐(9,9′‐di‐POSS‐2,7‐fluorene)‐co‐[2,5‐bis(octyloxy)‐1,4‐phenylene]} (PFDOPPOSS) and poly{(9,9′‐dioctyl‐2,7‐fluorene)‐co‐(9,9′‐di‐POSS‐2,7‐fluorene)‐co‐bithiophene} (PFT2POSS), were synthesized by the Pd‐catalyzed Suzuki reaction of polyhedral oligomeric silsesquioxane (POSS) appended fluorene, dioctyl phenylene, and bithiophene moieties. The synthesized polymers were characterized with ¹H NMR spectroscopy and elemental analysis. Photoluminescence (PL) studies showed that the incorporation of the POSS pendant into the polyfluorene derivatives significantly enhanced the fluorescence quantum yields of the polymer films, likely via a reduction in the degree of interchain interaction as well as keto formation. Additionally, the blue‐light‐emitting polyfluorene derivative PFDOPPOSS showed high thermal color stability in PL. Moreover, single‐layer light‐emitting diode devices of an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration fabricated with PFDOPPOSS and PFT2POSS showed much improved brightness, maximum luminescence intensity, and quantum efficiency in comparison with devices fabricated with the corresponding pristine polymers PFDOP and PFT2. In particular, the maximum external quantum efficiency of PFT2POSS was 0.13%, which was twice that of PFT2 (0.06%), and the maximum current efficiency of PFT2POSS was 0.38 cd/A, which again was twice that of PFT2 (0.19 cd/A). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2943–2954, 2006     

Synthesis,photophysics, structure‐tunable photoluminescence,and electrochemical properties of soluble poly(p‐phenylenevinylene)‐based polymers with adjacent 1,3,4‐oxadiazoles in the backbone

Three new poly(p‐phenylenevinylene)‐based polymers containing two 1,3,4‐oxadiazole moieties in the main chain per repeat unit were synthesized by Heck coupling. A single, double, or triple bond was introduced between the oxadiazoles to provide a means for modifying the polymer properties. The polymers were readily soluble in common organic solvents and showed T_g values lower than 50 °C. The color of the emissive light in both the solid state and the solution could be tuned by a change in the nature of the bond between the oxadiazole rings. The polymers emitted ultraviolet‐green light in solution with a photoluminescence (PL) emission maximum at 345–483 nm and blue‐green light at 458–542 nm in thin films. The PL quantum yields in solution were 0.36–0.43. The electrochemical properties are affected by the nature of the bond between the oxadiazoles as well. In polymers with a single bond between the oxadiazoles, a lower ionization potential was observed than in polymers with a double or triple bond. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3079–3090, 2005     

Crystallization and stereocomplexation behavior of poly(D‐ and L‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) block copolymers

The thermal properties, crystallization, and morphology of amphiphilic poly(D ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PDLA‐b‐PDMAEMA) and poly (L ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were studied and compared to those of the corresponding poly(lactide) homopolymers. Additionally, stereocomplexation of these copolymers was studied. The crystallization kinetics of the PLA blocks was retarded by the presence of the PDMAEMA block. The studied copolymers were found to be miscible in the melt and the glassy state. The Avrami theory was able to predict the entire crystallization range of the PLA isothermal overall crystallization. The melting points of PLDA/PLLA and PLA/PLA‐b‐PDMAEMA stereocomplexes were higher than those formed by copolymer mixtures. This indicates that the PDMAEMA block is influencing the stability of the stereocomplex structures. For the low molecular weight samples, the stereocomplexes particles exhibited a conventional disk‐shape structure and, for high molecular weight samples, the particles displayed unusual star‐like shape morphology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1397–1409, 2011     

Synthesis of dendrimer‐like copolymers based on the star[Polystyrene‐Poly(ethylene oxide)‐Poly(ethoxyethyl glycidyl ether)] terpolymers by click chemistry

The dendrimer‐like copolymers [PEEGE‐(PS/PEO)]_n (n ≥ 2) based on the star[Polystyrene‐Poly(ethylene oxide)‐Poly(ethoxyethyl glycidyl ether)] [star(PS‐PEO‐(PEEGE‐OH))] terpolymers were synthesized by click chemistry. First, the star‐shaped copolymers star[PS‐PEO‐(PEEGE‐Alkyne)] (also termed as [PEEGE‐(PS/PEO)]₁) were synthesized by the reaction of hydroxyl end group at PEEGE arm (on star[PS‐PEO‐(PEEGE‐OH)]) with propargyl bromide. Then, the small molecule 1,4‐diazidobutane (DAB) with two azide groups and pentaerythritol tetrakis (2‐azidoisobutyrate) (PTAB) with four azide groups were synthesized and reacted with [PEEGE‐(PS/PEO)]₁ by the click chemistry for dendrimer‐like [PEEGE‐(PS/PEO)]₂ and [PEEGE‐(PS/PEO)]₄, respectively. However, in the latter case, only the [PEEGE‐(PS/PEO)]₃ was formed as the main product because of the steric effect. The final dendrimer‐like [PEEGE‐(PS/PEO)]_n copolymers were characterized by SEC and ¹H‐NMR in detail. Comparing with the SEC of their precursor [PEEGE‐(PS/PEO)]₁, the curves of [PEEGE‐(PS/PEO)]₂ was shifted to the shorter elution time, while that of [PEEGE‐(PS/PEO)]_n (n ≥ 3) was shifted to the longer elution time, which was attributed to the different hydrodynamic volume derived from their separate structures and compositions in THF solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4800–4810, 2009     

Improved Spectral Coverage and Fluorescence Quenching in Donor–acceptor Systems Involving Indolo[3‐2‐b]carbazole and Boron‐dipyrromethene or Diketopyrrolopyrrole

A novel π‐conjugated triad and a polymer incorporating indolo[3,2‐b]‐carbazole (ICZ) and 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) were synthesized via a Sonogashira coupling. Compared to the parent BODIPY the absorption and fluorescence spectrum were for both compounds broader and redshifted. The redshift of the fluorescence and the decrease of the fluorescence quantum yield and decay time upon increasing solvent polarity were attributed to the formation of a partial charge‐transfer state. Upon excitation in the ICZ absorption band the ICZ fluorescence was quenched in both compounds mainly due to energy transfer to the BODIPY moiety. In a similar ICZ–π–DPP polymer (where DPP is diketopyrrolopyrrole), a smaller redshift of the absorption and fluorescence spectra compared to the parent DPP was observed. A less efficient quenching of the ICZ fluorescence in the ICZ–π–DPP polymer could be related to the unfavorable orientation of the transition dipoles of ICZ and DPP. The rate constant for energy transfer was for all compounds an order of magnitude smaller than predicted by Förster theory. While in a solid film of the triad a further redshift of the absorption maximum of nearly 100 nm was observed, no such shift was observed for the ICZ–π–BODIPY polymer.