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Alternating Copolymer (alternating + copolymer)
Selected AbstractsCopolymers of Cyclopentadithiophene and Electron-Deficient Aromatic Units Designed for Photovoltaic ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Johan C. Bijleveld Abstract Alternating copolymers based on cyclopentadithiophene (CPDT) and five different electron-deficient aromatic units with reduced optical band gaps are synthesized via Suzuki coupling. All polymers show a significant photovoltaic response when mixed with a fullerene acceptor. The frontier orbital levels of the new polymers are designed to minimize energy losses by increasing the open-circuit voltage with respect to the optical band gap, while maintaining a high coverage of the absorption with the solar spectrum. The best cells are obtained for a copolymer of CPDT and benzooxadiazole (BO) with a band gap of 1.47,eV. This cell gives a short-circuit current of 5.4,mA cm,2, an open-circuit voltage of 0.78,V, and a fill factor of 0.6, resulting in a power conversion efficiency of about 2.5%. [source] Benzoyl peroxide,p -acetylbenzylidenetriphenyl arsoniumylide initiated copolymerization of citronellol and styrenePOLYMER INTERNATIONAL, Issue 8 2001K Srivastava Abstract Alternating copolymers, containing styrene and citronellol sequences, have been synthesized by radical polymerization using benzoylperoxide (BPO),p -acetylbenzylidenetriphenyl arsoniumylide (pABTAY) as initiator, in xylene at 80,±,1,°C for 3,h under inert atmosphere. The kinetic expression is Rp , [BPO]0.88 [citronellol]0.68 [styrene]0.56 with BPO and Rp , [pABTAY]0.27 [citronellol]0.76 [styrene]0.63 with pABTAY, ie the system follows non-ideal kinetics in both cases, because of primary radical termination and degradative chain transfer reactions. The activation energy with BPO and pABTAY is 94,kJ,mol,1 and 134,kJ,mol,1, respectively. Different spectral techniques, such as IR, FTIR, 1H NMR and 13C NMR, have been used to characterize the copolymer, demonstrating the presence of alcoholic and phenyl groups of citronellol and styrene. The alternating nature of the copolymer is shown by the product of reactivity ratios r1 (Sty),=,0.81 and r2 (Citro),=,0.015 using BPO and r1 (Sty),=,0.37 and r2 (Citro),=,0.01 using (pABTAY), which are calculated by the Finemann,Ross method. A mechanism of copolymerization is proposed. © 2001 Society of Chemical Industry [source] High-Performance Polymer Solar Cells of an Alternating Polyfluorene Copolymer and a Fullerene Derivative,ADVANCED MATERIALS, Issue 12 2003M. Svensson Solar cells prepared using the alternating copolymer shown in the Figure blended with a C60 derivative (PCBM) are demonstrated to have a high performance, with a power conversion efficiency of 2.2,% under simulated solar light. The molecular weight of the polymer is low due to limited solubility, and films of the polymer exhibit red-shifted absorption. [source] Lower critical solution temperature determination of smart, thermosensitive N -isopropylacrylamide- alt -2-hydroxyethyl methacrylate copolymers: Kinetics and physical propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Mohammad M. Fares Abstract The lower critical solution temperatures (LCSTs) were verified and determined for different molar feed ratios of N -isopropylacrylamide (NIPAAm) and 2-hydroxyethyl methacrylate (HEMA) monomers with ultraviolet spectroscopy and differential scanning calorimetry techniques. Increases in the NIPAAm monomer content played a crucial role in the LCST, which increased up to 36.7°C at 50 mol %. However, a further increase in the NIPAAm monomer content steadily reduced the LCST, which decreased to 33°C at 100 mol % NIPAAm [i.e., pure poly(N -isopropylacrylamide)]. The rate of copolymerization, assessed by the conventional conversion (%),time method, and the apparent activation energies were determined. The reactivity ratios of the monomers, determined by the Kelen,Tudos and Fineman,Ross techniques, together with the results of an equation, showed that the copolymer which formed was an alternating copolymer. The Q,e values for the NIPAAm monomer were determined. The equation showed the linear Arrhenius behavior of ln(r1r2) versus the reciprocal of the temperature (where r1 and r2 are the reactivity ratios of NIPAAm and HEMA, respectively): the activation energy difference [i.e., (E12 + E21) , (E11 + E22), where E12, E21, E11, and E22 are various activation energies] was found to be ,109 kJ/mol. The copolymers were characterized with 1H-NMR, 13C-NMR, Fourier transform infrared, ultraviolet,visible, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy techniques. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] A paradigm for the mechanisms and products of spontaneous polymerizationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009H. K. Hall Jr. Abstract In spontaneous vinyl and ring-opening copolymerizations, polar and resonance effects on the intermediates from bond-forming initiation offer a continuous spectrum of reactivities and polymer structures. In bond-forming initiation, an electron-rich donor monomer forms a bond to an acceptor monomer. The donor monomer may be a vinyl monomer with O, N, or aryl substituent or it may be an aza- or oxacycle. The acceptor monomer may be a vinyl monomer carrying CN, COOR, or SO2R substituent or it may be a cyclic anhydride or maleimide. Beyond this, the donor may have a ,-like strained single bond, whereas the acceptor may be an electrophilic quinodimethane. Lewis acids may be used to enhance the electrophilicity of acceptor monomers. Reaction rates and polymer composition are determined by systematically varying the stability of the first intermediate, designated P (for polymethylene). The nature of the intermediate will vary from a highly reactive trans biradical, which initiates chain alternating copolymerization, to a cis/gauche zwitterion, which can initiate chain ionic homopolymerization, to an extremely stabilized zwitterion, which cannot add monomer, but builds up in concentration and terminates by combination, forming alternating copolymer. This model embraces the existing literature for a wide variety of monomers and possesses predictive power. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] Benzoyl peroxide-initiated copolymerization of citronellol and vinyl acetateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2002Prachi Pandey Abstract The radical copolymerization of citronellol with vinyl acetate (VA) in xylene at 60 ± 0.1 °C for 90 min in the presence of benzoyl peroxide follows ideal kinetics and results in the formation of an alternating copolymer as demonstrated by the values of the reactivity ratios [r1 (VA) = 0.02 and r2 (citronellol) = 0.0002], which have been calculated with the Kelen,Tüdos method. The overall activation energy is computed to be 75 kJ/mol. The IR spectrum of the copolymer shows the presence of bands at 3400 cm,1 due to an alcoholic group and 1750 cm,1 due to a ,CO group. The values of the Mark,Houwink constants for this copolymer system have been determined with gel permeation chromatography to be , = 0.375 and K = 2.4 × 10,4. The glass-transition temperature, determined with differential scanning calorimetry, is 68.32 °C. The mechanism has been elucidated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1243,1252, 2002 [source] Polymers from Multifunctional Isocyanates, 15,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2007A Novel Alternating Copolymer Containing an Isocyanate, a Cyanate Group in the Repeating Unit Abstract N -(4-cyanatophenyl)maleimide and 2-isocyanato propene were copolymerised to give an alternating copolymer, which is the first example of a polymer having an isocyanate as well as a cyanate reactive functional group in the repeating unit. The polymer analogous reaction with methanol proceeded selectively at the isocyanate groups. Crosslinking of the cyanate-urethane copolymers by cyclotrimerisation of cyanate groups occurred at elevated temperature. Reaction with dibutylamine at 20,°C led to complete reaction of both the cyanate and isocyanate moieties in a non-selective manner. [source] Determination of reactivity ratios and kinetics of free radical copolymerization of linalool with styrenePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2004Anjali Shukla Abstract Copolymerization of acyclic monoterpenoid, namely linalool (LIN), with styrene (STY) initiated by benzoyl peroxide (BPO) p -acetyl benzylidene triphenyl arsonium ylide (p -ABTAY) in xylene separately at 80°C for 180,min under inert atmosphere of nitrogen was performed. The results give a nearly alternating copolymer as evidenced from reactivity ratios (r1,=,0.016, r2,=,0.057) w.r.t. BPO; (r1,=,0.017, r2,=,0.052) w.r.t. p-ABTAY (i.e. r1,=,0.0165,±,0.0005 and r2,=,0.0545,±,0.0025 per initiator set) using Kelen,Tudos method. The FT-IR spectrum shows a band at 3026,cm,1 due to the aromatic ring of polystyrene and an alcoholic band of linalool at 3408,cm,1. 1H-NMR spectrum shows peaks at , 7.0,7.7,ppm of OH protons and peaks at , 7.5,8.0,ppm due to phenyl protons of styrene. The system follows ideal kinetics i.e. Rp,,,[LIN]1.0[STY]1.0[BPO]0.5/[p-ABTAY]0.5. The overall energy of activation in the temperature range 75,85°C is 77.0,kJ,mol,1 and 90.0,kJ,mol,1, respectively. The values for Mark,Houwink constants for the functional copolymer has been evaluated as a,=,0.40 and K,=,1.60,×,10,4 with the help of gel permeation chromatography (GPC). Alfrey,Price, Q and e parameters for linalool have been evaluated as Q2,=,0.80; e2,=,1.25,w.r.t. BPO and Q2,=,0.90; e2,=,1.54,w.r.t. p-ABTAY. Thermal properties of copolymers were investigated by thermogravimetric analysis (TGA) techniques. Copyright © 2004 John Wiley & Sons, Ltd. [source] Regulation of comonomer-Sequenceand stereosequence in radical copolymerization of methyl methacrylate and styrene,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-5 2003Hidefumi Hirai Abstract The radical copolymerization of methyl methacrylate (MMA) and styrene (St) in the presence of various metal halides was conducted to achieve the advanced regulation of comonomer-sequence and stereosequence in the resulting copolymers. The alternation-regulating activities of various metal halides were determined quantitatively by the MMA content in the copolymer prepared under the specific conditions. Boron trichloride, aluminum tribromide and ethyl boron dichloride were found to have large alternation-regulating activities, yielding the strictly alternating MMA-St copolymers with high regulation of comonomer-sequence. The cotacticities of the -MMA-St- diad, the -St-MMA-St- triad and the-MMA-St-MMA- triad in the alternating copolymer were determined by 1H- and 13C-NMR spectroscopies. The cotacticities depend on the species and the concentrations of the metal halides, and on the polymerization temperatures. The alternating MMA-St copolymer with the highest coheterotacticity has been prepared by using boron trichloride at,,,95,°C. The mechanism of the stereosequence regulation is described in detail. Copyright © 2003 John Wiley & Sons, Ltd. [source] Facile synthesis of functional polyperoxides by radical alternating copolymerization of 1,3-dienes with oxygenTHE CHEMICAL RECORD, Issue 5 2009Eriko Sato Abstract We have developed a facile synthesis of degradable polyperoxides by the radical alternating copolymerization of 1,3-diene monomers with molecular oxygen at an atmospheric pressure. In this review, the synthesis, the degradation behavior, and the applications of functional polyperoxides are summarized. The alkyl sorbates as the conjugated 1,3-dienes gave a regiospecific alternating copolymer by exclusive 5,4-addition during polymerization and the resulting polyperoxides decomposed by the homolysis of a peroxy linkage followed by successive , -scissions. The preference of 5,4-addition was well rationalized by theoretical calculations. The degradation of the polyperoxides occurred with various stimuli, such as heating, UV irradiation, a redox reaction with amines, and an enzyme reaction. The various functional polyperoxides were synthesized by following two methods, one is the direct copolymerization of functional 1,3-dienes, and the other is the functionalization of the precursor polyperoxides. Water soluble polyperoxides were also prepared, and the LCST behavior and the application to a drug carrier in the drug delivery system were investigated. In order to design various types of degradable polymers and gels we developed a method for the introduction of dienyl groups into the precursor polymers. The resulting dienyl-functionalized polymers were used for the degradable gels. The degradable branched copolymers showed a microphase-separated structure, which changed owing to the degradation of the polyperoxide segments. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 000,000; 2009: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.200900009 [source] Role of the Preparation Procedure in the Formation of Spherical and Monodisperse Surfactant/Polyelectrolyte ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Yuxia Luan Dr. Abstract Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed. [source] Observation of a Charge Transfer State in Low-Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence StudiesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Yi Zhou Abstract The presence of charge transfer states generated by the interaction between the fullerene acceptor PCBM and two alternating copolymers of fluorene with donor,acceptor,donor comonomers are reported; the generation leads to modifications in the polymer bandgap and electronic structure. In one of polymer/fullerene blends, the driving force for photocurrent generation, i.e., the gap between the lowest unoccupied molecular orbitals of the donor and acceptor, is only 0.1,eV, but photocurrent is generated. It is shown that the presence of a charge transfer state is more important than the driving force. The charge transfer states are visible through new emission peaks in the photoluminescence spectra and through electroluminescence at a forward bias. The photoluminescence can be quenched under reverse bias, and can be directly correlated to the mechanism of photocurrent generation. The excited charge transfer state is easily dissociated into free charge carriers, and is an important intermediate state through which free charge carriers are generated. [source] Synthesis and properties of new fluorinated polymers bearing pendant imidazole groups for fuel cell membranes operating over a broad relative humidity rangeJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2010Guillaume Frutsaert Abstract New alternating copolymers comprising a chlorotrifluorinated backbone and imidazole-terminated pendant ethylene oxide groups have been prepared with a view to their use as a component of proton-conducting membranes in polymer electrolyte fuel cells. A vinyl ether containing an imidazole (Imi) function protected by a benzyl group (BVI) was first synthesized in a three-step reaction. It was then copolymerized in solution with chlorotrifluoroethylene (CTFE) by conventional radical copolymerization leading to alternating poly(BVI-alt-CTFE) copolymers in good yields. Deprotection of the benzyl group under hydrogen produced a chlorotrifluorinated poly(Imi-alt-CTFE) copolymer. The polymer was subsequently used to form blend membranes with sulfonated poly(ether ether ketone) (sPEEK). The conductivity of blend membranes of poly (Imi-alt-CTFE) with sPEEK lies in the range of 4,10 mS cm,1 at 40,70 °C and, for blend membranes rich in poly(Imi-alt-CTFE), is little dependent on relative humidity between 30 and 100%. It is surmised that the polymer and membrane composition favor microstructural phase separation into chlorotrifluorinated polymer backbone domains and regions in which imidazole groups are clustered. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 223,231, 2010 [source] Photoinitiated alternating copolymerization of vinyl ethers with chlorotrifluoroethylenePOLYMER INTERNATIONAL, Issue 7 2002Manuel Gaboyard Abstract The photoinitiated copolymerization of chlorotrifluoroethylene (CTFE) with several vinyl ethers [ethyl vinyl ether (EVE), 2-chloroethyl vinyl ether (CEVE), cyclohexyl vinyl ether (CHVE), 4-hydroxybutyl vinyl ether (HBVE)] was studied. CTFE is an acceptor monomer (e,,,1.5) whereas vinyl ethers are donor monomers (e,,,,1.5), and therefore their copolymerization led to alternating copolymers, as indicated by elementary analysis. The equilibrium constant (KF) of the charge-transfer complex formation (CTC) was determined by 19F NMR spectroscopy. Under our experimental conditions, KF was low for CHVE/CTFE and HBVE/CTFE systems, 0.058 and 0.013,l mol,1 respectively. It can be assumed that the copolymerization involves the free monomers rather than propagation via the donor,acceptor complex. The alternating structure arises from the great difference in polarity between the two types of monomers. Several functional copolymers were prepared in good yield and with molecular weight close to 15,000,g,mol,1. © 2002 Society of Chemical Industry [source] | |||||||||||||||||||||||||