Number-average Molecular Weight (number-average + molecular_weight)

Distribution by Scientific Domains

Selected Abstracts

Enhanced photodegradation efficiency of polyethylene-TiO2 nanocomposite film with oxidized polyethylene wax

Wenjun Fa
Abstract A novel photodegradable polyethylene-oxidized polyethylene wax-TiO2 (PE-OPW-TiO2) nanocomposite film was prepared by embedding the organically modified TiO2 nanoparticles into commercial PE in the presence of OPW. The photocatalytic degradation behavior under ultraviolet light or solar light was investigated by examining the weight loss of the composite films, UV,vis transmittance spectrum, scanning electron microscope (SEM), and gel permeation chromatogram (GPC). The results show that OPW, as a dispersant and a compatibiliser, markedly improves the dispersion and compatibility of TiO2 nanoparticles in PE resins. The PE-OPW-TiO2 composite film demonstrates much higher photodegradation efficiency and much better mechanical property than either the PE-TiO2 composite film or the pure PE film. The weight-average molecular weight (Mw) of the PE-OPW-TiO2 composite film decreased 94.3% and the number-average molecular weight (Mn) decreased 84.5% after 38 days solar light irradiation. The photocatalytic degradation mechanism of the film is briefly discussed. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Ring opening polymerization of aliphatic cyclic carbonates in the presence of natural amino acids

Jiyan Liu
Abstract Poly(dimethyl trimethylene carbonate) (PDTC) and poly(trimethylene carbonate) (PTMC) were synthesized by ring-opening polymerization (ROP) of dimethly trimethylene carbonate (DTC) and trimethylene carbonate (TMC) in the presence of five kinds of natural amino acids (L -alanine, L -valine, L -leucine, L -proline, and L -phenylalanine). PDTCs with number-average molecular weight (Mn) from 6700 to 18,900 g/mol and PTMCs with Mn from 7200 to 17,800 g/mol were obtained at a feed ratio of [monomer]/[L -phenylalanine] ranging from 50 to 200. The results of 1H nuclear magnetic resonance and titration proved amino acid connecting onto the polymer backbone. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Synthesis of a linear polyethylene macromonomer and preparation of polystyrene- graft -polyethylene copolymers via grafting-through atom transfer radical polymerization,

Hiromu Kaneyoshi
Abstract A vinyl-terminated linear polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight = 1.7, functionality = 92%) prepared by ethylene coordination polymerization was transformed into a monohydroxy-terminated linear polyethylene by hydroalumination of the vinyl group with diisobutylaluminum hydride and subsequent oxidation and hydrolysis. This monohydroxy-terminated linear polyethylene was quantitatively converted into a linear polyethylene macromonomer with a terminal ,-methacrylate group through esterification followed by dehydrobromination. A grafting-through atom transfer radical polymerization of the ,-methacrylate-terminated polyethylene and styrene was performed to yield a well-defined polystyrene- graft -polyethylene copolymer. The number-average molecular weight of the graft copolymers, measured by gel permeation chromatography, was lower than the predetermined number-average molecular weight, presumably because of the intramolecular aggregation of polyethylene side chains. The ,-methacrylate-terminated polyethylene content and number-average molecular weight of polystyrene- graft -polyethylene were determined by 1H-NMR. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 3,13, 2007 [source]

Synthesis and characterization of a thiadiazole/benzoimidazole-based copolymer for solar cell applications

Guan-yu Chen
Abstract In this study, we synthesized a new polymer, PCTDBI, containing alternating carbazole and thiadiazole-benzoimidazole (TDBI) units. This polymer (number-average molecular weight = 25,600 g mol,1), which features a planar imidazole structure into the polymeric main chain, possesses reasonably good thermal properties (Tg = 105 C; Td = 396 C) and an optical band gap of 1.75 eV that matches the maximum photon flux of sunlight. Electrochemical measurements revealed an appropriate energy band offset between the polymer's lowest unoccupied molecular orbital and that of PCBM, thereby allowing efficient electron transfer between the two species. A solar cell device incorporating PCTDBI and PCBM at a blend ratio of 1:2 (w/w) exhibited a power conversion efficiency of 1.20%; the corresponding device incorporating PCTDBI and PC71BM (1:2, w/w) exhibited a PCE of 1.84%. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source]

Synthesis of magnetic, reactive, and thermoresponsive Fe3O4 nanoparticles via surface-initiated RAFT copolymerization of N -isopropylacrylamide and acrolein

Zhong-Peng Xiao
Abstract A reversible addition-fragmentation chain transfer (RAFT) agent was directly anchored onto Fe3O4 nanoparticles in a simple procedure using a ligand exchange reaction of S -1-dodecyl- S,-(,,,,-dimethyl-,,-acetic acid)trithiocarbonate with oleic acid initially present on the surface of pristine Fe3O4 nanoparticles. The RAFT agent-functionalized Fe3O4 nanoparticles were then used for the surface-initiated RAFT copolymerization of N -isopropylacrylamide and acrolein to fabricate structurally well-defined hybrid nanoparticles with reactive and thermoresponsive poly(N -isopropylacrylamide- co -acrolein) shell and magnetic Fe3O4 core. Evidence of a well-controlled surface-initiated RAFT copolymerization was gained from a linear increase of number-average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive, and thermoresponsive core-shell nanoparticles exhibited temperature-trigged magnetic separation behavior and high ability to immobilize model protein BSA. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 542,550, 2010 [source]

Synthesis of gradient copolymers with complexing groups by RAFT polymerization and their solubility in supercritical CO2

Tiphaine Ribaut
Abstract We report the synthesis of new gradient fluorinated copolymers with complexing groups and soluble in supercritical carbon dioxide (scCO2). Poly(1,1,2,2-tetrahydroperfluorodecyl acrylate- co -acetoacetoxyethyl methacrylate) (poly(FDA- co -AAEM)) and poly(1,1,2,2-tetrahydroperfluorodecyl acrylate- co -vinylbenzylphosphonic acid diethylester) (poly(FDA- co -VBPDE)) gradient copolymers were synthesized by reversible addition fragmentation chain transfer polymerization in ,,,,,-trifluorotoluene. Poly(1,1,2,2-tetrahydroperfluorodecyl acrylate- co -vinylbenzylphosphonic diacid) (poly(FDA- co -VBPDA)) gradient copolymer was efficiently obtained by cleavage of the phosphonic ester groups of poly(FDA- co -VBPDE). The cloud points of these gradient copolymers in dense CO2 were measured in a variable volume view cell at temperatures between 25 and 65 C. The gradient copolymers show very good solubility in compressed CO2 with the decreasing order: poly(FDA- co -AAEM) , poly(FDA- co -VBPDE) > poly(FDA- co -VBPDA). Following a green chemistry strategy, poly(FDA- co -AAEM) gradient copolymer was successfully synthesized in scCO2 with a good control over number-average molecular weight and composition. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5448,5460, 2009 [source]

The kinetics of enhanced spin capturing polymerization: Influence of the nitrone structure

Edgar H. H. Wong
Abstract Several nitrones and one nitroso compound have been evaluated for their ability to control the molecular weight of polystyrene via the recently introduced radical polymerization method of enhanced spin capturing polymerization (ESCP). In this technique, molecular weight control is achieved (at ambient or slightly elevated temperatures) via the reaction of a growing radical chain with a nitrone forming a macronitroxide. These nitroxides subsequently react rapidly and irreversibly with propagating macroradicals forming polymer of a certain chain length, which depends on the nitrone concentration in the system. Via evaluation of the resulting number-average molecular weight, Mn, at low conversions, the addition rate coefficient of the growing radicals onto the different nitrones is determined and activation energies are obtained. For the nitrones N - tert -butyl-,-phenylnitrone (PBN), N -methyl-,-phenylnitrone (PMN), and N -methyl-,-(4-bromo-phenyl) nitrone (pB-PMN), addition rate coefficients, kad,macro, in a similar magnitude to the styrene propagation rate coefficient, kp, are found with spin capturing constants CSC (with CSC = kad,macro/kp) ranging from 1 to 13 depending on the nitrone and on temperature. Activation energies between 23.6 and 27.7 kJ mol,1 were deduced for kad,macro, congruent with a decreasing CSC with increasing temperature. Almost constant Mn over up to high monomer to polymer conversions is found when CSC is close to unity, while increasing molecular weights can be observed when the CSC is large. From temperatures of 100 C onward, reversible cleavage of the alkoxyamine group can occur, superimposing a reversible activation/deactivation mechanism onto the ESCP system. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1098,1107, 2009 [source]

Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensors

Jichang Feng
Abstract A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5,-Divinyl-2,2,-bipyridyl with tris(4-bromophenyl)amine and with 4,4,-dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, 1H NMR, and 13C NMR. The polymer HTP had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV,vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer-based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222,230, 2009 [source]

Novel fluorescent (p -phenylene ethynylene)-calix[4]arene-based polymer: Design, synthesis, and properties

Alexandra I. Costa
Abstract A novel fluorescent (p -phenylene ethynylene)-calix[4]arene-based polymer (CALIX-PPE) has been successfully synthesized by cross-coupling polymerization of bis-calix[4]arene 1 with 1,4-diethynylbenzene. The polycondensation was carried out in toluene/NEt3 at 35 C for 24 h, using PdCl2(PPh3)2/CuI as the catalytic system, furnishing CALIX-PPE in excellent isolated yields (higher than 95%, several runs). The yellow polymer is freely soluble in several nonprotic organic solvents. The GPC trace of the isolated polymer showed a monomodal distribution and a number-average molecular weight of 23,300 g mol,1 (Mw/Mn = 2.05). No evidence was found in the structural analysis (FTIR and 1H/13C NMR) regarding the formation of alkyne homocoupled segments along the polymer chain. For comparative purposes, the synthesis of an analogous poly(p -phenylene ethynylene) containing p - t -butyl-phenoxymethyl side chains (TBP-PPE) was also undertaken. A great similarity was found between the photophysical properties of CALIX-PPE and TBP-PPE in solution (UV,vis and laser induced luminescence), clearly demonstrating their unique dependence on the structure and conformation of the conjugated PPE backbone. The fluorescence spectra of polymers are of nearly identical shape, displaying their maximum emission around 420 nm. The calculated solution photoluminescence quantum yields of CALIX-PPE and TBP-PPE are of similar magnitude (,F(CALIX-PPE) = 0.43; ,F(TBP-PPE) = 0.51). 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6477,6488, 2008 [source]

Synthesis of hyperbranched polymer having binaphthol units via oxidative cross-coupling polymerization

Tomohisa Temma
Abstract The oxidative coupling polymerization of triphenylamine derivatives having 2-naphthol moieties with a CuCl-2,2,-isopropylidenebis(4-phenyl-2-oxazoline) catalyst under an O2 atmosphere was carried out. The polymerization of the monomer bearing both the hydroxynaphthoate and naphthol units afforded a hyperbranched polymer with a high cross-coupling selectivity of > 99%, which showed a number-average molecular weight of 20.3 103. In addition, the obtained polymer was quite soluble in THF. The photoluminescence and electrochemical properties of the obtained polymers were also examined. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1034,1041, 2008 [source]

Synthesis and characterization of multiblock copolymers composed of poly(5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one) outer blocks and poly(L -lactide) inner blocks

Jamie M. Messman
Abstract Ethylene glycol (EG) initiated, hydroxyl-telechelic poly(L -lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring-opening polymerization of 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) with the goal of creating A,B,A-type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A,(B,A)n,B,A type were actually obtained, where A is poly(5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one), B is PLLA, and n is greater than 0. 1H and 13C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number-average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C6H8O4 units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number-average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide-angle X-ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high-conversion L -lactide polymerizations resulted in excessive randomization, presumably because of residual L -lactide monomer. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817,6835, 2006 [source]

Synthesis and characterization of poly(ethylene oxide- co -ethylene carbonate) macromonomers and their use in the preparation of crosslinked polymer electrolytes

Anette Munch Elmr
Abstract Methacrylate-functionalized poly(ethylene oxide- co -ethylene carbonate) macromonomers were prepared in two steps by the anionic ring-opening polymerization of ethylene carbonate at 180 C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number-average molecular weight of 2650 g mol,1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self-supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 10,6 S cm,1 at 20 C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195,2205, 2006 [source]

Effect of the molecular weight and architecture on the size and glass transition of arborescent polyisobutylenes

Judit E. Puskas
Abstract This article discusses the characterization of arborescent (hyperbranched) polyisobutylenes (arb-PIBs) by size exclusion chromatography and differential scanning calorimetry, in comparison with linear PIB standards. The radius of gyration (,r,1/2 = Rz), measured from the angle dependence of light scattering of high-molecular-weight arb-PIBs, was significantly larger than the hydrodynamic radius (Rh) from size exclusion chromatography/viscometry, and the Rh values were significantly smaller than Rh of linear PIBs. The glass-transition temperature of arb-PIBs having a branch molecular weight higher than the critical entanglement molecular weight was dependent on both the total number-average molecular weight and BR up to BR , 15. A modified Fox,Flory equation is proposed to describe the effect of architecture on the thermal transition. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1770,1776, 2006 [source]

Acyclic diene metathesis polymerization of 2,5-dialkyl-1,4-divinylbenzene with molybdenum or ruthenium catalysts: Factors affecting the precise synthesis of defect-free, high-molecular-weight trans -poly(p -phenylene vinylene)s

Kotohiro Nomura
Abstract Factors affecting the syntheses of high-molecular-weight poly(2,5-dialkyl-1,4-phenylene vinylene) by the acyclic diene metathesis polymerization of 2,5-dialkyl-1,4-divinylbenzenes [alkyl = n -octyl (2) and 2-ethylhexyl (3)] with a molybdenum or ruthenium catalyst were explored. The polymerizations of 2 by Mo(N -2,6-Me2C6H3) (CHMe2 Ph)[OCMe(CF3)2]2 at 25 C was completed with both a high initial monomer concentration and reduced pressure, affording poly(p -phenylene vinylene)s with low polydispersity index values (number-average molecular weight = 3.3,3.65 103 by gel permeation chromatography vs polystyrene standards, weight-average molecular weight/number-average molecular weight = 1.1,1.2), but the polymerization of 3 was not completed under the same conditions. The synthesis of structurally regular (all- trans), defect-free, high-molecular-weight 2-ethylhexyl substituted poly(p -phenylene vinylene)s [poly3; degree of monomer repeating unit (DPn) = ca. 16,70 by 1H NMR] with unimodal molecular weight distributions (number-average molecular weight = 8.30,36.3 103 by gel permeation chromatography, weight-average molecular weight/number-average molecular weight = 1.6,2.1) and with defined polymer chain ends (as a vinyl group, CHCH2) was achieved when Ru(CHPh)(Cl)2(IMesH2)(PCy3) or Ru(CH-2-OiPr-C6H4)(Cl)2(IMesH2) [IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene] was employed as a catalyst at 50 C. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6166,6177, 2005 [source]

Synthesis of well-defined three-armed polystyrene having thiourethane,isocyanurate as the core structure derived from trifunctional five-membered cyclic dithiocarbonate

Akane Suzuki
Abstract The synthesis of a three-armed polymer with an isocyanurate,thiourethane core structure is described. Monofunctional reversible addition,fragmentation chain transfer (RAFT) agent 2 and trifunctional RAFT agent 5 were prepared from mercapto-thiourethane and tris(mercapto-thiourethane), which were obtained from the aminolysis of mono- and trifunctional five-membered cyclic dithiocarbonates, respectively. The radical polymerization of styrene in the presence of 2,2,-azobis(isobutyronitrile) and RAFT agent 2 in bulk at 60 C proceeded in a controlled fashion to afford the corresponding polystyrene with desired molecular weights (number-average molecular weight = 3000,10,100) and narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight < 1.13). On the basis of the successful results with the monofunctional RAFT agents, three-armed polystyrene with thiourethane,isocyanurate as the core structure could be obtained with trifunctional RAFT agent 5 in a similar manner. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5498,5505, 2005 [source]

Controlled radical polymerization of a trialkylsilyl methacrylate by reversible addition,fragmentation chain transfer polymerization

M. N. Nguyen
Abstract The reversible addition,fragmentation chain transfer (RAFT) polymerization of a hydrolyzable monomer (tert -butyldimethylsilyl methacrylate) with cumyl dithiobenzoate and 2-cyanoprop-2-yl dithiobenzoate as chain-transfer agents was studied in toluene solutions at 70 C. The resulting homopolymers had low polydispersity (polydispersity index < 1.3) up to 96% monomer conversion with molecular weights at high conversions close to the theoretical prediction. The profiles of the number-average molecular weight versus the conversion revealed controlled polymerization features with chain-transfer constants expected between 1.0 and 10. A series of poly(tert -butyldimethylsilyl methacrylate)s were synthesized over the molecular weight range of 1.0 104 to 3.0 104, as determined by size exclusion chromatography. As strong differences of hydrodynamic volumes in tetrahydrofuran between poly(methyl methacrylate), polystyrene standards, and poly(tert -butyldimethylsilyl methacrylate) were observed, true molecular weights were obtained from a light scattering detector equipped in a triple-detector size exclusion chromatograph. The Mark,Houwink,Sakurada parameters for poly(tert -butyldimethylsilyl methacrylate) were assessed to obtain directly true molecular weight values from size exclusion chromatography with universal calibration. In addition, a RAFT agent efficiency above 94% was confirmed at high conversions by both light scattering detection and 1H NMR spectroscopy. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5680,5689, 2005 [source]

Synthesis of well-defined AB20 -type star polymers with cyclodextrin-core by combination of NMP and ATRP

Yutaka Miura
Abstract The synthesis of an AB20 -type heteroarm star polymer consisting of a polystyrene arm and 20-arms of poly(methyl methacrylate) or poly(tert -butyl acrylate) was carried out using the combination of nitroxide-mediated polymerization (NMP) and atom transfer radical polymerization (ATRP). The NMP of styrene was carried out using mono-6-[4-(1,-(2,,2,,6,,6,-tetramethyl-1,-piperidinyloxy)-ethyl)benzamido]-,-cyclodextrin peracetate (1) to afford end-functionalized polystyrene with an acetylated ,-cyclodextrin (,-CyD) unit (prepolymer 2) with a number-average molecular weight (Mn) of 11700 and a polydispersity (Mw/Mn) of 1.17. After deacetylation of prepolymer 2, the resulting polymer was reacted with 2-bromoisobutyric anhydride to give end-functionalized polystyrene with 20(2-bromoisobutyrol)s ,-CyD, macroinitiator 4. The copper (I)-mediated ATRP of methyl methacrylate (MMA) and tert -butyl acrylate (tBA) was carried out using macroinitiator 4. The resulting polymers were isolated by SEC fractionation to produce AB20 -type star polymers with a ,-CyD-core, 5. The well-defined structure of 5 with weight-average molecular weight (Mw)s of 13,500,65,300 and Mw/Mn's of 1.26,1.28 was demonstrated by SEC and light scattering measurements. The arm polymers were separated from 5 by destruction with 28 wt % sodium methoxide in order to analyze the details of their characteristic structure. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4271,4279, 2005 [source]

Synthesis of photosensitive and thermosetting poly(phenylene ether) based on poly[2,6-di(3-methyl-2-butenyl)phenol- co -2,6-dimethyl-phenol] and a photoacid generator

Kazuya Matsumoto
Abstract A chemically amplified photosensitive and thermosetting polymer based on poly[2,6-di(3-methyl-2-butenyl)phenol (15 mol %)- co -2,6-dimethylphenol (85 mol %)] (3c) and a photoacid generator [(5-propylsulfonyloxyimino-5H-thiophen-2-ylidene)-(2-methylphenyl)acetonitrile] was developed. Poly[2,6-bis(3-methyl-2-butenyl)phenol]- co -2,6-dimethylphenol)] (3) with high molecular weights (number-average molecular weight , 24,000) was prepared by the oxidative coupling copolymerization of 2,6-di(3-methyl-2-butenyl)phenol with 2,6-dimethylphenol in the presence of copper(I) chloride and pyridine as the catalyst under a stream of oxygen. The structures of 3 were characterized with IR, 1H NMR, and 13C NMR spectroscopy. 3 was crosslinked by a thermal treatment at 300 C for 1 h under N2. The 5% weight loss temperatures and glass-transition temperatures of the cured copolymers reached around 420 C in nitrogen and 300 C, respectively. The average refractive index of the cured copolymer (3c) film was 1.5452, from which the dielectric constant at 1 MHz was estimated to be 2.6. The resist showed a sensitivity of 35 mJ cm,2 and a contrast of 1.6 when it was exposed to 436-nm light, postexposure-baked at 145 C for 5 min, and developed with toluene at 25 C. A fine negative image featuring 8-,m line-and-space patterns was obtained on a film exposed to 100 mJ cm,2 with 436-nm light in the contact-printed mode. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 149,156, 2005 [source]

Dendrimers as scaffolds for multifunctional reversible addition,fragmentation chain transfer agents: Syntheses and polymerization

Xiaojuan Hao
Abstract The synthesis and characterization of novel first- and second-generation true dendritic reversible addition,fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3-benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z-group architecture based on 1,1,1-hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free-radical polymerization at 60 C. The novel dendrimer-based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number-average molecular weight (Mn) with the monomer,polymer conversion, yielding star polymers with molecular weights of up to Mn = 160,000 g mol,1 for PBA (based on a linear PBA calibration) and up to Mn = 70,000 g mol,1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1-hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star-shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star-shaped polymeric materials. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877,5890, 2004 [source]

Stereoselective polymerization of rac -lactide with a bulky aluminum/Schiff base complex

Zhaohui Tang
Abstract An aluminum/Schiff base complex {[2,2-dimethyl-1,3-propylenebis(3,5-di- tert -butylsalicylideneiminato)](isopropanolato)aluminum(III) (2)} based on a bulky ligand and aluminum isopropoxide was prepared and employed for the stereoselective ring-opening polymerization (ROP) of rac -lactide (rac -LA). The initiator was characterized with nuclear magnetic resonance (NMR), crystal structure measurements, and elemental analysis. It contained a five-coordinate aluminum atom that was trigonal bipyramidal in the solid state according to the crystal structure measurements. The two conformational stereoisomers of 2 exchanged quickly on the NMR scale. Compound 2 polymerized rac -LA into a crystalline polymer that was characterized with 1H NMR, wide-angle X-ray diffraction, electrospray ionization mass spectrometry, and gel permeation chromatography. The kinetics of the polymerization were first-order in both the monomer and initiator, and there was a linear relationship between the rac -LA conversion and the number-average molecular weight of poly(rac -LA) with a narrow molecular distribution (1.04,1.08). These features showed that the polymerization was well controlled. The high melting temperature (196,201 C) and isotacticity of poly(rac -LA) indicated that complex 2 was a highly stereoselective initiator for the ROP of rac -LA. The stereoselectivity was as high as 90%, and the stereoblocks of poly(rac -LA) by complex 2 contained an average of 20 units (average block length = 20) of enantiomerically pure lactic acid. The activation energy (23.6 kJ mol,1) was obtained according to an Arrhenius equation. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5974,5982, 2004 [source]

Synthesis of soluble branched polyimides derived from an ABB, monomer

Kun-Li Wang
Abstract A novel ABB, monomer, an isomeric mixture of 4-[4-(2,4-diaminophenoxy)phenoxy]phthalic acid 2-methyl ester, was successfully prepared. The direct polycondensation of the ABB, monomer was carried out to form polyamic acid monomethyl ester as a precursor with an inherent viscosity of 0.30 dL/g and a number-average molecular weight of 12,000. The degree of branching of the precursor, determined by 1H NMR, was 0.07. The low degree of branching was caused by the differences in the reactivities of the amino groups. The shape factor was calculated to be 0.72. End-modified reactions with acetyl chloride, benzoyl chloride, and phthalic anhydride were carried out. After the chemical imidization of the end-modified precursors, end-modified polyimides were successfully prepared. The end-modified polyimides were soluble in dimethyl sulfoxide, dimethylformamide (DMF), and N -methyl-2-pyrrolidinone. On the basis of thermogravimetry and differential scanning calorimetry measurements of the polyimides, the 5 wt % thermal loss temperatures were determined to be 400,520 C, and the glass-transition temperatures were determined to be 200,258 C. According to the X-ray diffraction measurements, the end-modified polyimides were amorphous. A strong but brittle film was prepared from an acetamide end-modified polyimide solution, via casting from a DMF solution, with a tensile strength of 46 MPa, an elongation at break of 4%, and a modulus of 1.3 GPa. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3200,3211, 2004 [source]

Synthesis of hydrophilic/CO2 -philic poly(ethylene oxide)- b -poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) block copolymers via controlled/living radical polymerizations and their properties in liquid and supercritical CO2

Zhi Ma
Abstract Hydrophilic/CO2 -philic poly(ethylene oxide)- b -poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) block copolymers were synthesized via reversible addition,fragmentation chain transfer (RAFT) polymerization, iodine transfer polymerization (ITP), and atom transfer radical polymerization (ATRP) in the presence of either degenerative transfer agents or a macroinitiator based on poly(ethylene oxide). In this work, both RAFT and ATRP showed higher efficiency than ITP for the preparation of the expected copolymers. More detailed research was carried out on RAFT, and the living character of the polymerization was confirmed by an ultraviolet (UV) analysis of the SC(S)Ph or SC(S)SC12H25 end groups in the polymer chains. The quantitative UV analysis of the copolymers indicated a number-average molecular weight in good agreement with the value determined by 1H NMR analysis. The properties of the macromolecular surfactants were investigated through the determination of the cloud points in neat liquid and supercritical CO2 and through the formation of water-in-CO2 emulsions. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2405,2415, 2004 [source]

Low-temperature route to thermoplastic polyamide elastomers,

Gouher Rabani
Abstract Thermoplastic polyamide elastomers were obtained by polymerization of aminobenzoyl-substituted telechelics derived from poly(tetrahydrofuran)-diols (number-average molecular weight: 1400 or 2000 g mol,1) with several diacid dichlorides (terephthaloyl dichloride, 4,4,-biphenyldicarbonyl dichloride, or 2,6-naphthalenedicarbonyl dichloride) and chlorotrimethylsilane in N,N -dimethylacetamide at 0,20 C. The as-prepared polymers had melting temperatures above 190 C and exhibited elastic properties at room temperature, as evidenced by dynamic mechanical analysis and stress,strain measurements. The polymer with 2,6-naphthalenedicarboxamide hard segments had the widest rubbery plateau within the series, the highest extension at break, and good recovery properties. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1449,1460, 2004 [source]

Modeling the reversible addition,fragmentation transfer polymerization process

Aileen R. Wang
Abstract A kinetic model has been developed for reversible addition,fragmentation transfer (RAFT) polymerization with the method of moments. The model predicts the monomer conversion, number-average molecular weight, and polydispersity of the molecular weight distribution. It also provides detailed information about the development of various types of chain species during polymerization, including propagating radical chains, adduct radical chains, dormant chains, and three types of dead chains. The effects of the RAFT agent concentration and the rate constants of the initiator decomposition, radical addition, fragmentation, disproportionation, and recombination termination of propagating radicals and cross-termination between propagating and adduct radicals on the kinetics and polymer chain properties are examined with the model. 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1553,1566, 2003 [source]

Reverse atom transfer radical solution polymerization of methyl methacrylate under pulsed microwave irradiation

Zhenping Cheng
Abstract The reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) was successfully carried out under pulsed microwave irradiation (PMI) at 69 C with N,N -dimethylformamide as a solvent and with azobisisobutyronitrile (AIBN)/CuBr2/tetramethylethylenediamine as an initiation system. PMI resulted in a significant increase in the polymerization rate of RATRP. A 10.5% conversion for a polymer with a number-average molecular weight of 34,500 and a polydispersity index of 1.23 was obtained under PMI with a mean power of 4.5 W in only 52 min, but 103 min was needed under a conventional heating process (CH) to reach a 8.3% conversion under identical conditions. At different [MMA]0/[AIBN]0 molar ratios, the apparent rate constant of polymerization under PMI was 1.5,2.3 times larger than that under CH. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3823,3834, 2002 [source]

Synthesis of comb-shaped poly(methyl methacrylate)- b -poly(polytetrahydrofuran acrylate) under 60Co ,-ray irradiation

Tao He
Abstract Comb-shaped graft copolymers with poly(methyl methacrylate) as a handle were synthesized by the macromonomer technique in two steps. First, polytetrahydrofuran acrylate (A-PTHF), prepared by the living cationic ring-opening polymerization of tetrahydrofuran, underwent homopolymerization with 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate as an initiator under 60Co , irradiation at room temperature; Second, the handle of the comb-shaped copolymers was prepared by the block copolymerization of methyl methacrylate with P(A-PTHF) as a macroinitiator under 60Co , irradiation. The two-step polymerizations were proved to be controlled with the following evidence: the straight line of ln[M]0/[M] versus the polymerization time, the linear increase in the number-average molecular weight with the conversion, and the relatively narrow molecular weight distribution. The structures of the P(A-PTHF) and final comb-shaped copolymers were characterized by 1H NMR spectroscopy and gel permeation chromatography. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3367,3378, 2002 [source]

Phthalide as an activating group for the synthesis of poly(aryl ether phthalide)s by nucleophilic aromatic substitution

Daniel M. Knauss
Abstract The phthalide ring was examined as an activating group for nucleophilic aromatic substitution. The proposed mechanism by which activation occurs is through a ring opening of the phthalide ring to form a Meisenheimer-like , complex. 3,3-Bis(4-fluorophenyl)phthalide was synthesized and examined under different reaction conditions to determine its suitability for polymer formation. Semiempirical calculations at the PM3 level suggested that 3,3-bis(4-fluorophenyl)phthalide is only moderately activated, whereas 1H, 13C, and 19F NMR spectroscopy suggested that the monomer was not sufficiently activated for nucleophilic aromatic substitution. However, low-molecular-weight polymers (number-average molecular weight < 7000 g/mol) were produced from bisphenol A, hydroquinone, and phenolphthalein. The polymers were characterized by gel permeation chromatography, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, NMR spectroscopy, and differential scanning calorimetry. The polymers displayed relatively high glass-transition temperatures. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3046,3054, 2002 [source]

Atom transfer radical homo- and block copolymerization of methyl 1-bicyclobutanecarboxylate

Xiao-Ping Chen
Abstract A non-olefinic monomer, methyl 1-bicyclobutanecarboxylate (MBC), was successfully polymerized by the controlled/"living" atom transfer radical polymerization (ATRP) technique, resulting in a well-defined homopolymer, PMBC, with only cyclobutane ring units in the polymer chain. An AB block copolymer poly(methyl 1-bicyclobutanecarboxylate)- b -polystyrene (PMBC- b -PS), having an all-ring unit segment, was also synthesized with narrow polydispersity and designed number-average molecular weight in addition to precise end groups. The 1H NMR spectra, glass-transition temperature, and thermal stability of PMBC, PMBC- b -PS, and PS- b -PMBC were investigated. The experimental results showed that the cyclobutane rings in the two block polymers improved their thermal stability. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1929,1936, 2002 [source]

Direct functionalization of polyisobutylene by living initiation with ,-methylstyrene epoxide

J. Song
Abstract This article describes the synthesis and characterization of polyisobutylene (PIB) carrying one primary hydroxyl head group and a tertiary chloride end group, [PhC(CH3)(CH2OH),PIB,CH2C(CH3)2Cl] prepared with direct functionalization via initiation. The polymerization of isobutylene was initiated with the ,-methylstyrene epoxide/titanium tetrachloride system. Living conditions were obtained from ,75 to ,50 C (198,223 K). Low molecular weight samples (number-average molecular weight , 4000 g/mol) were prepared under suitable conditions and characterized by Fourier transform infrared and 1H NMR spectroscopy. The presence of primary hydroxyl head groups in PIB was verified by both methods. Quantitative Fourier transform infrared with 2-phenyl-1-propanol calibration and 1H NMR performed on both the hydroxyl-functionalized PIB and its reaction product with trimethylchlorosilane showed that each polymer chain carried one primary hydroxyl head group. The synthetic methodology presented here is an effective and simple route for the direct functionalization of PIB. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1005,1015, 2002 [source]

Synthesis of poly(methyl methacrylate) in a pyridine solution by atom transfer radical polymerization

Jos Luis de la Fuente
Abstract Pyridine was used as a solvent for the atom transfer radical polymerization (ATRP) of methyl methacrylate. The homopolymerizations were carried out with methyl 2-halopropionate (MeXPr, where X was Cl or Br) as an initiator, copper halide (CuX) as a catalyst, and 2,2,-bipyridine as a ligand from 80 to 120 C. The mixed halogen system methyl 2-bromopropionate/copper chloride was also used. For all the initiator systems used, the polymerization reaction showed linear first-order rate plots, a linear increase in the number-average molecular weight with conversion, and relatively low polydispersities. In addition, the dependence of the polymerization rate on the temperature is presented. These data are compared with those obtained in bulk, demonstrating the effectiveness of this solvent for this monomer in ATRP. 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3443,3450, 2001 [source]