Temperature-rise fractionation of poly(3-alkyl thiophenes)

In this article, we have investigated a temperature-rise fractionation procedure for poly(3-hexyl thophene) (P3HT) and poly(3-octyl thophene) (P3OT) that provides well-defined molecular weight (MW) fractions with improved molecular weight distributions (MWD) when compared with Soxhlet extraction. This process involves dispersing the material over C18-boned silica stationary phase in a jacketed column and using incremental rises in column temperature (T_col) to gradually improve solvent quality and selectively dissolve higher molecular weight samples with a narrow polydispersity (PDI). Fractionation of P3HT with ΔT_col = 5 °C in methylene chloride (MC) yielded 7 fractions ranging from M_p of 20 to 53 kg/mol with an average PDI of 1.80 compared with a mother sample of 3.10. Predominant recovery of P3HT was acquired for fractions with T_col > 20 °C (30 wt %). Subsequent separation of P3OT in methylene chloride, with a reduced ΔT_col of 3 °C per fraction, due to increased solubility from the longer alkyl chain, generated 8 fractions with a weight range of M_n = 22 to 57 kg/mol with an mean PDI of 1.23 with the mother sample having PDI = 2.34, demonstrating the tunability of this method. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2547–2555, 2009     

Control of macromolecular architecture of polyamides by poly-functional agents. 2. Use of oligomerization in polycondensation study

In the first paper of the series, a statistical model for star-branched polycondenzation of AB type monomers in the presence of a polyfunctional agent RA_f was completely developed. The analytical expressions obtained for the number-average (D̄P̄_n̄) and weight-average (D̄P̄_w̄) degree of polymerization, and the dispersion index (D) for whole polymer species, linear and star macromolecular chains, are now derived as function of the feed and of end-group analysis. Also the important molecular parameter, mole fraction of star-branched polymer, can be evaluated. Some numerical examples are presented. It is illustrated that the molecular weight properties of the linear and star-branched polymers in the mixture of the products, very important factors for the application of this kind of polymeric materials, can be determined starting from the feed and terminal group analysis. Polymerization and oligomerization of 6-aminocaproic acid were carried out in the presence of trimesic (T3) acid and 2,2,6,6-tetra(β-carboxyethyl)cyclohexanone (T4) and EDTA as tri- and terra-functional agents. The molecular weights calculated are in good agreement with those obtained by Size Exclusion Chromatography (SEC), end group analysis and NMR spectra.     

Ethylene Polymerization over Supported Titanium-Magnesium Catalysts: Heterogeneity of Active Centers and Effect of Catalyst Composition on the Molecular Mass Distribution of Polymer

New experimental approach was used for analysis of molecular weight distribution (MWD) of polymers produced over titanium-magnesium catalysts (TMC). Polymers were fractionated on to fractions with narrow MWD (polydispersity (PD) values Mw/Mn ≤ 2). Then some of these fractions were combined to get the minimal quantity of fractions with PD values close to 2 (Flory components). It was found that three fractions corresponding to three groups of active centers are sufficient for proper fitting experimental MWD curve for PE obtained over TMC with different Ti content and with different hydrogen concentration in polymerization.     

Properties of optically addressed liquid crystal spatial light modulators studied by mach-zehnder interferometry

In this work optically addressed liquid crystal spatial light modulators are experimentally investigated. Local reorientation of molecules in the modulator and local changes of effective refractive index n_eff (x,y) are induced by modulated light intensity I (x,y). We present preliminary results of measurements of phase shifts in optically addressed liquid crystal panels using a Mach-Zehnder interferometer. Experiments were performed for the panels filled with nematic and dye-doped nematic liquid crystals. Optical addressing was realized by Ar+ laser beam (λ = 514.5 nm) while the reading beam was supplied by He-Ne laser (632.8 nm). The operation voltage was in the range 4 - 20 V. The total phase shift under the influence of addressing light for the studied systems was 2 - 6 pagr;, sensitivity to the addressing light ∼ μW/cm² per 2π phase change and speed of response to the light was 20 ms - 30 s with total recovery time 0.5 - 120 s.     

Short Chain Branches Distribution Characterization of Ethylene/1-Hexene Copolymers by Using TREF + 13C-NMR and TREF + SC Methods

Summary: Short chain branches distribution (SCBD) is the key factor for high density polyethylene (HDPE) pipe materials to achieve their excellent performance for long term (50 years) applications. However, the precise SCBD characterization of these HDPE materials with relatively low content of comonomer incorporation still remained as a challenge in this field. In this work, two characterization methods, namely temperature rising elution fractionation (TREF) cross step crystallization (SC) (TREF + SC) and TREF cross ¹³C-NMR (TREF + ¹³C-NMR), have been respectively used to qualitatively and quantitatively investigate the SCBD for two HDPE pipe materials (PE-1 and PE-2 with different long term performances) with small amount of 1-hexene incorporation prepared from SiO₂-supported silyl chromate catalyst system (S-2 catalyst) during UNIPOL gas phase polymerization. The comparison of SCBD between the two samples showed that: although short chain branches of PE-2 with good performance were less than those of PE-1 with bad performance, PE-2 showed less comonomer incorporation on the low crystallinity and low molecular weight (MW) fractions keeping even higher comonomer incorporation on the high crystallinity and high MW parts compared with PE-1. This difference on the SCBD for PE-1 and PE-2 was thought to be the key factor which is responsible for their great difference on environment slow crack resistance (ESCR). Moreover, TREF + SC method further reflected the intra- and inter-molecular heterogeneities of each fraction from the two HDPE samples through the lamella thickness distribution compared with TREF + ¹³C-NMR.     

Effect of the reaction parameters on the particle size in the dispersion polymerization of 2‐hydroxyethyl and glycidyl methacrylate in the presence of a ferrofluid

The precipitation of Fe₃O₄ from an aqueous solution with ammonium hydroxide produced nanoparticles that were coated with a layer of oleic acid [or, in some cases, poly(ethylene oxide) or poly(vinylpyrrolidone)] before their dispersion into the organic phase. The encapsulation of magnetite nanoparticles in poly(2‐hydroxyethyl methacrylate) or poly(2‐hydroxyethyl methacrylate‐co‐glycidyl methacrylate) microparticles was achieved by dispersion polymerization in toluene/2‐methylpropan‐1‐ol. Magnetic poly(glycidyl methacrylate) microparticles were obtained in the presence of poly(ethylene oxide) at the magnetite/monomer interface. The particles containing up to 20 wt % iron maintained their discrete nature and did not aggregate. The effect of the reaction medium polarity, the concentrations of the monomer, initiator, and stabilizer, and the temperature on the particle size, particle size distribution, and iron and oxirane group contents was studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1848–1863, 2003     

Monte Carlo simulation of diepoxides and monoepoxides cured with amines

The diepoxide–monoepoxide–diamine curing systems are investigated with a Monte Carlo simulation. The dependence of the molecular weight distribution (MWD), gel fraction, and cycle rank of the polymers on the differences in the epoxy reactivities and the contents of the monoepoxide as a reactive diluent are discussed. Before gelation, the MWD of the curing systems with a lower content of the monoepoxide is broader than the MWD of the curing systems with a higher content, and it leads to a lower critical conversion. The gel fraction and cycle rank of the polymers decrease with an increasing amount of the diluent. Even fully cured, the system with a 0.6 epoxy molar fraction of the monoepoxide still has a large fraction of sol, about 49%. Although the various reactivities of the monoepoxide result in different ways of forming gels during curing, the final gel fractions are always near 100% as long as the epoxy molar fraction of the diluent is no more than 0.2. The profiles of the molecular weights of the polymers calculated by the model are in agreement with the experimental data. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1857–1868, 2002     

Characterization of Metallo Bis(terpyridine) Diblock Polymers by Nonaqueous Capillary Zone Electrophoresis

A method of nonaqueous capillary zone electrophoresis (CZE) has been developed to characterize block (co)polymers of poly(ethylene oxide) and poly(styrene) containing metallo bis(terpyridine) complexes as bridging units. Specific CZE separation conditions had to be applied, with barium perchlorate dissolved in N-methylformamide (NMF) as background electrolyte and OV-1701-OH deactivated capillaries. For detection UV absorption was measured at a wavelength of 316 nm. Metallo diblock polymers with molecular weights up to 30,000 Da could be analyzed by the proposed nonaqueous CZE method. Experiments performed with polymeric compounds containing Fe, Ni or Ru as central metal ions showed that their electrophoretic mobilities were independent of the type of metal ion. Therefore, the data on the size of the polymeric compounds could be obtained using just one set of calibration standards. Polydispersities of the samples calculated from the experimental results were in correlation with the polydispersities of the polymers used in the synthesis of the metallo diblock polymers. Several polymeric samples contained metallo mono(terpyridine) complexes as impurities. These by-products could be separated from the main product. With symmetrical diblock polymers only one by-product was detected, while with an asymmetric diblock polymer two types of mono-complexes were found. The amount of the mono-complexes present as impurities was dependent on the type of central metal ion (Ni > Fe >> Ru).     

New ferrocene-containing structures: Poly(silyl ester)s

Two new polymeric structures containing ferrocene units along the chains, namely poly(silyl ester)s, have been synthesized and characterized: a geminal poly(silyl ester) (g-PSE) and one having a disiloxane spacer between the silyl ester groups (s-PSE). The condensation polymerization of AA/BB monomer systems in solution was used in both cases as preparation method involving a silicon-containing diol, (diphenylsilane diol or 1,3-bis(hydroxy)-tetramethyldisiloxane), and 1,1′-di(chlorocarbonyl)ferrocene. The polymers were investigated by differential pulse voltammetry in order to evaluate the redox behavior. Due to the presence of the silyl ester groups in the chain, these polymers are hydrolytically degradable.     

Application of a crystallization kinetics model to simulate the effect of operation conditions on Crystaf profiles and calibration curves

Crystallization analysis fractionation (Crystaf) is a polymer characterization technique used to estimate chemical composition distributions (CCDs) of semicrystalline copolymers. The Crystaf profile can be transformed into a CCD using a calibration curve that relates average comonomer content to peak crystallization temperature. The calibration curve depends on copolymer molecular properties and Crystaf operation conditions. In this investigation, we applied a crystallization kinetics model to simulate Crystaf calibration curves and to quantify how Crystaf calibration curves depend on these factors. We applied the model to estimate the CCDs of three ethylene/1‐hexene copolymers from Crystaf profiles measured at different cooling rates and showed that our predictions agree well with the CCDs described by Stockmayer's distribution. We have also used this new methodology to investigate the effects of cooling rate, molecular weight, and comonomer type on Crystaf profiles and calibration curves. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 866–876, 2009     

Step‐Growth Polymerizing Systems of General Type “AfiBgi”: Calculating the Bivariate (Molecular Size) × (Number of Branch Points) Weight Distribution Using Generating Functions and Recurrences

This study considers step‐growth polymerizing systems of general type “AfiBgi” whereby one or more of the reacting monomer species bear at least three reactive groups. The random polymerization process will lead to a population of polymer molecules in which the individual molecules may differ widely with respect to degree of polymerization and number of branch points. This study presents an algorithmic method to calculate the statistical distribution of weight over these two molecular properties. The method uses bivariate generating functions, recurrences, and integer arithmetic.

     

Magnetic poly(N‐isopropylacrylamide) microspheres by dispersion and inverse emulsion polymerization

The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe₂O₃ nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe₂O₃, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe₂O₃ nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007     

Aromatic and rigid rod polyelectrolytes based on sulfonated poly(benzobisthiazoles)

Aromatic polyelectrolytes based on sulfonated poly(benzobisthiazoles) (PBTs) have been synthesized by a polycondensation reaction of sulfo-containing aromatic dicarboxylic acids with 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT) in freshly prepared polyphosphoric acid (PPA). Several sulfonated PBTs, poly[(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl)-2-sulfo-1,4-phenylene] sodium salt (p-sulfo PBT), poly[(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl)-5-sulfo-1,3-phenylene] sodium salt (m-sulfo PBT), their copolymers, and poly[(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl)-4,6-disulfo-1,3-phenylene] potassium salt (m-disulfo PBT), have been targeted and the polymers obtained characterized by ¹³C-NMR, FT-IR, elemental analysis, thermal analysis, and solution viscosity measurements. Structural analyses confirm the structures of p-sulfo PBT and m-disulfo PBT, but suggest that the sulfonate is cleaved from the chain during synthesis of m-sulfo PBT. m-Disulfo PBT dissolves in water as well as strong acids, while p-sulfo PBT dissolves well in strong acids, certain solvent mixtures containing strong acids, and hot DMSO. TGA indicates that these sulfonated PBTs are thermally stable to over 500°C. Free-standing films of p-sulfo PBT, cast from dilute neutral DMSO solutions, are transparent, tough, and orange in color. Films cast from basic DMSO are also free standing, while being opaque and yellow-green. p-Sulfo PBT was incorporated as the dopant ion in polypyrrole, producing conductive films with conductivities as high as 3 S/cm and electrical anisotropies as high as 10. © 1996 John Wiley & Sons, Inc.     

Radical‐mediated modification of polypropylene: Selective grafting via polyallyl coagents

Selective graft modifications of polypropylene (PP) are demonstrated in which desirable functionality is introduced without the degradation that accompanies conventional radical‐mediated processes. A range of modification strategies is presented, each exploiting triallyl trimellitate (TATM) or its derivatives to counteract the effects of macroradical fragmentation on the molecular weight. Model compound studies, as well as examinations of atactic PP reaction products, show that allylic ester activation occurs predominately by a radical‐addition/hydrogen‐transfer sequence, with a limited propensity for telomerization. The cografting of TATM and maleic anhydride leads to maleated PP of a high melt viscosity, whereas the apparent incompatibility of TATM with vinyltrimethoxysilane requires the use of TATM‐assisted thiol–ene addition and/or diallyl silane grafting to produce moisture‐curable PP derivatives. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4882–4893, 2005     

Synthesis and characterization of fluorinated liquid-crystalline elastomers containing chiral liquid-crystalline crosslinking units

Fluorinated chiral liquid-crystalline elastomers (LCEs) were graft copolymerized by a one-step hydrosilylation reaction with polymethylhydrogenosiloxane, a fluorinated LC monomer 4-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoyloxy)phenyl 4-(undec-10-enoyloxy)benzoate (PPUB) and a chiral crosslinking LC monomer (3R,3aR,6S,6aR)-6-(undec-10-enoyloxy)hexahydrofuro[3,2-b]furan-3-yl 4′-(4-(allyloxy)benzoyloxy)biphenyl-4-carboxylate (UHAB). The chemical structure, liquid-crystalline behavior and polarization property were characterized by use of various experimental techniques. The effective crosslink density of the LCEs was characterized by swelling experiments. The thermal analysis results showed that the temperatures at which 5% weight loss occurred were greater than 250 °C for all the LCEs, and the residue weight nearby 600 °C increase with increasing chiral crosslinking components in the polymer systems. All the samples showed chiral smectic C mesophase when they were heated. The glass transition temperature and mesophase-isotropic phase transition temperature of fluorinated elastomers increased slightly with increase of chiral crosslinking mesogens in the polymer systems, but the enthalpy changes of mesophase-isotropic phase transition decreased slightly. In XRD curves, all the samples exhibited strong sharp reflections at small angles suggesting smectic layered packing arrangement. These fluorinated chiral LCEs showed 0.1–0.2 μC/cm² of spontaneous polarization with increasing chiral crosslinking component.     

SYNTHESES AND OPTOELECTRONIC PROPERTIES OF A HEXA-ARMED FLUORENE-BENZENE COPOLYMER BASED ON 2,4,6,8,10,12-HEXABENZYL-2,4,6,8,10,12-HEXAAZAISOWURTZITANE CAGED-CORE

A novel kind of hexa-armed fluorene-benzene copolymer based on a hexaazaisowurtzitane core was synthesized through Suzuki coupling polycondensation.The introduction of this bulky caged-core could not only enhance the photoluminescence quantum efficiency,but also improve the electroluminescence properties,especially suppress the common green-color emission of polyfluorenes(PFs) material during device operation.These features can be attributed to the successful suppression of PF's chain aggregation which p...     

MOLECULAR WEIGHT DISTRIBUTION OFAB, B TYPE CONDENSATION POLYMERS OBTAINED BY ADDING AB MONOMERS IN BATCHES

The molecular weight distribution function (MWD) of AB, B type condensation polymers obtained by adding AB monomers in batches has been derived by statisticaland kinetic methods. Calculations show that the MWD of condensation polymers obtained by this process is much narrower than the Flory distribution and agrees with the Monte Carlo results very well.     

Microwave‐assisted suzuki coupling reaction for rapid synthesis of conjugated polymer–poly(9,9‐dihexylfluorene)s as an example

Long reaction period (dozens of hours) is often required for the synthesis of conjugated polymers by palladium‐catalyzed Suzuki polymerization reaction. This work shows that microwave can accelerate Suzuki polymerization to realize the ultra‐rapid synthesis of conjugated polymers, here poly(9,9‐dihexylfluorene)s (PDHFs) as an example. The effects of reaction conditions on the polymerization have been systematically investigated, including the mode of microwave irradiation, microwave power, reaction temperature, reaction time, solvents, catalyst species, and catalyst concentrations. Compared with the conventional heating method (oil bath) for the synthesis of PDHFs (48 h, M_w = 20,000 g/mol), Suzuki polymerization under optimized microwave condition can yield PDHFs with higher molecular weight (M_w = 40,000 g/mol) in a much shorter time (14 min). The structures of obtained PDHFs samples are fully characterized spectroscopically, demonstrating well‐defined PDHFs have been prepared through microwave‐assisted (MA) Suzuki polymerization reaction. In addition, the mechanism of MA Suzuki polymerization is proposed preliminarily. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013