Molecular Weight Distribution Of Poly Research Articles

Poly(vinyl ester) Star Polymers via Xanthate-Mediated Living Radical Polymerization: From Poly(vinyl alcohol) to Glycopolymer Stars

Poly(vinyl ester) stars have been synthesized via different macromolecular design via interchange of xanthate (MADIX)/reversible addition−fragmentation chain transfer (RAFT) polymerization methodologies. Two approaches were investigated. The first method involved attaching the xanthate functionality to the core via a nonfragmenting covalent bond (Z-group approach). The second approach involved attaching the xanthate functionality to the core via a fragmenting covalent bond (R-group approach). The R-group approach yielded well-defined poly(vinyl acetate), poly(vinyl pivalate), and poly(vinyl neodecanoate) stars with narrow polydispersities (PDI ≤ 1.4). In contrast, the molecular weight distributions of poly(vinyl acetate) stars prepared using the Z-approach tended to broaden at moderate to high conversions. We attribute this broadening to steric congestion around the xanthate functionality, restricting the access of monomer to the CS bonds. The R-group approach was also found to be superior for preparing p...

Study on Relationship between Electroluminescence Properties and Molecular Weight Distribution of Poly(9,9'-dioctylfluorene) Using Photoluminescence

Polyfluorenes (PFs) have attracted attention as conjugated polymer materials that can be promising as polymer-based emissive displays. PFs have a blue emission, a high photoluminescence (PL) quantum yield and thermal and chemical stabilities. The highly efficient blue emission from the PF structure is attractive for a display consisting of polymer light-emitting diodes (LEDs). We synthesized 10 kinds of poly(9,9'-dioctylfluorene) (PDOF) of different molecular weight distributions and studied their PL and electroluminescence properties. Moreover, we also studied their fluorescent lifetime. As a result, we found that optimum molecular weight of PF-based LEDs is about 105. From this result, it is thought that it is important to control the molecular weight of PDOF for PF-based LEDs.

Chain transfer to monomer and polymer in the radical polymerization of vinyl neo-decanoate

Molecular weight distributions of poly(vinylneo-decanoate) produced by the bulk polymerization of the monomer to low conversions were investigated to obtain values of the rate constants for the chain transfer to monomer (CM). The value ofC M of 7.5 (± 0.6)× 10−4 was obtained from a logarithmic plot of the number distribution at 5, 25, and 50°C, which suggests that the activation energy for chain transfer is on the order of 20–25 kJ mol−1. These plots were linear between the number and weight-average degrees of polymerization, but not over the whole molecular weight range for which a significant signal was observed in the gel permeation chromatography (GPC) trace. Modeling suggests that the deviations observed at high molecular weights can be explained by branching of the chains through chain transfer to the polymer, with a branching density as low as 10−5, without affecting the slope at low values of the number of monomer unit,N. This deviation from the expected distribution of linear chains was used to estimate the branching densities at low conversion.

Molecular weight distribution of poly(dimethyl diallyl ammonium chloride): Analysis within the framework of irreversible aggregation models

AbstractThe results of the present study have shown that the molecular weight distribution of polydimethyldiallyl ammonium chloride is simulatable and predictable within the framework of the irreversible cluster–cluster aggregation model. The shape and position of a curve of molecular weight distributiion are influenced by a number of factors, for example, by macromolecular coil structure, stochastic contribution of a coil environment to polymerization intensity, and level of coil destruction during polymerization. These factors can be linked by simple relationships to technical characteristics of the polymerization process, which is especially important for fractal applictions of the proposed theoretical model. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3144–3147, 2004

Simulation of Molecular Weight Distributions of Poly(N-[10-(n-docosane[oxycarbonyl])-n-decyl maleimide]) from Isothermal Fractional Precipitation Data and Comparison with Distributions from Size Exclusion Chromatography of Fractions

Twenty fractions of an unfractionated sample of poly(N-[10-(n-docosane[oxycarbonyl])-n-decyl)maleimide])(PEMI10-22) were obtained by isothermal fractional precipitationat 25°C using toluene/methanol as the solvent/precipitant system. Weight-average molecular weights (in the range M ¥ w =6.06 2 10 3 to 3.21 2 10 5 ) of 11 of these fractions were measured by static light scattering. The molecular weight distribution (MWD) of PEMI 10-22 was analyzed by comparing the results obtained from isothermal fractional precipitation with size exclusion chromatography (SEC). The analysis of SEC data was carried out by means of a nonlinear autocalibration of log M ¥ w versus elution time at the peak, t e (peak). The calibration was determined by an iterative computer method devised for use with polydisperse samples. The results of isothermal fractional precipitation are simulated and compared with SEC data. Good agreement between the distribution determined by the SEC autocalibration method and isothermal fractional precipitation was obtained. Poly( N -[10-( n -docosane[oxycarbonyl])- n -decyl maleimide]) Isothermal fractional precipitation Size exclusion chromatography Autocalibration Molecular weight distribution Simulation

Deviation from Single-Site Behavior in Zirconocene/MAO Catalyst Systems, 2. Influence of Polymerization Temperature

The effect of polymerization temperature on the polymerization of 1-hexene with the catalyst systems Cp2ZrCl2/MAO, Me2SiCp2ZrCl2/MAO, EtInd2ZrCl2/MAO, Me2SiInd2ZrCl2/MAO and iPrCpFluZrCl2/MAO is investigated in this paper. The molecular weight and the molecular weight distribution of poly(1-hexene) provide experimental evidence for a deviation from single-site behavior at certain polymerization temperatures, depending on the catalyst system. Experimental results are interpreted in terms of different active species prevailing at different polymerization temperatures, and coexisting under certain reaction conditions.

Molecular Weight Distribution of Poly(Methyl Methacrylate) Produced in a Starved Feed Reactor

A starved feed reactor (SFR) is a semi-batch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. The added initiator decomposes instantaneously and the added monomer polymerizes immediately. The molecular weight (MW) and the molecular weight distribution (MWD) of the polymer can be effectively controlled by the feed ratio of monomer to initiator. This paper presents a study on the MWD of methyl methacrylate (MMA) polymerization in a SFR. The MWD model parameters are regressed with experimental data. Although the solids fraction in the SFR is high (higher than 50%), viscosity is not high and the gel effect is weak due to the low molecular weight of the products. It is found that the termination rate constant is a power function of the polymer concentration in the system; radicals terminate via disproportionation and combination. The fraction of disproportionation is about 0.9-0.96 at temperatures in the range of 100°C-170°C. The initiation efficiency f is about 0.82-0.55, and it decreases with increasing reaction temperature.

Synthesis and characterization of poly(methylphenylsilylene)-poly(ethylene oxide) and poly(methylphenylsilylene)-polyisoprene multiblock copolymers

Multiblock copolymers were synthesized through condensation reactions of end-groups of a,co-dichloro-poly(methylphenylsilylene) with hydroxyl end-groups of poly(ethylene glycol) or the chain-ends of 'living' polyisoprenyl disodium. Optimum conditions have been sought through kinetic studies and by investigation of model reactions. The overall molecular weight distribution of poly(methylphenylsilylene)-block-poly(ethylene oxide) is characterized in terms of Flory's theory of condensation reactions, while the limiting step in the reaction is tentatively attributed to the formation of aggregates. (C) 2001 Society of Chemical Industry.

The Effect of Reducing Monosaccharides on the Atom Transfer Radical Polymerization of Butyl Methacrylate

The effect of various reducing monosaccharides on the rate of atom transfer radical polymerization (ATRP) of butyl methacrylate is reported in this study. The addition of reducing sugars affects the rate of ATRP positively with a 100% increase in the rate of polymerization in some cases. In addition, these organic reducing agents have little effect on the molecular weight and molecular weight distribution of poly(butyl methacrylate) with polydispersity indexes that remain well below 1.2. A possible explanation for these observations is the ability of the reducing sugars to reduce part of the Cu2+ species, which deactivate the growing radicals, to Cu1+, thereby ensuring a shift in the equilibrium between active and dormant chains in the direction of the former with a resulting increase in the rate of reaction.

The influence of RAFT on the rates and molecular weight distributions of styrene in seeded emulsion polymerizations

Seeded emulsion polymerizations of styrene in the presence of two reversible addition–fragmentation chain-transfer (RAFT) agents were studied. We designed the seed to be small to observe the effects of exit and, we made the seed of poly(methyl methacrylate) so that the molecular weight distributions of poly(styrene) by gel permeation chromatography could be obtained independently by UV detection. The rates were significantly retarded by the presence of a RAFT agent, with the retardation being greater with an EMA RAFT agent [2-(ethoxycarbonyl)propyl-2-yl dithiobenzoate] than with a cumyl RAFT agent (2-phenylprop-2-yl dithiobenzoate). We propose that exit from the particles after fragmentation was the main cause of retardation. In addition, the number-average molecular weight and polydispersities (broad) did not resemble the characteristic living behavior found in bulk or solution. This was a result of the continuous transportation of RAFT agent into the particles during interval II and the transportation of a small amount during interval III. A conspicuous red layer was also observed at the beginning of the polymerization. The red layer consisted of low molecular weight dormant species swollen with monomer. Once the switch from interval II to interval III occurred, the low molecular weight species coalesced to form a red coagulant. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3864–3874, 2000

Peroxide-controlled degradation of poly(propylene): rheological behaviour and process modelling

The control of the molecular weight distribution of poly(propylene) resins by peroxide degradation is widely used in polymer industry. It allows to adjust the viscosity of these resins to the level required for processing applications. The purpose of this work was to characterise the influence of peroxide degradation on the rheological behaviour of an homopolymer PP and a block copolymer PP/PE, and to use these results to obtain a predictive model of the degradation in a twin-screw extruder. By coupling a thermomechanical model of the twin-screw extrusion process, a kinetic model of the considered reactions and the rheological behaviour, it was possible to calculate the changes in molecular weight along the extruder, during the peroxide-controlled degradation.

Liquid Adsorption Chromatography near Critical Conditions of Adsorption Coupled with Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Chemical heterogeneities and molecular weight distributions of poly(ethylene oxide) (PEO)-co-polymethylene (PM) model oligomers, which are relevant to the synthesis of commonly used tensides, were investigated. For analytical characterization, the well-known principle of liquid adsorption chromatography at ‘critical conditions’ (LACCC) was modified. Near the critical conditions of adsorption of the PEO unit, e.g., at slight adsorption conditions of PM, the copolymers could be separated according to their PM chain length. The eluates were separated and single fractions of each peak were continuously transferred onto the MALDI target by means of a commercially available device. Simultaneously, the MALDI matrix solution was continuously added with a second pump. This procedure offers the possibility of the formation of homogeneous matrix-polymer textures. By MALDI-MS a complete characterization of the chemical composition (PEO and PM chain length) of each peak could be achieved. The obtained MALDI mass spectra of the eluates at different retention times could be used for the molecular weight calibration of the LAC system. In this way, an additional application of SEC, as in conventional 2D-chromatography, was avoided by using the MALDI method as quasi chromatographic separation.

The influence of RAFT on the rates and molecular weight distributions of styrene in seeded emulsion polymerizations

Seeded emulsion polymerizations of styrene in the presence of two reversible addition-fragmentation chain-transfer (RAFT) agents were studied. We designed the seed to be small to observe the effects of exit and, we made the seed of poly(methyl methacrylate) so that the molecular weight distributions of poly(styrene) by gel permeation chromatography could be obtained independently by UV detection. The rates were significantly retarded by the presence of a RAFT agent, with the retardation being greater with an EMA RAFT agent [2-(ethoxycarbonyl)propyl-2-yl dithiobenzoate] than with a cumyl RAFT agent (2-phenylprop-2-yl dithiobenzoate). We propose that exit from the particles after fragmentation was the main cause of retardation. In addition, the number-average molecular weight and polydispersities (broad) did not resemble the characteristic living behavior found in bulk or solution. This was a result of the continuous transportation of RAFT agent into the particles during interval II and the transportation of a small amount during interval III. A conspicuous red layer was also observed at the beginning of the polymerization. The red layer consisted of low molecular weight dormant species swollen with monomer. Once the switch from interval II to interval III occurred, the low molecular weight species coalesced to form a red coagulant.

Determination of the polydispersity of poly(tetramethylene ether) glycol by means of high‐performance liquid chromatography and curve fitting

AbstractA modified high‐performance liquid chromatographic method for the analysis of the molecular weight distribution of poly(tetramethylene ether) glycol (PTMEG) is described. The weight percentage of the polymer homologues, up to a degree of polymerization X of 79, can be determined. This covers about 93 wt.‐% of the material with number‐average molecular weight M̄n = 1000, but only 65 wt.‐% of that with M̄n = 2000. Direct calculation of the means M̄n, M̄w, and M̄z from these percentages leads to erroneous results because of the neglect of the summands with X > 79. Therefore, a curve fit is performed and M̄n, M̄w, and M̄z are calculated from the fitting parameters. From the known molecular weight distribution functions, Wesslau's and Kubin's function yielded the best fit. The results of this method are compared with those of gel permeation chromatography, viscosimetric measurements, supercritical fluid chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and evaporative light scattering detector methods. The scope and the limitations of this method are discussed.

Time-lag focusing and cation attachment in the analysis of synthetic polymers by matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry

Ultraviolet matrix-assisted laser desorption/ionization-mass spectrometry has been employed with time-lag focusing to explore its utility for the characterization of synthetic polymers with broad distributions. Mixtures of five polymer standards with narrow molecular weight distributions were analyzed. The spectra were found to be broadly those expected for three different types of polymer systems—poly(styrene), poly(methyl methacrylate), and poly(ethylene glycol)—when equimass mixtures were used. Large changes in the apparent molecular weight distribution of poly(ethylene terephthalate) were observed when the cation was varied. The shift in the envelope was found to be related to the size and the ability of the oligomers to solvate the cation.

Effect of interchange reactions on the molecular weight distribution of poly(ethylene terephthalate): A Monte Carlo simulation

The effect of the interchange reactions of poly(ethylene terephthalate) (PET) on its molecular weight distribution (MWD) was analyzed using a Monte Carlo simulation method. Three kinds of motions, which correspond to the direct ester(SINGLEBOND)ester interchange reaction, alcoholysis, and internal alcoholysis in polyester, were performed in this simulation: bond flip, end attack, and backbite. Two systems with two different types of nonequilibrium distribution (monodisperse and bimodal distribution) were initially prepared. The initial biases from equilibrium MWD are rapidly relaxed to an equilibrium MWD as the reaction progresses. The MWD at equilibrium is well described by the most probable MWD proposed by Flory. From the polydispersity data, it is concluded that about 0.3 interchanges per segment are sufficient to equilibrate the nonequilibrium system. For the validity of the simulation, the variation of MWD of the mixtures of two PETs having different molecular weights were monitored using gel permeation chromatography. The agreement between simulation and experiment is remarkably good. © 1996 John Wiley & Sons, Inc.

Anionic Polymerization of N-Phenylitaconimide

N-Phenylitaconimide (N-PII) can be readily polymerized with basic initiators that involve carbide, nitride, and oxide anions such as sec-butyllithium, lithium diethylamide, and alkali metal tert-butoxide. Poly(N-PII) was obtained in 84, 73, and 78% yields with sec-butyllithium, lithium diethylamide, and lithium tert-butoxide, respectively, in THF at 0 °C for 3 h polymerization. The effect of countercation size on the anionic polymerization rate of N-PII (1,1-disubstituted ethylene type monomer with cyclic imide structure) with alkali metal tert-butoxides is inverse to that of N-phenylmaleimide (N-PMI) (1,2-disubstituted ethylene type one); i.e., it was observed that the polymerization rate increased as the ion radius of a countercation decreased. NMR spectroscopic data and molecular orbital calculations suggest that the anionic polymerization of N-PII took place only at the vinylidene group and no appreciable side reaction would occur. In the case of using the initiators with Li+ as a countercation, the molecular weight distribution of poly(N-PII) is apparently unimodal and polydispersity is relatively small. The mechanism of the anionic polymerization of N-PII was discussed in detail. The thermal properties of poly(N-PII) obtained were also presented: it possessed a Tg under its decomposition temperature and could form a film by the cast method while those could not be observed for poly(N-PMI).

Molecular weight distribution of poly(dimethylsiloxane) by combining matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with gel‐permeation chromatography fractionation

AbstractMatrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) allows detection of large molecules such as those present in synthetic and natural macromolecules. Until recently, it was reported that MALDI‐TOF measurements can provide correct molecular weight (MW) estimates only for nearly monodisperse polymer samples. We have now developed a methodology for polydisperse samples. We recorded the gel‐permeation chromatography (GPC) trace of a polydisperse polymeric sample of poly(dimethylsiloxane) (PDMS), collecting 42 fractions. Selected fractions were analyzed by MALDI‐TOF and the average MW of each fraction was determined, allowing a calibration of GPC curves against absolute MW. The calibrated GPC trace was then used to compute average MW and molecular‐weight distribution (MWD) of the unfractionated poly(dimethylsiloxane) sample. In the spectra of low molecular‐weight fractions, the resolution is high enough to resolve the contributions of the various PDMS oligomers as separate signals.

Anionic polymerization of t-butyl methacrylate using a new type of bifunctional initiator

The living character of the anionic polymerization of t-butyl methacrylate (BMA) using 2,3-diphenylbutadienemagnesium (DPB-Mg) as a bifunctional initiator was investigated by varying the polymerization conditions. Anionic polymerization of BMA at both −78 and −45°C involved no transfer reaction and the molecular weight distribution of poly(t-butyl methacrylate) was very narrow ( M ̄ w M ̄ n = 1.20 ). However, the polymerization at 0°C involved a small amount of side reaction, i.e. attack of the living ends of the ester molecules. The structure of the DPB-Mg complex was characterized by spectroscopic analysis and quantitative titration of Mg metal.

A Study of the Molecular Weight Distribution of Poly(Amino Acid)s Synthesized by Diphenyl Phosphoryl Azide

Abstract Direct polycondensations of β-benzyl-l-aspartate (Asp.Bz) and β-benzyl-l-glutamate (Glu.Bz) were carried out in the presence of diphenyl phosphoryl azide (DPPA) as a condensation agent and triethyl amine (TEA). Poly(amino acid)s were obtained by this convenient approach whose structure was confirmed by IR and 1H-NMR spectroscopy. The effects of the monomer concentration, the polymerization time and temperature, the ratios [DPPA]/[monomer] and [TEA]/[monomer], and the solvent used on the molecular weight distribution of the polymer were studied. When the monomer concentrations were higher than 0.2 g/mL, poly(Asp.Bz) with a bimodal molecular weight distribution was obtained (Mw of 37,000 and Mw/Mn of 1.68). The polycondensations carried out in THF or in bulk provided the highest molecular weight (Mw ⋍ 40,000). Several other amino acids were also polymerized by DPPA.