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Weight Average Molecular Weight (weight + average_molecular_weight)
Selected AbstractsDetermination of block size in poly(ethylene oxide)- b -polystyrene block copolymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometryJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2009Marion Girod Abstract Characterization of block size in poly(ethylene oxide)- b -poly(styrene) (PEO- b -PS) block copolymers could be achieved by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) after scission of the macromolecules into their constituent blocks. The performed hydrolytic cleavage was demonstrated to specifically occur on the targeted ester function in the junction group, yielding two homopolymers consisting of the constitutive initial blocks. This approach allows the use of well-established MALDI protocols for a complete copolymer characterization while circumventing difficulties inherent to amphiphilic macromolecule ionization. Although the labile end-group in PS homopolymer was modified by the MALDI process, PS block size could be determined from MS data since polymer chains were shown to remain intact during ionization. This methodology has been validated for a PEO- b -PS sample series, with two PEO of number average molecular weight (Mn) of 2000 and 5000 g mol,1 and Mn(PS) ranging from 4000 to 21,000 g mol,1. Weight average molecular weight (Mw), and thus polydispersity index, could also be reached for each segment and were consistent with values obtained by size exclusion chromatography. This approach is particularly valuable in the case of amphiphilic copolymers for which Mn values as determined by liquid state nuclear magnetic resonance might be affected by micelle formation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3380,3390, 2009 [source] Online estimation and control of polymer quality in a copolymerization reactorAICHE JOURNAL, Issue 5 2002Myung-June Park The validity of an online state estimator for a semi-batch MMA/MA solution copolymerization reactor was established using online densitometer and viscometer. Using the conventional extended Kalman filter (EKF) as the state estimator, the experiment was conducted under both isothermal and nonisothermal conditions for application to the control of copolymer properties. Further analysis was made by using ofline measurement data for the mol fraction of MMA in the remaining monomers and the solid content. The EKF was found to provide a good estimate for the state of the copolymerization system. A model predictive controller was designed and implemented to obtain copolymers with uniform copolymer composition and the desired weight average molecular weight by adopting the feed flow rate of MMA and the reaction temperature as control inputs. The controller was proven effective with a satisfactory performance for the control of polymer properties in the semi-batch copolymerization reactor. [source] Synthesis and Properties of a New Poly(arylene ethynylene) Containing 1,3,5-Triazine Units,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2004Qiang Fang Abstract Summary: A new photoluminescent poly(arylene ethynylene) containing 1,3,5-triazine units was prepared by polycondensation between 2,4-diphenyl-6- N,N -bis(4-bromophenyl)amino-1,3,5-triazine and 1,4-didodecyloxy-2,5-diethynylbenzene using Pd(PPh3)4 and CuI as the catalysts in the presence of triethylamine. The polymer showed good solubility in common organic solvents and had a number average molecular weight, , of 3,400, and a weight average molecular weight, , of 8,100. In toluene the polymer exhibited an intrinsic viscosity [,] of 0.11 dL,·,g,1 at 30,°C. The polymer showed photoluminescence (PL) with emission peaks at 479 nm in CHCl3 and at 509 nm in the solid state; quantum yield of the PL in CHCl3 was 21%. Electrochemical reduction (or n-doping) of the polymer started at about ,2.05 V versus Ag/AgNO3 and gave a peak at ,2.30 V versus Ag/AgNO3. The 1,2,3-triazine unit-containing poly(arylene ethynylene) (PATZ) polymer synthesized and investigated here. [source] Model Reduction in Emulsion Polymerization Using Hybrid First Principles/Artificial Neural Networks Models, 2,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2005Gurutze Arzamendi Abstract Summary: A "series" hybrid model based on material balances and artificial neural networks to predict the evolution of weight average molecular weight, , in semicontinuous emulsion polymerization with long chain branching kinetics is presented. The core of the model is composed by two artificial neural networks (ANNs) that calculate polymerization rate, Rp, and instantaneous weight-average molecular weight, from reactor process variables. The subsequent integration of the material balances allowed to obtain the time evolution of conversion and , along the polymerization process. The accuracy of the proposed model under a wide range of conditions was assessed. The low computer-time load makes the hybrid model suitable for optimization strategies. Effect of the monomer feed rate on . [source] Incipient stable bubble formation during bulk polymerization of methyl methacrylate under near-isothermal conditions.POLYMER ENGINEERING & SCIENCE, Issue 12 2009Methyl methacrylate is polymerized under near-isothermal conditions in a 1-l stainless steel batch reactor having a glass bottom and stirred with an anchor agitator. A camcorder is used to obtain images of the entrapped vapor bubbles at different times so as to identify the point, Bi, where stable clusters of vapor bubbles first (incipient) get formed. This is being referred to as the transition point. Data on the monomer conversion, xm,Bi, the weight average molecular weight, Mw,Bi, and the viscosity, ,Bi, of the reaction mass at this point have been generated for a variety of experimental conditions. It is observed that the pressure above the liquid reaction mixture and the RPM of the stirrer have little effect on the results in the ranges studied. Correlations have been developed for xm,Bi, Mw,Bi, and ,Bi, relating these to the initiator loading, Io, and the constant set-point temperature, T. Results are compared with those obtained earlier for reactors stirred with ribbon agitators. The transition point is useful for the design of the first stage of polymerization reactors. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Incipient bubble formation during bulk polymerization of methyl methacrylate under near-isothermal conditions using a ribbon agitatorPOLYMER ENGINEERING & SCIENCE, Issue 5 2009Gurpreet J. Singh The polymerization of methyl methacrylate (MMA) is carried out under near-isothermal conditions in a 1-liter stainless steel stirred batch reactor with a glass bottom. A ribbon agitator is used to study the incipient stable-bubble formation point, Bi, during the bulk polymerization of MMA. A camcorder has been used to get images of the bubbles from the beginning of the polymerization till just beyond the incipient stable-bubble formation point. Experimental data on the monomer conversion, xm,Bi, the weight average molecular weight, Mw,Bi, and the viscosity, ,Bi, of the reaction mass have been generated at this important point. Data have been taken at several values of the (near-isothermal) temperature, initiator loading, reactor pressure, and the RPM of the ribbon stirrer. No significant effect of pressure and the RPM of the stirrer were observed over the ranges of these variables studied. Correlations have been developed for xm,Bi, Mw,Bi, and ,Bi, relating these to the initiator loading and the temperature. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Multiobjective optimization of polymerization reaction of vinyl acetate by genetic algorithm technique with a new replacement criterionPOLYMER ENGINEERING & SCIENCE, Issue 5 2008Maryam Sadi A multiobjective optimization procedure based on genetic algorithm has been developed to determine optimum operational conditions of polymerization reaction. In this article by using a new selection criterion to choose the next generation members with better quality, optimization efficiency is improved and the number of generations to obtain Pareto optimal set reduced. In this proposed method a novel replacement criterion based on ranking level information and proximity of solutions to the Pareto optimal front is used to choose the next generation members. The polymerization of vinyl acetate has been chosen as an example. Two objective functions, which used in this study, are maximization of the weight average molecular weight up to the desired value and minimization of the residual initiator concentration. A Pareto optimal set of objective functions has been obtained by application of a Pareto set filter operator. Furthermore, the influence of genetic algorithm parameters on the efficiency and convergence of genetic algorithm is studied by changing cross over and mutation probabilities. Because of the flexibility and generality of genetic algorithm, this optimization method is a useful technique with lots of potentials in determination of optimum value of operation parameters. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Synthesis, static, and dynamic light scattering studies of soluble aromatic polyamidePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2008Sonia Zulfiqar Abstract Aromatic polyamide was synthesized via condensation polymerization of 4-aminophenyl sulfone (APS) with isophthaloyl chloride (IPC) using N,N -dimethyl acetamide (DMAc) as a solvent under anhydrous conditions. The purified aramid was studied by laser light scattering (LLS) in dimethyl sulfoxide (DMSO), a thermodynamically good solvent at 20°C. Static and dynamic light scattering studies permitted to determine the weight average molecular weight , radius of gyration , second virial coefficient A2, the hydrodynamic radius RH, and the diffusion coefficient D. Light scattering experiments were conducted at five concentrations ranging from 0.27 to 2.5,g/L. LLS measurement is also a very useful technique to study the aggregation or association in a polymer system as long as the large "clusters" are reasonably stable in time. The intensity autocorrelation function obtained on the quasi-elastically scattered light showed a simple diffusive relaxation mode. The ratio of radius of gyration to the hydrodynamic radius, i.e. ,,,1.3 indicates that the polyamide chain has coil conformation in DMSO at 20°C. Copyright © 2008 John Wiley & Sons, Ltd. [source] Highly soluble diphenylfluorene-based cardo copolyimides containing perylene units,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7-8 2006Shengang Xu Abstract Two series of novel ternary copolyimides containing perylene and fluorene units in the backbone were synthesized by one-step polycondensation of diamine (4,4,-(9H-fluoren-9-ylidene)bisphenylamine, FBPA) with perylene dianhydride (3,4,9,10-perylenetetracarboxylic dianhydride, PTCDA) and a comonomer [4,4,-(hexafluoroisopropylidene) diphthalic anhydride, 6FDA or 3,3,,4,4,-benzophenonetetracarboxylic dianhydride, BDTA]. The polymers were named as PFFx (PTCDA-FBPA-6FDA) and PFBx (PTCDA-FBPA-BTDA), respectively, and their chemical structures were identified by FT-IR spectra and elemental analyses. Perylene contents in the copolyimides were determined through a quantitative UV-vis spectroscopy method, which are in agreement with the values calculated from the added raw materials both for PFFx and PFBx. Gel permeation chromatography (GPC) measurement suggested that the weight average molecular weight (Mw) is in the range 2.1,5.09,×,104 and the molecular weight distribution (MWD) is 1.86,2.72 for PFFx, and those for PFBx are 2.64,4.73,×,104 and 2.44,2.92, respectively. Thermogravimetric analysis (TGA) measurements showed that the copolyimides are very thermally stable with a temperature of 10% weight loss (T10) in the range 546,563°C for PFFx, and 538,548°C for PFBx. The copolyimides also have good solubility in common organic solvents such as chloroform and tetrahydrofuran. These unique properties can be attributed to the existence of the bulky diphenylfluorene moieties in the polymer backbone. All the copolyimides can emit strong fluorescence both in solution and in films, which make them possibly be used as thermostable light-emitting materials for organic light-emitting diodes. Copyright © 2006 John Wiley & Sons, Ltd. [source] Characterization of perfluoroalkyl acrylic oligomers by electrospray ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2008Timothy J. Romack Electrospray ionization time-of-flight mass spectrometry (ESI-ToF-MS) has been successfully employed for the characterization of molecular weight, molecular weight distribution and end groups for bromine-terminated perfluoroalkyl acrylate oligomers prepared using atom transfer radical polymerization. Intact oligomers and smaller quantities of common side products were observed from m/z 1000 to 4000 cationized with a sodium ion, a difluorobenzyl cation or a proton with a minimum of multiply charged species. Number average molecular weight and weight average molecular weight for both the samples that were characterized were in reasonable agreement with independent measurements conducted using GPC-MALS and 1H NMR spectroscopy. Copyright © 2008 John Wiley & Sons, Ltd. [source] A sensitive and specific HPGPC-FD method for the study of pharmacokinetics and tissue distribution of Radix Ophiopogonis polysaccharide in ratsBIOMEDICAL CHROMATOGRAPHY, Issue 8 2010Xiao Lin Abstract Interest in antimyocardial ischemic activity of a graminan-type fructan with a weight average molecular weight of 4.8,kDa extracted from Radix Ophiopogonis (ROP) has necessitated the study of its pharmacokinetics and tissue distribution. For that, a simple HPGPC,FD method was developed for the sensitive and specific determination of FITC-ROP (fluorescein,isothiocyanate-labeled ROP) in plasma and rat tissues (heart, liver, spleen, lung, kidney, brain and stomach). The analyte was separated on a Shodex Sugar KS-802 high-performance gel column with 0.1,M phosphate buffer (pH 7.0) as mobile phase at a flow rate of 0.5,mL/min, and fluorescence detection at ,ex 495,nm and ,em 515,nm. The calibration curve for FITC-ROP was linear over the range 0.25,20.0 or 50.0,,g/mL in all studied biosamples with correlation coefficients >0.995. The inter-day and intra-day precisions of analysis were not more than 10%, and assay accuracy ranged from 93 to 105% for plasma and from 89 to 108% for tissue homogenates. This method has been confirmed here to be suitable for the study of pharmacokinetics and tissue distribution of ROP and the achieved results are highly instructive for the further pharmaceutical development of ROP, suggesting the promising application of the method to the increasingly important carbohydrate-based drugs. Copyright © 2009 John Wiley & Sons, Ltd. [source] Polylactide copolymers: Effect of copolymer ratio and end capping on their propertiesADVANCES IN POLYMER TECHNOLOGY, Issue 2 2005D. M. Bigg Abstract Racemic copolymers of polylactic acid were investigated to determine the effect of copolymer ratio on melting point, degree of crystallinity, mechanical properties, and processing behavior. The copolymer ratio was found to have a strong influence on the crystallization behavior of the polymer. In addition to the ratio of the L -form to a random mixture of the D and L forms of the lactic acid in the copolymer, the effect of the polymer's molecular weight was examined. The copolymers were produced from the lactide form of the monomer to achieve weight average molecular weights above 100,000. The molecular weight had a profound influence on processability and rate of crystallization. Other notable factors influencing the properties and processing of the copolymers were the concentration of residual monomer in the polymer, the processing time-temperature history, and the extent of molecular weight degradation during processing. An important factor in the commercial development of biodegradable polymers is the ability to control the rate of degradation. Ideally, the polymer should not degrade during functional use, but degrade quite rapidly when discarded. This paper discusses various aspects associated with the control of the rate of degradation of polylactide copolymers; both from the perspective of stabilizing the polymer during processing and product use, and subsequently accelerating the rate of degradation after disposal. Of particular interest are the influences of molecular weight, crystallinity, end capping, and plasticization. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:69,82, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20032 [source] Model Development in Thermal Styrene PolymerizationMACROMOLECULAR SYMPOSIA, Issue 1 2007Bryan Matthews Abstract Summary: The thermal polymerization of styrene is usually modeled by relying on a reaction scheme and a set of equations that were developed more than three decades ago by Hui and Hamielec. Many detailed models of styrene polymerization are available in the open literature and they are mostly based on the work of Hui and Hamielec, which nearly makes this the standard to follow in explaining the behavior of polystyrene reactors. The model of Hui and Hamielec does a very nice job of describing monomer conversion data but discrepancies are seen between observed and predicted values of number and weight average molecular weights, Mn and Mw. Discrepancies in number average molecular weight seem to be the result of random noise. Discrepancies in weight average molecular weight grow as the polymerization temperature decreases and some of the trends observed in the residuals over the entire temperature range cannot be attributed to random noise. Hui and Hamielec attributed the observed deficiencies to a standard deviation of ±10% in their GPC measurements. A new data set with an experimental error of 2% for average molecular weights is presented. The set contains measured values of Mn, Mw and Mz, so the polymerization scheme has been extended to include third order moments. The data set also includes the effect of ethylbenzene as a chain transfer agent. We present the results of comparing model predictions to our measurements and the adjustments made in the original set of kinetic parameters published by Hui and Hamielec. [source] Kinetics and modeling of charge transfer polymerization of methyl methacrylateASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2009P. G. Rao Abstract The charge transfer polymerization of methyl methacrylate (MMA) in presence of n -butyl amine (nBA) and carbon tetrachloride (CCl4) with dimethyl sulfoxide (DMSO) as solvent was experimentally investigated. The variables include concentrations of MMA, nBA, CCl4, DMSO and reaction temperature. The effect of these variables on monomer conversion, number and weight average molecular weights is discussed. A reaction mechanism is proposed and overall kinetics, propagation, chain transfer and termination constants are evaluated. A mathematical model is proposed for estimating monomer conversion, number and weight average molecular weights. The proposed model is validated using the kinetic constants and compared satisfactorily with experimental data of the present study. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||