Jorge R Vega | Tecnologica Nacional Facultad Regional Santa Fe (original) (raw)

Papers by Jorge R Vega

CRC Press eBooks, Oct 12, 2009

Mecánica Computacional, Nov 24, 2019

Resumen. Este trabajo propone una metodología basada en un enfoque estadístico Bayesiano para la ... more Resumen. Este trabajo propone una metodología basada en un enfoque estadístico Bayesiano para la adaptación automática de un sensor inferencial. A diferencia de los métodos clásicos, en esta propuesta se utiliza información estadística disponible (por ejemplo, el valor medio y el desvío estándar del error de predicción) para estimar el bias del sensor. La metodología propuesta se evaluó en base a simulaciones numéricas correspondientes al monitoreo en-línea de variables de calidad asociadas a un proceso continuo de síntesis de caucho estireno-butadieno. En particular, se estudió el desempeño del sensor inferencial en presencia de diferentes perturbaciones en las variables del proceso. Los resultados mostraron la eficiencia de la corrección Bayesiana del bias en comparación con las estrategias clásicas utilizadas.

Measurement of Particle Size Distribution of Polymer Latexes, 2010

The importance of the particle size distribution (PSD) of polymer latexes is first discussed; and... more The importance of the particle size distribution (PSD) of polymer latexes is first discussed; and definitions of differential / cumulative distributions and average diameters are presented. Main analytical techniques for latex PSD measurement are classified. Some ensemble techniques such as turbidimetry (T), elastic light scattering (ELS), and dynamic light scattering (DLS) are thorougly treated, and evaluated by considering the characterization of industrial latexes of unknown composition. The effect of uncertainties in the particle refractive index (PRI) on the PSD is also studied. A brief discussion on problems associated to the PSD measurement by standard electron microscopy (EM) is presented, together with the analysis of latex nanoparticles by atomic force microscopy (AFM), and the applicattion of new EM developments for the characterization of wet samples in their environment. Also, the principles of main fractionation techniques are briefly discussed, including sedimentation, unpacked/packed olumn chromatography, and field flow fractionation methods, together with an analysis of their detection systems, with emphasis on the estimation of the PSD ordinates from singlewavelength T measurements.Fil: Gugliotta, Luis Marcelino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Clementi, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Fil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cienti... more Fil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Desarrollo Tecnologico para la Industria Quimica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnologico para la Industria Quimica; Argentina

AJEA, 2020

En el presente trabajo se desarrolla una metodología que facilita la transición de una red eléctr... more En el presente trabajo se desarrolla una metodología que facilita la transición de una red eléctrica centralizada tradicional a una configuración de red eléctrica basada en microredes. Se incorporan generadores inyectando potencia en posiciones estratégicas de la red. Además, partiendo de la topología de una red radial centralizada, se delimitan microredes con el propósito de otorgarles la mayor capacidad para que puedan funcionar de forma aislada. Esta optimización se realiza considerando la minimización de las pérdidas de la red y maximizando la autonomía potencial de las microredes obtenidas. Para desarrollar la metodología propuesta, se emplea recocido simulado como algoritmo metaheurístico de optimización.

Polymer, 2020

Blends of a butadiene rich-tapered diblock copolymer (DC) with polystyrene (PS) and/or polybutadi... more Blends of a butadiene rich-tapered diblock copolymer (DC) with polystyrene (PS) and/or polybutadiene (PB) in ethylbenzene (EB) were investigated to better understand the phenomena occurring during the synthesis of high impact polystyrene (HIPS). For the first time, the apparent partitioning of components between the demixedphases of quaternary blends PS/PB/DC/EB was determined, involving variations of DC concentration, PS molar mass, simulated conversion of styrene and temperature. The new methodology combines FTIR, solvent extraction, TLC and mass balances and verifies important results by TEM and SEC. During demixing, a molecular fractionation occurs which depends on the DC composition distribution, the ratio between the molar masses of each of the copolymer blocks and the respective homopolymers and the viscosity ratio between the continuous and dispersed phases. The affinity between the low molar mass PS and the PS block in DC favors the stabilization of PS domains in the PB-rich phase.

An inefficient operation of the utility grid can be inferred from low power quality indexes. Unde... more An inefficient operation of the utility grid can be inferred from low power quality indexes. Under such conditions, reductions in the useful life of equipments and loads, grid instabilities, service interruptions and breakdowns can be expected, which would produce meaningful economic losses for the end-users as well as for the power supply company. In this context, it is useful to have a diagnosis tool able to identify the underlying cause of a given disturbance. This article proposes a one-step extreme learning machine-based method for the diagnosis of voltage dips detected on an electrical distribution grid. The proposed method was evaluated on the basis of synthetic data generated by the simulation of a real power grid. The performance of 10 hyperparameter combinations on the diagnosis of 20 different classes of voltage dips was assessed through two different strategies, i.e.: 1) a one-for-all approach, with a common classifier for all disturbance classes; and 2) a one-against-al...

Complexity, 2017

The lack of online information on some bioprocess variables and the presence of model and paramet... more The lack of online information on some bioprocess variables and the presence of model and parametric uncertainties pose significant challenges to the design of efficient closed-loop control strategies. To address this issue, this work proposes an online state estimator based on a Radial Basis Function (RBF) neural network that operates in closed loop together with a control law derived on a linear algebra-based design strategy. The proposed methodology is applied to a class of nonlinear systems with three types of uncertainties: (i) time-varying parameters, (ii) uncertain nonlinearities, and (iii) unmodeled dynamics. To reduce the effect of uncertainties on the bioreactor, some integrators of the tracking error are introduced, which in turn allow the derivation of the proper control actions. This new control scheme guarantees that all signals are uniformly and ultimately bounded, and the tracking error converges to small values. The effectiveness of the proposed approach is illustra...

Encyclopedia of Chromatography, Third Edition (Print Version), 2009

Latin American Applied Research, Oct 1, 2006

European Polymer Journal, Sep 1, 2013

The incorporation of polybutadiene in waterborne polystyrene nanoparticles by miniemulsion polyme... more The incorporation of polybutadiene in waterborne polystyrene nanoparticles by miniemulsion polymerization is expected to positively combine the properties of both materials, improving the impact resistance and toughness. The kinetics of the miniemulsion polymerization used to synthesize these hybrid nanomaterials and the effect of the reaction variables on the polymer microstructure and particle morphology were investigated. Both molecular microstructure and final particle morphology (core-shell, ''salami'' or threephase type) depended on the nature of the employed polybutadiene based rubbers and initiators. The mechanisms responsible for these effects were discussed.

Journal of Colloid and Interface Science, May 1, 2003

Multiangle dynamic light scattering (DLS) provides a better estimate of particle size distributio... more Multiangle dynamic light scattering (DLS) provides a better estimate of particle size distributions (PSD) than single-angle DLS. However, multiangle data treatment requires appropriate weighting of each autocorrelation measurement prior to calculation of the PSD. The weighting coefficients may be directly obtained from (i). the autocorrelation baselines or (ii). independent measurement of the average light intensity by elastic light scattering. However, the propagation of errors associated with such procedures may intolerably corrupt the PSD estimate. In this work, an alternative recursive least-squares calculation is proposed that estimates the weighting coefficients on the basis of the complete autocorrelation measurement. The method was validated through a numerical example that simulates the analysis of a polystyrene latex with a bimodal PSD and with "measurements" taken at 10 detection angles. The ill-conditioned nature of the problem determines that the "true" PSD cannot be recovered, even in the absence of errors. A sensitivity analysis was carried out to determine the effect of errors in the weighting coefficients on the PSD recoveries.

Journal of Applied Polymer Science, Sep 15, 2008

Four batch and unseeded emulsion polymerizations of styrene were investigated, which included iso... more Four batch and unseeded emulsion polymerizations of styrene were investigated, which included isooctyl 3-mercaptopropionate (iOMP) as chain transfer agent (CTA). This compound was analyzed by 13 C NMR and GC/ MS, resulting in a mixture of over 10 isomers. Because of different reactivities of the CTA isomers, the produced polystyrenes presented broad and bimodal molecular weight distributions (MWDs). A mathematical model was adjusted to the measurements, and the measured MWDs were adequately predicted when assuming the CTA as a binary mixture of high but different reactivities.

Computers & Chemical Engineering, Sep 1, 2007

This theoretical article investigates an industrial emulsion copolymerization of acrylonitrile (A... more This theoretical article investigates an industrial emulsion copolymerization of acrylonitrile (A) and butadiene (B), for the production of grades BJLT and AJLT of a nitrile rubber (NBR). The simulated process involves a train of eight continuous stirred-tank reactors operating at 10 • C. The product quality is determined by its molecular structure (average copolymer composition, average molecular weights, and average level of branching), and by its final latex characteristics (number particle concentration and number-average particle diameter). The mathematical model by Vega et al. [

Macromolecular Symposia, Nov 1, 2007

This article reviews some recent developments on the determination of the Band Broadening Functio... more This article reviews some recent developments on the determination of the Band Broadening Function (BBF) in Size Exclusion Chromatography (SEC) of polymers. It was carried out in the frame of the IUPAC Project: ''Data Treatment in Size Exclusion Chromatography of Polymers''. The correction for band broadening (BB) is important for quantitative determinations of the molar mass distribution (MMD) of narrow-distributed (or highly multimodal) polymers, and of derived variables such as kinetic parameters. In the narrow range of a molar mass standard, the BBF is uniform and of positive skewness. In a broad chromatographic range, the BBF is non-uniform and skewed; and it can be adequately represented by an exponentially-modified Gaussian function (EMG) of 2 parameters that vary slightly with elution volume: an increasing Gaussian variance and a decreasing exponential decay. Additionally, the total BBF variance remains almost constant if not close to the total exclusion limit. The following methods for determining BBF parameters are reviewed: a) a direct method based on assuming Poisson-distributed MMDs; b) a direct method based on measuring the mass-and molar mass chromatograms of narrow standards; c) a theoretical method based on a stochastic model that is equivalent to the Giddings-Eyring model; and d) a theoretical method based on a deterministic model obtained through an extension of the classical van Deemter expression. Ideally, the correction for BB requires a robust numerical inversion algorithm. However, alternative simplified solutions are also possible.

Journal of Applied Polymer Science, 2009

This work investigates a batch and unseeded emulsion polymerization of isoprene at 10 C with n-do... more This work investigates a batch and unseeded emulsion polymerization of isoprene at 10 C with n-dodecylmercaptan as chain transfer agent (CTA). The obtained polyisoprene (PI) was analyzed by size exclusion chromatography (SEC) with on-line viscometry. A global polymerization model was adjusted to the measurements of conversion, average particle size, and average molecular weights. The CTA concentration strongly affects the average molecular weights but has a negligible effect on conversion, average particle diameter, and average branching. Due to the combined effects of chain transfers to the polymer and to the CTA, the final molar mass distributions exhibited dispersity indexes higher than 10. The polymerization model predictions on the average degree of branching was combined with an ideal SEC model for adjusting the branching exponent of PI in tetrahydrofuran at 25 C that resulted e ¼ 2.5. A sensitivity analysis showed that þ20% errors in M w induced variations in e lower than À10%.

Journal of Polymer Research, Dec 10, 2014

The molar mass distribution (MMD) and branching distribution (BD) of the graft terpolymer present... more The molar mass distribution (MMD) and branching distribution (BD) of the graft terpolymer present in MBS (methyl methacrylate-butadiene-styrene, MMA-B-St) were estimated by size exclusion chromatography (SEC) with a series of three detectors: a UV photometer, a specific viscometer (SV), and a differential refractometer (DR). A solvent extraction procedure was employed to isolate the main MBS constituents: unreacted polybutadiene (PB), a PMMA-PS free copolymer (FC), and the PB-g-(PMMA-PS) graft terpolymer (GT). The FC was analyzed by UV + DR, yielding an almost uniform St mass fraction. The analysis of the GT involved the following assumptions: (i) the composition of the grafted branches coincides with that of the FC; (ii) the volumetric contractions of the molecules are represented by the Zimm-Stockmayer equations for randomly branched homopolymers; (iii) the low molar mass fraction exhibits a single branch per molecule; and (iv) the Mark-Houwink-Sakurada (MHS) parameters of the hypothetical homologous linear terpolymer are estimated by weighting the MHS constants of the PB and FC according to their mass fractions in the GT. The data treatment employed also enabled the branching exponent (ε) that relates the geometric and hydrodynamic contraction factors to be estimated, yielding ε≈1.45.

Journal of Applied Polymer Science, Jul 15, 2010

1Instituto de Desarrollo Tecnológico para la Industria Quımica (INTEC), Universidad Nacional del ... more 1Instituto de Desarrollo Tecnológico para la Industria Quımica (INTEC), Universidad Nacional del Litoral– CONICET, Güemes 3450, Santa Fe 3000, Argentina 2Facultad Regional Santa Fe (Universidad Tecnológica Nacional), Lavaisse 610, Santa Fe 3000, Argentina

International Journal of Polymer Analysis and Characterization, Feb 1, 2001

... Nacional Del Litoral CONICET), Guemes 3450 (3000) Santa Fe, Argentina; bEs ... the chroma-tog... more ... Nacional Del Litoral CONICET), Guemes 3450 (3000) Santa Fe, Argentina; bEs ... the chroma-tograms obtained with an on-line viscometer and a differential refractometer to study the effect of the injected sample concentration on parameters such as the Mark-Houwink constants K ...

Latin American Applied Research, Oct 1, 2006

ABSTRACT

CRC Press eBooks, Oct 12, 2009

Mecánica Computacional, Nov 24, 2019

Resumen. Este trabajo propone una metodología basada en un enfoque estadístico Bayesiano para la ... more Resumen. Este trabajo propone una metodología basada en un enfoque estadístico Bayesiano para la adaptación automática de un sensor inferencial. A diferencia de los métodos clásicos, en esta propuesta se utiliza información estadística disponible (por ejemplo, el valor medio y el desvío estándar del error de predicción) para estimar el bias del sensor. La metodología propuesta se evaluó en base a simulaciones numéricas correspondientes al monitoreo en-línea de variables de calidad asociadas a un proceso continuo de síntesis de caucho estireno-butadieno. En particular, se estudió el desempeño del sensor inferencial en presencia de diferentes perturbaciones en las variables del proceso. Los resultados mostraron la eficiencia de la corrección Bayesiana del bias en comparación con las estrategias clásicas utilizadas.

Measurement of Particle Size Distribution of Polymer Latexes, 2010

The importance of the particle size distribution (PSD) of polymer latexes is first discussed; and... more The importance of the particle size distribution (PSD) of polymer latexes is first discussed; and definitions of differential / cumulative distributions and average diameters are presented. Main analytical techniques for latex PSD measurement are classified. Some ensemble techniques such as turbidimetry (T), elastic light scattering (ELS), and dynamic light scattering (DLS) are thorougly treated, and evaluated by considering the characterization of industrial latexes of unknown composition. The effect of uncertainties in the particle refractive index (PRI) on the PSD is also studied. A brief discussion on problems associated to the PSD measurement by standard electron microscopy (EM) is presented, together with the analysis of latex nanoparticles by atomic force microscopy (AFM), and the applicattion of new EM developments for the characterization of wet samples in their environment. Also, the principles of main fractionation techniques are briefly discussed, including sedimentation, unpacked/packed olumn chromatography, and field flow fractionation methods, together with an analysis of their detection systems, with emphasis on the estimation of the PSD ordinates from singlewavelength T measurements.Fil: Gugliotta, Luis Marcelino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Clementi, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Fil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cienti... more Fil: Vega, Jorge Ruben. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Desarrollo Tecnologico para la Industria Quimica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnologico para la Industria Quimica; Argentina

AJEA, 2020

En el presente trabajo se desarrolla una metodología que facilita la transición de una red eléctr... more En el presente trabajo se desarrolla una metodología que facilita la transición de una red eléctrica centralizada tradicional a una configuración de red eléctrica basada en microredes. Se incorporan generadores inyectando potencia en posiciones estratégicas de la red. Además, partiendo de la topología de una red radial centralizada, se delimitan microredes con el propósito de otorgarles la mayor capacidad para que puedan funcionar de forma aislada. Esta optimización se realiza considerando la minimización de las pérdidas de la red y maximizando la autonomía potencial de las microredes obtenidas. Para desarrollar la metodología propuesta, se emplea recocido simulado como algoritmo metaheurístico de optimización.

Polymer, 2020

Blends of a butadiene rich-tapered diblock copolymer (DC) with polystyrene (PS) and/or polybutadi... more Blends of a butadiene rich-tapered diblock copolymer (DC) with polystyrene (PS) and/or polybutadiene (PB) in ethylbenzene (EB) were investigated to better understand the phenomena occurring during the synthesis of high impact polystyrene (HIPS). For the first time, the apparent partitioning of components between the demixedphases of quaternary blends PS/PB/DC/EB was determined, involving variations of DC concentration, PS molar mass, simulated conversion of styrene and temperature. The new methodology combines FTIR, solvent extraction, TLC and mass balances and verifies important results by TEM and SEC. During demixing, a molecular fractionation occurs which depends on the DC composition distribution, the ratio between the molar masses of each of the copolymer blocks and the respective homopolymers and the viscosity ratio between the continuous and dispersed phases. The affinity between the low molar mass PS and the PS block in DC favors the stabilization of PS domains in the PB-rich phase.

An inefficient operation of the utility grid can be inferred from low power quality indexes. Unde... more An inefficient operation of the utility grid can be inferred from low power quality indexes. Under such conditions, reductions in the useful life of equipments and loads, grid instabilities, service interruptions and breakdowns can be expected, which would produce meaningful economic losses for the end-users as well as for the power supply company. In this context, it is useful to have a diagnosis tool able to identify the underlying cause of a given disturbance. This article proposes a one-step extreme learning machine-based method for the diagnosis of voltage dips detected on an electrical distribution grid. The proposed method was evaluated on the basis of synthetic data generated by the simulation of a real power grid. The performance of 10 hyperparameter combinations on the diagnosis of 20 different classes of voltage dips was assessed through two different strategies, i.e.: 1) a one-for-all approach, with a common classifier for all disturbance classes; and 2) a one-against-al...

Complexity, 2017

The lack of online information on some bioprocess variables and the presence of model and paramet... more The lack of online information on some bioprocess variables and the presence of model and parametric uncertainties pose significant challenges to the design of efficient closed-loop control strategies. To address this issue, this work proposes an online state estimator based on a Radial Basis Function (RBF) neural network that operates in closed loop together with a control law derived on a linear algebra-based design strategy. The proposed methodology is applied to a class of nonlinear systems with three types of uncertainties: (i) time-varying parameters, (ii) uncertain nonlinearities, and (iii) unmodeled dynamics. To reduce the effect of uncertainties on the bioreactor, some integrators of the tracking error are introduced, which in turn allow the derivation of the proper control actions. This new control scheme guarantees that all signals are uniformly and ultimately bounded, and the tracking error converges to small values. The effectiveness of the proposed approach is illustra...

Encyclopedia of Chromatography, Third Edition (Print Version), 2009

Latin American Applied Research, Oct 1, 2006

European Polymer Journal, Sep 1, 2013

The incorporation of polybutadiene in waterborne polystyrene nanoparticles by miniemulsion polyme... more The incorporation of polybutadiene in waterborne polystyrene nanoparticles by miniemulsion polymerization is expected to positively combine the properties of both materials, improving the impact resistance and toughness. The kinetics of the miniemulsion polymerization used to synthesize these hybrid nanomaterials and the effect of the reaction variables on the polymer microstructure and particle morphology were investigated. Both molecular microstructure and final particle morphology (core-shell, ''salami'' or threephase type) depended on the nature of the employed polybutadiene based rubbers and initiators. The mechanisms responsible for these effects were discussed.

Journal of Colloid and Interface Science, May 1, 2003

Multiangle dynamic light scattering (DLS) provides a better estimate of particle size distributio... more Multiangle dynamic light scattering (DLS) provides a better estimate of particle size distributions (PSD) than single-angle DLS. However, multiangle data treatment requires appropriate weighting of each autocorrelation measurement prior to calculation of the PSD. The weighting coefficients may be directly obtained from (i). the autocorrelation baselines or (ii). independent measurement of the average light intensity by elastic light scattering. However, the propagation of errors associated with such procedures may intolerably corrupt the PSD estimate. In this work, an alternative recursive least-squares calculation is proposed that estimates the weighting coefficients on the basis of the complete autocorrelation measurement. The method was validated through a numerical example that simulates the analysis of a polystyrene latex with a bimodal PSD and with "measurements" taken at 10 detection angles. The ill-conditioned nature of the problem determines that the "true" PSD cannot be recovered, even in the absence of errors. A sensitivity analysis was carried out to determine the effect of errors in the weighting coefficients on the PSD recoveries.

Journal of Applied Polymer Science, Sep 15, 2008

Four batch and unseeded emulsion polymerizations of styrene were investigated, which included iso... more Four batch and unseeded emulsion polymerizations of styrene were investigated, which included isooctyl 3-mercaptopropionate (iOMP) as chain transfer agent (CTA). This compound was analyzed by 13 C NMR and GC/ MS, resulting in a mixture of over 10 isomers. Because of different reactivities of the CTA isomers, the produced polystyrenes presented broad and bimodal molecular weight distributions (MWDs). A mathematical model was adjusted to the measurements, and the measured MWDs were adequately predicted when assuming the CTA as a binary mixture of high but different reactivities.

Computers & Chemical Engineering, Sep 1, 2007

This theoretical article investigates an industrial emulsion copolymerization of acrylonitrile (A... more This theoretical article investigates an industrial emulsion copolymerization of acrylonitrile (A) and butadiene (B), for the production of grades BJLT and AJLT of a nitrile rubber (NBR). The simulated process involves a train of eight continuous stirred-tank reactors operating at 10 • C. The product quality is determined by its molecular structure (average copolymer composition, average molecular weights, and average level of branching), and by its final latex characteristics (number particle concentration and number-average particle diameter). The mathematical model by Vega et al. [

Macromolecular Symposia, Nov 1, 2007

This article reviews some recent developments on the determination of the Band Broadening Functio... more This article reviews some recent developments on the determination of the Band Broadening Function (BBF) in Size Exclusion Chromatography (SEC) of polymers. It was carried out in the frame of the IUPAC Project: ''Data Treatment in Size Exclusion Chromatography of Polymers''. The correction for band broadening (BB) is important for quantitative determinations of the molar mass distribution (MMD) of narrow-distributed (or highly multimodal) polymers, and of derived variables such as kinetic parameters. In the narrow range of a molar mass standard, the BBF is uniform and of positive skewness. In a broad chromatographic range, the BBF is non-uniform and skewed; and it can be adequately represented by an exponentially-modified Gaussian function (EMG) of 2 parameters that vary slightly with elution volume: an increasing Gaussian variance and a decreasing exponential decay. Additionally, the total BBF variance remains almost constant if not close to the total exclusion limit. The following methods for determining BBF parameters are reviewed: a) a direct method based on assuming Poisson-distributed MMDs; b) a direct method based on measuring the mass-and molar mass chromatograms of narrow standards; c) a theoretical method based on a stochastic model that is equivalent to the Giddings-Eyring model; and d) a theoretical method based on a deterministic model obtained through an extension of the classical van Deemter expression. Ideally, the correction for BB requires a robust numerical inversion algorithm. However, alternative simplified solutions are also possible.

Journal of Applied Polymer Science, 2009

This work investigates a batch and unseeded emulsion polymerization of isoprene at 10 C with n-do... more This work investigates a batch and unseeded emulsion polymerization of isoprene at 10 C with n-dodecylmercaptan as chain transfer agent (CTA). The obtained polyisoprene (PI) was analyzed by size exclusion chromatography (SEC) with on-line viscometry. A global polymerization model was adjusted to the measurements of conversion, average particle size, and average molecular weights. The CTA concentration strongly affects the average molecular weights but has a negligible effect on conversion, average particle diameter, and average branching. Due to the combined effects of chain transfers to the polymer and to the CTA, the final molar mass distributions exhibited dispersity indexes higher than 10. The polymerization model predictions on the average degree of branching was combined with an ideal SEC model for adjusting the branching exponent of PI in tetrahydrofuran at 25 C that resulted e ¼ 2.5. A sensitivity analysis showed that þ20% errors in M w induced variations in e lower than À10%.

Journal of Polymer Research, Dec 10, 2014

The molar mass distribution (MMD) and branching distribution (BD) of the graft terpolymer present... more The molar mass distribution (MMD) and branching distribution (BD) of the graft terpolymer present in MBS (methyl methacrylate-butadiene-styrene, MMA-B-St) were estimated by size exclusion chromatography (SEC) with a series of three detectors: a UV photometer, a specific viscometer (SV), and a differential refractometer (DR). A solvent extraction procedure was employed to isolate the main MBS constituents: unreacted polybutadiene (PB), a PMMA-PS free copolymer (FC), and the PB-g-(PMMA-PS) graft terpolymer (GT). The FC was analyzed by UV + DR, yielding an almost uniform St mass fraction. The analysis of the GT involved the following assumptions: (i) the composition of the grafted branches coincides with that of the FC; (ii) the volumetric contractions of the molecules are represented by the Zimm-Stockmayer equations for randomly branched homopolymers; (iii) the low molar mass fraction exhibits a single branch per molecule; and (iv) the Mark-Houwink-Sakurada (MHS) parameters of the hypothetical homologous linear terpolymer are estimated by weighting the MHS constants of the PB and FC according to their mass fractions in the GT. The data treatment employed also enabled the branching exponent (ε) that relates the geometric and hydrodynamic contraction factors to be estimated, yielding ε≈1.45.

Journal of Applied Polymer Science, Jul 15, 2010

1Instituto de Desarrollo Tecnológico para la Industria Quımica (INTEC), Universidad Nacional del ... more 1Instituto de Desarrollo Tecnológico para la Industria Quımica (INTEC), Universidad Nacional del Litoral– CONICET, Güemes 3450, Santa Fe 3000, Argentina 2Facultad Regional Santa Fe (Universidad Tecnológica Nacional), Lavaisse 610, Santa Fe 3000, Argentina

International Journal of Polymer Analysis and Characterization, Feb 1, 2001

... Nacional Del Litoral CONICET), Guemes 3450 (3000) Santa Fe, Argentina; bEs ... the chroma-tog... more ... Nacional Del Litoral CONICET), Guemes 3450 (3000) Santa Fe, Argentina; bEs ... the chroma-tograms obtained with an on-line viscometer and a differential refractometer to study the effect of the injected sample concentration on parameters such as the Mark-Houwink constants K ...

Latin American Applied Research, Oct 1, 2006

ABSTRACT