Individual Monomer Conversions Research Articles

Modelling of a continuous kneader reactor for the polymerization of partially neutralized acrylic acid

AbstractA mathematical model and analysis of the continuous polymerization of partially neutralized acrylic acid (AA) in a continuous kneader reactor is presented here as an initial attempt to simulate the synthesis of a superabsorbent polymer. A detailed kinetic model has been used to describe the copolymerization of AA and sodium acrylate (NaA) in aqueous medium. This model is used to describe batch and continuous operations. The polymerization is initiated by a mixture of potassium persulphate (K2S2O8, KPS) and hydrogen peroxide (H2O2) as oxidizing agent and ascorbic acid (AsA) as reducing agent. A novel set of kinetic parameters has been estimated by fitting experimental data from different literature sources. The operation of a continuous kneader reactor modelled as a plug‐flow reactor with axial dispersion is theoretically investigated to predict temperature profile, total and individual monomer conversion, consumption of KPS, H2O2, and AsA, and polymer average molecular weights. The simulation results show the presence of a hot spot close to the reactor entrance that could be potentially severe during startup and could have a detrimental impact on polymer quality. This model is a first step in the direction of achieving optimal operating protocols and exploring improved polymerization reactor designs.

Modeling of batch production of high vinyl styrene/butadiene copolymers for high performance tires

AbstractMathematical modeling of batch production of high vinyl random styrene/butadiene copolymers in an industrial batch reactor was accomplished. Mass and energy balance equations were solved to model the nonisothermal anionic copolymerization of styrene/butadiene performed in an industrial batch reactor. The simulation model allows to predict the variation of the individual and global monomer conversion(s), temperature, pressure, and volume level of reactor with the time. Simulation model was used to determine the optimal polymerization conditions to maximize the production of a high vinyl random styrene/butadiene copolymer used in the manufacture of high performance tires.

Fundamental investigations into the free‐radical copolymerization of N‐phenylmaleimide and norbornene

ABSTRACTA fundamental investigation into the copolymerization of N‐phenylmaleimide and norbornene via conventional free‐radical polymerization techniques was conducted. Reaction conditions were optimized for molecular weight and percent yield by tuning overall concentration and initiator loading. The copolymerization kinetics were monitored using in‐situ, variable temperature nuclear magnetic resonance and first‐order behavior was observed with respect to each monomer. Although the related copolymerization of norbornene and maleic anhydride was well‐known to proceed in a perfectly alternating manner, the copolymerization of norbornene and N‐phenylmaleimide was found to deviate from strictly alternating copolymerization behavior, producing significant amounts of sequentially enchained N‐phenylmaleimide units within the polymeric backbone. This deviation from perfectly alternating behavior was confirmed by analysis of individual monomer conversion rates and by measurement of monomer reactivity ratios using the Mayo–Lewis graphical analysis method. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 985–991

Co(acac)2 mediated controlled radical copolymerization of vinyl acetate and methyl acrylate initiated by benzoyl peroxide

Cobalt mediated radical copolymerization of vinyl acetate (VAc) and methyl acrylate (MA) was successfully performed in the presence of cobalt(II) acetylacetonate (Co(acac)2), dimethylformamide (DMF) and benzoyl peroxide (BPO) as catalyst, cobalt coordinating agent and initiator, respectively, at 45°C. The individual monomer conversion and comonomer composition of copolymers were determined by 1H NMR spectroscopy. Molecular weight (Mn) and its distribution (Mw/Mn) were analyzed by GPC technique. The time dependence of ln[M]0/[M], the variation of molecular weight with respect to the conversion, and molecular weight distribution of copolymers were studied to evaluate controlled characteristics of copolymerization. It was found that Co(acac)2 successfully mediated the radical copolymerization of VAc and MA. Moreover, copolymer molecular weight and copolymerization rate increased with increasing initial MA ratio. The spectroscopy analysis revealed VAc content in the copolymer increased with conversion regardless of VAc initial ratio, indicating a gradient sequence distribution of the copolymer.

Acrylic-Alkyd Hybrids: Secondary Nucleation, Particle Morphology, and Limiting Conversions

The chemical incorporation of an unsaturated alkyd into an acrylic polymer created via miniemulsion polymerisation was studied. The variation of the number ratio of polymer particles to initial droplets with conversion, and changes in individual monomer conversions with increasing alkyd levels were the main quantities used to study the effect of increasing alkyd quantity in the hybrid system. Homogeneous nucleation was more significant in systems rich in the more hydrophilic methyl methacrylate (MMA). Changes in particle morphology with monomer conversion, as well as limited monomer conversion were observed. The results emphasize the importance of proper pairing of the miscibility between the specific acrylics and alkyds used in these hybrid polymers.

Monitoring of visible light photopolymerization of an epoxy/dimethacrylate hybrid system by Raman and near-infrared spectroscopies

Hybrid systems formulated with epoxy and methacrylate monomers at mass fraction either 50:50 or 75:25 were studied. The individual monomer conversions during photopolymerization with visible light were monitored by Raman and near-infrared spectroscopies. The rate of polymerization and final degree of conversion of the methacrylate groups were raised when the epoxy monomer was present. This is attributed to enhancement of the mobility of the reactive species caused by the presence of the epoxy monomer. Conversely, the earlier vitrification of the system due to the faster polymerizing methacrylate network resulted in reduced conversion of epoxy rings.

Prediction of Bivariate Molecular Property Distributions in Free-Radical Polymerization Systems Using Monte Carlo and Sectional Grid Methods

An efficient Monte Carlo (MC) algorithm and a two-dimensional fixed pivot technique (2-D FPT) are described for the calculation of the average and distributed molecular properties of polymers in batch free-radical polymerization and copolymerization reactors. Simulations are carried out, under different reactor conditions, to calculate the individual monomer conversions, the leading moments of the 'live' and 'dead' polymer chain length distributions as well as the dynamic evolution of the distributed molecular properties (i.e., molecular weight distribution (MWD), long chain branching distribution (LCBD), copolymer composition distribution (CCD), joint LCB-MW and CC-MW distributions, etc.). The validity of the numerical calculations is examined via a direct comparison of the simulation results, obtained by the two numerical methods, with experimental data on the styrene-methyl methacrylate and vinyl acetate batch free-radical polymerization systems. Additional comparisons between the MC and the 2-D FPT methods are carried out for both polymerization systems, under different polymerization conditions. It is clearly shown that both numerical methods are capable of predicting the distributed molecular, branching and copolymer properties, with high accuracy, up to very high monomer conversions.

Miniemulsion Copolymerization of Styrene and γ-Methacryloxypropyltrimethoxysilane: Kinetics and Mechanism

The kinetics of the miniemulsion copolymerization of styrene (St) and γ-methacryloxypropyltrimethoxysilane (MPS) was investigated by studying the effects of the MPS/St weight ratio, the nature and amount of initiator, the suspension pH, and the surfactant concentration on the overall and individual monomer conversions. It was found that the introduction of MPS accelerates the free radical copolymerization reaction due to its higher propagation rate constant and higher water solubility compared to styrene. On the other hand, MPS decreases the copolymerization rate mainly during the second half of the reaction. This is presumed to be due to the formation of alkoxysilane-rich copolymers on the particles surface providing a barrier to radical’s entry. The rate of hydrolysis is pH-dependent, and for a given pH, the influence of the surfactant concentration on the hydrolysis rate suggests that the interface between the latex particles and water is the main locus of hydrolysis. 29Si solid-state NMR analysis showed that the hydrolyzed alkoxysilyl moieties did not condense under neutral conditions even for high MPS/St feed ratios. Premature cross-linking could be also minimized under basic conditions but could not be avoided in acidic media.

Dynamic prediction of the bivariate molecular weight–copolymer composition distribution using sectional-grid and stochastic numerical methods

In the present study, a two-dimensional fixed pivot technique (2-D FPT) and an efficient Monte Carlo (MC) algorithm are described for the calculation of the bivariate molecular weight–copolymer composition (MW–CC) distribution in batch free-radical copolymerization reactors. A comprehensive free-volume model is employed to describe the variation of termination and propagation rate constants as well as the variation of the initiator efficiency with respect to the monomer conversion. Simulations are carried out, under different reactor conditions, to calculate the individual monomer conversions, the leading moments of the ‘live’ and ‘dead’ polymer chain length distributions as well as the dynamic evolution of the distributed molecular properties (i.e., molecular weight distribution (MWD), copolymer composition distribution (CCD) and joint MW–CC distribution). The validity of the numerical calculations is examined via a direct comparison of the simulation results, obtained by the two numerical methods, with experimental data on the styrene–methyl methacrylate batch free-radical copolymerization. Additional comparisons between the 2-D FPT and the MC methods are carried out for different polymerization conditions. It is clearly shown that both numerical methods are capable of predicting the distributed molecular and copolymer properties, with high accuracy, up to very high monomer conversions. It is also shown that the proposed dynamic MC algorithm is less computationally demanding than the 2-D FPT.

Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d6 using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line 1H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r 2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k p . k t −0.5 was then estimated. It was observed that k p . k t −0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.

Kinetic study of radical polymerization. VII. Investigation into the solution copolymerization of acrylonitrile and itaconic acid by real‐time 1H NMR spectroscopy

AbstractFree radical solution copolymerization of acrylonitrile (AN) and itaconic acid (IA) was performed with DMSO‐d6 as the solvent and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. Weight ratio of the monomers to solvent and molar ratio of initiator to monomers were constant in all experiments. The initial comonomer composition was the only variable in this study. On‐line 1H NMR spectroscopy was applied to follow individual monomer conversion. Mole fraction of AN and IA in the reaction mixture (f) and in the copolymer chain (F) were measured with progress of the copolymerization reaction. Overall monomer conversion versus time and also compositions of monomer mixture and copolymer as a function of overall monomer conversion were calculated from the data of individual monomer conversion versus time. Total rate constant for the copolymerization reaction was calculated by using the overall monomer conversion versus time data and then kp/kt0.5 was estimated. The dependency of kp/kt0.5 on IA concentration was studied and it was found that this ratio decreases by increasing the mole fraction of IA in the initial feed. The variation of comonomer and copolymer compositions as a function of overall monomer conversion was calculated theoretically by the terminal model equations and compared with the experimental data. Instantaneous copolymer composition curve showed the formation of alternating copolymer chain during copolymerization reaction. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3253–3260, 2007

Kinetic Study of Radical Polymerization VI. Copolymer Composition and Kinetic Parameters for Coplymerization of Styrene‐Itaconic Acid by On‐Line 1H‐NMR

Free radical solution copolymerization of styrene (St) and itaconic acid (IA) in dimethylsulfoxide‐d6 (DMSO‐d6) as the solvent and the use of 2,2′‐azobisisobutyronitrile (AIBN) as the initiator at 78°C was investigated by an on‐line 1H‐NMR spectroscopy technique. Individual monomer conversion vs. reaction time, which was calculated from the 1H‐NMR spectra data, was used to study the drift in monomer mixture composition vs. conversion. It was found that in general, both monomers were incorporated almost equally into the copolymer. However, when the mole fraction of IA was low, the tendency of IA toward incorporation into the copolymer chain was somewhat higher than St and by increasing the mole fraction of IA in the reaction mixture, the inverse tendency was observed. Overall monomer conversion as a function of time was calculated from individual monomer conversion data and used for the estimation of kp /kt 0.5 for various monomer mixture compositions. This ratio was decreased with increasing the amount of IA in the initial feed, indicating a decrease in the rate of copolymerization. Changes in the copolymer composition vs. overall monomer conversion were investigated experimentally from the NMR spectra. This was in good agreement with the changes in monomer mixture composition vs. reaction progress. Plotting the copolymer composition vs. initial monomer feed showed tendency of the system toward alternating copolymerization.

Off-line monitoring of styrene/butyl acrylate copolymerizations in toluene using ATR-FTIR spectroscopy

The solution copolymerization of styrene/butyl acrylate in toluene was monitored off-line using an ATR-FTIR probe. The probe was used to track the concentration of the starting materials, thereby providing conversion and polymer composition data. Off-line gravimetry and 1H NMR spectroscopy were used as standard methods to provide a comparison to the ATR-FTIR data. A non-calibrated univariate method was first used to calculate individual monomer conversions by monitoring the peak height of characteristic IR absorbances for each monomer. An alternative, calibrated method using partial least squares (PLS) regression to relate the whole IR spectral changes to monomer concentration was also attempted. The ATR-FTIR spectroscopy with multivariate analysis showed improvement in monitoring the monomer conversion compared to the univariate method. The results agreed with those determined by traditional gravimetric and 1H NMR spectroscopy analysis.

Free‐radical copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate studied by 1H NMR kinetic experiments

AbstractThe free‐radical copolymerization of m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) and styrene was studied with 1H NMR kinetic experiments at 70 °C. Monomer conversion vs time data were used to determine the ratio kp × kt−0.5 for various comonomer mixture compositions (where kp is the propagation rate coefficient and kt is the termination rate coefficient). The ratio kp × kt−0.5 varied from 25.9 × 10−3 L0.5 mol−0.5 s−0.5 for pure styrene to 2.03 × 10−3 L0.5 mol−0.5 s−0.5 for 73 mol % TMI, indicating a significant decrease in the rate of polymerization with increasing TMI content in the reaction mixture. Traces of the individual monomer conversion versus time were used to map out the comonomer mixture composition drift up to overall monomer conversions of 35%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed was observed. This depletion became more pronounced at higher levels of TMI in the initial comonomer mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1064–1074, 2002

IN-LINE MONITORING OF EMULSION HOMO- AND COPOLYMERIZATIONS USING ATR-FTIR SPECTROMETRY

An ATR-FTIR spectrometry technique with light conduit and diamond-composite sensor was used to perform in-line monitoring of butyl acrylate, methyl methacrylate, and vinyl acetate batch emulsion homo- and copolymerizations. This technique was found to be ideal for determining individual monomer conversions and copolymer composition changes as a function of time when those polymerizations were carried out in aqueous media. The results obtained from the ReactIR™ 1000 reaction analysis system agreed well with those determined by traditional gravimetric and 1H-NMR spectrometry methods.

ON-LINE MONITORING OF EMULSION TERPOLYMERIZATION PROCESSES

A new estimator for the on-line monitoring of emulsion terpolymerization is presented. A high gain observer is used to estimate the individual monomer conversions, the instantaneous and cumulative terpolymer composition, and the total number of moles of radicals in the polymer particles on-line. The estimator requires the input of the overall conversion. This input is obtained by calorimetry in the current case, but can be provided by any other type of in-line probe. The estimator has been experimentally validated (on- and offline) for hydrophobic and slightly water soluble monomers, in 3 liter and 250 liter pilot scale reactors. The results obtained demonstrate the usefulness of the high gain approach.

Multivariate statistical analysis of mid‐infrared spectra for the online monitoring of 2‐ethylhexyl acrylate/styrene emulsion copolymerization

This article describes the application of multivariate statistical process control techniques to a series of mid-infrared spectra collected online from a styrene/2-ethylhexyl acrylate emulsion copolymerization process. Principal component analysis of the mid-infrared spectral data indicated that in situ monitoring of the complex copolymerization process was feasible in the spectral region of interest. It was also observed that projection to latent structures or partial least squares (PLS) could be used for the effective indirect online prediction of individual monomer conversions and copolymer compositions over a substantial range of process operating conditions. A combination of the developed PLS methodology with a mid-infrared attenuated total reflection probe proved to be an effective tool for the efficient online characterization of polymer quality, thereby overcoming the lack of robust online conversion and composition measuring devices. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1776–1787, 2001

Free-radical copolymerization of styrene and itaconic acid studied by1H NMR kinetic experiments

The free-radical copolymerization of itaconic acid (IA) and styrene in solutions of dimethylformamide and d(6)-dimethyl sulfoxide (50 wt %) has been studied by H-1 NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio k(p).k(t)(-0.5) for various comonomer mixture compositions. The ratio K-p.k(t)(-0.5) varies from 5.2.10(-2) for pure styrene to 2.0.10(-2)mol(0.5)L(-0.5)s(-0.5) for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture-composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/ styrene copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5. (C) 2001 John Wiley & Sons, Inc.

Multivariate statistical analysis of mid-infrared spectra for the online monitoring of 2-ethylhexyl acrylate/styrene emulsion copolymerization

This article describes the application of multivariate statistical process control techniques to a series of mid-infrared spectra collected online from a styrene/2-ethylhexyl acrylate emulsion copolymerization process. Principal component analysis of the mid-infrared spectral data indicated that in situ monitoring of the complex copolymerization process was feasible in the spectral region of interest. It was also observed that projection to latent structures or partial least squares (PLS) could be used for the effective indirect online prediction of individual monomer conversions and copolymer compositions over a substantial range of process operating conditions. A combination of the developed PLS methodology with a mid-infrared attenuated total reflection probe proved to be an effective tool for the efficient online characterization of polymer quality, thereby overcoming the lack of robust online conversion and composition measuring devices. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1776–1787, 2001

Inter and intramolecular structure predictions in 2-hydroxyethyl methacrylate– tert-butyl acrylate copolymers obtained at high conversion

Radical copolymerization at 50°C of 2-hydroxyethyl methacrylate and tert-butyl acrylate in a 3 mol l −1 N, N′-dimethylformamide (DMF) solution has been analysed over a wide range of conversion and monomer feed compositions with the purpose of predicting the variation of inter and intramolecular structures. To do this, the previously obtained monomer reactivity ratios along with the coisotactic and statistical parameters were used. Overall copolymerization rate coefficients and individual monomer conversions for each monomer on the full range of conversion were also obtained. From the results obtained it follows that the Mayo–Lewis terminal model (MLTM) provides an excellent prediction across the complete conversion range for all comonomer feed compositions.