bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the evolution of particle size average and size distribution in suspension polymerization processes
Authors: Jahanzad Fatemeh , Sajjadi Shahriar , Brooks Brian W. 
Published: February 2004

AbstractThe dispersion of methyl methacrylate (MMA) and its suspension polymerization were used as models to elaborate the evolution of particle size average and size distribution in the course of suspension polymerization. The underlying mechanisms for the occurrence of the dynamic and static steady states in the population of drops were defined and their effects on the evolution of drop/particle size average and size distributions were examined. The characteristic intervals of suspension polymerizations (transition, steady‐state, growth, and identification) were elaborated. The formation of satellite droplets and their evolution in the course of polymerization were also discussed.
Achieving high conversions in nitroxide‐mediated living styrene miniemulsion polymerization
Authors: Lin Marcus , Cunningham Michael F. , Keoshkerian Barkev 
Published: February 2004

AbstractNitroxide‐mediated living radical polymerizations of styrene were run in miniemulsion. Using a modified miniemulsion process that does not require the use of a volatile costabilizer, near complete conversions could be achieved in 2‐3 hours while preserving narrow molecular weight distributions and a high degree of chain livingness. Increased rates and final conversions were achieved by semi‐batch addition of the nitroxide scavenger ascorbic acid.
Determination of polybutylene terephthalate polycondensation equilibrium constant using a batch reactor
Authors: Darda Pranay Jairam , Hogendoorn Kees , Molenkamp Tjaart , Versteeg Geert 
Published: February 2004

AbstractThe PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m ‐ cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 $P^{-1.44}_{bdo}$
). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory ‐ Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: $K_e = {0.187 \over 1 -19243 e^{-0.3932}} $ in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics.
Multi‐objective dynamic optimization of semi‐batch polymerization processes
Authors: Martins da Silva Cláudia , Chalbaud Biscaia Evaristo 
Published: February 2004

AbstractAn improved evolutionary algorithm is proposed to perform multi‐objective dynamic optimization of a semi‐batch styrene polymerization process. The target is to determine the optimal feeding trajectories and the reactor operating temperature, which maximize the monomer conversion rate and minimize the initiator residue concentration in the final product. The optimization problem has been formulated as a multi‐objective mixed‐integer nonlinear problem (MOMINLP). The proposed approach allows the effective computation of the optimal operating strategies for the production of polymers with the average molecular weight and the polydispersity index required.
Kinetic modeling of aggregation and gel formation in quiescent dispersions of polymer colloids
Authors: Lattuada Marco , Sandkühler Peter , Wu Hua , Sefcik Jan , Morbidelli Massimo 
Published: February 2004

AbstractIn this work, a methodology suitable for the description of aggregation and gel formation processes of polymeric colloidal dispersions in quiescent conditions is presented. The modeling of aggregation is based on the use of populations balance equations to describe the time evolution of the aggregate distribution. Monte‐Carlo simulations are used to generate the structural properties of individual aggregates, which are necessary to compute the average radius of gyration and hydrodynamic radius that are compared to the values measured using light scattering. The agreement between model predictions and measured sizes is good in both diffusion‐limited and reaction‐limited conditions. For the description of progress toward gel formation, the cumulatively occupied volume, a measure of the fraction of space occupied by the clusters, is defined. Due to the fractal nature of clusters, during the aggregation the system can reach a condition of space filling, after which the formation of gel is a result of the interconnection of the clusters. It is found that in diffusion‐limited conditions the interconnection step is much faster than the preceding aggregation, while in reaction‐limited conditions the aggregation and the interconnection are of comparable duration.
Ultrasound‐induced polymerization of methyl methacrylate in liquid carbon dioxide: a clean and safe route to produce polymers with controlled molecular weight
Authors: Kemmere Maartje , Kuijpers Martijn , Jacobs Leon , Keurentjes Jos 
Published: February 2004

AbstractUltrasound‐induced cavitation is known to enhance chemical reactions as well as mass transfer at ambient pressures. Ultrasound is rarely studied at higher pressures, since a high static pressure hampers the growth of cavities. Recently, we have shown that pressurized carbon dioxide can be used as a medium for ultrasound‐induced reactions, because the static pressure is counteracted by the higher vapor pressure, which enables cavitation. With the use of a dynamic bubble model, the possibility of cavitation and the resulting hot‐spot formation upon bubble collapse have been predicted. These simulations show that the implosions of cavities in high‐pressure fluids generate temperatures at which radicals can be formed. To validate this, radical formation and polymerization experiments have been performed in CO2‐expanded methyl methacrylate. The radical formation rate is approximately 1.5*1014 s−1 in this system. Moreover, cavitation‐induced polymerizations result in high‐molecular weight polymers. This work emphasizes the application potential of sonochemistry for polymerization processes, as cavitation in CO2‐expanded monomers has shown to be a clean and safe route to produce polymers with a controlled molecular weight.
Microemulsion polymerization for producing fluorinated structured materials
Authors: Apostolo Marco , Biressi Giovanni 
Published: February 2004

AbstractWhen perfluoropolyether microemulsions are used during polymerization of fluoropolymers, the structure of the reaction environment can be strictly controlled. In particular, the number and size of polymer particles in latexes can be set freely, yielding a number of advantages.First, as a result of radical segregation, terminations can be decreased without reducing polymerization rate: in this way high molecular weights are easily obtained also with poorly reactive monomers.Moreover, in combination with a reversible chain transfer mechanism based on iodine, particle segregation allows establishing pseudo‐living polymerization conditions. In this situation formation of long branches in the polymer can be controlled by using bifunctional molecules that are able to link two different polymer chains to each other during polymerization. This is the so‐called “branching and pseudo‐living” technology.Finally, by co‐coagulating latexes of different polymers prepared by microemulsion polymerization, very small particles and, thus, high interface areas are generated. In this way properties of different polymers, such as fluoroelastomers and fluorinated semicrystalline polymers, are matched effectively, generating new nanocomposite materials that exhibit outstanding properties.In this paper these results are reported and an overview of some novel sophisticated fluoropolymers obtained in microemulsion is given.
Rate mechanisms of a novel thiol‐ene photopolymerization reaction
Authors: Reddy Sirish K. , Cramer Neil B. , O' Brien Allison K. , Cross Tsali , Raj Rishi , Bowman Christopher N. 
Published: February 2004

AbstractA novel thiol‐ene photopolymerization reaction involving copolymerization of tetrathiol monomer with vinyl silazane is experimentally characterized and is modeled successfully. The overall polymerization rate is found to be controlled by the ratio of the propagation to chain transfer kinetic parameters. The polymerization rate of this mixture, in the presence of added photoinitiator, is approximately first order in ene functionality and is independent of thiol functional group concentration. Initiation rates in this system, when cured utilizing a light centered around 365 nm light, and in the presence of no added photoinitiator, are shown to be proportional to the ene monomer concentration. When the mixture is polymerized utilizing light centered at 254 nm light, and without photoinitiator, the initiation rates are proportional to the thiol monomer concentrations. This novel reaction scheme is further utilized to form ultra rapidly polymerizable polymer derived ceramic structures with high aspect ratios.
Syndiospecific polymerization of styrene with embedded metallocene catalysts
Authors: Chung Jin Suk , Woo Boo Gon , Choi Kyu Yong 
Published: February 2004

AbstractSyndiotactic polystyrene (sPS) is a highly crystalline polymer with high melting point (270°C). The syndiospecific polymerization of styrene to sPS with metallocene catalysts is characterized by significant phase changes that lead to global gelation. Since sPS does not dissolve in styrene or solvents such as toluene and n‐heptane, sPS precipitates out immediately from the liquid phase with the start of polymerization. The polymer crystallites aggregate to primary particles and they develop to a gel. The gelation is not due to cross‐linking polymerization but due to strong molecular interactions between the polymer and monomer molecules. In this work, homogeneous Cp*Ti(OMe)3 catalyst is heterogenized or embedded into sPS prepolymer particles. The embedded catalyst has been tested in a laboratory scale diluent slurry process to illustrate the feasibility of slurry phase polymerization for the synthesis of sPS particles.
New routes to high solid content latexes: a process for in situ particle nucleation and growth
Authors: Boutti Salima , Graillat Christian , McKenna Timothy F. 
Published: February 2004

AbstractA means of generating latices with solid contents well over 70% (v/v) without the use of intermediate seeds is proposed. It is demonstrated that the use of an electrically neutral initiation system (hydrogen peroxide) in the initial stages of the process, followed by an initiator yielding negatively charged free radicals (ammonium persulphate) changes the way in which the system generates stable particles. The reason for this change is the need to avoid stabilising small, homogeneously nucleated particles during the first portion of the process, and the desire to generate controlled quantities of them during the second portion. The processes are highly reproducible, as are the particle size distributions and rheological properties of the final latices.
Simulating acrylate polymerization reactions: toward improved mechanistic understanding and reliable parameter estimates
Authors: Busch Markus , Müller Matthias 
Published: February 2004

AbstractIt is well accepted that free‐radical acrylate polymerizations are governed by a complex coupled kinetic mechanism consisting of propagation, termination and inter‐molecular transfer to small species such as monomer or modifiers, together with intra‐ and inter‐molecular transfer reactions to polymer. Propagation, β‐scission or termination of the transient secondary/tertiary radicals formed following transfer to polymer is possible. This reaction cascade strongly affects the micro‐structural characteristics of the polymer and its application properties. Individual parts of this mechanism have been discussed on many occasions. However, a general approach for determining the rate coefficients for the full kinetic scheme has been missing. Such an approach is developed in this communication.
Simulation of gel permeation chromatography measurement for long chain branched metallocene polyethylene
Authors: Liu Nannan , Wood‐Adams Paula 
Published: February 2004

AbstractThe research about the polymerization reaction mechanism of long chain branched polymer provides a method to simulate the generation of LCB mPE (long chain branched metallocene polyethylene).[1‐3] In this work, after simulating the generation of one million LCB mPE molecules, we calculate the sizes (i.e. radii of gyration) of molecules in good solvents to obtain the molecular size distributions. Then we simulate the fractionation in GPC (gel permeation chromatography) measurement and the different GPC detector responses to obtain simulated GPC MWDs (molecular weight distributions). The simulated MWDs are compared to the real GPC results provided by the Dow Chemical Company.
On‐line monitoring of emulsion polymerisation using conductivity measurements
Authors: Graillat Christian , Santos Alexandre , Pinto José Carlos , McKenna Timothy F. 
Published: February 2004

AbstractThis work investigates the feasibility of implementing conductivity measurements for the purpose of the on‐line monitoring of particle generation by following the evolution of free surfactant concentration during SDS/styrene emulsion polymerisations. The conductivity and temperature were measured on‐line during the reactant addition and reaction stages of a number of batch emulsion polymerisations. Samples were collected for off‐line analysis of particle size and conversion. Observation of the evolution of the conductivity enabled us to measure the effect of surfactant and monomer addition. The maximum size of the monomer droplets was calculated from the decrease in conductivity that represented the adsorption of surfactant molecules onto the droplet surface. The division of SDS between the particle interface and the aqueous phase was also determined giving an indication of the particle stability.
Simulation of free radical high‐pressure copolymerization in a multi‐zone autoclave reactor: compartment model investigation
Authors: Ghiass Majid , Hutchinson Robin A. 
Published: February 2004

AbstractA compartment model is used to describe the complex flow of a high‐pressure ethylene copolymerization process in an industrial multi‐feed multi‐zone autoclave reactor at steady state operation conditions. To capture the imperfect mixing effects due to fresh initiator injection, each zone is considered as a set of three interconnected well mixed CSTRs with recycle streams. Volumes of the reactors and the recycle flow are adjusted to get the best fit with results of steady state well mixed analysis for each zone. Once the temperature and conversion as state variables in each reaction volume are known, the properties of polymer produced in each zone and those of final polymer can be determined. Using a realistic set of kinetic mechanisms, temperature, monomer conversion, molecular weights and short and long chain branching frequencies in each zone and at the exit point of the reactor are estimated. Some of the model results are compared with experimental data obtained for an industrial reactor.
The influence of the counter‐ion MeB(C6F5)3− and solvent effects on ethylene polymerization catalyzed by [(CpSiMe2NR)TiMe]+: a combined density functional theory and molecular mechanism study
Authors: Xu Zhitao , Vanka Kumar , Ziegler Tom 
Published: February 2004

AbstractA combined density functional theory and molecular mechanism (QM/MM) method has been used to study the first (R = Me) and the second (R = propyl) insertion of the ethylene monomer into the Ti‐R bond of (CpSiMe2Nt Bu)(R)Ti‐m‐MeB(C6F5)3. The computational results, in agreement with experimental findings, show the influence of the counter‐ion and the solvent not only changes the reaction barriers, but also alters the rate‐determining step for the second ethylene propagation, from insertion to uptake. The total reaction barrier for the first ethylene propagation has been calculated to be slightly higher than that for the second ethylene propagation, in general agreement with experimental results. The total barriers in solution are 11.7 kcal/mol and 10.5 kcal/mol for the first and second ethylene insertions, respectively. These insertion barriers are comparable to the activation energy (13.3 kcal/mol) found experimentally for the same catalyst (CGC).
Dispersing behavior of recycled rubber particles
Authors: Shahidi Nima , Teymour Fouad , Arastoopour Hamid 
Published: February 2004

AbstractThe hydrophobic nature of recycled rubber particles presently limits their use only in non‐aqueous media. Recycled rubber particles were chemically modified by preparation of amphiphilic semi‐interpenetrating polymer networks using poly(acrylic acid) as the hydrophilic polymer. The resulting composite particles are water dispersible and suitable for various aqueous media applications.
A discretization method for computing chain length distributions
Authors: Peklak A. David , Butté Alessandro , Storti Giuseppe , Morbidelli Massimo 
Published: February 2004

AbstractThe method of Kumar and Ramkrishna is a numerical technique to solve population balance equations (PBEs) by discretization while preserving two moments of the distribution. When the method is used to calculate chain length distributions in polymerization reactions, the polydispersity, which depends on the first three moments of the distribution, cannot be estimated correctly. This work presents a modification of the method that allows to preserve three moments and thus calculate the polydispersity correctly, independently of the number of grid points. The modified method is applied to a model of controlled radical polymerization via RAFT and compared with the original one.
Investigating the impact of operating parameters on molecular weight distributions using functional regression
Authors: Hutchinson R.A. , McLellan P.J. , Ramsay J.O. , Sulieman H. , Bacon D.W. 
Published: February 2004

AbstractMolecular weight distributions (MWDs) are inherently functional observations in which differential weight fraction is expressed as a function of chain length. Conventional approaches for analyzing and predicting MWDs include discretization and treatment as multi‐response estimation problems, characterization using moments, and detailed mechanistic modeling to predict fractions for each chain length. However, these approaches can be sensitive to loss of information, complexity and problem conditioning. An alternative is to treat the MWDs as functional observations, and to use techniques from Functional Data Analysis (FDA), notably functional regression. The objective of this paper is to develop and apply empirical modeling techniques based on functional regression for investigating the impact of operating parameters on MWDs.
Process modelling and optimization of styrene polymerization
Authors: Gao J. , Hungenberg K.D. , Penlidis A. 
Published: February 2004

AbstractPolystyrene is a common commodity with thin margin, it is desirable for industry to reduce the production cost by optimizing the process and producing polystyrene with desired properties. This paper has reviewed several commonly used process optimization policies from the literature. The kinetics of styrene polymerization with mono‐ or bifunctional initiator has also be described. It has been demonstrated that by using a temperature profile combined with selective mono‐ or bifunctional initiators, one can decrease bach time while still maintaining the desired molecular weight averages. The recently developed new tetra‐functional initiator by Elf‐Atochem provides a new tool for controlling/optimization purposes. Industrial process configurations of polystyrene production has also be discussed.
Inelastic sports pricing
Authors: Fort Rodney 
Published: February 2004

AbstractA recurrent finding in estimates of the gate demand for sports events is pricing in the inelastic portion of demand. With few exceptions, this finding has either been ignored or (rather poorly) explained away. In this paper, the recurrent outcome is detailed and the explanations given by past authors are discussed. Then, profit maximization theory is explored for its inelastic pricing implications. It ends up that the local TV revenue relationships between MLB teams satisfy the situation that theory predicts would generate inelastic gate pricing. This suggests two things. First, inelastic pricing is consistent with profit maximizing team behavior. Second, fuller specification of revenue functions will enhance future work in the area. Copyright © 2004 John Wiley & Sons, Ltd.
Subsidies as incentive mechanisms in sports
Authors: Fort Rodney 
Published: February 2004

AbstractApplying even the most fundamental public choice principles suggests that subsidies to sports team owners will be inversely related to ticket prices. The primary aim of this paper is to demonstrate the impact of such an inverse relationship on the pricing behavior of owners. Theory shows that if either the rent or concessions/parking response by policy makers is elastic (percentage change in subsidy is greater than the percentage change in prices by teams), then the other one cannot be. A (very) cursory look at readily available NFL data lends support to the theory, at least for single‐use stadiums. The outcomes here may inform any future analysis that extends the idea into the full‐blown analysis of the politics of subsidies and for those interested in the rationing by waiting that often occurs at sports events. Copyright © 2004 John Wiley & Sons, Ltd.
Player salary share and the distribution of player earnings
Authors: Scully Gerald W. 
Published: February 2004

AbstractVeteran free agency in professional team sports has led to higher average player compensation, an increase in the share of league revenues going to players, and increased dispersion in player earnings. Tests on the distributions of player salaries in the last decade reject that they are the same in the early and later years. The variance in baseball player compensation is decomposed into share and marginal revenue product effects for 1990 and 1998, and it is found that both effects contributed to the increased variance in player salaries. A simulation of the effect of universal free agency in baseball suggests a modest increase in player salary share and a drop in compensation inequality among players. Copyright © 2004 John Wiley & Sons, Ltd.
Strategic measure of competitiveness for ranked data
Authors: Rohm Andrew J. , Chatterjee Sangit , Habibullah Mohamed 
Published: February 2004

AbstractThis study offers a method of evaluating the stability of ranks of a data vector over time. In particular, we study improvement of a process observed over time where the data is ranked. The degree of competition at a major tennis championship (Wimbledon) as well as how trends in the level of competition have changed over time is studied. A metric for shifts in competitiveness and a new statistical methodology is proposed. The findings suggest that competitiveness at Wimbledon has been extremely high. The study offers implications for the sport of tennis as well as an approach to measuring competitive dynamics that can be applied to other contexts. Copyright © 2004 John Wiley & Sons, Ltd.