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Transport of monomer from droplets to growing latex particles in emulsion polymerization in general is assumed to proceed via diffusion through the aqueous phase. Especially in miniemulsion polymerizations the direct transfer of very hydrophobic species from droplet to droplet is assumed to also proceed via collisions. Amongst the hydrophobic species where this is shown to play a role are monomers, initiators, inhibitors and (catalytic) chain transfer agents. It is well known that the reactor geometry and the stirring speed can have a profound effect on emulsion polymerizations. The 1972 paper of Nomura on the effect of stirring on emulsion polymerization is cited more than 100 times and until today keeps scientists intrigued. Diffusion limitations of monomer going from the droplet into the aqueous phase can occur for very hydrophobic monomers. The alternative route of transport via collisions is often not considered. In this perspective, paper will discuss the evidence for collision based transfer in miniemulsion polymerization and also consider whether collision based monomer transport can play a role in regular emulsion polymerizations. [ABSTRACT FROM AUTHOR]

In this paper, a detailed description of particle adsorption/diffusion model in batch systems is presented. The phenomenological equations are based on a mechanism combining mass transfer by convection from bulk phase to particle surface, intraparticle mass diffusion and equilibrium adsorption processes. The change of bulk and particle concentration is modeled through differential mass balance equations, leading to a system of one ordinary differential equation and one partial differential equation. When adsorption equilibrium follows a linear relationship, this system of equations can be solved by the Laplace transform method. The purpose of this paper is the development of a generalized analytical solution, that is rewritten specifically for each of the traditional particle shapes: slab, cylinder, and sphere. Finally, this analytical solution is evaluated through several simulations in different batch conditions and compared to simulated experimental data, showing the capability of this analytical solution to predict batch adsorption processes when adsorbate concentration is low. This result clearly indicates the feasibility of applying the analytical solution presented in this paper, which is based on phenomenological concepts, to describe the adsorption kinetics of processes, when the linear isotherm can be considered adequate to represent the adsorption equilibrium. [ABSTRACT FROM AUTHOR]

Celebrating the 60th birthday of José Carlos Pinto This I Macromolecular Reaction Engineering i special issue is dedicated to I Celebrate the 60 SP th sp birthday of José Carlos Pinto i , or Zé, as he likes to be called by his friends and colleagues. José Carlos is now a full Professor of the Chemical Engineering Program at Instituto Alberto Luiz Coimbra de Pós-Graduação e Pesquisa em Engenharia (COPPE), Federal University of Rio de Janeiro, and a permanent member of the Graduate Program in Chemical and Biochemical Process Engineering at the School of Chemistry, Federal University of Rio de Janeiro. [Extracted from the article]

One of the questions still remaining regarding emulsion polymerization is the issue of mass transfer versus reaction limitation since, by its nature, emulsion polymerization requires monomer transport across an aqueous phase. This question is brought into focus lately by the growing use of miniemulsion polymerization in which the monomer transport step is much less important. This paper will explore the possible rate of monomer transport via collision and ratio this to the maximum rate of polymerization using the Damkohler analysis formality. Results indicate that systems relying on monomer transport by collision will be almost universally monomer‐transport‐limited, thus exhibiting lower‐than‐expected rates of polymerizations. [ABSTRACT FROM AUTHOR]

In the present paper, a dynamic optimization problem regarding grade transitions in bulk poly(propylene) polymerization processes is formulated and solved for the first time. Initially, a detailed dynamic process model is presented and implemented, comprising mass and energy balances, some of the polymer properties (such as the melting flow index and the xylene solubles) and regulatory control loops. Additionally, the effects of cocatalyst and electron donor on the propagation rate constant are taken into account. Then, the dynamic optimization problem is formulated and an evolutionary algorithm is used to solve the resulting nonlinear programming problem. It is shown that there is significant coupling among the manipulated variables and the controlled performance and polymer property variables, which adds complexity to the grade transition problem and demands the simultaneous manipulation of multiple variables during transitions. Despite the inherent open‐loop unstable nature of the analyzed process, it is shown that smooth grade transition trajectories can be accomplished through proper adjustment of the objective function weights. Finally, it is shown that the obtained optimum trajectories can significantly diminish the transition time, which can be of paramount importance for the plant economics. [ABSTRACT FROM AUTHOR]

Damkohler Number (Da) analysis can identify monomers and emulsion polymerization operating regimes where the polymerization may be monomer‐transport, rather than reaction‐limited. In these cases, the expected monomer concentration in the growing polymer particles will be reduced due to the transport limitation. This will reduce the expected rate of polymerization, and require the design of a larger polymerization reactor for a given production rate. In heterogenous catalysis, an effectiveness factor is used to quantify the reduction in reaction rate and necessarily increase reactor size to compensate. This paper will show that it is possible to use Da (functionally equivalent to the Thiele Modulus in heterogeneous catalysis) to estimate an effectiveness factor for emulsion polymerization. Also shown is a procedure for calculating the monomer feed ratio during binary copolymerization when one must not only take into account the reactivity ratios but also the possibility that one of the monomers is monomer‐transport limited. The method provides the monomer feed ratio during the semibatch phase of a binary copolymerization. This alternative to starved‐feed polymerization shall result in much faster polymerization and higher polymerization kettle utility. [ABSTRACT FROM AUTHOR]

In high‐pressure free‐radical ethylene polymerization tubular reactors, fouling often occurs due to polymer deposition onto the reactor's wall surface. This results in a decrease in the overall heat transfer coefficient. Note that a high‐pressure tubular reactor must be capable of removing about half of the generated polymerization heat to the cooling water flowing into the reactor's jackets. Therefore, reactor fouling can have serious implications including decrease of heat removal rate and monomer conversion, increase in the overall initiator(s) consumption, change of polymer quality, decline of reactor's safe operation, and significant economic losses due to lower plant productivity and longer reactor maintenance periods. In rare cases, the loss of reactor's heat removal capacity may result in the appearance of local hot spots that eventually can trigger ethylene decomposition. In the present review paper, the fundamental physical and chemical phenomena regarding polymer fouling and ethylene decomposition in high‐pressure low density polyethylene (LDPE) reactors are critically discussed. The effects of shear rate, polymer molecular weight, and wall surface energy on polymer adsorption and desorption are analyzed. Moreover, the effect of characteristic initiator decomposition and micromixing times and process conditions on initiator dispersion, polymer fouling, and ethylene decomposition are assessed. [ABSTRACT FROM AUTHOR]

The paper investigates the effects of counter anions of varying sizes including BF4–, PF6–, SbF6–, and Tf2N– on the rheological properties of a range of hyperbranched polyethylene ionomers containing covalently bound quaternary ammonium cations. While the choice of counter anions has no significant effect on thermal properties, distinct effects on rheological properties have been demonstrated. With the increase of counter anion size in the order from BF4– to PF6–, SbF6–, and Tf2N–, the ionic interactions of the counter anion with the quaternary ammonium ion weaken, leading to reduced terminal relaxation time, zero‐shear viscosity, and flow activation energy. The differences in these properties are most pronounced with the ionomer having Tf2N– counter anion since it is significantly larger than the others. [ABSTRACT FROM AUTHOR]

This paper builds on the theoretical framework of the previous articles on the solubility of vapors in semicrystalline polyethylenes produced in the gas phase process. The present article clarifies the theoretical basis for an activity coefficient approach, which results from a constraint on the amorphous phase within semicrystalline polymers. This concept is coupled to an advanced equation of state for use in polyolefin reaction engineering, and presented in a modular way the procedure for computing the requisite thermodynamic quantities. A temperature dependence on polymer crystallinity is also introduced. In the interest of developing a more predictive model for solubility, the model using single pure gas isotherms are parameterized. The results demonstrate the ability to predict single and mixed gas absorption, including new data published herein. The validity of the model is further demonstrated through comparisons with literature studies on batch scale ethylene polymerization. Finally, how a simple correlation to standard polymer characteristics yields accurate predictions in the absence of measured data for parametrization is demonstrated. [ABSTRACT FROM AUTHOR]

A simple mathematical model of the transport of monomer from the monomer droplets to the polymerizing polymer particles during batch emulsion homopolymerization has been developed and published previously. A Damkohler number for monomer transport in emulsion polymerization is proposed as the ratio of the maximum rate of polymerization divided by the maximum rate of monomer transport out of the monomer droplets. This Damkohler number is calculated from literature values for a number of common monomers. Following standard practice for the use of such a Damkohler number in other reaction‐with‐transport systems, monomers with a Damkohler number above 0.1 are considered to be transport limited. In a third paper the analysis is extended to batch binary copolymerization. Here the analysis is extended to the more industrially relevant cases of batch terpolymerization, starved‐feed copolymerization, and the combination of the two (starved‐feed terpolymerization). [ABSTRACT FROM AUTHOR]

Ab initio emulsion atom transfer radical polymerization (ATRP) differs from regular emulsion polymerization because the kinetic and thermodynamic aspects of each process are very unlikely alike. This paper presents a kinetic analysis of activator generated by electron transfer (AGET) ATRP of methyl methacrylate (MMA) in a stirred emulsion reactor. The focus of the study is to assess the variation of the monomer content in the organic phase and the rate polymerization for different reaction temperatures, as well as the impact of surfactant content and stirring speed on latex stability. Poly(methyl methacrylate) (PMMA) polymer samples are analyzed by means of gravimetry, dynamic light scattering, gel permeation chromatography, and HNMR techniques to determine monomer conversion, polymer particle diameter, molecular weight distribution, and polymer molecular structure, respectively. The results show the production of PMMA of narrow polydispersity index (Ð) and low molar mass (Mn) for MMA conversion around 60% and detect two‐regions instead of a three‐regions trend of rate of polymerization (Rp) as conventional emulsion polymerization. The reaction rate increases during the nucleation stage and then flattens over an invariant trend which confirms a living feature of the AGET ATRP polymerization. The average number of radicals per latex particle (ñ) is also debated. [ABSTRACT FROM AUTHOR]

Abstract: In order to implement nonlinear control, nonlinear system identification must be performed, however, there are open questions concerning this field of process control, for example, experimental planning, model structure selection, parameter estimation, and validation. Therefore, the study of nonlinear model identification is a relevant unsolved problem that needs to be handled for nonlinear control synthesis. This paper presents the use of bifurcation theory, dynamic and stability analysis for nonlinear identification, and control of polymerization reactors. Peroxide‐initiated styrene‐solution polymerization reactors (lumped‐distributed) are investigated: batch, continuous stirred‐tank reactor (CSTR), and tubular reactors. Open and closed loop analyses are carried out using jacket temperature and weight average molecular weight setpoints as the bifurcation parameters. Phenomenological mathematical models, neural network nonlinear models, and an experimental data from a polymerization unit are employed for validating the proposed methodology in order to implement confident nonlinear controllers. [ABSTRACT FROM AUTHOR]

Polypropylene is one of the commercially most important polymers and is produced via coordinative polymerization with supported metal‐organic catalysts in different processes. While kinetic measurements for slurry and gas‐phase polymerization of propene are well‐established, for bulk phase polymerization of propene, often the only kinetic information obtained from an experiment is the yield. In this paper, two calorimetric methods and their application for measurement of kinetics of bulk phase polymerization of propene are discussed. On the one hand a special calibration‐free heat flow calorimeter and on the other hand power compensation calorimetry coupled with a software sensor for online baseline correction. [ABSTRACT FROM AUTHOR]

The molecular weight distribution (MWD) is possibly the most important characteristic of a polymer. Polymers derive many of their physical properties from their MWD. Therefore, since the origins of polymer science, the theory provides a link between the kinetic mechanism and the mathematical expression of the MWD, and there are analytical solutions for ideal cases. However, the MWD formed in real‐life polymerization processes is usually more complex; the solution of the mathematical models that describe them can be quite challenging and has been the focus of enormous research efforts. These models may consist of systems of very large dimension: thousands of differential equations, often stiff, which demand special numerical techniques for their solution. In this paper the numerical techniques that can be used to solve this challenging problem are reviewed and contrasted, including weighted residual methods, direct integration, numerical inversion of transformed equations, and lumping methods. Stochastic techniques are also surveyed. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of long-chain branched polyolefins has been an important research topic for both academic and industrial researchers for many decades. This is particularly true since the discovery and successful commercialization of the constrained geometry catalyst systems in 1990s. The type of single site catalysts allows control in the synthesis and the precision in the characterization. Long-chain branched polyolefins exhibit improved melt processability, such as higher melt strength and better shear thinning, compared to their linear counterparts having the same molecular weight and distribution. In the previous papers, the catalyst systems and reaction conditions for the controlled synthesis of long-chain branched polyolefins have been reviewed. This paper aims at summarizing the literatures pertinent to the precise characterization of long-chain branched polyolefins. The major methods of long-chain branching characterization include: nuclear magnetic resonance, gel permeation chromatography, rheometry, dynamical mechanical analysis, differential scanning calorimetry, neutron scattering, and Fourier transform infrared spectroscopy. Recent progresses of these characterization methods, as well as their advantages and limitations, have been discussed in details. [ABSTRACT FROM AUTHOR]

Long-chain branching plays an important role in the performance of polyolefins (POs). The existence of a very small amount of long-chain branches (LCBs), i.e., <1 per 10 000 carbons, can significantly improve processability of the polyolefin materials, which is highly desired for those intractable polyolefins with narrow molecular weight distribution and high degree of crystallinity. Numerous literatures have been published on the controlled synthesis of long-chain-branched POs. In the previous paper, the major literatures of single catalyst systems have been summarized. This paper provides a comprehensive review for the binary and multiple catalyst systems and a brief summary of some other methods for the controlled synthesis of long-chain-branched POs. The controllability of long-chain-branched structures in the various preparation procedures with single or two reactor systems, and in one or two-step processes, is analyzed and compared in-depth. [ABSTRACT FROM AUTHOR]

In this paper, the state estimation of semi-continuous and batch processes for a set of emulsion polymerization reactions is addressed. Specifically, the autocovariance least-squares (ALS) and the moving horizon estimation (MHE) techniques are implemented to determine the covariance matrices and monitor the reactions in two steps, respectively. A collection of four polymerization reaction data sets that include gravimetric analysis are considered and used for validation of the proposed methods. The major process states estimated are the overall heat transfer coefficient and the conversion. The estimation results are in good agreement with the experimental data, independently of the initial overall heat transfer coefficient employed. They also indicate that a unique set of covariance matrices can represent the four reactions studied. The developed procedure offers a robust alternative for state estimation of industrial and experimental polymerization systems. [ABSTRACT FROM AUTHOR]

Abstract: The solubility of vapors within semicrystalline polyethylenes produced in the gas phase process is examined. Experimentally measured solubilities of ethylene, 1‐butene, isobutane, isopentane, 1‐hexene, and n‐hexane as a function of temperature, pressure, and vapor composition are reported for a series of semicrystalline linear low density polyethylenes, and a model for predicting these results is presented in detail. This paper demonstrates that conventional thermodynamic methods, which accurately predict polymer phase behavior in fluid systems, fail to account for a critical concept associated with semicrystalline polymers; the elastic constraint. Through application of a simple thermodynamic model addressing this effect, vapor solubility in such systems can be accurately predicted using a limited number of adjustable parameters. [ABSTRACT FROM AUTHOR]

This paper explains the reasons behind the very low polydispersity index (PDI) obtained in living anionic polymerizations in microstructured reactors. From the results, it can be explained that a narrow molecular weight distribution can be obtained due to the presence of a highly segregated flow behavior, even in microflow conditions, provided that the mean residence time is high enough. This paper investigates the feasibility of a living anionic polymerization reaction under micro-fluidic conditions. This is accomplished using a multiphysics model that accounts for the changes in viscosity and diffusivity. These properties descend with the increase in weight of the polymer, and could not be un-coupled from hydrodynamics and mass transfer. The results of the model are used to understand the reasons behind the very low PDI that can be experimentally obtained in microflow conditions. This leads to the conclusion that the increased viscosity almost 'suppresses' the diffusion of the monomer, even at the very short characteristic lengths of a micro-device. These conditions generate a fully segregated flow that yields an almost monodisperse polymer regardless of the effective residence time distribution encountered in the reactor. [ABSTRACT FROM AUTHOR]

Polymeric materials are present in various industrial sectors and in daily life, presenting advantages such as low cost and durability. Several processes for manufacturing have been developed. To achieve safety and operational goals measurement methods for proper process monitoring and effective control are needed. However, in real polymer plants, measuring devices are subject to uncertainties and are not always available. Hence, this paper proposes a virtual sensor scheme based on a particle filter and artificial neural network (ANN) that is applied to a simulated polymerization reactor. This scheme reduces uncertainties and enables the observation of latent variables. The ANN is also used for predicting the final properties of the polymer. The goal is to provide controllers with more complete and improved information. The results show that the virtual sensor scheme improves the process control, providing accurate estimates and action times that are consistent with industrial sampling intervals, which highlights its potential for practical applications. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including polymerization reaction mechanisms, Markovian chain approaches to analyze the effects of chain branching, and analysis of the viscoelastic properties of low-density polyethylenes.

The effect of solvents and monomer concentration on rate coefficients of propagation in radical polymerization has received tremendous interest during recent years, but a quantitative explanation and method of prediction of the medium effect is still missing. In this paper, it is shown that the thermodynamic formulation of the transition state theory is able to explain such effects almost quantitatively for a wide variety of monomers and solvents, including not only organic solvents but also less common solvents like ionic liquids or water, and monomers ranging from styrene to water-soluble monomers like acrylic acid or N-vinylformamide and also bulky monomers like isobornyl methacrylate. The medium effect is dictated by the activity coefficient of the monomer as well as by the ratio of the activity coefficients of the growing chain and the transition state. The solvent and concentration effects are, thus, a consequence of the degree of nonideality of the system. This interpretation based on the thermodynamics of real solutions offers for the first time a straightforward method to estimate the propagation rate coefficient of a given monomer in various solvents once the corresponding coefficient in bulk monomer is known. [ABSTRACT FROM AUTHOR]

The transfer of copolymerization processes from discontinuous plants to continuous plants has become a topic of industrial interest in the recent years. The motivations for such a transfer are better product consistency, smaller capital investment, and smaller footprint of the plants. However the experiences of the F3 project show that some copolymerization processes cannot be transferred to continuous production if the product quality must remain the same because in a continuous reactor, feeds can be added only at certain points along the reactor. This paper discusses the transferability of semibatch polymerization processes to a continuous plug-flow reactor with side injections in a generic fashion. Transferability of a semibatch recipe here means the possibility of the production of the same product in both modes of operation (semibatch and continuous). To determine the limits of the transferability from semibatch to continuous production, a model-based analysis has been performed based on a simplified kinetic model and realistic kinetic parameters. The ranges of product qualities that can be produced in both modes of operation and the minimum changes in the product qualities, if no 1:1 transfer is possible are determined by means of model-based optimization. Besides the numerical results, also an analytical treatment is presented. This provides a sound basis for an analysis of the transferability from a kinetic and an economic point of view. [ABSTRACT FROM AUTHOR]

Polyolefins (POs) are the largest polymer product in the world. The innovation in converting commodity olefin monomers to highly value added high-performance POs has been and will continue to be a major theme in both academic research and industry practice. The excellent properties of POs can be achieved through precise engineering of their chain architectures, which largely involves control of the chain branching structures. Long-chain branching is one of the most important parameters in the aspect of various chain branching structures. A huge amount of literatures have been reported to achieve better control of long-chain branched structures over the last two decades. Recently, good effort has been made in reviewing all the major literatures and summarizing the catalytic systems and synthetic strategies for the controlled synthesis of long-chain branched POs. This paper represents the first of the series, that is, controlled synthesis of long-chain branched POs via single catalyst systems. [ABSTRACT FROM AUTHOR]

Due to its complexity, free-radical polymerization of ethylene at high pressure still remains to be fully understood. This paper investigates factors that contribute to shape the MWD, one of the main features of LDPE, such as the structure of primary chains and the reactor operation in one/two phases. Using plant data and different models, it is found that chain transfer to small species is the controlling chain termination step and it is explained why one-phase operation leads to more branched polymer. Simulations with the Polyred software package provide a set of kinetic parameters that reproduce the observed trends in number average molecular weight and MWD dispersity in the reactor. [ABSTRACT FROM AUTHOR]

Reversible addition fragmentation transfer (RAFT) polymerization can be used to produce highly branched polymer approximating the structure of dendrimers, but with less regularity and much less synthetic complexity. This can be accomplished by using a RAFT agent with a polymerizable double bond. Thus, the stoichiometry is fixed, with one branch point (RAFT agent double bond) per chain. Since each of these branch points will also branch, a highly regular highly branched material is formed. If this RAFT chemistry is applied to the monomer N-isopropyl-acrylamide (NIPAAm), the resulting water-soluble polymer has unique applications in drug delivery, due to the hyperbranched nature of the polymer, and also to the lower critical solution temperature exhibited by poly(NIPAAm). In this paper, a previous mathematical model of the RAFT-pNIPAAm system is extended, and validated against experimental polymerization data. [ABSTRACT FROM AUTHOR]

Drying of wet Nylon 6 chips is a significant process for dehydration after granulation. During the process, the flow pattern of gas-solid phases is countercurrent flow, while the mass transfer and solid-state polymerization (SSP) are deeply coupled with each other. In this paper, the mass transfer behavior for dehydration at drying conditions has been investigated by single pellet experiments using Thermogravimetric Analyzer (TGA). A diffusion model for dehydration has been developed and the diffusion coefficient has been estimated by TGA test data. Besides, the SSP reaction characteristic has been independently studied in a polymerization tube at different temperatures. The reaction kinetics parameters, including the rate constants and equilibrium constants for both forward and reverse reactions, have been obtained by fitting the experimental data. Based on that, an integrated model combining the mass/heat transfer and polymerization reaction has been presented for the industrial continuous Nylon 6 drying process. The influences of drying conditions including the initial number average degree of polymerization, inlet nitrogen temperature, and flow rate, on distribution profiles of temperatures, water contents, and degree of polymerization of chips along the column height have been simulated. The integrated model can be used to predict the industrial drying process. [ABSTRACT FROM AUTHOR]

In textbooks, there is a dynamic equilibrium between the monomer α-methylstyrene (AMS) and its polymer (PAMS) when the temperature is greater than 61 °C. When giving these phenomena deliberate thought we come to the basic conclusion that there probably exists a dynamic equilibrium between fragmentation and coupling of polymeric chains by a radical mechanism when heated. Thus, a systematic exploration of the synthesis of AMS copolymers as potential sources of chain radicals has been carried out in our laboratory. This paper reviews the results we have achieved in the past decade: (1) The preparation of various AMS copolymers including (meth) acrylate, acrylic acid, styrene, and maleic anhydride. (2) The application of copolymers containing AMS structural units as very efficient free radical initiators. (3) The preparation of various functional copolymers including block copolymers and core-shell polymer particles with AMS copolymers as macroinitiators. (4) The steady increase of the molecular weight of the copolymer with the monomer conversion for some systems, which is characteristic of living polymerization. (5) The finding that AMS copolymers with functional groups can act as in situ compatibilizers through the formation of graft polymers, and that AMS copolymers can be used to modify MWCNTs by a free radical grafting-onto mechanism. [ABSTRACT FROM AUTHOR]

In the open literature, there is a lack of comprehensive predictive models that can provide detailed information on the distributed molecular properties of LDPE (e.g bivariate molecular weight-long-chain distribution, seniority-priority long-chain branching distributions, etc.) produced in a high-pressure process. To address this problem, Meimaroglou and Kiparissides (2010) developed a novel kinetic-molecular topology Monte Carlo (MC) algorithm to predict the exact molecular architecture of nonlinear polyethylene chains. In the present paper, the molecular information obtained from the kinetic-topology MC algorithm is introduced into a comprehensive rheological model, the so-called 'branch on branch' model of Das et al. (2006), to predict the rheological behavior of the LDPE melt in a high-pressure ethylene polymerization tubular reactor. The model uses an ensemble of branched polymer chains generated by the kinetic-chain topology MC algorithm to calculate several important viscoelastic properties, including the viscosity-shear rate curve, the storage and loss moduli, etc. The predictive capabilities of the new proposed computational approach, combining the solutions of kinetic, chain topology, and rheology models, are fully assessed via a direct comparison of model predictions with available experimental measurements on the molecular weight distribution, long-chain branching, and linear viscoelastic properties of two LDPE grades produced in industrial-scale reactors. [ABSTRACT FROM AUTHOR]

It gives us great pleasure to see this special edition of I Macromolecular Reaction Engineering i (MREN) dedicated to our colleague and friend Professor Joao Soares on the occasion of his 60 SP th sp birthday. In 2013 he moved to the University of Alberta, and significantly expanded his areas of interested to include many different areas, applying his unique approach to PRE problem solving to study water soluble polymers, structure property relationships, and nanocomposites as well. An article from POLYMAT discussed the importance of polymer characterisation, and another paper looks at structure-property relationships using a basic PRE approach. [Extracted from the article]

The stopped-flow (SF) technique has been extensively used for active site analyses and kinetic investigations in heterogeneous Ziegler-Natta olefin polymerization catalysis, whereas a poor polymer yield due to a short polymerization period has been a major drawback of the conventional SF system, which later has been improved by the development of a large-scale SF (LSF) technique. In order to further improve the scalability of the LSF technique, the present paper reports a new polymerization quenching method, which has been established by applying a three-vessel-type analogue of the LSF system. The new quenching method endows identical kinetic profiles, but the scalability is successfully improved. [ABSTRACT FROM AUTHOR]

This paper presents the results of a detailed investigation on propylene polymerization kinetics and microstructural characterization of polypropylene samples made with a 4th generation Ziegler-Natta catalyst under varying hydrogen pressures, external donor concentrations, and polymerization temperatures. Hydrogen had a positive effect on the mmmm pentad fraction at low donor concentrations, in agreement with our previous Monte Carlo model. Estimated activation energies for activation, propagation, and deactivation were very close to the values previously reported by our group for a narrower set of experiments with the same catalyst. [ABSTRACT FROM AUTHOR]

Owing to their good cost-performance ratio polyolefins are very attractive polymers which are used in a variety of applications. However, painting or bonding of PP parts can cause problems due to inadequate adhesiveness. Today, different methods are available for pretreating the surface in order to improve its adhesive properties. These methods have the disadvantage that they are carried out as an additional fabrication step. Depending on the type of pretreatment this leads to high equipment and energy costs. In situ surface modification during molding is a new method to avoid such disadvantages. It was applied up to now for different thermoplastics. In this paper its application for the surface modification of polyolefins is reported. The differences in the processing details due to the use of a liquid modifier, which is advantageous for polyolefins, to the solid modifier films used, e.g., for polycarbonate are identified. [ABSTRACT FROM AUTHOR]

This paper presents a model to describe the dynamic behavior of bulk propylene polymerizations performed in a continuous reactor, assuming that three catalysts can be used. The model takes into account mass, energy, and statistical moment balances used to estimate the final polymer properties, including the melt index (MI) and extractables in xylene (XS). As the catalysts present different sensitivities to hydrogen, the proposed controller scheme considers that the MI control loop must be reconfigured in line and in real time when the catalysts are exchanged. Simulation results indicate that the reactor stability is maintained during specified production programs and that the desired final properties can be achieved satisfactorily. It is shown that control reconfiguration represents an alternative to overcome existing operation limits and recover operability when multiple catalysts are used at plant site. [ABSTRACT FROM AUTHOR]

An essay is presented on polymerization reaction engineering's mathematical tools and approaches. It notes the significance of these mathematical approaches and tools for polymer reaction technology development. It attributes the detailed mathematical models' implementation to rapid computer resource evolution.

This paper summarizes a functionalization approach that can prepare functional PP with desirable molecular structures, including functional groups, microstructures, high molecular weight, and narrow molecular weight and composition distributions. A newly-developed catalysis technology with several designed 'reactive' comonomers to circumvent the inevitable deactivation of the transition metal cationic active site by functional groups in the direct polymerization process has been applied. The reactive comonomers, containing organoborane, benzylic protons (ϕ-CH3), and styrene moieties exhibit three essential properties, including (a) stability with the active site, (b) solubility in the polymerization media, and (c) versatility for interconversion to desirable functional groups under mild reaction conditions. With proper choice of metallocene catalysts, they resemble to high a-olefin monomers and can be effectively incorporated into the PP structure. In addition to the interconversion of the incorporated reactive sites to the desirable functional groups in PP copolymers, some reactive sites have been also transformed into 'living' radical or anionic initiators to initiate graft-from polymerization of polar monomers to obtain PP graft copolymers. [ABSTRACT FROM AUTHOR]

The 12 principles of green chemistry are reviewed and applied specifically to polymer production. Examples of how the principles relate to current practice in polymer reaction engineering and which areas show the greatest potential impact for implementation of these principles are discussed. This paper does not attempt to be exhaustive but rather to target specific areas for further development. [ABSTRACT FROM AUTHOR]

The natural ability of geckos and spiders to climb almost all surfaces using the compliant, nano-structured components on their feet provides motivation for making bio-inspired adhesives. The goal of the studies in this paper is to create an analytical technique for improving the ability to characterize dry adhesives modeled after these biological systems. The technique described herein uses a scanning probe microscope to manipulate a flat test surface in contact with biomimetic fibrillar arrays while monitoring the adhesion forces. Adhesion forces were measured after both normal contact and shear-induced contact between the nano-structured fibrils and the test surface. Results confirm that the adhesion forces are higher for bio-inspired adhesives after a shear-induced contact. Variations in these forces can be measured across the sample with micrometer-scale lateral resolution. This method of analysis can be extended to evaluate bio-inspired dry adhesives with realistic mechanisms of attachment utilized in robotic and similar applications of these materials. [ABSTRACT FROM AUTHOR]

A computational framework, consisting of a turbulent computational fluid dynamics (CFD) simulation coupled to a multi-zonal population balance is used to efficiently simulate the scale-up of a semi-batch emulsion polymerization, specifically one where the mixing issues are confined over a short period of time. Fluent™ CFD software is used to generate flow fields inside a series of reactors of varying production scale; these flow fields are subsequently used to generate a multi-zonal grid. The effects of reactor scale and inhomogeneous mixing on the latex particle size distribution are simulated by running a detailed emulsion polymerization model on the multi-zonal grid. In this paper, the second of two parts, the capabilities of the framework are demonstrated by simulating the scale-up of a semi-batch styrene emulsion polymerization. [ABSTRACT FROM AUTHOR]

A computational framework, consisting of a turbulent computational fluid dynamics (CFD) simulation coupled to a multi-zonal population balance is used to efficiently simulate the scale-up of a semi-batch emulsion polymerization, specifically one where the mixing issues are confined over a short period of time. Fluent CFD software is used to generate flow fields inside a series of reactors of varying production scale; these flow fields are subsequently used to generate a multi-zonal grid. The effects of reactor scale and inhomogeneous mixing on the latex particle size distribution are simulated by running a detailed emulsion polymerization model on the multi-zonal grid. In this paper, the first of two parts, the interplay between the CFD simulation and the automatic zoning algorithm is presented in depth. [ABSTRACT FROM AUTHOR]

Advanced models of penetrant transport and reaction in spatially 3D porous polyolefin particles reconstructed from X-ray µCT images require proper determination of particle morphology. Moreover, polyolefins exhibit a relatively low absorptivity for X-rays, therefore their investigation using µCT can be difficult. In this paper, a low-resolution µCT built into an SEM is used to examine how the µCT resolution and several user-selected parameters associated with the scanning/reconstruction affect the resulting particle morphology. Using samples with known morphology and independent imaging techniques, the performance of the µCT device is critically assessed. Finally, a method suitable for the reliable reconstruction of polyolefin particles using low-resolution µCT is proposed. [ABSTRACT FROM AUTHOR]

PZQ is the primary drug for treatment of schistosomiasis, but its efficiency is severely affected by its bitter taste. The main objective of this paper is the preparation of PMMA nanoparticles loaded with PZQ through in situ miniemulsion polymerizations and intended for oral formulations. Polymerizations are performed with an ultra turrax and a high-pressure homogenizer. Obtained nanoparticles are analyzed by DSC, HPLC, DLS, GC, SEM, and PZQ dissolution profiles. Obtained results indicate the successful encapsulation of PZQ in all runs. Obtained data also show that the high-pressure homogenizer leads to the best performance, allowing for preparation of stable latexes, with narrower particle size distributions and higher encapsulation efficiencies. [ABSTRACT FROM AUTHOR]

The article provides information on the articles within the journal on topics including emulsion polymerization, polymerization in aqueous solutions, and controlling tubular reactors.

This study addresses the challenges of time‐delay and low accuracy in online gas‐phase composition monitoring during olefin copolymerization processes. Three flowmeters based on different mechanisms are installed in series to measure the real‐time exhaust gas flow rate from the reactor. For the same gas flow, the three flowmeters display different readings, which vary with the properties and composition of the gas mixture. Consequently, the composition of the mixed gas can be determined by analyzing the reading of the three flowmeters. Fitting equations and three machine learning models, namely decision trees, random forests, and extreme gradient boosting, are employed to calculate the gas composition. The results from cold‐model experimental data demonstrate that the XGBoost model outperforms others in terms of accuracy and generalization capabilities. For the concentration of ethylene, propylene, and hydrogen, the determination coefficients (R2) were 0.9852, 0.9882, and 0.9518, respectively, with corresponding normalized root mean square error (NRMSE) values of 0.0352, 0.0312, and 0.0706. The effectiveness of the online monitoring device is further validated through gas phase copolymerization experiments involving ethylene and propylene. The yield and composition of the ethylene and propylene copolymers are successfully predicted using the online measurement data. [ABSTRACT FROM AUTHOR]

Herein, the poly(ɛ‐caprolactone)‐poly(ethylene glycol)‐poly(ɛ‐caprolactone) (PCL‐PEG‐PCL) macro xanthate reversible addition–fragmentation chain‐transfer agent is obtained on the polyethylene glycol (PEG) (600, 1000, and 1500 g mol−1) block, after the addition of ɛ‐caprolactone via ring‐opening polymerization. Then, poly (styrene‐b‐ɛ‐caprolactone‐b‐PEG‐b‐ɛ‐caprolactone‐b‐styrene) pentablock copolymer is synthesized reversible addition–fragmentation chain‐transfer (RAFT) solution polymerization technique via mediated PCL‐PEG‐PCL xanthate macro‐RAFT agents and 2,2′‐azobisisobutyronitrile as initiator. The products are demonstrated using Fourier transform infrared spectrophotometer (FT‐IR), proton nuclear magnetic resonance (1H‐NMR), carbon nuclear magnetic resonance (13C‐NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC) analyses. First‐order linear kinetic graphs of the reaction mechanism are observed with an increase in molecular weights (MW) between 16 000 and 36 000 g mol−1. The narrow dispersity (Đ = 1.40–1.48) polymer formation of styrene (St) controlled by RAFT polymerization confirms the increase in molecular weight according to the polymerization time. The reaction kinetics are first order and the rate constants are found to be k1 = 6.16 × 10−4s−1, k2 = 6.91 × 10−4 s−1 and k3 = 7.33 × 10−4 s−1. Thermal and spectroscopic analyses prove that the reactions are carried out successfully. [ABSTRACT FROM AUTHOR]

The crystallinity of Linear Low‐Density Polyethylene (LLDPE) is influenced significantly by short‐chain branches (SCBs) present in the backbone of the polymer. Despite the importance of this aspect, with only a few linear comonomers being currently used in the commercial production of LLDPE. It is found that by introducing branched comonomers, the melting point and crystallinity of LLDPE can be influenced to a greater extent than with linear comonomers. Since only a few linear comonomers are currently used in the production of LLDPE, the characterization of LLDPEs with branched comonomer has been often overlooked. By combining High‐Temperature‐Size‐Exclusion Chromatography (HT‐SEC), Nuclear Magnetic Resonance (NMR) spectroscopy, and Infrared (IR) spectroscopy, it is shown that standard HT‐SEC analysis using an IR detector is also applicable to polymers containing branched comonomers. [ABSTRACT FROM AUTHOR]

A multicomponent Flory‐Huggins model is implemented and utilized to describe the liquid–liquid equilibrium phenomenon in mixtures of polypropylene and xylene, in the context of the well‐known xylene solubles (XS) test. The XS experiment is a common procedure in many polymer laboratories, used to determine the percentage of xylene solubles in samples of polypropylene, which provides an approximate measure of the atactic and oligomeric chains. Despite the importance of the test, the literature lacks a thermodynamic perspective regarding the description of this extraction phenomenon. In the present study, the Flory‐Huggins interaction parameter is adjusted in a multicomponent framework to ensure that equilibrium chain length distributions calculated with the proposed model best match experimental distributions. It is shown that the experimental data obtained from XS analyses can be accurately fitted by the proposed model and that the estimated Flory‐Huggins interaction parameter is more sensitive to the polymer average molar mass than to the degree of tacticity, when a particular catalyst is considered. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various articles within the issue on topics including development of polymer reaction engineering in China; research on industrial application of neodymium-based catalyst for polybutadiene; and cobalt catalyst in ethylene polymerization.

A mathematical model is proposed that couples the decomposition kinetics of persulfate (S2O82−) and the free radical polymerization kinetics of itaconic acid (IA); the results are compared with experimental data reported in the literature. It is found that the former is highly affected by the acidification of the aqueous medium which is caused by the equilibrium dissociation of IA but mainly by HSO4− produced by side reactions of the S2O82− decomposition. This qualitatively explains the dependence of d[S2O82−]/dt with [IA] and the initial concentration of persulfate ([S2O82−]0), reported in the literature. According to the model results, temperature overshoots are very likely to occur in the experiments so there is doubt whether the reaction order >1 with respect to [IA] that is sometimes reported in the literature for the rate of polymerization (Rp) is an artifact related to an imprecise temperature (T) control or is due to a more complex mechanism. Due to the higher activation energy of the persulfate decomposition compared to the propagation reaction, small variations of T can lead to significant variations of d[S2O82−]/dt but to an almost imperceptible effect on Rp. Recommendations for future experimental work and refinement of the kinetic model are provided. [ABSTRACT FROM AUTHOR]