Timothy F.L. McKenna

• Ph.D., H.d.R.
• Directeur de Recherche DR1, Directeur du Laboratoire at Centre National de Recherche Scientifique, Lyon, France

The impact of different agitator configurations used during the emulsion polymerization of vinylidene fluoride (VDF) is studied with the goal of achieving a solids content of 55 wt% while minimizing particle coagulation and maintaining low levels of surfactant. The design and number of impellers, their spacing and the agitation speed are shown to h...

In the current study, the ability of two data‐driven machine learning tools, the extreme learning machine (ELM) and the adaptive neuro‐fuzzy inference system (ANFIS), to predict the polymerization rate and melt flow index of linear low‐density polyethylene produced in a gas phase process was investigated. The level of interaction between the input...

A model is proposed to describe the impact of interphase monomer transfer on the emulsion polymerization of vinylidene fluoride (VDF). The model is validated with experimental data of the rate of polymerization and particle size distribution (PSD). During a typical emulsion polymerization process, the VDF monomer is in a gas or supercritical state,...

Understanding the sorption equilibrium of penetrants into a polymer is key to mastering the kinetics and properties of the final product. These systems are non‐ideal meaning the presence of multiple components in the continuous phase changes the solubility of individual species with respect to pure component solubilities. For this reason, measureme...

The solubility of different alkanes in polyethylene (PE) of different densities, as well as the solubility of the polymers in the alkanes, and the degree of swelling of the powders are studied as a function of temperature. It is found that the solubility of linear low‐density polyethylene (LLDPE) is as much as 6 times greater than that of high‐dens...

It is well known that ultra‐high molecular weight polyethylene (UHMWPE) is a polymer with long chains and very high molecular weight that poses difficulties in terms of processability due to the presence of chain entanglements. In many cases is thus necessary to treat the material in different ways after the polymerization to minimize the amount of...

This work focuses on increasing the solids content of water‐based coating materials such as paints, other coatings or adhesives while attempting to reduce the amount of surfactant in the final latex. The synthesis of a latex with a bimodal particle size distribution was carried out by combining RAFT and classical emulsion polymerization processes....

The performance of isopropyl myristate, methyl trimethylacetate, and dibutyl sebacate (IPM, MTMA, and DBS respectively) as activity limiting agents (ALA) were evaluated using a post phthalate Ziegler Natta catalyst system...

Several commercial silicas were used to support metallocene active centres, and the resulting precatalysts were used to study the impact of the pore size and pore size distribution of the support on the polymerization kinetics and resulting polymer properties. Pore volume distribution played a major role in the fragmentation of silica‐supported cat...

An innovative approach, designated as supported activator (SA), allows preparation of high density polyethylene (HDPE)-based highly performant hybrid materials. This procedure makes use of a nano-sized supported methylaluminoxane (MAO)-activator, based on halloysite natural nanotubes (HNT), combined with an in situ supporting concept. The new proto...

The impact of common process catalyst poisons on the performance of a 6th generation Ziegler Natta catalysts during the gas phase polymerization of propylene were examined using two approaches: introducing propylene without purification, or with one or two sets of purification columns, and by introducing carbon dioxide (CO2), oxygen (O2), water (H2...

A systematic study of the impact of gas phase composition on the estimation of the reactivity ratios of a Ziegler‐Natta catalyst during the gas phase copolymerization of ethylene with 1‐butene and 1‐hexene has been carried out. The results of the study show that if one uses a realistic equation of state to estimate the co‐ and anti‐solubility effec...

Catalysts and polymerization processes have evolved over the years. Such significant developments have allowed producers to broaden the range of polymer microstructure and process productivity, thereby making it possible to offer a wide range of end‐use properties at a reasonably low cost. However, these advantages in catalyst performance and react...

A multi‐reactor stopped‐flow apparatus has been developed to study gas‐phase olefin polymerization at short times under industrially meaningful reaction conditions. A simplified single‐phase 1D dynamic model of the reactor was used to develop an estimator of the polymerization rate from the recorded measurements of temperature, pressure, and flow r...

This article gives a wide overview of different types of mathematical models that can be used to describe the polymerization of linear olefins with coordination catalysts. We expanded the conventional classification of mathematical models into micro‐, meso‐, and macroscale, to include seven modelling levels: catalysis, polymerization kinetics, ther...

A study of the multicomponent diffusion of important processes gases in linear low density polyethylene is presented. It is demonstrated that, much like in the case of multicomponent solubilities, one cannot use pure component diffusivities to predict mass transfer rates in multicomponent systems. It is postulated that interaction between the penet...

A set of dendrimeric silica (DS) reinforced polyethylene-based nanocomposites is prepared using a novel and straightforward in-situ catalyst supporting procedure by means of “in-situ” polymerization technique, labeled DS-SA. These materials are characterized with regard to molar masses, filler dispersion, thermal stability, crystalline characterist...

The direct and interactive effects of process variables, including the use of iso-pentane as an inert condensing agent (ICA), on the rate of polymerization and main physical properties of linear low-density polyethylene (LLDPE) were studied using two different statistical methods. RSM based on a three level five factor Box-Behnken design (BBD) was...

In this study, an innovative methodology for the preparation of high-performance polyolefin-based materials combining a unique dendrimeric silica (DS) catalyst carrier, a straightforward in-situ supporting procedure and in-situ ethylene polymerization...

Rheological measurements of polyethylene solutions in a novel nontoxic solvent were used to determine the Mark-Houwink parameters for PE of widely different molecular weights to assess the viscosity average molar mass for PE of several millions of g/mol. Solutions of high density polyethylene that had been previously characterized by size exclusion...

A single particle model for homopolymerization of ethylene in the presence of hydrogen is used to predict the impact of induced condensing agents on the evolution of concentration profiles in the growing particle, the rate of homopolymerization, and the evolution of the molecular weight distribution. The model formulation is based on the random‐por...

In order to contribute to a better understanding of the emulsion polymerization of vinylidene fluoride (VDF), an experimental study under conditions of temperature and pressure similar to those found in industrial processes was carried out. It is shown that the initial rate of polymerization is strongly influenced by the agitation of the reactor, w...

Different approaches to modeling the gas phase polymerization of ethylene that have been considered in the literature are reviewed. It is shown that while simple, well‐mixed models can give an adequate representation of the average performance of a given polymerization reactor, they do not allow one to analyze certain modeling problems such as the...

The total solubility of ethylene in LLDPE in presence of propane, isobutane and 1-butene is measured using a gravimetric technique at 70 °C and pressures up to 5 bars. In order to overcome the lack of experimental partial solubility data in ternary systems, a novel approach for the estimation of the Sanchez-Lacombe interaction parameters is propose...

The feasibility of co- and terpolymerizing vinylidene fluoride (VDF) with ethylene (C2) and/or vinyl actetate in an emulsion polymerization process was studied for different C2 pressures, initiator concentration, surfactant concentration, pH, C2 injection protocols and the influence of vinyl acetate (VAc) in the reaction medium. Pressure drop and t...

This paper presents a numerical study of emulsion latex coagulation processes in continuous coagulators based on the full computational fluid dynamics approach. The RANS approach together with the k‐ε turbulence model was used to describe the detailed flow field in the coagulators. The coagulant mixing process was modelled by the convection‐diffusi...

The potential of spatially resolved spectroscopy (SRS) for in situ monitoring is evaluated in this work. SRS is based on near‐infrared spectroscopy. It is well adapted to heterogeneous systems and collects information about both physical and chemical properties. In this work, the polymer content in emulsion copolymerization is predicted using SRS....

An alternative approach for the synthesis of styrene butadiene rubber (SBR) copolymer latexes was explored in order to obtain low gel fractions and high solid contents. The ultra-turrax-assisted miniemulsion stabilized by in situ surfactant generation was adopted as the main strategy since this technique can inhibit the eventual presence of seconda...

A SiO2/MgCl2-bisupported Ziegler–Natta-type catalyst is studied in gas-phase ethylene/1-butene copolymerization. With a minimal amount of alkylaluminum required to activate the catalyst, polymerization kinetics is profoundly affected by the dosage of it. High dosage of alkylaluminum retards the polymerization but does not kill the catalyst. Through...

An off‐line dynamic optimization procedure is employed to optimize the transition between different grades of linear low density polyethylene in a fluidized bed reactor. This type of reactor is frequently operated under condensed mode, which consists of injecting induced condensing agents (ICA) to absorb part of the reaction heat. However, the pres...

Front Cover : Surface of a gas‐phase, prepolymerized polypropylene particle. Prepolymerizing in the presence of limited amounts of mineral oil allows one to obtain sustainably high activities and exert good control over the particle morphology. In article 1900052, Yue Yu and Timothy F. L. McKenna report that the oil plasticizes the nascent polymer,...

Gas phase copolymerizations of ethylene and an α‐olefin comonomer are performed using a commercial Ziegler–Natta catalyst in the presence of different induced condensing agents (ICA). The impact of these factors on the yield and final polyethylene properties such as the melt flow index, crystallinity, and incorporation of comonomer is studied. It h...

A systematic investigation is carried out on the gas phase of propylene during the initial instants of polymerization. The results confirm the positive impact of small amounts of mineral oil on the initial reaction rate and morphology. It is shown that polymerizing under conditions of mild temperature and pressure alone are not enough to achieve th...

The Sanchez–Lacombe Equation of State (SL EoS) is used to model the solubility of different industrial alkane penetrants in polyethylene to explain the importance of considering different diluents for different processes, and the impact that this choice can have on operating conditions, especially for the production of linear low density polyethyle...

The binary and ternary diffusion coefficients for gas/polymer systems can be estimated from solubility data and an equation of state to the free volume of penetrant/polymer systems. The system free volume can be calculated by the Sanchez Lacombe equation-of-state (SL-EoS), eliminating the need for viscoelastic data in determination of free volume p...

Back Cover: In article number 1900148 by Timothy F. L. McKenna and co‐workers, a two‐step semi‐batch process is proposed to create core–shell latex particles that serve the dual purpose of enhancing the adhesion of the layers in an aluminum‐PET laminate and enhancing the barrier properties of the final material. A hydrophobic core surrounded by a s...

The effect of chain transfer agents (CTA) ethyl acetate (EA), octyl acetate (OA) and isopropyl alcohol (IPA) on the rate of polymerization of vinylidene fluoride (VDF) in an emulsion polymerization and in solution polymerization in dimethyl carbonate (DMC) initiated by Tert-butyl Peroxypivalate was investigated. Pressure profiles of the polymerizat...

The development and formulation of core–shell latex‐based adhesives to improve the adhesion of aluminium to poly(ethylene terephthalate) (PET) films and enhance the permeability of the final laminate to oxygen and water is described. All particles have a soft acrylic component (the shell in core–shell particles) to improve adhesion, and occasionall...

The crystallization of high‐density polyethylene (HDPE) alone, and in the presence of n‐hexane (a common induced condensing agent [ICA]) is studied using differential scanning calorimetry. The presence of a noncrystallizable ICA which is partially soluble in the amorphous phase of HDPE reduces the rate of crystallization. This is reflected by a shi...

In processes that rely on the use of heterogeneous catalysis as the major means of production, it should be quite obvious that understanding how the catalyst particles evolve will play an important role in many aspects related to quality and reactor performance. At the risk of oversimplifying things, the principal roles of the heterogeneous catalys...

This work reports the use of acrylated fatty acid methyl ester (AFAME) as a biomonomer for the synthesis of bio‐based hybrid magnetic particles poly(styrene‐co‐AFAME)/γ‐Fe2O3 produced by miniemulsion polymerization. Poly(styrene‐co‐AFAME)/γ‐Fe2O3 can be tailored for use in various fields by varying the content of AFAME. The strategy employed is to...

The emulsion polymerization of vinylidene fluoride (VDF) is used to produce a range of commercially important products. Despite this, the current review article will show that very little is known about the kinetics of polymerization, particle nucleation, and role of chain transfer reactions. This is at least in part due to the extreme conditions n...

This review gives an overview of the evolution of the technology of condensed mode cooling, primarily for the case of ethylene polymerization on supported catalysts in fluidized bed reactors. It is well known that this mode of heat removal is quite effective in allowing polyolefin manufacturers to increase significantly production rates. What is pe...

The objective of this work was to evaluate the effect of the physical properties of several different commercial silicas on the performance of metallocene catalysts when used in gas and slurry phase polymerization. A lot is known about how the chemistry of the silica effects the polymerization and the final product, but very little is described in...

The polymer flow model is employed to predict the transient behavior of the concentration and temperature profiles within the growing particles during gas-phase ethylene polymerization in the absence and presence of n-hexane as the induced condensing agent. It is demonstrated that by accurate estimation of the model parameters, one can precisely de...

The solubility of propylene, ethylene, and propylene–ethylene mixtures in isotactic polypropylene (iPP) is measured with a high-pressure sorption balance at different temperatures and pressures. The obtained sorption isotherms of both binary systems (propylene–iPP and ethylene–iPP) are fitted with the Sanchez–Lacombe equation of state. It is found...

Front Cover: The fragmentation of supported catalysts for olefin polymerization is a critical, and as yet poorly understood step in the definition of polymer particle morphology. This article takes a look at the current state of our ability to describe and model particle morphology during the polymerization process. Further details can be found in...

Particle coagulation, in conjunction with nucleation and growth, plays a significant role in determining the evolution of particle size distribution in emulsion polymerizations. Therefore, many modelling and experimental studies have been carried out to have a better understanding and control of the particle coagulation phenomenon in order to achie...

High impact polypropylene (hiPP) powders are made in a 2.5 L semi‐batch gas‐phase reactor using a Ziegler–Natta catalyst and two sequential polymerization steps. The amount of copolymer, reactor temperature and pressure, the relative amounts of ethylene and propylene, and the presence of hydrogen are varied systematically to understand their impact...

The Sanchez-Lacombe Equation of State (SL EoS) was used to estimate the concentration of ethylene and different induced condensing agents (ICA) in polyethylene, and the effects of adding an ICA on parameters such as reactor temperature, production rate and particle size were discussed. A simple CSTR-like reactor model was validated from production...

The morphology of the growing polymer particles is important in olefin polymerisation on supported catalysts. It has a significant impact on the rate of mass and energy transport, and consequently on the polymerisation rate, comonomer incorporation, and the molecular weight distribution. The ability to quantify the evolution of morphology during th...

This chapter presents a brief look at different methods for the polymerization of ethylene using supported metallocene catalysts, then focuses on the effects that the properties of silica gel supports can have on catalyst behavior and the polymerization process. A review of the literature reveals that surprisingly little work has been done on the r...

In slurry and gas phase catalytic ethylene polymerization processes, aluminum alkyl (AlR3) compounds are usually present inside the reactor and their role either as co-catalyst or scavenger is of considerable importance. Silica supported metallocene/methyl aluminoxane (MAO) catalysts show specific interactions with AlR3 compounds. Therefore, this s...

An experimental investigation of the impact of changes in temperature on the observed rate of polymerization of ethylene in the gas phase using a commercial Ziegler–Natta catalyst in the presence of induced condensing agents (ICAs) reveals some unexpected behavior. In the absence of ICA, the effect of temperature is as expected: raising the tempera...

The size of a silica supported metallocene/MAO (methylaluminoxane) catalyst plays an important role in determining its productivity during ethylene polymerization. From a chemical engineering point of view, this size dependency of catalytic activity of supported metallocenes is mathematically connected with the different levels of mass-transfer res...

Leaching of (n-BuCp)2ZrCl2/MAO catalyst from silica supports has been studied in slurry phase ethylene homopolymerisation by changing i) the polymerization protocol ii) aluminum alkyl scavengers and iii) by adding butylated hydroxytoluene (BHT-H) along with aluminum alkyl scavengers. The impact of these three variations on the ethylene polymerizati...

Strategies have been successfully developed for the monitoring of the homo and copolymerization of styrene and butyl acrylate in a miniemulsion system using near-infrared (NIR) spectroscopy. Different concentrations of costabilizer, stearyl methacrylate, are tested to obtain the best stabilization condition. The spectral data are associated with th...

In this study a framework consisting of a computational fluid dynamics simulation coupled to a population balance model for the modeling of emulsion polymerizations is proposed. The combined approach is used to understand the impact of changing length and time scales, as well as mixing conditions on the particle size distribution (PSD) of a polymer...

Significant progress has been made over the past 20–30 years in terms of the ability to develop and solve mechanistic models of emulsion polymerization processes, and in particular models for prediction of the particle size distribution. However, this does not imply that modeling of these economically important processes is by any means a “solved p...

In the current work, gas phase propylene polymerizations were performed on ZN catalysts in a stopped flow reactor to understand the effect that the injection conditions (dry, as received, or wetted with a commercially available paraffinic mineral oil) have on initial temperature profiles, nascent polymer properties, and polymerization kinetics. Tem...

Polymers based on renewable sources are promising materials, and can find many uses in coatings and adhesive applications. The goal of this work was to synthesize and characterize bio-based styrene/acrylated fatty acid methyl ester (AFAME) copolymer—poly(styrene-co-AFAME) prepared by miniemulsion polymerization. The main strategy adopted was to fun...

A process model based on the thermodynamic models of Sanchez-Lacombe and PC-SAFT EoS is developed to simulate and analyze the impact of vaporized n-hexane as an induced condensing agent on the rate of gas phase ethylene polymerization on supported catalyst. The simulation results of the process model indicate that the cosolubility phenomenon (i.e.,...

The invention relates to a method for the preparation of polyethylene having a molecular weight of at least 1 million g/mol, comprising the following steps: -introducing the following compounds into a gas phase reactor: an olefin polymerisation catalyst; at least one unreactive compound having a molecular weight of less than 150 g/mol; said unreact...

Semi-batch propylene polymerizations were performed in slurry and gas phase using a supported Ziegler-Natta catalyst. The obtained instantaneous reaction rates were fitted with a kinetic model, and the influence of bulk temperature and reaction phase on kinetic parameters was studied. The estimated propagation constant increased with increasing rea...

A practical approach was implemented to follow the kinetics of the polymerization of supercritical vinylidene fluoride via emulsion polymerization using reaction calorimetry on a 4L laboratory scale reactor, in batch and semi-batch mode. The heat flow term was studied by determining the dynamic evolution of the system under both non-reactive and re...

The determination of the xylene soluble fraction in high impact polypropylene is used to estimate the rubber content in the polymer material. In analytical laboratories, the soluble fraction is measured by a solvent extraction using gravimetric methods according to ASTM5492 or ISO6427. These methods require large quantity of polymers, large volume...

The effect of the final morphology and the role of ethylene propylene rubber (EPR) content and (iPP) particle size on the mechanical properties of (iPP/EPR) in situ blends are investigated. The addition of EPR causes a significant improvement in the impact strength of the composites, from 20 kJ/m2 in unthoughned composite iPP to 100 kJ/m2 in iPP/EP...

Propylene is polymerized in the gas phase in a 2.5 L semibatch reactor using a commercially available supported Ziegler–Natta (ZN) catalyst. The mode of injection (wet vs dry), the impact of including a prepolymerization step, and of changing the composition of the gas phase are systematically investigated in terms of their influence on the instant...

Packaging industry field is in constant growing due to the existence of innumerous possibilities to solve the most variable challenges. Regardless the kind of product one is working with, the purpose of the packaging is to create a physicochemical separation between this product and the surrounding environment, so it is imperative that the material...

The presence of different commonly used induced condensing agents (ICAs) in the gas phase polymerization of ethylene on the supported catalyst has a significant impact on the crystallinity and the molecular weight distribution of the resulting high density polyethylene. The crystallinity of the polymer is found to be higher in the presence of vapor...

Morphology and particle size distribution (PSD) of high density polyethylene (HDPE) produced in slurry and gas phase ethylene homopolymerisations have been analysed in connection with the catalytic activity of silica supported (n-BuCp)2ZrCl2/Methylaluminoxane (MAO) catalysts. It has been shown that the silica dehydroxylation temperature affects the...

The impact of injection conditions of a supported Ziegler Natta catalyst on the rate of polymerization of propylene in a gas phase process is investigated. It is observed that the instantaneous rate of propylene polymerization is higher if the catalyst is injected wetted with a hydrocarbon before being charged to the reactor. This is attributed to...

A new methodology for the rapid and robust evaluation of the electrostatic stabilization of latex particles has been developed. It is based on the interpretation of the backscattering profile obtained using a Turbiscan Lab®. The experimental approach employs Multiple Light Scattering (MLS) in agitated measurement cells so the colloidal stability st...

The current study aims to explore the link between the role of silica dehydroxylation temperature and the catalytic performance of an (n-BuCp)2ZrCl2 metallocene precursor supported on silica impregnated with methylaluminoxane (MAO) in ethylene homopolymerization. Diffuse Reflectance Fourier Transform Infrared Spectroscopy (FT-IR-DRIFT) and Solid St...

Experimental mixed-gas sorption/dilation data and mixture densities estimated by the fitted Sanchez–Lacombe equation of state have been used to estimate the partial molar volumes (PMV) of gases and polymers in multicomponent mixtures (i.e., ternary) at conditions of industrial relevance. The method developed estimates accurately the PMV and volumet...

The effect of commonly used induced condensing agents (ICAs) on the rate of polymerization of ethylene on a supported Ziegler–Natta catalyst in a gas‐phase process is investigated. It is observed that the instantaneous rate of ethylene polymerization is promoted in presence of all ICAs studied. This is attributed to the effect of the heavy ICAs in...

A systematic analysis methodology is proposed in order to be able to evaluate the role and the significance of the impact of the physical and chemical phenomena during the gas phase ethylene copolymerization in presence of 1-pentene and 1-hexene comonomers in the gas phase composition. In addition, the effect of inert n-hexane on the instantaneous...

A 2D high gain observer has been constructed to estimate the reaction rate parameters in a laboratory scale stopped flow fixed bed reactor for gas phase ethylene polymerisation. The observer is based on the heat balances of a validated model of the reactor and the measured variable is the outlet temperature of the fixed bed. To create an observable...

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 in...

A study is carried out in order to better understand the kinetic behavior of two different metallocene precursors supported on an activating silica support, and, in particular, to attempt to reduce the significance of catalyst deactivation through the use of different alkylating agents. It is observed that it is difficult to prevent the deactivatio...

The relative importance of the higher solubility of n-hexane (with respect to ethylene) and its associated heat of sorption on the thermal behavior of the growing polymer particles during gas phase ethylene polymerization on supported catalysts are investigated. It is found that if a polymerizing particle begins to heat-up, the partial desorption o...

Inert condensing agents (ICAs) are used principally to cool down gas-phase fluidized bed reactors used to polymerize ethylene over supported catalysts. While these ICAs are chemically inert, it appears that they might nevertheless increase the polymerization rate. n-Hexane is used as an ICA, and an enhancement in the instantaneous rate of ethylene...

Polyurethane (PU)/acrylic hybrid particles with different PU contents were synthesized by miniemulsion polymerization and subsequently dried to give solid adhesive films. The morphologies of the particles and the morphologies and mechanical properties of the resulting films were investigated by Transmission Electron Microscopy combined with selecti...

Over the past decade, we have developed an integrated approach to the study of novel materials, methods, and processes for the production of waterborne coatings. This approach is based on a combination of conventional and free radical chemistries, micro-, mini-, and macro-emulsion polymerization, and different reactor and dispersion technologies. I...