On the Reaction Characteristics of Miniemulsion Polymerization with Aqueous Phase Initiation – Experiments and Modeling

Miniemulsions, consisting of submicron droplets of very hydrophobic lauryl methacrylate or 4‐tert‐butyl styrene, are successfully polymerized using water‐soluble sodium persulfate. Monitoring the calorimetric profile as well as the droplet and particle size distribution with conversion manifests a process of monomer redistribution, droplet disappearance, and narrowing of the particle size distribution. The observed reaction characteristics could be modeled adequately, using thermodynamic principles. The results of the work presented do not only have predicting value, but also enfeeble the idea of a one‐to‐one translation of monomer droplets into polymer particles in miniemulsion polymerization.     

Estimation of Apparent Kinetic Constants of Individual Site Types for the Polymerization of Ethylene and α‐olefins with Ziegler–Natta Catalysts

This article proposes a method to quantify the polymerization kinetics of ethylene and α‐olefins with commercial TiCl₄/MgCl₂ Ziegler–Natta catalysts. The method determines the leading apparent polymerization kinetic constants for each active site in a Ziegler–Natta catalyst by simultaneously fitting the instantaneous polymerization rate, cumulative polymer yield, and polymer molecular weight distribution measured at different times during a series of semi‐batch polymerization experiments. This approach quantifies the behavior of olefin polymerization with multisite catalysts using the least number of adjustable parameters needed to consistently model polymerization kinetics and polymer microstructural data.

     

Network Formation by Free Radical Polymerization in Isothermal Continuous Flow Stirred Reactors

The authors apply the method of moments to the study of network formation in continuous flow stirred reactors when chain transfer to polymer and coupling are present in the reaction scheme. This approach leads to analytical solutions for the various moments involved. The authors start by assuming that the rate of coupling is proportional to the length of dead chains, which allow them to review and extend previous work in this area. This is followed by similar derivations when a coupling agent is present and the rate of coupling is proportional to the number of coupling groups that such agent leaves in dead polymer molecules, demonstrating that higher values of second order moments can be reached at lower levels of unreacted coupling agent.

     

Mathematical Modeling of the Internal Surface Area of Copolymer Particles Based on Elementary Gel Structures

The present work describes a kinetic approach which is able to predict how the internal surface area of polymer particles evolve during suspension copolymerization in the presence of porogen. For such a purpose, the concept of elementary gel structures has been introduced by modeling their surface area through the numerical fractionation technique. Thus, variables such as diluents composition, divinyl monomer concentration, and dilution degree could be assessed in the simulations. The present mathematical model is validated by using different experimental data from literature and a fair agreement is reached. Furthermore, the developed model is also capable of predicting the most significant copolymerization variables, e.g., conversion rate, concentration of species, and average molecular weights.

     

Analysis of Ethylene/1‐Olefin Copolymers Made with Ziegler–Natta Catalysts by Deconvolution of Molecular Weight and Average Short Chain Branching Distributions

In this article a systematic method is proposed to deconvolute the time‐dependent molecular weight distributions (MWD) and average comonomer fraction profiles of ethylene/1‐olefin copolymers made with heterogeneous Ziegler–Natta catalysts. These distributions with a high‐temperature gel permeation chromatography equipped with an infrared detector at four different polymerization times have been measured and used this information to infer how the fractions of polymer made on each site type varied with polymerization time. The model estimates here the minimum number of active site types needed to describe these copolymers, the MWD of polymer populations made on each site type, and their average comonomer fractions. This method is useful to quantify the microstructure of olefin copolymers made with multiple site type catalysts using the least number of adjustable parameters.

     

Polymer Micro‐ and Nanocapsules as Biological Carriers with Multifunctional Properties

The design and development of multifunctional polymer capsules with controlled chemical composition and physical properties has been the focus of academic and industrial research in recent years. Especially in the biomedical field, the formulation of novel polymer‐based encapsulation systems for the early‐stage disease diagnostic and effective delivery of bioactive agents represent one of the most rapidly advancing areas of science. The stimuli‐responsive release of cargo molecules from the carrier gains remarkable attention for in vitro and in vivo delivery of contrast agents, genes, and pharmaceutics. In this Review, the current status and the challenges of different polymer‐based micro‐ and nanocapsule formulations are considered, emphasizing on their potential biological application as carriers for specific drug targeting and controlled release upon applying of external stimulus.     

Propylene Polymerization Reactor Control and Estimation Using a Particle Filter and Neural Network

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.

     

Modeling the Radical Batch Homopolymerization of Acrylamide in Aqueous Solution

A kinetic model for the radical homopolymerization of acrylamide in aqueous solution is developed, incorporating propagation and termination rate coefficients as functions of monomer concentration and including the formation and reaction of midchain radicals based on the insights and measured rate coefficients from recent pulsed‐laser studies. The model successfully represents the batch conversion profiles measured using an in situ NMR technique between 40 and 70 °C with initial monomer concentrations of 5 to 40 wt%, as well as the associated polymer molar mass distributions. In particular, the model captures the decreased rate that occurs at lowered monomer concentrations as a result of the formation of less‐active midchain radicals by backbiting. Previous literature data are also well represented by the model.

     

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 1, Single Catalyst Systems

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.

     

UV‐Free Microfluidic Particle Fabrication at Low Temperature Using ARGET‐ATRP as the Initiator System

A new way to fabricate monodisperse polymer particles in a microfluidic device without UV‐light and without the need for high temperatures is described in this article. By applying an activator regeneration by electron transfer ‐ atom transfer radical polymerization (ARGET‐ATRP) initiator system in a co‐capillary microfluidic setup and by separating the monomer mixture in an initiator and a catalyst phase, a fast polymerization of the droplets at low temperature without premature curing and thus clogging of the capillaries can be achieved. The influence of the flow rates on the particle sizes and their polydispersity as well as the controlled character of the polymerization are investigated. The particle size is well adjustable, but the reaction is not controlled due to the high radical concentration needed for rapid polymerization. In addition, particles with incorporated UV‐dyes are produced as a proof of concept at low temperature.

     

Estimation of Polymerization Conditions Needed to Make Ethylene/1‐olefin Copolymers with Specific Microstructures Using Artificial Neural Networks

Two artificial neural network models (forward and inverse) are developed to describe ethylene/1‐olefin copolymerization with a catalyst having two site types using training and testing datasets obtained from a polymerization kinetic model. The forward model is applied to predict the molecular weight and chemical composition distributions of the polymer from a set of polymerization conditions, such as ethylene concentration, 1‐olefin concentration, cocatalyst concentration, hydrogen concentration, and polymerization temperature. The results of the forward model agree well with those from the kinetic model. The inverse model is applied to determine the polymerization conditions to produce polymers with desired microstructures. Although the inverse model generates multiple solutions for the general case, unique solutions are obtained when one of the three key process parameters (ethylene concentration, 1‐olefin concentration, and polymerization temperature) is kept constant. The proposed model can be used as an efficient tool to design materials from a set of polymerization conditions.

     

Coupling of CFD Simulations and Population Balance Modeling to Predict Brownian Coagulation in an Emulsion Polymerization Reactor

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 latex under different conditions. It is shown that the effect of agitation rate can have a profound impact on the distribution of ionic species in the reactor, and thus on the evolution of the PSD.

     

Synthesis of Poly(n‐butyl acrylate/methyl methacrylate)/CNC Latex Nanocomposites via In Situ Emulsion Polymerization

Cellulose nanocrystals (CNCs) are renewable, nontoxic and naturally available organic nanoparticles derived from cellulosic resources such as cotton and wood pulp. Poly(n‐butyl acrylate‐co‐methyl methacrylate)/CNC latexes are successfully synthesized via in situ emulsion polymerization. The effect of CNC loading on overall conversion, polymer particle size, glass transition temperature (T_g), gel content, latex viscosity, and storage and loss moduli of dried latex are studied. While the effect of CNC content on overall conversion, polymer particle size, and T_g of the resulting latexes is negligible, significant increase in gel content, latex viscosity, and storage and loss moduli are observed.

     

State‐of‐the‐Art and Progress in Method of Moments for the Model‐Based Reversible‐Deactivation Radical Polymerization

Reversible‐deactivation radical polymerization (RDRP) techniques have received lots of interest for the past 20 years, not only owing to their simple, mild reaction conditions and broad applicability, but also their accessibility to produce polymeric materials with well‐defined structures. Modeling is widely applied to optimize the polymerization conditions and processes. In addition, there are numerous literatures on the kinetic and reactor models for RDRP processes, which show the accessibility on polymerization kinetics insight, process optimization, and controlling over chain microstructure with predetermined molecular weight and low dispersity, copolymer composition distribution, and sequence distribution. This review highlights the facility of the method of moments in the modeling field and presents a summary of the present state‐of‐the‐art and future perspectives focusing on the model‐based RDRP processes based on the method of moments. Summary on the current status and challenges is discussed briefly.

     

Is Modeling the PSD in Emulsion Polymerization a Finished Problem? An Overview

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 problem,” or that it is no longer necessary to perform fundamental research in this area. There are a number of areas where strong scientific work would increase the understanding of the process, including events in the aqueous phase, radical entry into growing particles, monomer partitioning, and especially the mechanisms and modeling of particle coagulation.

     

Synthesis of Narrow Molecular Weight Distribution Copolymers for ArF Photoresist Materials by Nitroxide Mediated Polymerization

ArF candidate photoresist polymers have been synthesized by nitroxide mediated polymerization (NMP). Statistical copolymerizations of α‐gamma butyrolactone methacrylate, 3‐hydroxy‐1‐adamantyl methacrylate, and 2‐methyl 2‐adamantyl methacrylate with 5–10 mol% of controlling comonomers (i.e., styrene, p‐acetoxystyrene, 2‐vinyl naphthalene, acrylonitrile, and pentafluorostyrene), which are necessary for controlled polymerization of methacrylates by NMP with the unimolecular alkoxyamine initiator BlocBuilder, have been used. As little as 5 mol% controlling comonomer in the feed is demonstrated to be sufficient to produce linear evolution of number average molecular weight against conversion (X) up to X = 0.7 for relatively low target degrees of polymerization. All of the resulting copolymers have relatively low dispersities and show relatively low absorbance at 193 nm, comparable to other 193 nm candidate photoresists reported previously, with the exception of VN‐containing copolymer.

     

Effects of Alkyl Aluminum on SiO2‐Supported Silyl‐Chromate(Cr)/Imido‐Vanadium(V) Bimetallic Catalysts for Producing Bimodal Polyethylene

SiO₂‐supported Cr–V bimetallic catalyst can be used for producing bimodal polyethylene which can be applied for high‐performance pipe material. Alkyl aluminum are used to prereduce the bimetallic catalysts, and the effects of alkyl aluminum for the bimetallic catalyst are fully studied by catalyst characterization, polymerization kinetics, and the properties of polymer product by the comparison with the catalyst without prereduction. The result shows that the optimum polymerization activity is almost double after the catalyst is prereduced by triisobutylaluminum (TIBA), and the needed dosage of alkyl aluminum also is decreased significantly. The alkyl aluminum of the prereduced catalyst can also act as a chain transfer agent, significantly reducing the molecular weight of the polymer. The diethylaluminum chloride (DEAC) is mostly deactivating the Cr species during the ethylene polymerization. The synthesized catalysts, prereduced by TIBA, triethylaluminum (TEA), and DEAC, all exhibited good hydrogen response and comonomer interposition ability, which will be favorable for the further application of the bimetallic catalyst in the industrial field.

     

Molecular Architecture of Multi‐Block Polymer Synthesized in a Dual‐Catalyst Single CSTR

This work aims at deriving analytical solutions for the molecular architecture of multi‐block polymer synthesized in a dual‐catalyst single CSTR. While the relevant equations are developed for homopolymerization, they can easily be extended to copolymerization. Special emphasis is placed on the quantities associated with each catalyst rather than the overall ones. However, if all rate parameters are available, the expressions can be used to calculate the properties of the material made by each catalyst as well as the overall ones under various process conditions. Given the reasonable assumption of large residence time, the solutions are simplified to elucidate the kinetics of chain‐shuttling involving two catalysts. It is shown that systems with low chain‐shuttling ability, if DP^P_n,0 ≠ DP^Q_n,0, may exhibit significant deviation from Flory's most probable distribution. Furthermore, systems with high chain‐shuttling ability produce macromolecules with more uniform architecture and polydispersity index close to 2.

     

Understanding the Formation of Linear Olefin Block Copolymers with Dynamic Monte Carlo Simulation

Chain‐shuttling polymerization with dual catalysts has introduced a new class of polyolefins called olefin block copolymers (OBCs). A dynamic Monte Carlo model to describe the kinetics of chain‐shuttling copolymerization in a semi‐batch reactor is developed, and used it to study how the microstructure of OBCs with different numbers of blocks per chain evolves during polymerization. The model also describes how chain‐shuttling rate constants and concentration of chain‐shuttling agent affect populations of OBCs with different numbers of blocks per chain. These model predictions are useful to make OBCs with precisely designed microstructures.

     

Molecular Weight Development of Surface and Solution Polymers in Surface‐Initiated Atom Transfer Radical Polymerization and Their Dependence on Radical Termination Modes

In the surface‐initiated atom transfer radical polymerization, the polymerization proceeds both in solution and on surface. This work reports a modeling study, describing the growth of the molecular weight and polydispersity of polymer both on surface and in solution. It is found that both surface radical termination and solution monomer consumption significantly suppress the growth rate of polymer layer. Besides, the former affects the molecular weights of polymer both on surface and in solution. If the termination rate constant in solution (k_t,sol–sol) is the same as that of surface and solution interfaces (k_t,sol–surf), and the surface termination (k_{t,surf–surf}) is negligible, then the polymers both on surface and in solution have the same molecular weight. However, if surface radicals terminate among themselves, the molecular weight of polymer on surface will lower than that in solution. Such termination is promoted by surface radical migration through activation/deactivation reactions in solution. When k_t,sol–surf <k_t,sol–sol, the molecular weight of surface polymer becomes higher than that in solution. This situation is resulted from surface radical trap due to a high grafting density.