Modified frontal polymerization of poly(methyl methacrylate)

In this work, we propose a modified frontal polymerization method to build a uniform reaction front by gradually immersing the reacting mixture in a thermal bath. This scheme allows uniform materials to be obtained with nearly constant molecular weights and polydispersities and a low residual monomer concentration. A comparative study of the molecular weight distributions of poly(methyl methacrylate)s obtained by bulk polymerization, frontal polymerization, and frontal polymerization with the proposed gradual immersion is presented. Samples obtained by these methods show that materials obtained by bulk polymerization and by frontal polymerization are less uniform than those obtained by frontal polymerization with gradual immersion in a thermal bath. The obtained uniformity is directly related to a stabilizing effect of the reaction front by the gradual immersion of the reactor in a constant‐temperature bath and to a reduction in the reaction rate promoted by a moderate transfer agent concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Numerical modeling and experimental study of the frontal polymerization of the diglycidyl ether of bisphenol A/diethylenetriamine epoxy system

Frontal polymerization is a process in which a spatially localized reaction zone propagates through a monomer by converting it into a polymer. In particular, the heat produced during the curing process is exploited to promote the reaction of the monomer lying next to the propagating front, making this latter able to self‐sustain. This approach represents an alternative solution to traditional polymerization methods and can be successfully applied to the preparation of many polymeric materials. In this study, frontal polymerization was numerically modeled to better understand it and to provide the basis for processing simulation. A finite‐difference method was used to solve the thermal problem coupled with the equation describing the cure evolution for a reactor with a cylindrical geometry. The implicit backward time–centered space method was used. First, a one‐dimensional model, able to describe the process in an adiabatic tube, was developed. The front ignition was simulated as if it were a hot surface warming one end of the reactor to trigger reactant polymerization. The model was able to predict the formation of a reactive front advancing in the unreacted zone with a constant speed. The influence of the chemical and physical properties of the resin on process evolution was also investigated. By applying the alternate direction implicit method, a more detailed two‐dimensional model able to describe a three‐dimensional problem for a cylindrical reactor was also developed. With this model, it was possible to study the influence of boundary conditions on process evolution, considering a convective heat exchange with the environment through the reactor walls. Diglycidyl ether of bisphenol A, cured with diethylenetriamine (DETA), was used as the model system. Differential scanning calorimetry was used to produce a phenomenological model able to describe the cure process and to determine the physical properties of the resin. The validity of the approach was confirmed experimentally using a small cylindrical reactor. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1756–1766, 2005     

Continuous infiltration-mediated SHS process in a coflow reactor: Numerical modeling

An SHS reaction in Metal-Gas systems under conditions of forced infiltration of gaseous reagent into a co-flow reactor was numerically modeled. It has been demonstrated that, at a constant rate of gas inflow into a reactor, the reaction front may acquire the configuration of the Saffman-Taylor fingers, which is inadmissible in the manufacturing process. The conditions ensuring frontal propagation of SHS reaction over the entire length of the reactor have been formulated.     

Macrokinetics of obtaining functional products based on polystyrene and polymethyl methacrylate under nonisothermal conditions

Thermal conditions of the process of manufacturing large-block, optically pure products based on polystyrene and polymethyl methacrylate (scintillators, light concentrators, bulletproof glass, etc.) have been experimentally and theoretically studied. The flow sheet of the process includes two sequentially connected reaction apparatuses, i.e., a tubular reactor for frontal polymerization and a semi-continuous molding reactor. Prepolymer is formed in the tubular reactor and is fed to the molding reactor. As this reactor is being filled, polymerization continues under autothermal heating conditions. After filling, the molding reactor is replaced by a similar one, while the filled reactor is kept in a temperature-controlled oven for final polymerization followed by cooling and removal of the product.     

Heterogeneous Catalytic Polymerization of Ethylene in Microtubular Reactor Systems

The feasibility of using a microtubular reactor for heterogeneous polymerization of ethylene was investigated experimentally. Chemically inert polymer tubing of 800–2300 μm in inner diameter was fabricated and used as a polymerization reactor. Nonporous silica nanoparticles with a diameter of 400 nm were synthesized and used as support for the high‐activity rac‐ethylene(indenyl)₂ZrCl₂ catalyst with methylaluminoxane as cocatalyst and toluene as diluent. Large‐diameter microtubular reactors were also successfully used to conduct heterogeneous polymerization of ethylene in continuous reaction operations. High initial catalyst activity was obtained and the overall polymerization activity per volume or reactor length was quite high. No particle fragmentation occurred and the polymer particles were covered with small subgrains or nanofibrils with a diameter of 30 nm.     

Online Monitoring of Vinyl Chloride Polymerization in a Microreactor Using Raman Spectroscopy

A novel capillary‐based microfluidic device has been designed to follow the vinyl chloride polymerization reaction. Monodisperse droplets of 200 μm diameter could be obtained by means of a co‐flow generation system, each one being considered as a polymerization reactor. Monomer droplets were visualized in a microchannel with a high‐speed camera. At the end of the reaction, PVC grains were observed with a scanning electron microscopy technique. Real‐time non‐invasive Raman measurement was performed on stationary vinyl chloride monomer droplets and provided values of effective reaction orders and rate constants. This microdevice allowed reaction investigation under difficult conditions of pressure and temperature with a minimal amount of reagents.     

Frontal polymerization of a cyanate ester

Thermal frontal polymerization is an exothermic process that uses a propagating wave to polymerize monomers via an external heat source, such as a soldering iron, to initiate front propagation. Herein, for the first time, the curing of a cyanate ester via thermal frontal polymerization is described with two different external heat sources. However, issues of bubbling due to vaporization of the amine catalyst generally resulted in incomplete frontal polymerization when a soldering iron was used as the external heat source. To counter this issue, dual‐strip polymerization systems were used, wherein the heat from the exothermic polymerization of a free‐radical system was used to initiate the frontal polymerization of a cyanate ester system with an amine catalyst. As a result, complete frontal polymerization occurred. Additionally, the effect of the width of the acrylate strip and its impact on the front temperature, initial velocity, and steady‐state velocity of the adjacent cyanate ester system were studied. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mass transfer and reaction performance of the downer and its hydrodynamic explanation

Catalytic decomposition of ozone was carried out in a 15‐m high, 90‐mm inner diameter downer reactor. Radial distributions of ozone concentration at different axial elevations under different operating conditions were measured. The results were explained from the flow structure experimental data and corresponding signal analysis in time domain and frequency domain. The aggregation status of solid particles, relative movement between the gas and solids, and the dynamic behaviour of clusters were considered to have a joint influence on the mass transfer and reaction process in the downer.     

Dynamic optimization of the methylmethacrylate cell‐cast process for plastic sheet production

Traditionally, the methylmethacrylate (MMA) polymerization reaction process for plastic sheet production has been carried out using warming baths. However, it has been observed that the manufactured polymer tends to feature poor homogeneity characteristics measured in terms of properties like molecular weight distribution. Nonhomogeneous polymer properties should be avoided because they give rise to a product with undesired wide quality characteristics. To improve homogeneity properties force‐circulated warm air reactors have been proposed, such reactors are normally operated under isothermal air temperature conditions. However, we demonstrate that dynamic optimal warming temperature profiles lead to a polymer sheet with better homogeneity characteristics, especially when compared against simple isothermal operating policies. In this work, the dynamic optimization of a heating and polymerization reaction process for plastic sheet production in a force‐circulated warm air reactor is addressed. The optimization formulation is based on the dynamic representation of the two‐directional heating and reaction process taking place within the system, and includes kinetic equations for the bulk free radical polymerization reactions of MMA. The mathematical model is cast as a time dependent partial differential equation (PDE) system, the optimal heating profile calculation turns out to be a dynamic optimization problem embedded in a distributed parameter system. A simultaneous optimization approach is selected to solve the dynamic optimization problem. Trough full discretization of all decision variables, a nonlinear programming (NLP) model is obtained and solved by using the IPOPT optimization solver. The results are presented about the dynamic optimization for two plastic sheets of different thickness and compared them against simple operating policies. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Polynomial ARMA model identification for a continuous styrene polymerization reactor using on‐line measurements of polymer properties

The multiinput–multioutput identification for a continuous styrene polymerization reactor using a polynomial ARMA model is carried out by both simulation and experiment. The pseudorandom multilevel input signals are applied for model identification in which input variables are the jacket inlet temperature and the feed flow rate, whereas the output variables are the monomer conversion and the weight‐average molecular weight. The use of a polynomial ARMA model for identification of the multivariable polymerization reaction system is validated by simulation study. For the experimental corroboration, correlations are developed to convert the on‐line measurements of density and viscosity of the reaction mixture to the monomer conversion and the weight‐average molecular weight. The on‐line values of the conversion and weight‐average molecular weight turn out to be in good agreement with the off‐line measurements. Despite the complex and nonlinear features of the polymerization reaction system, the polynomial ARMA model is found to satisfactorily describe the dynamic behavior of the polymerization reactor. Therefore, one may apply the polynomial ARMA model to the optimization and control of polymerization reactor systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1889–1901, 2000     

Modelling and control of different types of polymerization processes using neural networks technique: A review

Polymerization process can be classified as a nonlinear type process since it exhibits a dynamic behaviour throughout the process. Therefore, it is highly complicated to obtain an accurate mechanistic model from the nonlinear process. This predicament always been a “wall” to researchers to be able to devise an optimal process model and control scheme for such a system. Neural networks have succeeded the other modelling and control methods especially in coping with nonlinear process due to their very conciliate characteristics. These characteristics are further explained in this work. The predicament that is encountered by researchers nowadays is lack of data which consequently lead to an imprecise mechanistic model that scarcely conforms to the desired process. The implementations of the neural network model not only restrict to polymerization reactor but to other difficult‐to‐measure parameters such as polymer quality, polymer melts index and mixture of initiators. This work is aimed to manifest ascendancy of neural networks in modelling and control of polymerization process.     

Photoinduced cationic frontal polymerization of epoxy–carbon fibre composites

UV‐activated frontal polymerization was exploited for the preparation of epoxy–carbon fibre composites. The curing process was investigated showing the frontal behaviour, and the final properties of UV‐cured composites were compared with those of the same composites obtained by thermal curing in the presence of amine as hardener. The best curing formulations were designed, defining the photoinitiator‐to‐thermal initiator ratio, which was 1.5:1.5. It was observed that the presence of the carbon fibres induced an acceleration of the front velocity. By comparing the thermomechanical properties of the thermally cured composite and the same composite crosslinked using the frontal process, we could observe that the latter showed higher T_g value and lower σ_f. This was attributed to the formation of a different polymeric network structure. © 2019 Society of Chemical Industry     

Increasing PVC suspension polymerization productivity by using temperature‐programmed reactions

Vinyl chloride polymerizations are known to be autoaccelerating. The reaction rate increases with conversion. Because of this phenomenon, substantial reactor productivity at early conversion can be lost because the heat‐removal capacity of the reactor is not fully utilized until near the end of the polymerization. For this reason it is desirable to speed up the polymerization at the beginning and slow it down near the end. This rate adjustment can be achieved by running the polymerization hotter in the beginning and then cooling. We have written a scientifically based computer model of the polymerization designed specifically to simulate such temperature‐programmed reactions. The model does a complete heat balance on the polymerization, has a molecular weight predictor, and will be described and demonstrated for a polymerization at 50°C using sec‐butyl peroxydicarbonate (SBP) as initiator. By using this single initiator and a very simple straight‐line temperature‐programmed reaction, the time to 80% conversion can be reduced from 335 minutes to 240 minutes. This is a substantial increase in productivity.     

Study on spatial–temporal kinetics of photo‐initiated frontal polymerization in stacked reaction cells

The spatial–temporal kinetics for photo‐initiated frontal polymerization(PFP) of isobornyl acrylate with 2,4,6‐trimethylbenzoyldiphenyl phosphine oxide (TPO) as photobleaching initiator was studied experimentally in stacked reaction cells. FTIR and NMR spectroscopy were employed to measure the polymerization conversion, which is dependent on the exposure time, sample depth, light intensity and photo‐initiator concentration. The experimental results are consistent with the theoretical model prediction and show that prolonged irradiation time, higher light intensity and lower photo‐initiator concentration are favorable in enhancing the advance of the polymerization front. The depth‐resolved GPC analysis shows that the average molecular weight of the PFP product dramatically increases with sample depth, while the molecular weight polydispersity reduces steadily with increase in sample depth. Copyright © 2006 Society of Chemical Industry     

A model study on the ionic polymerization in a flow reactor

A general theoretical study of heterogeneous ionic polymerization in a continuous stationary reactor is presented. Equations have been calculated that describe the dependence of the substances' concentration in the reaction vessel, of the polymer yield and molecular weight on the initial concentration of the monomer, catalyst and chain-transfer agent. The problem is solved with assumptions based on actual anion processes. The obtained functional dependences have been analysed for different values of their parameters. The characteristic features of the reaction are also emphasized.     

TEMPO‐controlled radical suspension polymerization of poly(styrene)‐block‐poly(styrene‐co‐acrylonitrile) and poly(styrene)‐block‐poly(styrene‐co‐butyl methacrylate)

Suspension polymerization expands the study of controlled radical polymerization to high conversions and is known as a method to synthesize polymers with high molecular weights. The radical block copolymerizations of styrene (S) and acrylonitrile (AN) or butyl methacrylate (BUMA) controlled by 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was performed in an oil/water pressure reactor system at a temperature of 125°C. TEMPO‐terminated styrene homopolymer was employed as macroinitiator. The systems were examined by varying the composition of the monomer mixture at a constant reaction time, as well as by varying the reaction time for a characteristic monomer composition to get all of the possible conversion range. The solubility effects of acrylonitrile in the suspension medium were considered. Furthermore, the yield of the reaction was improved through initiator addition by taking control of the reaction. The polymerizations could proceed under control up to a conversion of 80–90%. By using the copolymerization equations, the solubility of pure acrylonitrile in the suspension medium could be calculated and was found to be 8 wt.‐%.     

Characterization of a photocatalytic reaction in a continuous‐flow recirculation reactor system

A continuous‐flow recirculation mode, generally called a recycle mode, is known to be practically meaningless except when the reactant is separated from the product at the reactor exit or when the reaction is autocatalytic, because when simply circulating a small amount of the fluid containing a reactant, the reactant concentration in this mode is lowered due to mixing of the fluid at the reactor entrance, leading to a decrease in the conversion at the reactor exit. This mode may, however, be meaningful in photocatalytic reactions with very large film‐diffusional resistance. To indicate the validity of this estimation, therefore, characteristics of a continuous‐flow recirculation reactor have been investigated both theoretically and experimentally. As a result, it is found that by increasing the circulation flow rate the conversion and productivity in this reactor is higher than that in a continuous‐flow reactor because the film‐diffusional resistance is remarkably reduced. Copyright © 2006 Society of Chemical Industry     

Multiobjective dynamic optimization of batch free radical polymerization process catalyzed by mixed initiator systems

The optimal control policies for batch free radical polymerization of styrene catalyzed by a binary mixture of monofunctional initiators have been determined using a multiobjective dynamic optimization technique. The process objectives considered in the optimization include monomer conversion, polymer molecular weight, initiator residue level, and total reaction time. It is illustrated through model simulations and experiments that the performance of the batch polymerization process can be improved significantly through the use of optimal initiator mixture and polymerization temperature programming. This paper also illustrates how the multiobjection optimization technique can be used effectively to solve complex polymerization reactor optimization problems with detailed reaction models.     

Geometrically Constrained Polymerization of Styrene Over Heterogeneous Catalyst Layer in Silica Nanotube Reactors

Styrene has been polymerized to syndiotactic polystyrene (sPS) over a layer of heterogeneous Cp*Ti(OCH₃)₃/MAO catalyst immobilized onto the surfaces of silica nanotube reactor (SNTR) arrays of 60–200 nm in diameter. The polymer produced in the SNTR arrays has been found to have the molecular weights much larger than the polymers synthesized by a liquid slurry polymerization over silica-supported catalysts. A dynamic reactor model that consists of diffusion and reaction terms has been derived and solved to quantify the kinetics of styrene polymerization in a single nanotube reactor. The two-site kinetic model applied to the silica nanotube reactor model shows that the experimentally observed high polymer molecular weight can be fitted if the chain transfer rate constants for monomer and β-hydride elimination are reduced significantly. The simulation results suggest that the presence of dense crystalline sPS nanofibrils filling the nanotubes constrain the molecular movements of polymer chain ends in the proximity of catalyst sites to limit the chain transfer reactions. POLYM. ENG. SCI., 60:700–709, 2020. © 2020 Society of Plastics Engineers     

Optimal reaction conditions for the minimization of energy consumption and by‐product formation in a poly(ethylene terephthalate) process

We determined the optimal reaction conditions to minimize the energy cost and the quantities of by‐products for a poly(ethylene terephthalate) process by using the iterative dynamic programming (IDP) algorithm. Here, we employed a sequence of three reactor models: the semibatch transesterification reactor model, the semibatch prepolymerization reactor model, and the rotating‐disc‐type polycondensation reactor model. We selectively chose or developed the reactor models by incorporating experimentally verified kinetic models reported in the literature. We established the model for the entire reactor system by connecting the three reactor models in series and by resolving some joint problems arising when different types of reactor models were interconnected. On the basis of the simulation results of the reactor system, we scrutinized the cause and effect between the reaction conditions and the final quality of the polymer product. Here, we set up the optimization strategy by using IDP on the basis of the integrated reactor model, and the process variables with significant influence on the properties of polymer were selected as control variables with the help of a simulation study. With this method, we could refine the reaction conditions at the end of each iteration step by contracting the spectra of control regions, and the iteration process finally stopped when the profile of the optimal trajectory converged. We also took the constraints on the control variables into account to guarantee polymer quality and to suppress side reactions. Constituting six different strategies by setting weighting vectors differently, we examined the differences in optimal trajectories, the trend of optimality, and the quality of the final polymer product. For each of the strategies, we conducted the optimization to examine whether the number‐average degree of polymerization approached the desired value. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 993–1008, 2002