Thermal ignition phenomena in chain-addition copolymerizations

Thermal ignition theory has been extended to include free-radical copolymerizations resulting in dimensionless criteria for runaway and ignition. These criteria were verified by computer simulation and preliminary experimentation. Approximate, but greatly simplified, material and energy balances describing nonisothermal copolymerizations were developed which are similar in form to those describing nonisothermal homopolymerizations. Regions of close agreement, as well as disagreement, between conversion and temperature histories from these approximations and those from the exact balances are described.     

Emulsion copolymerization of alpha-methylstyrene and styrene

Fast copolymerizations of styrene and alpha-methylstyrene can be achieved in emulsion systems where free-radical reactions in the bulk or solution are inefficient. The Smith–Ewart–Gardon theory of emulsion polymerization was developed for homopolymerizations but should extend to this copolymerization since the particular comonomers meet the basic assumptions of this model. Sodium lauryl sulfate surfactant provided faster initial polymerization rates, but steady-state conversions were faster with potassium laurate, especially at higher alpha-methylstyrene contents. This is ascribed to acceleration of potassium persulfate decomposition by the former soap. Monomer concentration in the polymerizing particles was constant during steady reaction rates. The rate of volume growth of particles during this interval was generally as predicted by theory. The number of particles and particle sizes could be predicted well if allowance was made for initiator wastage reactions. The observed average number of radicals per particle appeared to be 0.5. Analysis of the composition of monomer droplets and proton NMR analyses of copolymer compositions provided independent confirmations that the present emulsion copolymerization was consistent with the terminal copolymerization model.     

Kinetics of isothermal and non‐isothermal degradation of cellulose: model‐based and model‐free methods

BACKGROUND: The kinetics of the thermal decomposition of cellulosic materials is of interest from the viewpoint of flame retardancy for safety, optimization of incineration processes and reducing energy production from fossil sources and associated pollution. One essential step in these processes is the thermal degradation through mass and energy transport, which determines the rate of evolution of various types of products from cellulosic materials. RESULTS: Kinetic parameters have been determined using various model‐based and model‐free methods in the thermal degradation of cellulose up to 700 °C in helium atmosphere. The values of the activation energy obtained in isothermal processes and non‐isothermal processes have been found to be not far from each other. From the integral method, the random nucleation (F₁)‐type mechanism has been found most probable for cellulose degradation having an activation energy, E_a, in the range 156.5–166.5 kJ mol^?1, lnA = 20–23 min^?1, for first‐order reaction during its decomposition process at heating rates of 2, 5 and 10 °C min^?1. Based on the high correlation coefficient, many types of mechanisms seem equally good for non‐isothermal degradation of cellulose. CONCLUSION: The linear correlation coefficient has a limitation for verifying the correctness of a reaction mechanism in the study of degradation kinetics. Therefore, the correctness of a mechanism should be considered on the basis of comparing the kinetic parameters obtained from isothermal as well as non‐isothermal methods. Copyright © 2008 Society of Chemical Industry     

A 3‐D finite element model for gas‐assisted injection molding: Simulations and experiments

To gain a better understanding of the gas‐assisted injection molding process, we have developed a computational model for the gas assisted injection molding (GAIM) process. This model has been set up to deal with (non‐isothermal) three‐dimensional flow, in order to correctly predict the gas distribution in GAIM products. It employs a pseudo‐concentration method, in which the governing equations are solved on a fixed grid that covers the entire mold. Both the air downstream of the polymer front and the gas are represented by a fictitious fluid that does not contributeto the pressure drop in the mold. The model has been validated against both isothermal and non‐isothermal gas injected experiments. In contrast to other models that have been reported in the literature, our model yields the gas penetration from the actual process physics (not from a presupposed gas distribution). Consequently, it is able to deal with the 3‐D character of the process, as well as with primary (end of gas filling) and secondary (end of packing) gas penetration, including temperature effects and generalized Newtonian viscosity behavior.     

Copolymerizations initiated by mechano-radicals on particle surfaces of poly(tetrafluoroethylene)

Mechanical fracture of solid poly(tetrafluoroethylene) (PTFE) produces main-chain scissions of the polymer, and free radicals, called mechano-radicals, are trapped on fresh surfaces generated by the fracture. These radical conversions were verified by ESR observation when several monomers—methylmethacrylate, vinylacetate, and ethylene—were brought into contact with these mechano-radical, and the copolymerizations of PTFE with these monomers were demonstrated. It was found that a new surface property, wettability of water, was added to the solid PTFE by the copolymerization with vinyl acetate, although the bulk nature of PTFE was not changed.     

3‐D non‐isothermal flow field analysis and mixing performance evaluation of kneading blocks in a co‐rotating twin srew extruder

We have developed a three‐dimensional non‐Newtonian and non‐isothermal flow analysis of the twin screw extruder (TSE) using the finite element method. This code can simulate the fully filled parts of several kinds of screw elements, such as full flight screws, kneading blocks, rotors and their combinations. A marker particle tracking analysis has also been developed to evaluate the mixing performance of the screw elements. In this paper, simulations for the kneading blocks in a co‐rotating TSE were carried out. The screw configurations are combinations of 2‐lobe kneading blocks with several stagger angles and disk widths. The effects of screw configurations on pressure and temperature distributions are examined. We also evaluate the dispersive and distributive mixing via stress magnitude and area stretch obtained by marker particle tracking analysis. Additionally, we discuss the desirable stagger, disk width and their combinations that promote the mixing performance.     

Synthesis and polymerizations of novel bisphosphonate‐containing methacrylates derived from alkyl α‐hydroxymethacrylates

The synthesis and polymerizations of four novel bisphosphonate‐containing monomers are reported. The monomers were synthesized from reaction of ethyl and tert‐butyl α‐bromomethacrylates with 3,3‐bis(diethoxyphosphoryl)propanoic acid or with tetraethyl 4‐hydroxybutane‐1,1‐diyldiphosphonate. Their thermal bulk polymerizations, photopolymerizations and copolymerizations with poly(ethylene glycol) methyl ether methacrylate were investigated. The homopolymerizations resulted in polymers with values of 25 000–83 000 g mol^?1; the copolymerizations yielded soluble polymers with 22–34% incorporation of the new monomers; the photopolymerizations gave some structure–reactivity correlation; and one of the homopolymers, upon hydrolysis of its bisphosphonate groups, could interact with hydroxyapatite. © 2013 Society of Chemical Industry     

The SCOPE dynamic model for emulsion polymerization I. Theory

The SCOPE dynamic process model has been developed to treat batch and semibatch emulsion copolymerizations. This computer-based model treats jacketed reactors of arbitrary size. It consists of a coupled set of ordinary differential and algebraic equations that describe material balances for the reacting species and energy balances for both the reactor and the cooling water jacket. The model also includes a feature that allows for proportional integral derivative (PID) control of the monomer emulsion and cooling water feed rates to a reactor temperature set point. The model is based largely upon the kinetic theories developed by Smith, Ewart, and Harkins to treat emulsion homopolymerizations. The SCOPE model improves upon and expands the classic theories by taking advantage of recent theoretical developments in emulsion polymerization. Such phenomena as diffusion-controlled termination and radical desorption—important for predicting accurate polymerization rates—are included in the model. More modern theories of particle nucleation, including both homogeneous and micellar mechanisms, have been incorporated into the model to predict accurate particle size distributions. SCOPE also extends the classic theories to treat the emulsion copolymerization of an arbitrary number of monomers. Output from the model includes species concentrations, residual monomer levels, particle size distributions, molecular weight distributions, instantaneous and cumulative copolymer compositions, and reactor temperatures as a function of time. The SCOPE model can be used to evaluate various process control strategies and to study the effects of process dynamics on polymer properties. In Part II, SCOPE model predictions are compared with experimental data for styrene-methyl methacrylate copolymerizations.     

On helical flows of polymer fluids

Isothermal and non‐isothermal steady helical flows are theoretically investigated under the assumption that the flow is fully developed in both the thermal and hydrodynamic senses. It is well known that the basic gross characteristics of steady isothermal helical flows of non‐Newtonian liquids can be found relatively easily if the flow curve (or non‐Newtonian viscosity) in simple shearing is known. Nevertheless, evaluation of more detailed viscoelastic properties in this type of flow is also sometimes desirable. These properties are shown to be exactly determined in both the isothermal and non‐isothermal cases as soon as a nonlinear viscoelatic constitutive equation is specified. Shear thinning due to fluid rotation and strong temperature dependence of Newtonian viscosity highly increase dissipative heat. This can produce significant non‐isothermal effects in intense helical flows, even when the wall temperature is kept uniform and constant. It is shown that the energy consumption in isothermal and non‐isothermal helical flows is always higher than in respective annular flows with the same flow rate. Comparisons between our calculations and available experimental data are also discussed.     

Input Multiplicity Analysis in a Non‐Isothermal CSTR for Acid‐Catalyzed Hydrolysis of Acetic Anhydride

Multiplicity analysis gives practical guidance for process design to eliminate difficult operating regions associated with input and output multiplicities. Continuous stirred tank reactors (CSTRs) present challenging operational problems due to complex behavior such as input and output multiplicities, ignition/extinction, parametric sensitivity, and nonlinear oscillations. In the absence of a unified mathematical theory for representing various nonlinear system characteristics, the present study was aimed at understanding the dynamic behavior of CSTRs by means of experiments and to link the experimental data to theoretical considerations for further detection and elimination of operating problems. Theoretical modeling and analysis of a non‐isothermal CSTR with acid‐catalyzed hydrolysis of an acetic anhydride system for input multiplicity are discussed. Theoretical modeling of a non‐isothermal CSTR using a root‐finding technique was carried out for predicting steady‐state temperatures. Alternatively, a mathematical model for a non‐isothermal CSTR using unsteady‐state mass and energy balance equations is proposed. Computer‐based simulation was carried out using a program developed in MATLAB for final transient temperature and time‐temperature data of the CSTR system under investigation. The results of a theoretical analysis conducted for confirming the existence of input multiplicity in non‐isothermal CSTRs with acid‐catalyzed hydrolysis of acetic anhydride were compared with experimental investigations for validation.     

Three‐dimensional simulation of thermoforming process and its comparison with experiments

Three‐dimensional solid element analysis and the membrane approximated analysis employing the hyperelastic material model have been developed for the simulation of the thermoforming process. For the free inflation test of a rectangular sheet, these two analyses showed the same behavior when the sheet thickness was thin, and they deviated more and more as the sheet thickness increased. In this research, we made a guideline for the accuracy range of sheet thickness for the membrane analysis to be applied. The simulations were performed for both vacuum forming and the plug‐assisted forming process. To compare the simulation results with experiments, laboratory scale thermoforming experiments were performed with acrylonitrile‐butadiene‐styrene (ABS). The material parameters of the hyperelastic model were obtained by uni‐directional hot tensile tests, and the thickness distributions obtained from experiments corresponded well with the numerical results. Non‐isothermal analysis that took into account the sheet, temperature distribution measured directly from the experiments was also performed. It was found that the non‐isothermal analysis greatly improved the predictability of the numerical simulation, and it is important to take into account the sheet temperature distribution for a more reliable simulation of the thermoforming process.     

Thermal and kinetic study of radical polymerization I. Melt state bulk polymerization of acrylamide by DSC

Radical‐initiated bulk polymerization of acrylamide in the presence of potassium persulfate in the melt phase has been investigated by differential scanning calorimetry (DSC). The method presented here has been carried out in isothermal condition. This not only saves energy and time but also has some less probable side effects. Side effects such as evaporation and imidization could affect the final yield and properties of the obtained product. Different temperatures have been examined for isothermal polymerization to find out the optimum temperature with complete conversion of acrylamide to its corresponding polymer. During the polymerization process, high‐molecular‐weight polyacrylamide is being produced without any significant loss in total yield. The molecular weight was determined by inherent viscosity measurement. Also, no side reaction such as imidization resulting in partial insolubility or crosslinked product was being observed. It is noteworthy that we believe DSC studies show the existence of living radicals that has not been reported before. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2335–2340, 2003     

Reversible chain transfer catalyzed polymerization (RTCP): A new class of living radical polymerization

This article introduces the new family of living radical polymerizations with germanium (Ge), tin (Sn), phosphorus (P), and nitrogen (N) catalysts which we recently developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity polymers are obtained in the homopolymerizations and random and block copolymerizations of styrene, methyl methacrylate, and functional methacrylates. The background, performance, and kinetic features of the polymerizations are described. Attractive features of the catalysts include their high reactivity, low toxicity (Ge, P, and N), low cost (P and N), and ease of handling (robustness).     

Solution and solid-state polymerizations of substituted p-quinodimethanes and p-quinone methides

This article describes the polymerization behavior of electron-accepting and electron-donating p-quinonoid monomers such as substituted p-quinodimethanes and p-quinone methides in solutions and solid states. In the solution polymerizations, the electron-accepting substituted p-quinodimethanes and p-quinone methides with same substituents such as cyano, ester, and sulfonyl groups at the exocyclic positions are not homopolymerizable, but copolymerizable with donor monomers like styrene in an alternating fashion. Their spontaneous polymerizations with donor monomers have been explained with the bond-forming initiation mechanism. The substituted p-quinodimethanes with ester groups are a first example to show an amphoteric behavior in alternating copolymerizations. Some electron-accepting substituted p-quinodimethanes and p-quinone methides with different substituents such as cyano, ester, acyl, alkylthio, and/or phenyl groups are homopolymerizable, and an anionic polymerization initiated with a butyllithium initiator proceeded in a living manner. Equilibrium polymerization behavior have been found in their radical homopolymerizations, and on the basis of the thermodynamic parameters determined for their polymerizations, it has been concluded that homopolymerizabilities of the electron-accepting substituted p-quinodimethanes and p-quinone methides are determined exclusively by a steric hindrance effect arising from the substituents at the exocyclic positions. A new concept for the radical alternating copolymerization have been proposed on the basis of the change in modes (random and alternating copolymerizations) for their copolymerizations with styrene and the cross-propagation step analysis by linear free energy relationship. The polymerizations of the electron-donating substituted p-quinodimethanes take place only in the presence of oxygen molecules. In the solid-state polymerizations, some electron-accepting substituted p-quinodimethanes with same ester substituents polymerized topochemically in vacuo, and the strict requirements of topochemical polymerization for substituted p-quinodimethane and p-quinone methide monomers have been determined on the basis of their crystallographic data. Topochemical alternating copolymerization with molecular oxygen in solid state was discovered for the first time.     

Modelling of emulsion copolymer microstructure

A model has been developed to describe stages II and III of batch emulsion copolymerization, and its predictive capabilities have been investigated by application to the system styrene-methyl acrylate. The main reaction site is considered to be the monomer-swollen polymer particle. Copolymerization rate and copolymer microstructure (molar-mass-chemical-composition distribution and sequence distribution at the triad level) are controlled by the local concentrations of monomers and free radicals inside the particles. The model accounts for radical absorption and desorption processes, bimolecular termination within the particles, and transfer to monomer and chain transfer agent. Monomer partitioning is described using experimentally determined relations. The results include rate of (co)polymerization. composition drift and copolymer microstructure. It is demonstrated that ‘apparent’ reactivity ratios are generally incapable of describing the course of emulsion copolymerizations in an adequate manner.     

Polymer crystallization kinetics,master quotients,master curves and Nakamura‐Ozawa‐equations of iPP and PTFE

Evaluation concepts related to Avrami master curves are described for the analysis of isothermal and non‐isothermal kinetic processes exhibiting topological nucleation and growth characteristics. These evaluation concepts are shown to be helpful for studies focusing on kinetic data of polymer crystallization experiments with iPP (isotactic polypropylene) and PTFE (polytetrafluoroethylene). An apparent m‐order reaction model is discussed with respect to the isokinetic nucleation and growth model of Nakamura as well as to the non‐isothermal crystallization kinetics theory of Ozawa. Thus, the cooling functions χ(T) of iPP and PTFE, obtained by analyzing DSC (differential scanning calorimetry) experiments with constant cooling rates, are calculated in two alternative ways by using clearly different mathematical approaches. Finally, master quotients, theoretical crystallization limits, and further types of master curves are defined. Polym. Eng. Sci. 44:2194–2202, 2004. © 2004 Society of Plastics Engineers.     

A systematic study of tert-butylacrylamide-methyl acrylate-acrylic acid radical solution terpolymerization

Multi-functional polymers used for personal care products can be synthesized by radical polymerization of acrylic acid (AA) in alcohol/water solutions with non-functional monomers such as methyl acrylate (MA) and N-tert-butylacrylamide (t-BuAAm). However, solvents capable of forming or disrupting hydrogen bonds cause the polymerization kinetics of these monomers to deviate from their polymerization behaviour in bulk and non-polar solvents. In this work, a previous mechanistic model developed for MA/t-BuAAm copolymerization is extended to represent the terpolymerization system MA/t-BuAAm/AA. The additional kinetic coefficients required for the system are estimated from fitting to AA homopolymerizations and AA/MA and AA/t-BuAAm copolymerizations conducted in an ethanol/water solution. In-situ nuclear magnetic resonance (NMR) spectroscopy is used to follow monomer conversions and composition drift behaviour, with the molar mass distributions of the polymer products characterized by size-exclusion chromatography. Although AA is more reactive than MA in non-polar solvents, the reactivities of the two monomers equalize under the experimental conditions examined. Thus, the batch and semi-batch terpolymerization data collected are represented equally well by a reduced acrylate/t-BuAAm copolymerization model and the full terpolymerization implementation.     

Styrene/Methacrylic Acid Monomer Reactivity Ratio Estimation in Bulk and Solution at High Temperatures

Abstract:

Styrene/methacrylic acid (Sty/MAA) free radical copolymerizations have been conducted in bulk and in m-xylene solution (60 wt% solvent level) at 100 and 130°C using tert-butyl peroxybenzoate as initiator. Monomer reactivity ratios and their temperature dependence have been determined from low conversion copolymer composition data using the computer software package RREVM, which is based on the error in variables model (EVM) method. It was found that the reactivity ratio values change with dilution by m-xylene from the values obtained in bulk at both temperatures.     

On‐line optimizing control of bulk polymerization of methyl methacrylate: Some experimental results for heater failure

An experimental unit has been assembled to carry out on‐line optimizing control of the bulk polymerization of methyl methacrylate (MMA). A rheometer‐reactor assembly is used. Temperature and viscosity measurements are used to describe the state of the system. The polymerization is carried out under an off‐line computed optimal temperature history, T_op(t). A planned disturbance (heating system failure) is introduced at time t₁. This disturbance leads to a fall in the temperature of the reaction mass. A new optimal temperature history, T_reop(t), is re‐computed on‐line and is implemented on the reaction mass at time t₂, when the heating is resumed. This procedure helps ‘save the batch’. A genetic algorithm is used to compute this reoptimized temperature history in a short period of ～2 min of real time. The feasibility of the on‐line optimizing control scheme has been demonstrated experimentally. Replicable results for the viscosity history, η(t), of the polymerizing mass under several non‐isothermal conditions have been obtained. These experimental results are quite trustworthy, even though the model predictions are only in approximate agreement with them, perhaps because of the extreme sensitivity of results to the values of the model parameters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2350–2360, 2002     

Cure kinetics modeling and process optimization of the vialux 81 epoxy photodielectric dry film (PDDF) material for microvia applications

The cure kinetics of a photodielectric dry film (PDDF) material called ViaLux 81 has been studied, with the aim of understanding and optimizing its curing schedule for the fabrication of sequentially built‐up (SBU) high‐density‐interconnect printed wiring boards (HDI‐PWB). Initial dynamic differential scanning calorimetry (DSC) scans on the material revealed a two‐stage curing mechanism due to the long lifetime of the photoinitiator catalyst, which could not be separated at lower heating rates. On the other hand, the heat flow exotherm from isothermal DSC experiments showed a rapid reaction rate at the beginning with only a single peak. Therefore, to capture the complexity of the process, the faster multiple heating rate DSC experiments are used to predict the degree‐of‐cure (DOC) evolution. Two approaches have been developed based on the dynamic DSC data: (1) a “model‐free” approach, which only requires information about the cure‐dependence of the activation energy; and (2) a practical scheme to deconvolute the two curing peaks. Excellent agreement is observed for the heating rate experiments, but the methods are inadequate for predicting the DOC evolution under isothermal conditions. Therefore, a modified autocatalytic model with temperature‐dependent kinetic parameters has been developed based on the isothermal DSC data. This model predicts the DOC evolution for isothermal curing profiles very well. However, some discrepancy is evident in predicting the DOC evolution for heating rate experiments, due to the underestimation of the activation energy. With appropriate corrections, excellent predictive capability is illustrated for complex cure schedules with combined heating rate and isothermal segments. In addition, a cure process optimization strategy has been suggested, and the fabrication of fine features and microvias is demonstrated. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 691–700, 2002; DOI 10.1002/app.2345