Free Radical Bulk Polymerization Research Articles

Empirical models for viscosity variation in bulk free radical polymerization

The validity of the Lyons-Tobolsky equation for bulk polymerization systems was verified by comparing simulation results to experimental data for different reaction conditions (temperature and initiator concentration). In this model, formerly applied for solution polymerization, the viscosity of the reaction mass was used instead of solvent viscosity. For example, the chemically initiated free radical polymerization of methyl methacrylate was considered to be achieved in a batch bulk process. In the Lyons-Tobolsky equation, the viscosity was calculated using the values of the conversion and molecular weight resulting from the kinetic model simulation. Consequently, a general discussion about the concordance between the simulation and experiment was useful, especially to emphasize the causes that generate modeling errors. It is more convenient to estimate the viscosity independently of conversion and molecular weight and, in this way, without solving the kinetic model. Empirical relations which correlate viscosity with time were elaborated using experimental viscosity data. Two kinds of models were proposed: a) two fifth order polynomials corresponding to the conversion domains before and after the gel effect; b) a model that fits the experimental data well in the whole conversion domain. Generally, these empirical models provide good simulation results and they can be easily handled.

Characterization of Drug Release and Diffusion Mechanism Through Hydroxyethylmethacrylate/Methacrylic Acid pH-Sensitive Hydrogel

Hydroxyethylmethacrylate/methacrylic acid copolymer cross-linked with ethylenglycol dimethacrylate was prepared by a bulk free radical polymerization method. The permeability studies of this pH-sensitive hydrogel to drugs with different water solubilities showed a water-content dependent diffusion or pore mechanism for ephedrine HCl (water-soluble model drug), whereas, a partition or solute-diffusion mechanism for indomethacin (a water-insoluble drug) was seen. Data analysis of release tests, according to the swelling interface number and Peppas equation for ephedrine HCl in pH 7.4, showed a biexponential model kinetic, whereas in pH 1.2 a swelling-controlled mechanism was seen. Indomethacin was released by an anomalous or non-Fickian release kinetics.

Modelling and Simulation of Complex Aspects of Multicomponent Emulsion Polymerization

The focus of this work is the refinement of a general mechanistic simulator for multi‐component free radical emulsion polymerization. The effort includes three main areas of simulator development, namely, model development, database development and simulator verification. The model is general and can predict the dynamic evolution of emulsion polymerizations for a variety of monomer systems while giving the user as many “model options” as possible for fine tuning. The model has been extensively tested for several copolymerization systems including combinations of the monomers, styrene, methyl methacrylate, methyl acrylate, butyl acrylate, acrylonitrile, 2‐ehtyl hexyl acrylate and vinyl acetate. The simulator has been developed using a mechanistic framework that is analogous to the multicomponent free radical bulk and solution polymerization model developed in Gao and Penlidis (1996&1998) and is a continuation of Gao and Penlidis ([2002]), which explored emulsion homopolymerization and preliminary copolymer...

Application of Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry in Pulsed Laser Polymerization. Chain-Length-Dependent Propagation Rate Coefficients at High Molecular Weight: An Artifact Caused by Band Broadening in Size Exclusion Chromatography?

The combination of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS) and size exclusion chromatography (SEC) combined with pulsed laser polymerization has been used to evaluate propagation rate coefficients (kp) in bulk free-radical polymerization for the systems methyl methacrylate and styrene. By varying laser frequencies, the relation between polymer chain length and observed propagation rate coefficient ( ) has been investigated in detail. It has been found that deviations between MALDI-ToF-MS and SEC at higher molecular weights are the result of instrumental effects in SEC. Moreover, using a model and taking into account experimental studies on the propagation of oligomeric species, it has been inferred that the relationship between and polymer chain length is the result of chain-length-dependent behavior of the true kp in the oligomeric range, therewith excluding any chain-length-dependent behavior at higher molecular weights.

Free Radical Bulk Polymerization of Styrene: Simulation of Molecular Weight Distributions to High Conversion Using Experimentally Obtained Rate Coefficients

AbstractPreviously obtained experimental conversion‐dependences of the propagation rate coefficient (kp), the termination rate coefficient (kt) and the initiator efficiency (f) for the free‐radical bulk polymerization of styrene at 70 °C have been used to simulate the full molecular weight distributions (MWD) to high conversion using the software package PREDICI, providing a robust test of the kinetic model adopted. Satisfactory agreement with the experimental MWD's (GPC) was obtained up to approximately 70% conversion. Beyond 70% conversion, the high MW shoulder that appears was correctly predicted, although the amount of such polymer was somewhat underestimated. This discrepancy is believed to probably have its origin in experimental error in the conversion‐dependences of kp, kt and f, in particular kt, that were employed in the simulations, rather than indicate a more fundamental short‐coming of the model employed.image

Injectable polymeric microspheres with X-ray visibility. Preparation, properties, and potential utility as new traceable bulking agents.

The copolymer of methyl methacrylate (MMA) and 2-[2',3',5'-triiodobenzoyl]oxoethyl methacrylate (1), ratio 3:1 (mass:mass), was prepared via a free-radical polymerization in bulk. The copolymer (M(w) = 97.8 kD and M(n) = 41.5 kD) was dissolved in chloroform and subsequently transformed into beads with a diameter in the micrometer range, using a solvent evaporation technique. The resulting microbeads were characterized by different techniques, including NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and scanning electron microscopy. The latter technique was used as the basis for statistical analysis of the bead size. Typically, an average diameter of 96 microm and a standard deviation of 21 microm were obtained. The beads were also subjected to some preliminary tests regarding cytotoxicity. The copolymer of MMA and 1 contains covalently bound iodine. Therefore, the material is intrinsically radiopaque, i.e., capable of absorbing X-radiation while no contrast additive is needed. Our interest in these microspheres stems primarily from their possible utility as injectable and afterward traceable (radiopaque) bulking agents, e.g., for use in urology for the treatment of female stress incontinence due to sphincter deficiency. As a first test into this direction, a sample of the microbeads was mixed with ethylene glycol, and the resulting suspension was studied with respect to injectability and radiopacity. The results suggest that the radiopaque microbeads may provide access to improved bulking agents. Further modification of the surface may be necessary in order to suppress the migratory aptitude of the radiopaque polymeric microspheres in vivo.

Scale-Up of Polymerization Process: A Practical Example

The scale-up/-down of polymerization reactors has to deal with large viscosity changes during the process, addressing mass- and heat-transfer issues. A practical example on scale-up of styrene and methyl methacrylate free radical bulk and solution polymerization is presented. The main critical parameters are mixing at molecular level (micromixing) and heat removal capacity. The operating parameters being kept constant are: reaction conditions (temperature, pressure, chemistry) and thus the reaction time. A pilot plant issued from scale-down of possible industrial sizes was developed to represent, at best, larger scales. The main parameter being scaled-up is the heat removal capacity, which has to be maintained constant among the different sizes. New concepts are adapted to dissipate the mixing energy where it is the most suitable, and the final step is the scale-up/-down strategy. Another issue addressed in this contribution is the need for in-line analytics that could operate at different plant scales and thus give important information for process control. Scale-up/-down strategy must include the whole process, not only the reaction stage but also what happens before, after, and simultaneously, i.e., upstream, downstream, and peripheral operations. Finally the measurable success of a scale-up/-down analysis could only be proved at industrial scale, where a good agreement between pilot- and larger scale should be observed. The concepts in terms of transfer phenomena, analytics, separation, product properties, feasibility, and economics should also be included in this analysis.

Easy Access to Chain-Length-Dependent Termination Rate Coefficients Using RAFT Polymerization

Chain-length-dependent termination rate coefficients of the bulk free-radical polymerization of styrene at 80 °C are determined by combining online polymerization rate measurements (DSC) with living RAFT polymerizations. Full kt versus chain-length plots were obtained indicating a high kt value for short chains (2 × 109 L · mol−1 · s−1) and a weak chain-length dependence between 10 and 100 monomer units, quantified by an exponent of −0.14 in the corresponding power law 〈kti,i〉 = kt0 · P−b. Double logarithmic plots of 〈kti,i〉 versus P, evaluated from experimental time-resolved Rp data according to the procedure described in the text, for different CPDA and AIBN concentrations. The best linear fit for (10 < P < 100) is indicated as full line.

Free radical bulk polymerization in cylindrical molds

AbstractBulk styrene homopolymerization in cylindrical molds was studied in order to simulate the reactive injection process when the reaction kinetics was much slower than the filling process. Mathematical models were built and implemented, allowing the analysis of certain kinetic phenomena, such as the gel‐effect, and the relevance of natural convection. Based on a detailed kinetic mechanism, the polymer properties (average molecular weight and polydispersity) and monomer conversion were calculated as functions of spatial coordinates and time. The results obtained show that polymer properties and monomer conversion may be very heterogeneous inside the cylindrical mold, although insensitive to variations of the diffusion coefficient, so that defects are expected to appear as a consequence of the heterogeneity of polymer properties inside the mold. Experiments confirmed the simulation results. Simulations indicate that heterogeneities may be expected to increase when the reaction rates are one order of magnitude higher, as in acrylic acid polymerizations.

Investigation of microstructure of the N‐vinyl‐2‐pyrrolidone/methyl methacrylate copolymers by NMR spectroscopy

AbstractThe copolymers containing N‐vinyl‐2‐pyrrolidone (V) and methyl methacrylate (M) units of different compositions were synthesized by free radical bulk polymerization. The copolymer composition of these copolymers was determined by CHN analysis. The distortionless enhancement by polarization transfer (DEPT) technique was used to resolve the methine, methylene, and methyl resonance signals in the V/M copolymer. Comonomer reactivity ratios were determined by the Kelen–Tudos (KT) and nonlinear least‐square error‐in‐variable (EVM) methods. 1H–13C Heteronuclear shift quantum correlation spectroscopy (HSQC) and 1H–1H homonuclear total correlation spectroscopy (TOCSY) spectra were used for the resolution of the proton nuclear magnetic resonance (1H NMR) spectrum of the V/M copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1328–1336, 2002

Selection of optimal process analyzers for plant-wide monitoring.

In this paper, the effect of process analyzer selection and positioning on plant-wide process monitoring is investigated. A fundamental problem in process analytical chemistry is the incomparability of different instrument characteristics. A fast but imprecise instrument is incomparable to a slow but precise instrument. Theory is developed to overcome this problem by using an abstract definition of a process analyzer. This definition allows us to put all instrument characteristics for a particular monitoring task on an equal footing. This results in a measurability factor M that expresses monitoring performance of any process measurement by combining instrument characteristics such as precision, sampling rate, grab size, response correlation, and delay time. Both the choice of location and the performance characteristics of different process analyzers can be evaluated using the measurability factor. The unifying nature of the measurability factor allows for a rational decision between completely different process analyzers and locations (Smilde et al., in this issue). The theory is illustrated and validated with an experiment. A tubular reactor for free-radical bulk polymerization of styrene is monitored by in-line short-wave near-infrared spectroscopy at different positions. Alternatively, product samples are collected for at-line near-infrared analysis. Both analyzers measure styrene monomer concentration. The analysis results are used to predict conversion as well as number and weight average molecular mass of the polystyrene reactor product. The theoretical measurability factors for this case study correspond well with the experimental findings.

Microstructure analysis of N‐vinyl‐2‐pyrrolidone/vinyl acetate copolymers by NMR spectroscopy

AbstractN‐Vinyl‐2‐pyrrolidone (V) and vinyl acetate (A) copolymers of different compositions were synthesized by free radical bulk polymerization. The copolymer composition of these copolymers was determined using quantitative 13C{1H} NMR spectra. The reactivity ratios for these comonomers were determined using the Kelen–Tudos (KT) and non‐linear least‐square error‐in‐variable (EVM) methods. The reactivity ratios calculated from the KT and EVM methods are rV = 2.86 ± 0.16, rA = 0.36 ± 0.09 and rV = 2.56, rA = 0.33, respectively. 1H, 13C{1H} and 1H–13C heteronuclear shift correlation spectroscopy (HSQC) and 1H–1H homonuclear total correlation spectroscopy (TOCSY) were used for the compositional and configurational assignments of V/A copolymers. The 13C distortionless enhancement by polarization transfer (DEPT) technique was used to resolve the methine, methylene and methyl resonance signals in the V/A copolymers.© 2002 Society of Chemical Industry

Modeling of the bulk free radical polymerization up to high conversion—three stage polymerization model. II. Number-average molecular weight and apparent initiator efficiency

The equations for predicting the number-average molecular weight are derived on the basis of the three stage polymerization model (TSPM) in this paper. By applying the equations, a plotting approach is proposed to determine the apparent initiator efficiency defined as f[( α td+1)/2] and the constant of chain transfer to monomer, where f is the initiator efficiency and α td denotes the fraction of the termination rate constants by disproportionation. Using the approach to plot the experimental data in the literature, it is found that the chain transfer to monomer can be neglected for both methylmethacrylate (MMA) and styrene (St) polymerizations, but it can exert a significant effect on ethylmethacrylate (EMA) polymerization. In addition, the apparent initiator efficiency is found to be independent of reaction temperature and initiator concentration at each stage. The values of f[( α td+1)/2] at gel effect stage are slightly reduced as compared with that at low conversion stage for MMA and EMA polymerizations. However, it decreases significantly at gel effect stage for St polymerization. Using the equations derived and the apparent initiator efficiencies obtained from TSPM plots, the number-average molecular weights at different conversions can be predicted. Comparisons show that the agreement between predictions and experimental data is satisfactory.

Termination Rate Coefficient of Dimethyl Itaconate: Comparison of Modeling and Experimental Results

The termination kinetics of dimethyl itaconate (DMI) in bulk free radical polymerization at 40 °C have been studied by both experimental and theoretical approaches. The chain length distributions obtained from pulsed laser polymerization experiments have been analyzed in combination with rate measurements to extract chain length dependent termination rate coefficients. The full chain length distributions were modeled using a comprehensive kinetic scheme with both experimentally determined and adjustable kinetic parameters. The chain length average termination rate coefficient, kt, was found to be close to 5.5 × 105 L mol-1 s-1. Termination occurs almost exclusively via disproportionation. Such low kt values are typical for sterically hindered monomers. The chain length dependence associated with the termination rate coefficient is almost negligible. The reasons for the very weak chain length dependence may be due to the solvent quality of the monomer toward its own polymer or due to the rigid structure of the formed polymer chains, therefore preventing the formation of a statistical coil.

STUDY OF THE EFFECT OF TWO BPO/AMINE INITIATION SYSTEMS ON THE FREE-RADICAL POLYMERIZATION OF MMA USED IN DENTAL RESINS AND BONE CEMENTS

ABSTRACT The kinetics of the free radical bulk polymerization of methyl methacrylate (MMA) was studied by DSC, using the benzoyl peroxide (BPO)/amine initiation system. N,N dimethyl-4-aminophenethyl alcohol (DMPOH), which is a newly synthesized and used amine in the preparation of acrylic dental resins and bone cements was examined, and the results compared to the most commonly used in these applications amine, the N,N dimethyl-p-toluidine (DMT). For both amines, the effect of the molar ratio of BPO/amine and of the reaction temperature, on the polymerization kinetics was investigated. The prepared polymers were characterized by determination of the average molecular weights (M¯ n and M¯ w ) and molecular weights distribution (M¯ w /M¯ n ) using Gel Permeation Chromatography. DMPOH was found to lead in slightly higher polymerization rates, lower gel times and lower molecular weights than DMT. The values of these parameters for both amines were influenced by the molar ratio of BPO to amine, when the product of the concentrations of these was kept constant. The highest polymerization rate occurred in the lowest gel time, resulting in polymers with the lowest molecular weight, and was observed when a molar ratio of about 1.5 BPO/amine was used. However, the final monomer conversion was found to be independent of the molar ratio and amine used. The activation energy of polymerization was found to be 51.8 kJ/mol K for BPO/DMPOH and 47.1 kJ/mol K for BPO/DMT.

Modeling of the bulk free radical polymerization up to high conversion—three stage polymerization model I. Model examination and apparent reaction rate constants

In this paper, a simple and useful model, the three stage polymerization model (TSPM) is proposed on the basis of recent experimental evidence and our preliminary treatment of the experimental kinetic results found in the literature. The model accounts for gel effect and glass effect in bulk free-radical polymerization. Equations for calculating the conversion of the polymerization reaction are derived based on TSPM. Using experimental kinetic data available in the literature, general expressions for apparent reaction rate constants in three stages for methylmethacrylate (MMA) and styrene (St) are obtained. In general, the experimental kinetic data can be treated very well with the TSPM from the low conversion stage to high conversion, except for some experimental data near the transition points. However, the deviation for this data may be reasonably explained by the non-isothermal effects that occur in this regime of experiments. This deviation is smaller for a smaller ampoule reactor used in polymerization experiments because of its better heat transfer ability. In order to establish that there is no glass effect stage when the reaction temperature is greater than the glass transition temperature for a polymerization process, some experimental data for ethylmethacrylate (EMA) bulk polymerization at a reaction temperature higher than its glass transition temperature were checked with TSPM. The plots show that the model is also suitable for EMA bulk polymerization.

High-Conversion Free-Radical Bulk Polymerization of Styrene: Termination Kinetics Studied by Electron Spin Resonance, Fourier Transform Near-Infrared Spectroscopy, and Gel Permeation Chromatography

The free-radical bulk polymerization of styrene initiated by dimethyl 2,2‘-azobisisobutyrate at 70 °C has been studied employing the techniques of Fourier transform near-infrared spectroscopy, electron spin resonance spectroscopy and gel permeation chromatography. The initiator efficiency (f) as a function of monomer conversion was estimated via an equation relating the instantaneous and the cumulative number average degrees of polymerization. The result was subsequently employed to calculate the conversion dependence of the termination rate coefficient (kt) from zero to the limiting conversion for different initiator concentrations. Over the course of the reaction, kt decreases by 5 orders of magnitude (107−102 M-1 s-1). At conversion levels approaching the limiting value, kt shows a marked dependence on initiator concentration; higher initiator concentration shifts the kt vs conversion curves toward higher conversion levels. The reaction diffusion constant was found to decrease with increasing conversion in the high-conversion regime.

Kinetic Model of a Methacrylate-Based Monolith Polymerization

Monolithic stationary phases are becoming more and more important in the field of liquid chromatography, because they enable extremely fast separations. Methacrylate-based monoliths are produced via a free-radical bulk polymerization of glycidyl methacrylate and ethylene dimethacrylate using a benzoyl peroxide as an initiator. Preparation of large monoliths represents a big problem because of the heat release during the polymerization, which consequently leads to the distortion of the structure. A closer investigation of the polymerization, using differential scanning calorimetry, was performed in order to determine global kinetic parameters. A multiple heating rate method, based on the work of Ozawa, Flynn, and Wall, was applied for estimation of the values of the apparent activation energy, preexponential factor, and reaction order. Global polymerization kinetics is of first order with A = 1.681 × 10 9 s -1 and E a,app = 81.5 kJ/mol, where the heat of polymerization is approximately 190 J/g. In addition, the influence of air and nitrogen atmosphere on polymerization is presented.

Spontaneous Polymerization in the Emulsion Polymerization of Styrene and Chlorobutadiene

Spontaneous initiation in emulsion polymerization may be more important: than in the corresponding bulk free-radical polymerization. A methodology is derived for finding the locus of spontaneous polymerization in emulsion polymerization, through use of spin traps and catalysts which can accelerate decomposition of peroxides. Applying this to both styrene and chloroprene (chlorobutadiene), it is found that this generation occurs to some degree within all phases present. The rate of spontaneous initiation is relatively small in styrene emulsion polymerization but large in chloroprene. A means of including this effect in modeling rates and molecular weight distributions is derived, which also shows how rate parameters for the process may be obtained from experimental molecular weight distributions. This methodology is applied to these two monomers, with a series of seeded emulsion polymerizations using polystyrene host seeds for both. For styrene polymerization, the spontaneous initiation rate is low and varies with latex preparation; consistent values for this rate coefficient for a given latex are obtained by independent measurements involving two different techniques, thereby verifying the methodology. Applying this methodology to chloroprene, it is found that the effect of spontaneous initiation is much larger and probably arises from peroxides formed by exposure to oxygen. For chloroprene, spontaneous radical generation occurs both within the particles and in any monomer droplets present, with different chain-stopping mechanisms occurring in these two phases. It is a major influence on rates and molecular weight distributions, even in the presence of large amounts of added initiator; chain stoppage in droplets is largely by transfer to monomer, whereas chain stoppage within particles is by termination with short radicals formed by spontaneous initiation. Arrhenius parameters for the rate coefficient for transfer to monomer are obtained from the molecular weight distributions for the chloroprene system: k(tr)/dm(3) mol(-1) s(-1) = 10(4.3) exp(-30.9 kJ mol(-1)/RT).

Investigation of free radical polymerization using diperoxyesters as bifunctional initiators

An experimental investigation and a detailed kinetic model of the bulk free radical polymerization of styrene initiated by diperoxyester initiators are presented. The experiments were conducted through the full conversion range at various temperatures and initiator concentrations. It is shown that the employing of such initiators leads to the formation of polymers having substantially higher molecular weight and narrower molecular weight distribution than those obtained by the conventional monofunctional initiators. The current investigation has also found that high monomer conversion and high molecular weight can be obtained simultaneously within a reduced reaction time period. Model predictions were compared with experimental data and were found to be in agreement.