Kinetics Of Radical Polymerization Research Articles

Simulation of styrene free radical polymerization over bi-functional initiators using Monte Carlo simulation method and comparison with mono-functional initiators

In the present study, based on a complete mechanism, a Monte Carlo simulation method is employed to investigate the kinetics of styrene free radical polymerization over bi-functional initiators in a bulk medium. The effects of the concentration of initiator and the monomer, of the temperature on monomer conversion, average molecular weights, polydispersity index, and molecular weight distribution are inspected and compared with mono-functional initiators. According to the simulation results, an increase in either the concentration of initiator or the temperature leads to the rise of the monomer conversion and to the reduction of the average molecular weights, while the increase of the monomer concentration results in the rise of both monomer conversion and molecular weights, which is in accord with predictions of the theory of free-radical polymerization. In addition, application of bi-functional initiators increases both monomer conversion and average molecular weight and results in narrower chain length distributions.

Kinetics of Nitroxide Mediated Radical Polymerization of Styrene with Unimolecular Initiators

AbstractSummary: This study examined the kinetics of nitroxide‐mediated radical polymerization of styrene with unimolecular (alkoxyamine) initiators. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide‐mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and initiator molecular weight on polymerization rate, molecular weight and polydispersity. In addition, the behavior of the unimolecular initiating systems was compared to that of the corresponding bimolecular system. The effective TEMPO concentration and degree of self‐initiation of styrene were proved to be significant in dictating magnitudes of molecular weight averages and widths of molecular weight distribution.

Role of Chain Transfer Agents in Free Radical Polymerization Kinetics

This study deals with modeling the propagation and the chain transfer reactions in the free radical polymerization of ethylene, methyl methacrylate (MMA), and acrylamide (AM). The chain transfer agents modeled in the free radical polymerization of ethylene are the experimentally widely used species such as ethylene, methane, ethane, propane, trimethylamine, dimethylamine, chloroform, and carbon tetrachloride. The role of 4-X-thiophenols as chain transfer agents in the polymerization of MMA and AM has been investigated. Geometry optimizations have been carried out with the B3LYP/6-31+G(d) methodology. Reaction rate constants are calculated via the standard transition-state theory with the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d), MPWB1K/6-311+G(3df,2p)//B3LYP/6-31+G(d), and M05-2X/6-311+G(3df,2p)//B3LYP/6-31+G(d) methodologies, which reproduce qualitatively the experimental trends for the chain transfer rate constants. The usage of simple continuum models with the MPWB1K/6-311+G(3df,2p)//B3LYP/6-31+G(d) meth...

Kinetics of Solution Polymerization and Seed Polymerization of 2-[p-(1,1,3,3-Tetramethyl-Butyl) Phenoxy-Polyethoxy] Ethyl Methacrylate Macromonomers

Macromonomers are convenient means for introducing a functional group to a produced polymer. Amphiphilic polymer particles having a 2-[p-(1,1,3,3-tetramethyl-butyl) phenoxy-polyethoxy] ethyl group are a good support of an immobilized enzyme for use in enzymatic reactions in an organic solvent. To synthesize the amphiphilic polymer particle, an amphiphilic methacrylic monomer (MAX-n) having a 2-[p-(1,1,3,3-tetramethyl-butyl) phenoxy-polyethoxy] ethyl group has been synthesized and polymerized. The radical polymerization kinetics of MAX-n in solution polymerization and seed polymerization were then studied. In solution copolymerization of styrene and MAX-n, when the number n of the ethylene oxide units is high, the steric hindrance of the side chain of MAX-n results in a low propagation rate constant and a high monomer reactivity ratio. In seed polymerization, using the kinetic parameter obtained in solution polymerization and the experimentally measured value of mass fraction of polymer at which the glass transition occurred, the time course of conversion of the seed copolymerization of MAX-n and styrene were simulated.

Copolymers Obtained by ε-Caprolactam and Methyl Methacrylate Polymerization in the Presence of Polyimides

New copolymers have been synthesized by anionic or radical photopolymerization of ε-caprolactam or methyl methacrylate (MMA) in the presence of dissolved polyimides bearing hexafluoroisopropylidene, fluorene or other groups. Using diimides as models it was shown that the kinetics of anionic polymerization of ε-caprolactam depends on the nature of spacer between the imide cycles. The mechanical and tribological properties of copolymers, their water absorbance and the microstructure of copolymer films were studied. It was found that upon the selection of polyimide activator it was possible to gain the desirable control over the polymer properties, namely, the gel fraction content, phase composition, compression modulus, notched Izod impact strength, friction coefficient and temperature of frictional contact. The kinetics of radical polymerization of MMA in the presence of polyimide and model diimide has been studied by differential scanning photocalorimetry and infrared spectroscopy. From the results of the reaction kinetics and the study of polymer structures by Fourier transform infrared spectroscopy, nuclear magnetic resonance, size-exclusion chromatography and thermogravimetric analysis it has been established that radical photopolymerization of MMA in the presence of polyimide leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. It has been established that the imide cycles play a significant role in the formation of both copolymers with ε-caprolactam and MMA, respectively.

Predictive control and verification of conversion kinetics and polymer molecular weight in semi-batch free radical homopolymer reactions

Polymer molar mass distributions critically affect macroscopic characteristics and performance of polymeric materials. While multi-detector methods coupled to size exclusion chromatography (SEC) are widely used to measure endproduct mass distributions, less progress has been made in simultaneously controlling and verifying the evolution of these distributions during synthesis. This work focuses on quantitative predictions and online verification of conversion kinetics and of molecular weight during free radical homopolymerization of acrylamide, where reagents were fed into the reactor during the reaction. The central task is to establish and experimentally test a formalism combining free radical polymerization kinetics with time dependent processes related to flows of material into and out of the reactor. Monomer feed experiments were performed that alternately hold molecular weight constant and ramp the weight up, in contrast to batch reactions, where molecular weight decreases. Three types of initiator feed ‘tapers’ were also used to produce predictable conversion kinetics and mass distributions: (i) constant initiator feed, (ii) linearly stepped feed to produce Gaussian conversion kinetics, and (iii) booster shots to produce multi-modal masses. Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) was used to follow the conversion and evolution of the average mass distribution, and multi-detector SEC was used to cross-check results and measure full distributions of endproducts. In general, there was good agreement between the predictions and results. In future work this approach can be used as an Ansatz for reaction trajectory prediction, and the online monitoring signals exploited to make feedback controlled corrections to the reagent flows and other reaction conditions.

Compartmentalization in Atom Transfer Radical Polymerization of Styrene in Dispersed Systems: Effects of Target Molecular Weight and Halide End Group

Compartmentalization effects on the kinetics of the atom transfer radical polymerization (ATRP) of styrene employing polystyrene-X/CuX/4,4′-dinonyl-2,2′-dipyridyl (dNbpy) (X = Br or Cl) in a dispersed system at low conversion at 70 or 75 °C have been investigated theoretically using modified Smith−Ewart equations. Compartmentalization always leads to improved livingness (end functionality) because of the segregation effect on propagating radicals reducing the overall termination rate. The control over the molecular weight distribution is, however, only improved if the particles are sufficiently small; that is, a particle size range exists where livingness is improved but control is not. Improved control is obtained as a result of the confined space effect causing an increase in the deactivation rate. The extent of compartmentalization increases with increasing target molecular weight and if Br is replaced with Cl. The present work provides further insight into how one can potentially employ particle size as an experimental parameter to influence ATRP.

Influence of Graft Density on Kinetics of Surface-Initiated ATRP of Polystyrene from Montmorillonite

Here we report the kinetics of the surface-initiated atom transfer radical polymerization (ATRP) of styrene from the surface of functionalized montmorillonite clay as a function of graft density. Compared with analogous ATRP reactions with free initiator, we observe a seven-fold increase in the polymerization rate at the highest graft density, ∼1 chain/nm2, whereas bulk kinetics are recovered as the graft density is reduced. We hypothesize that this phenomenon is a consequence of local concentration heterogeneities that shift the ATRP equilibrium in favor of the active state and present a simple phenomenological kinetic model that accounts for our data. These findings present an important consideration relevant to the design of precisely defined molecular architectures from surfaces via surface-initiated ATRP.

Kinetics of Phase Transfer Agent-aided Free–Radical Polymerization of Acrylonitrile and Methyl Methacrylate Using Water-Soluble Initiator

This paper deals with the kinetics of radical polymerization of acrylonitrile (AN) and methyl methacrylate (MMA), using water-soluble potassium peroxydisulphate initiator in the presence of cetyldimethylbenzylammonium chloride (PTC), at 60°C under oxygen-free atmosphere. The role of concentrations of monomer, initiator, catalyst and temperature on the rate of polymerization were ascertained. Based on the results obtained, a suitable kinetic scheme has been proposed to account for the experimental observation.

Kinetics of copolymerization of tetrafluoroethylene with perfluoro(3,6-dioxa-4-methyl-7-octen)sulfonyl fluoride

Effect of composition of a monomers mixture on the kinetics of radical polymerization in solution of tetrafluoroethylene with perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride is studied.

Copolymers Formation by Photopolymerization of (Meth)acrylates Containing Dissolved Polyheteroarylenes

Radical photopolymerization of (meth)acrylates in the presence of dissolved polyheteroarylenes has been investigated. The kinetics of radical polymerization of unsaturated monomers in the presence of polyheteroarylenes and model compounds has been studied by Differential Scanning Photocalorimetry and Infrared Spectroscopy. From the results of investigations into the kinetics and the polymer structures (Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance, Size-exclusion Chromatography, Thermogravimetric analysis), it has been established that radical photopolymerization of vinyl monomers in the presence of polyheteroarylenes leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. Using Electron Spin Resonance Spectroscopy the novel radicals upon the addition of model compounds for the polyheteroarylenes have been detected, and a mechanism of copolymer formation has been proposed.

Direct Monitoring of the Cross‐Over from Diffusion‐Controlled to Decomposition‐Controlled Initiation in Free Radical Polymerization

AbstractHigh‐resolution free radical polymerization kinetics was obtained using automatic continuous online monitoring of polymerization reactions (ACOMP). A sharp cross‐over from diffusion‐controlled initiation at low [monomer] to initiator decomposition control at higher [monomer] was found, and agrees with the quasi‐steady state approximation (QSSA). The cross‐over was also measurable within individual experiments. The kinetic implications for polymer weight average molecular weight $\overline M _{\rm w}$ and intrinsic viscosity (η)w were analyzed, and the QSSA‐predicted trends for the ratios of final to initial $\overline M _{\rm w}$, and (η)w, confirmed. Analytical expressions for conversion are contrasted, and it was found that first‐order fits, while not fully justified theoretically, nonetheless are robust, which simplifies calculations needed for controlling molecular weight distributions in “semi‐batch” reactions, where reagents are fed to the reactor through programmable flow profiles. At the low monomer concentrations used, there was no evidence that propagation or termination rate coefficients changed during the reactions.magnified image

Radical polymerization of N-vinylcaprolactam in benzene solutions in a wide conversion range

The kinetics of radical polymerization of N-vinylcaprolactam initiated by the thermal decomposition of AIBN at 60°C in monomer solutions in benzene has been studied in a wide range of conversions. The heat of polymerization of N-vinylcaprolactam is 76.0 ± 0.9 kJ/mol; at initial conversions, the polymerization of N-vinylcaprolactam is of the first order with respect to the monomer and of the 0.5th order with respect to the initiator. The ratio of chain propagation and chain termination rate constants kp/kter0.5 is 0.578 l0.5/(mol s)0.5, thus suggesting a high propagation rate constant kp > 103 l/(mol s). At a high initial concentration of the monomer, the kinetic curves demonstrate a weakly pronounced gel effect, and, in the gel permeation chromatography curves of the polymers, the second high-molecular-mass mode emerges, whose intensity grows with conversion. The observed kinetic features are interpreted in terms of the diffusion control of the gel effect.

Modeling of temperature-dependent diffusion and polymerization kinetics and their effects on two-photon polymerization dynamics

Two-photon polymerization (2PP) is an effective technique for the fabrication of complex polymeric 3-D micro/nanofeatures and structures using ultrashort pulses from a NIR laser source. The interaction of laser pulses with photoresponsive resin creates a voxel (volumetric pixel) that defines the resolution of the 2PP process. In this work, we present a mathematical model of the 2PP process that considers the effects of radical diffusion and polymerization kinetics on polymerization dynamics. The increase in temperature during the polymerization process and its effect on polymerization kinetics are considered in the model. The developed model is solved numerically to obtain a better understanding of the polymerization dynamics at various time scales. The effects of diffusion and polymerization kinetics on the growth of voxels are analyzed from the presented simulations. A comparison between high and low pulse repetition rate systems is also presented, showing different polymerization dynamics.

Radical polymerization of methyl methacrylate in the presence of low-molecular-weight poly(methyl methacrylate)

The kinetics of the bulk radical polymerization of methyl methacrylate and the structure and properties (physicomechanical and thermomechanical, as well as diffusion and sorption) of the polymers were examined in relation to the amount of low-molecular-weight poly(methyl methacrylate) added.

Stable Free Radical Polymerization in Emulsion: Modeling the Thermodynamics of Monomer Transfer between Droplets and Particles

AbstractA mathematical model is developed from polymer solution thermodynamics and stable free radical polymerization kinetics to predict the monomer swelling behavior of large droplets and small particles that coexist during the seeded polymerization of styrene in emulsion. This model is used to predict the sensitivity of polymerized latex stability (based on the persistence of large particles) to changes in seed particle size and final latex target molecular weight. Simulation results show that the use of small seed particles (diameter ≤ 50 nm) in recipe formulation will lead to polymerization occurring preferentially in the large droplets, and offers theoretical evidence that TEMPO‐mediated ab initio emulsion polymerizations will not be feasible. Our predictions are consistent with experimental evidence suggesting that the presence of large particles leads to the formation of undesirable coagulum in the final product.magnified image

Polymerization of 1-vinyl-3-amino-1,2,4-triazole and some properties of related polymers

The kinetics of radical polymerization of 1-vinyl-3-amino-1,2,4-triazole was studied. The results show that the presence of the amino group as a substituent on the heterocycle decreases the polymerization activity of the triazole-containing monomer. It was found that water has an accelerating effect on the 1-vinyl-3-amino-1,2,4-triazole polymerization process. The substitution of the amino group on the triazole cycle enhances the hydrophilic properties of the polymer relative to those of unsubstituted polyvinyltriazole and opens up possibilities for its further modification.

Monomers for Adhesive Polymers, 7a

AbstractHomopolymerization and copolymerization of N‐(2‐hydroxyethylmethyl)acrylamide (1) with N,N′‐diethyl‐1,3‐bis(acrylamido)propane (2) have been studied in ethanol/water solvents or in bulk. The polymerization rate exponent depends on the polymerization temperature and increased from 0.99 at 50 °C to 1.21 at 75 °C. The initial polymerization rate dependence on temperature between 50 and 75 °C in Arrhenius coordinates was linear. However, the slope increased with an increase in monomer concentration. The overall activation energy Ea varied from 64 kJ · mol−1 at 0.5 mol · L−1 to 76 kJ · mol−1 at 2.0 mol · L−1 monomer concentration. In addition, the reaction order with respect to the initiator AIBN deviated from the standard free radical polymerization kinetics. The exponent 0.42 indicated a significant participation of primary radicals in termination reactions. The polymerization reaction order declined from ideality as well, and the Ea and polymerization enthalpy changed with the batch composition variation, which could be explained through monomer/monomer, monomer/solvent, or monomer/polymer complexation. The chain transfer to polymer was considered as an origin for the polymer network formation in monomer 1 homopolymerization if its concentration in the batch was 1 mol · L−1 or higher. The more intensive polymerization acceleration with the monomer dilution and the greater heat released reduction with decrease in the monomer 1 to 2 ratios were evidenced in copolymerization. Nevertheless, the deviations from conventional reaction kinetics were not as pronounced as with acrylic or methacrylic acid polymerizations.magnified image

Kinetics of nitroxide-controlled radical polymerization during the non-stationary state

The activation–deactivation equilibrium of nitroxide-controlled radical polymerization of styrene at 123°C was investigated. For this purpose the reaction solution was examined time dependently during the initial phase of the polymerization by using an SEC column combination providing a very good separation of the low-molecular weight species. By time-dependent measurement of the alkoxyamine concentration the activation rate of the alkoxyamines PhEt-TIPNO (N-tert-butyl-N-(2-methyl-1-phenyl-propyl)-O-(1-phenyl-ethyl)-hydroxylamine) kact=3.2×10−3s−1 and PhEt-BIPNO (N-tert-butyl-N-(1-isopropyl-2-methyl-propyl)-O-(1-phenyl-ethyl)-hydroxylamine) kact=6.4×10−3s−1 can be determined directly.Considering the Persistent Radical Effect theory, the measurement of the free nitroxide concentration allows to determine the pseudo-equilibrium constant of dissociation/combination between dormant and active species for polystyryl-TIPNO and polystyryl-BIPNO, K=7.5×10−9mol/L and 1.08×10−8mol/L, respectively.

The Cutthroat Competition Between Termination and Transfer to Shape the Kinetics of Radical Polymerization

AbstractThere is a fascinating interplay between termination and transfer that shapes the kinetics of radical polymerization (RP). In one limit all dead‐chain formation is by termination, in the other by transfer. Because of chain‐length‐dependent termination (CLDT), the rate law for RP takes a different form in each limit. However, common behavior is observed if one instead considers how the average termination rate coefficient varies with average degree of polymerization. Examples are given of using these principles to understand trends in actual RP data, and it is also demonstrated how to extract quantitative information on CLDT from simple steady‐state experiments.