Kinetics of radical polymerization,LIII. The absolute rate constants in the radical polymerization of ethyl acrylate

The dependence of dilution on the chain propagation and termination rate constants was investigated in the polymerization of ethyl acrylate in benzene solution at 50°C, with the rotating sector method. The errors of the above rate constants were determined and, by our method applied to decrease these errors, the errors of the propagation rate constant was reduced to its half value. By the application of our earlier results in polymerization kinetics, we found that in this system the chain propagation step is exclusively responsible for the solvent effects observed. Our experimental results can be quantitatively described in terms of the hot redical theory.     

Discussion of treatments for the kinetics of radical polymerization with primary radical termination

Without knowledge of the familiar geometric mean, the following equation was derived for the radical polymerization with primary radical termination under the condition that reaction between primary radicals is negligible: where both A and B are constants depending on various rate constants. This equation was mathematically and experimentally dealt with.     

Non-ideal kinetics in vinyl polymerization primary radical termination and chain transfer to solvent in benzoyl peroxide initiated polymerization of vinyl acetate in benzene

The kinetics of vinyl acetate polymerization initiated by benzoyl peroxide in benzene at 60°C have been studied. Deviation of the rate of polymerization from kinetic orders of 0.5 in initiator and 1.0 in monomer is discussed in terms of primary radical termination and chain transfer to solvent.     

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.     

Chain length dependence of termination rate constant: computer experiment of effects on the kinetics of radical polymerization of styrene

The kinetics of the radical polymerization of styrene, initiated by AIBN, have been studied by computer experiments. The models adopted assume a termination rate constant for polystyryl radicals with degrees of polymerization m and n, given by:

k_t,mn=km^-n^-

Deviations from simple kinetic rules have been found for 0.0. For example, the rate of polymerization is roughly proportional to the 0.45 power of initiator concentration for = 0.1. Conventional methods for the kinetic study of radical polymerizations are shown to come to erroneous conclusions if the effects of the chain length dependence of termination rate constant are not taken into account.     

Synthesis of polysulfone-b-polystyrene block copolymers by mechanistic transformation from condensation polymerization to free radical polymerization

Synthesis of polysulfone-b-polystyrene (PSU-b-PS) block copolymers by a combination of condensation polymerization and free radical polymerization processes are described. First, a new macroazoinitiator (MAI) containing polysulfone (PSU) units was prepared by direct esterification of 4,4-azobis(4-cyanopentanoic acid) with α,ω-hydroxyl PSU telechelics at ambient conditions. The macroinitiator was then used in conventional free radical polymerization of styrene leading to the formation of desired block copolymers. In this process, initiating macroradicals were generated by thermal cleavage of the azo group present in the macroazoinitiator structure. The precursor polysulfone macroazoinitiator (PSU-MAI) and resulting block copolymers were characterized by spectral analysis using FT-IR, ¹H-NMR, GPC, TGA, and DSC.     

On the modelling of continuous emulsion polymerization using a population balance with instantaneous radical termination

An analytical solution of a population balance is used to mathematically describe continuous emulsion polymerization. Steady state performance is examined. The assumption of instantaneous free radical termination within particles is made. The desorption mechanism is included. Particle size distribution information is obtained, and the effect of the desorption mechanism is noted. A desorption rate constant is calculated when the model is fit to data found in the literature.     

Inverse dependencies on the polymerization rate in atom transfer radical polymerization of N-isopropylacrylamide in aqueous medium

The controlled and fast atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAm) initiated by ethyl 2-chloropropionate (ECP) and catalyzed by copper chloride ligated with tris(2-dimethylaminoethyl)amine (CuCl·Me₆TREN) is reported in water:DMF (1:1 volume based) for a broad range of polymerization conditions (targeted polymerization degree: 50–188; [NIPAm]₀ = 0.5–2 M; T: 10–30 °C). For temperatures below 30 °C, a faster ATRP is obtained with decreasing temperature, which is explained by the exothermic formation of a pre-reactive complex during propagation. For sufficiently high initial deactivator concentrations (?20 mol%) a faster ATRP also results, which is proposed to be caused by Lewis acid–base interactions between the Cu(II) species and NIPAm. The kinetic study indicates a limited importance of cyclization reactions implying a limited loss of end-group fidelity. Moreover, for an initial NIPAm concentration of 2 M, catalyst disproportionation can be sufficiently suppressed.     

The viscosity effect on autoacceleration of the rate of free radical polymerization

The reaction kinetics at 70°C were investigated for the suspension polymerization of methyl methacrylate initiated by benzoyl peroxide in the presence of variable amounts of dodecyl mercaptan. A dilatometric method designed to follow a suspension polymerization was used. It showed that the autoacceleration of the rate of polymerization begins at higher conversions and becomes less pronounced as the concentration of chain transfer agent is increased. The investigations focused on the determination of the viscosities of the reaction mixtures at the onset of autoacceleration. It was concluded from the flow curves obtained for different reaction mixtures that there exists a critical solution viscosity at which the autoacceleration begins, which supports the accepted theory about the nature of this phenomenon. Measured at a shear rate of 10,000 s^?1 and at 25°C this viscosity was found to equal 0.6 poise regardless of the molecular weight of the growing polymer.     

Controlling properties of acrylate/epoxy interpenetrating polymer networks by premature termination of radical polymerization of acrylate

An approach is presented to control properties of sequentially synthesized acrylate/epoxy interpenetrating polymer networks (IPNs) and is used to print uniform and graded properties. These IPNs are constructed by partial formation of the acrylate network, removal of the excess components, expansion with the epoxy system, and curing. The partial crosslinking of the initial network is controlled by photo polymerization and used to manipulate the final properties. The process is used to print homogeneous and graded IPNs with properties in the range of 10 to 1000 MPa. The curing of acrylate, the control mechanism, is studied by Fourier Transform Infrared Spectroscopy (FTIR) during curing on a temperature and environment controlled attenuated total reflection system. Fast scanning calorimetry is used to study network formation, nanoindentation is used to characterize local change of modulus, and uniaxial tensile testing is used to characterize stress response of the printed systems. POLYM. ENG. SCI., 59:1729–1738 2019. © 2019 Society of Plastics Engineers     

Determination of hydroxyl radical rate constants in a continuous flow system using competition kinetics

It is important to determine reaction kinetics of the hydroxyl radical (OH) with various water pollutants for understanding advanced oxidation processes (AOPs). Hence, a simple competition kinetics in a continuous flow system was employed to determine the second-order rate constants of OH with 14 organic and inorganic solutes selected in this study. In this method, p-nitrosodimethylaniline (PNDA) was specifically employed as a well-known reference probe for OH, which gave a competitive relationship between the PNDA and each solute over OH radicals. PNDA decay with OH radicals obeyed reaction kinetics in a first-order as long as the initial concentrations of H₂O₂ and PNDA were less than 30 μM and 2 μM, respectively. The second-order rate constants of OH radical with 14 solutes obtained in this study were found to be consistent with literature values using pulse radiolysis method.     

Unexpected effect of the monomer concentration on the rate of a radical polymerization

The radical polymerization of vinyl monomers is usually initiated by physical and chemical means. After an increasing polymerization rate, R_p, at low monomer concentrations, some reactive systems show an unexpected minimum for R_p at high enough monomer concentrations. The radical polymerization of methyl methacrylate (MMA) initiated by the redox system D -glucose–ceric ion at varying MMA concentration is discussed. The peculiar behaviour of R_p is explained by the presence of two circumstances: the initiation rate from D -glucose radicals does not depend on MMA concentration when most of the D -glucose radicals formed react by adding to monomer, and the radical chains initiated by D -glucose radicals undergo mutual termination with a portion of the radical chains initiated by monomer radicals. Some information about the nature of the polymer end-groups is reached from the mechanistic approach.     

Evaluation of rate constants from experimental batch reactor data for anionic polymerization of poly(methyl methacrylate) at high temperatures

At high temperatures, in anionic polymerization, depolymerization and autocyclization reactions cannot be ignored and the molecular weight distribution (MWD) results based on irreversible polymerization give erroneous results. In this article, we have developed a semianalytical solution for the MWD of the polymer for a general complex mechanism. We then show that the various rate constants can be directly determined from the experimental data on MWD. After evaluating these, it is possible to model the anionic polymerization more rationally, as we have demonstrated using the experimental data from the literature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:845–859, 1997     

Controlled polymerization of methylmethacrylate from fumed SiO2 nanoparticles through atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) is a promising method to synthesize well‐defined polymer/inorganic nanoparticles. However, the surface‐initiated ATRP from commercially mass produced inorganic nanoparticles has seldom been studied. In this study, the surface‐initiated ATRP of methylmethacrylate (MMA) from commercially mass produced fumed silica (SiO₂) nanoparticles was investigated. Unlike the ATRP of MMA initiated from a free initiator, the controllability of ATRP of MMA from the surface of fumed silica nanoparticles was much better using ligand 2,2'‐bipyridine (bpy) than N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) as the initiator was immobilized on the surface of the SiO₂ nanoparticles and the presence of the SiO₂ nanoparticles made the CuCl/bpy catalyst system a homogeneous catalyst system and CuCl/PMDETA a heterogeneous one. The appropriate molar ratio of monomer and initiator was essential for preparing controlled PMMA/SiO₂ nanoparticles. The entire process of ATRP of MMA from the surface of SiO₂ nanoparticles was controllable when using bpy as ligand, xylene as solvent and with a monomer to initiator ratio of 300:1. The ¹H NMR results indicated that the PMMA on the surface of the SiO₂ was prepared via ATRP initiated from 4‐(chloromethyl)phenyltrimethoxysilane. The well‐defined PMMA/SiO₂ nanoparticles obtained have good thermal stability and are well dispersed in organic media as proved by TGA, dynamic light scattering and transmission electron microscopy. © 2013 Society of Chemical Industry     

Determination of recombination and attachment rate constants from ballistic experiments

We present measurements of the electron concentration in wakes behind aluminum spherical models flying in air with velocity 3.4–5.7 km/sec at a pressure of 10–80 torr. We have calculated the heating and entrainment of aluminum from the surface of the models as they move within the flight range. We show that condensation of Al vapor may occur at distances of more than 100 diameters of the body and pressure ≳80 torr. We pose and solve the inverse problem of determining (from experimental data) the effective attachment coefficient for attachment to air molecules and the attachment rate constants for AlO+e→AlO⁻, AlO₂+e→AlO₂ ⁻. Scientific-Research Institute of Mechanics, Moscow State University, Moscow 119899. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 5, pp. 70–82, September–October, 1995.     

Self-condensing vinyl polymerization in the presence of multifunctional initiator with unequal rate constants: Monte Carlo simulation

Monte Carlo method was applied to simulate self-condensing vinyl polymerization (SCVP) in the presence of multifunctional initiator with unequal reactive rate constants. Simulations showed that, with the increase of reactivity of multifunctional initiator, the molecular weight distribution decreases, the fraction of multi-armed hyperbranched polymers increases, and the best reactivity ratio of multifunctional initiator to inimor is 10/1; the reactivity difference of two active sites in inimer has strong effects on the molecular weight distribution and degree of branching. The branch degree and fraction of branch-points depend on both the conversion of double bonds and reactivity difference of two active centers in inimer, and have no relation with the adding of multifunctional initiator. The density distribution of degree of branching further shows common self-similarity in SCVP.     

Synthesis of substituted polymethylenes from acenaphthylene by radical polymerization and copolymerization

Radical polymerization of acenaphthylene (Ace) as a 1,2-disubstituted ethylene was investigated. It was found that the polymerization rate (R_p) was expressed as follows: R_p = k[Ace]^1.0[AIBN]^0.68, and that the overall activation energy was 113 kJ/mol for polymerization with 2,2'-azobisisobutyronitrile (AIBN) in benzene at 50–70°C. Poly(Ace) obtained was characterized by NMR spectroscopy and GPC. Some substituted copolymethylenes were also prepared by radical copolymerization of Ace with other 1,2-disubstituted ethylenes, that is, maleic anhydride, diisopropyl fumarate, and N-cyclohexylmaleimide. The monomer reactivity ratios were determined from comonomer–copolymer composition curves.