Overall Rate Of Polymerization Research Articles

Copper(I) Bromide/N-(n-Octyl)-2-pyridylmethanimine−Mediated Living-Radical Polymerization of Methyl Methacrylate Using Carbosilane Dendritic Initiators

The zeroth (Si{(CH2)3SiMe2(C6H4CH2OC(O)CMe2Br)}4), 2, and first (Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2OC(O)CMe2Br))3}4), 3, generation of 2-bromoisobutyryl functionalized carbosilane dendrimers have been successfully applied as initiators for the copper(I) bromide/N-(n-octyl)-2-pyridylmethanimine-mediated living-radical polymerization of methyl methacrylate. The overall rate of polymerization are comparable for the two dendritic initiators studied, 2 (3.4 × 10-5 mol L-1 s-1) and 3 (4.8 × 10-5 mol L-1 s-1) with the benzylic model compound C6H5CH2OC(O)CMe2Br (1) showing a lower rate of polymerization for both dendritic initiators, (7.3 × 10-5 mol L-1 s-1) where [initiator sites] = 1.87 × 10-2 mol L-1. We postulate that this is caused by initial intramolecular termination. The molecular weight distribution is less than 1.3 after 3 h reaction time. Initiator 3, however, produces star−star coupling throughout the polymerization. When the dendritic periphery is partialy functionalized (statistically two and six arms of the first generation dendrimer, respectively, 4 and 5) the control of the molecular weight distribution was lost (PDI > 3) for 4 as a result of too low of a value for [initiator site], i.e., 3.12 × 10-3 mol L-1.

Bulk Terpolymer Composition Prediction from Copolymer Reactivity Ratios

ABSTRACTBulk terpolymerization of butyl acrylate (BA), methyl methacrylate (MMA) and vinyl acetate (VAc) up to full conversion levels was studied at BA/MMA/VAc initial mass ratios of 20/50/30, 50/20/30, 20/60/20, 60/20/20, 10/40/50, and 40/10/50. The experiments were carried out to high conversion levels at 50°C with an initiator concentration of 0.071 mol/L (2,2'-azo-(bis)isobutyronitrile) and a chain transfer agent concentration of 0.0058 mol/L (n-dodecyl mercaptan). For each experiment, samples were analyzed for conversion by gravimetry and for composition by proton nuclear magnetic resonance (1H-NMR) spectroscopy.The overall rate of polymerization was greatly influenced by the amount of BA in the feed and to a lesser degree by the ratio of acrylic monomers (BA + MMA) to VAc in the feed. Using reactivity ratios previously estimated from low conversion bulk copolymerization experiments, the bulk terpolymerization composition data were well predicted by terminal model kinetics up to high conversion levels.

Influence of N-oxyls on the free radical autopolymerization of styrene

Through comparative studies on the controlled thermally initiated radical polymerization of styrene in the presence of N-oxyls, the effect of the type of the N-oxyls (2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (OH-TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (oxo-TEMPO) and 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl (acetamido-TEMPO)), as well as the concentration of the N-oxyls (3–20 mmol L–1) are discussed. The radical formation proceeds exclusively through the thermal initiation of styrene, i.e. without using any initiator. It is observed, that the thermal self-initiation of styrene increases the radical yield remarkably with the N-oxyls concentration, independent of the type of the N-oxyl. The concentration-dependent side reactions of substituted N-oxyls are remarkably more pronounced than those of unsubstituted N-oxyl. This leads to the reduction of the overall rate of polymerization (vbr) as compared to TEMPO (vbr = vbr (thermal polymerization)) with respect to the concentration, but independent of the type of substituents. Durch vergleichende Untersuchungen der kontrollierten thermisch initiierten radikalischen Polymerisation von Styrol in Gegenwart eines N-Oxyls wird der Einfluß der Art des N-Oxyls (2,2,6,6-Tetramethylpiperidin-N-oxyl (TEMPO), 4-Hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl (OH-TEMPO), 4-Oxo-2,2,6,6-tetramethylpiperidin-N-oxyl (Oxo-TEMPO), 4-Acetamido-2,2,6,6-tetramethylpiperidin-N-oxyl (Acetamido-TEMPO)) und der Konzentration des N-Oxyls (3–20 mmol L–1) diskutiert. Die Radikalbildung erfolgt ausschließlich durch die thermische Initiierung von Styrol, also ohne Zusatz eines Initiators. Beobachtet wird eine wesentliche Erhöhung der Radikalausbeute der thermischen Selbstinitiierung von Styrol in Abhängigkeit von der Konzentration des N-Oxyls, unabhängig von der Art des N-Oxyls. Die konzentrationsabhängigen Nebenreaktionen substituierter N-Oxyle sind wesentlich ausgeprägter. Das führt zur Reduzierung der Bruttopolymerisationsgeschwindigkeit (vbr) im Vergleich zu TEMPO (vbr = vbr (thermische Polymerisation)) in Abhängigkeit von der Konzentration, aber unabhängig von der Art der Substituenten.

Atom transfer radical polymerization of styrene initiated by polychloroalkanes and catalyzed by CuCl/2,2?-bipyridine: A kinetic and mechanistic study

A series of polychloroalkanes, known as telogen agents for redox telomerization, were used as initiators for atom transfer radical polymerization (ATRP) of styrene using the heterogeneous CuCl/2,2′-bipyridine catalyst. In copper-catalyzed redox telomerization, the reactivity of RCCl3-type telogens is strongly influenced by the nature of the R group. In ATRP, the 2,2′-bipyridine ligand levels the activity of the catalytic system in such a way that all 1,1,1-trichloroalkanes are efficient initiators in ATRP, whatever the R group. The nature of this substituent influences the overall rate of polymerization through both the number of active sites per chain and the [Cu (I)]/[Cu (II)] ratio. By the combining of several analytical techniques, it is proved that some polychloroalkanes such as CCl3CO2CH3, CCl3CF3, or CCl4 are bifunctional initiators. Finally, a general mechanism of initiation is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2933–2947, 1998

Role of mixing in copolymerizations of styrene andn-butyl acrylate

The effect of agitation speed and impeller type on the kinetics of emulsion copolymerization of styrene and n-butyl acrylate was investigated. It was shown that the solids content was an important variable in these studies. At low solids (30%), the impeller type and speed did not have any significant effect on the final number of particles and the overall rate of polymerization. Particle size distributions were unimodal in all the cases. At high solids (50%), some differences were observed when 2 different impellers (Rushton and A310 fluidfoil) were used. The polymerization carried out with the Rushton impeller was faster. Bimodal particle size distributions were obtained for both cases; however, the bimodality was more significant when the A310 fluidfoil impeller was used. Greater numbers of particles and unimodal particle size distributions with high rates of polymerization at 30% solids contrasted the lower numbers of particles and bimodal particle size distributions with lower rates of polymerization seen at 50% solids. These differences were attributed to the partitioning behavior of the surfactant (Triton X-405; octylphenoxy polyethoxy ethanol; Union Carbide, Danbury, CT). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2277–2289, 1998

Kinetics of adiabatic anionic copolymerization of ?-caprolactam in the presence of various activators

Adiabatic temperature rise has been recorded as a function of polymerization time to investigate an adiabatic copolymerization kinetics of ϵ-caprolactam (CL) in the presence of several activators, considering different initial copolymerization temperatures ranging from 130 to 160°C. The copolymerization of CL and PEG-diamine has been performed using activators such as tolylene dicarbamoyl dicaprolactam (TDC), hexamethylene dicarbamoyl dicaprolactam (HDC), and cyclohexyl carbamoyl caprolactam (CCC), and sodium caprolactamate as a catalyst. The effect of PEG-diamine on the overall rate of polymerization of CL has been studied by fitting the experimental temperature rise with a new polymerization kinetic equation involving the polymerization exotherm, polymerization-induced crystallization exotherm, and the heat loss due to nonideal adiabatic condition in the experimental situation. Like homopolymerization, the net copolymerization rate is influenced by the variation of activator types in the initiation step. The temperature rise due to polymerization-induced crystallization in copolymerization is drastically decreased with the increasing initial polymerization temperature in the course of polymerization. The high molecular weight and large polydispersity index of copolymers using bifunctional activators indicate that the Claisen type condensation can occur in the course of polymerization processes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1195–1207, 1997

Kinetics of adiabatic anionic copolymerization of ε‐caprolactam in the presence of various activators

Adiabatic temperature rise has been recorded as a function of polymerization time to investigate an adiabatic copolymerization kinetics of ϵ-caprolactam (CL) in the presence of several activators, considering different initial copolymerization temperatures ranging from 130 to 160°C. The copolymerization of CL and PEG-diamine has been performed using activators such as tolylene dicarbamoyl dicaprolactam (TDC), hexamethylene dicarbamoyl dicaprolactam (HDC), and cyclohexyl carbamoyl caprolactam (CCC), and sodium caprolactamate as a catalyst. The effect of PEG-diamine on the overall rate of polymerization of CL has been studied by fitting the experimental temperature rise with a new polymerization kinetic equation involving the polymerization exotherm, polymerization-induced crystallization exotherm, and the heat loss due to nonideal adiabatic condition in the experimental situation. Like homopolymerization, the net copolymerization rate is influenced by the variation of activator types in the initiation step. The temperature rise due to polymerization-induced crystallization in copolymerization is drastically decreased with the increasing initial polymerization temperature in the course of polymerization. The high molecular weight and large polydispersity index of copolymers using bifunctional activators indicate that the Claisen type condensation can occur in the course of polymerization processes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1195–1207, 1997

Radical Polymerization Kinetics of Poly(ethylene oxide) Macromonomers

Radical polymerization of poly(ethylene oxide) macromonomers carrying a methoxy group on the one end and a p-vinylbenzyl or a (p-vinylphenyl)butyl group on the other end was investigated in benzene and water. The overall rate of polymerization was found to be more than 50 times higher in water than that in benzene. Apparent rate constants of propagation and termination were evaluated based on ESR measurements under irradiation, while initiator efficiency was estimated from inhibition period measurements. Very rapid polymerization in water was then reasonably attributed to a combined result of locally concentrated propagating radicals and monomers in their micellar organization, together with high initiator efficiency, enhanced rate of propagation, and reduced rate of termination there.

Kinetic and mechanistic studies on the block copolymerization of methyl methacrylate initiated by Ce4+-poly (ethylene glycol) redox system

The kinetic and mechanistic features of tetravalent cerium-poly(ethylene glycol) (PEG, molecular weight 6000) redox couple initiated block copolymerization of methyl methacrylate (MMA) have been investigated in aqueous acidic medium in the temperature range 30–50°C. The block copolymerization behavior as a function of [Ce4+], [PEG], [MMA], [H+], [NO3−], as well as temperature, have been studied. The overall rate of polymerization (Rp), the rate of disappearance of Ce4+ (RCe), and the number average molecular weight (Mn) have been determined from gravimetry, cerimetry, and gel permeation chromatography, respectively. Rp has been found to bear a square dependence on [MMA] and independent of both [Ce4+] and [H+]. RCe has been found to be directly proportional to [Ce4+] and [H+], and independent of [MMA]. Both Rp and RCe have been found to be retarded on adding nitrate ions, while increase of temperature accelerated the rates. The Mn of the block copolymer has been found to depend on [Ce4+], [PEG], [MMA], and [H+] as well as on temperature. A plausible reaction scheme has been derived and suitable kinetic expressions have been evaluated based on these observations. It has been concluded that by varying the temperature and concentration of the components of the redox system, it is possible to control the rate of polymerization and the molecular weight of the resulting block copolymer. © 1997 John Wiley & Sons, Inc.

Monomers in Polymer Dispersions. Part IV: Partition of Acrylonitrile in Rubber Latex as Studied by Raman Spectroscopy

The swelling of polymeric latex particles with monomers and the partition of slightly water soluble monomers between the particle and aqueous phases are of great importance in understanding the kinetics of emulsion polymerization and particle structure formation. The overall rate of polymerization is directly influenced by the monomer concentration at the loci of chain propagation reaction (latex particle, monomer droplet, or aqueous phase). In addition, initiator efficiency, rates of radical transfer, and copolymer or graft composition (in multistage reactions) also depend on monomer concentration and partition.

High pressure polymerization of ethylene with a homogeneous metallocene catalyst

AbstractSoluble metallocene catalysts can be easily metered into high pressure polymerization reactors. The performance of a homogeneous zirconocene catalyst for the polymerization of ethylene under high pressures was tested at 1500 bar and temperatures between 80 and 260°C in the presence of methyl aluminoxane as cocatalyst. Besides the productivity of the catalyst and the overall rate of polymerization, the most important properties of the prepared polymers were determined. The results were compared with those found earlier with a heterogeneous titanium catalyst supported on magnesium dichloride.

The reactivity of 3-methyl- and 5-methyl-1-vinylpyrazoles in free-radical polymerization

3-Methyl-l-vinylpyrazole (M3VP) and 5-methyl-1-vinylpyrazole (M5VP) were isolated as individual substances by vacuum rectification of their mixture (M3VP: M5VP ≈ 60 ∶ 40). For each of them the kinetics of free-radical polymerization in MeOH were measured at low conversions. In both cases the rate of polymerization is proportional to 0.5 order with respect to the initiator (AIBN) concentration. On the other hand, a first order of reaction with respect to monomer concentration is observed only when the latter is relatively low (≤3M). At higher initial concentrations of monomers the order of reaction becomes less than unity. The overall rate of polymerization for M5VP was higher than for M3VP, whereas the initiation rate remained constant in the whole range of monomer concentrations and did not depend on the exact structure of the monomer. The difference in the rates of polymerization observed for M3VP and M5VP is probably connected with the difference in the key parameterkp/kt1/2 for each of the two isomers. It is concluded that the correct kinetic information about homo- and co-polymerization of M3VP and M5VP cannot be obtained without their adequate separation.

Kinetic investigation of the radical polymerization of N‐acryloylpiperidine in solution

AbstractThe kinetics of free radical polymerizations of N‐acryloylpiperidine (NAPi) were studied in benzene (Bz) using 2,2′‐azobisisobutyronitrile (AIBN) as initiator. The activation energy was determined to be 111.7 kJ mol−1. The overall rate of polymerization of the NAPi‐AIBN‐Bz system at 60°C was investigated as a function of monomer and initiator concentrations. Deviation from normal kinetics was observed with an order of 1.48 with respect to the monomer. The observed dependence of the rate constants kp/k on monomer concentration could not be explained by the diffusion theory or the theory of electron donor‐acceptor (EDA) complexes. The observed data have, however, been satisfactorily interpreted by the ‘hot’ radical theory.

Effect of chain transfer agent and the reaction medium on the limiting conversion of methyl methacrylate free radical polymerization

The kinetics of free radical homopolymerization of methyl methacrylate in the presence of n-dodecyl mercaptan have been studied at 70° in bulk, using a 3 mol/l solution in benzene. The results indicate that, when the polymerization is carried out in solution, the chain transfer agent does not influence the overall rate of polymerization or the limiting conversion. Also, in bulk polymerization, the presence of n-dodecyl mercaptan does not significantly modify the limiting conversion when polymer is isolated by lyophilization. For the bulk polymerization, the differences in both molecular weight and limiting conversion, when polymers are isolated by lyophilization or by precipitation, have been qualitatively correlated with current theories on free radical polymerization at high conversion.

Chain-length-dependent termination rate processes in free-radical polymerizations. 1. Theory

A complete set of rate equations describing the kinetics of free-radical polymerization is deduced, in which termination rate coefficients are allowed to depend on chain length. The rate equations are applicable to bulk, solution, and heterogeneous (e.g., emulsion) polymerization systems. They incorporate the following kinetic processes: initiation, propagation, transfer, chain-length-dependent termination, and, for emulsion systems, exit and reentry (i.e., aqueous-phase kinetic processes are taken into account). It is shown that, despite their apparent complexity, the full set of population balance equations can, to a good approximation, be reduced to a single first-order differential equation. This equation and that for the overall rate of polymerization form a pair of coupled differential equations that can be solved easily and are thus suitable for routine modeling of experiment. The key parameters required in the model are the rate coefficients for transfer and propagation and the diffusion coefficient of the monomer as a function of the polymer weight fraction (conversion), this variation being used in expressions for the dependence of the termination rate coefficient on the length of a growing chain. In accord with previous experiment and theory (Adams, M. E.; Russell, G. T.; Casey, B. S.; Napper, D. H.; Gilbert, R. G.; Sangster, D. F. Macromolecules 1990, 23, 4624), the present theory indicates that, at intermediate conversions, termination is dominated by interactions between short chains formed by transfer and entangled long chains. In the regime in which propagation is diffusion-controlled, most termination events involve two highly entangled chains, whose ends move by the reaction-diffusion process (Russell, G. T.; Napper, D. H.; Gilbert, R. G. Macromolecules 1988, 21, 2133). The mathematical treatments of this paper are of very general applicability and should inter alia be useful in addressing practical problems such as minimizing the residual monomer content of polymer products.

Living ring-opening polymerization of l,l-lactide initiated with potassium t-butoxide and its 18-crown-6 complex

Living polymerization of L,L-lactide initiated by potasium t-butoxide and its 18-crown-6 complex was investigated in THF solution at room temperature. The results support a reversible polymerization mechanism consisting of first order in monomer propagation and of unimolecular depropagation. The presence of 18-crown-6 has a strong MWD narrowing effect (Mw/Mn<1.2), slows down the overall rate of polymerization and gives rise to slow initiation. The polymerizations yield optically pure polymers both in the presence and absence of 18-crown-6.

Contribution of primary radical termination to radical polymerization of diethyl fumarate estimated from absolute rate constants

Diethyl fumarate was radically polymerized under UV irradiation and concentration of the propagating radical was determined to be of the order of 10-5 mol/L by scavenge with a stable free radical. The absolute rate constant for propagation (kp) was evaluated from the overall rate of polymerization at 30°C: Kp =(2.9 ± 0.3) × 10-2 L/mol · s. The rate constant for mutual termination of the polymer radical (kt) was calculated from the decreasing rate of the radical concentration in the dark: kt=8.0 L/mol·s. The kt value determined is one twentieth of that evaluated previously by a rotating sector method. This discrepancy is accounted for by contribution of much faster primary radical termination.

Effects of large ring‐substituents on radical polymerization behaviour of 2,6‐diisopropylphenyl methacrylate

Abstract2,6‐Diisopropylphenyl methacrylate (DIPPMA) noted as a monomer bearing the largest ring substituents among polymerizable o‐substituted phenyl methacrylates was homo‐ and copolymerized. Steric hindrance caused by the substituents significantly reduced the overall rate of polymerization and reactivities in copolymerization. Suppression of termination by the steric effect seems to be of minor importance. The ceiling temperature was determined to be 49°C at a concentration of 1 mol · dm−3 in benzene. The overall rate and the degree of polymerization were confirmed to decrease with increasing temperature under the influence of the ceiling temperature. Triad tacticity of poly(methyl methacrylate) derived from poly(DIPPMA) was determined to be rr = 29%, rm = 53%, and mm = 18% at 40°C, indicating that the steric effect of the large substituents on propagation rendered almost random addition.

Cationic ring‐opening polymerization of lactones in the presence of alcohol

AbstractCationic ring‐opening polymerization of e‐caprolactone using triethyloxonium hexafluorophosphate initiator in the presence of alcohol to produce low molecular weight polyester glycol was examined. The polymerization proceeded by an activated monomer mechanism; thus the polymer molecular weight increased directly with the monomer conversion. Polymerization of lactones other than ϵ‐caprolactone were also examined, and the overall rate of polymerization was in the order δ‐valerolactone&gt; ϵ‐caprolactone&gt;&gt; β‐butyrolactone&gt; diketene&gt; γ‐butyrolactone.

Determination of absolute rate constants for radical polymerization of diisopropyl fumarate based on a quantitative scavenge of propagating radical

During polymerization of diisopropyl fumarate (DiPF), the propagating poly(DiPF) radical was scavenged quantitatively by a stable free radical, because of its long-lived nature and high steady-state concentration. By addition of a known amount of 1,3,5-triphenylverdazyl to the polymerization mixture, the concentration of poly(DiPF) radical was determined to be 10 −5−10 −4 mol dm −3, which allowed the evaluation of the propagation rate constant ( k p) from the overall rate of polymerization: k p = 0.31 ± 0.07 dm 3 mol −1 s −1 at 30°C. The lifetime of the polymer radical was too long for a rotating sector experiment. The rate constant for bimolecular termination of the radical ( k t) was calculated from the decay of poly(DiPF) radical followed by the scavenger method: k t = 0.84 dm 3 mol −1 s −1. These rate constants, which are exceptionally small, are accounted for by the steric factor of the ester alkyl group accumulated along the polymer chain and extremely slow diffusion of the polymer radical. Because the termination rate determined is too slow to interpret the molecular weight of the polymer formed, primary radical termination is to be considered as an additional termination process in the actual polymerization.