Dependence Of Polymerization Rate Research Articles

Macromolecular Design via an Organocatalytic, Monomer-Specific and Temperature-Dependent "On/Off Switch". High Precision Synthesis of Polyester/Polycarbonate Multiblock Copolymers.

The employment of a monomer-specific “on/off switch” was used to synthesize a nine-block copolymer with a predetermined molecular weight and narrow distribution (Đ = 1.26) in only 2.5 h. The monomers consisted of a six-membered cyclic carbonate (i.e., 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC)) and ε-caprolactone (εCL), which were catalyzed by 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD). The dependence of polymerization rate with temperature was different for the two monomers. Under similar reaction conditions, the ratio of the apparent rate constant of AOMEC and εCL [kpapp(AOMEC)/kpapp(εCL)] changes from 400 at T = −40 °C to 50 at T = 30 °C and 10 at T = 100 °C. Therefore, by decreasing the copolymerization temperature from 30 °C to −40 °C, the conversion of εCL can be switched “off”, and by increasing the temperature to 30 °C, the conversion of εCL can be switched “on” again. The addition of AOMEC at T = −40 °C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of εCL along with a simultaneous temperature change leads to the formation of multiblock copolymers. This result provides a new straightforward synthetic route to degradable multiblock copolymers, yielding new interesting materials with endless structural possibilities.

Kinetic and Mechanistic Studies of Photopolymerizations of Acrylates in the Presence of Iniferters

In this particular study, the reaction mechanisms of bulk polymerization of acrylates in the presence of tetraethylthiuram disulfide (TED) are investigated using hexyl acrylate as a model acrylate. TED's presence impacts the termination mechanisms of the acrylate polymerization by two pathways: (1) dissociation of TED to generate dithiocarbamate radicals, which could terminate the acrylic radicals, and (2) chain transfer to TED. The impact of TED concentration as well as the initiation rate on the hexyl acrylate polymerization rate was investigated for polymerizations initiated by both UV and visible light. It was observed that for the polymerizations initiated by UV light, the initial polymerization rate (averaged between 5 and 20% conversion) scaled with the initiation rate by a power of 0.86 ± 0.02 at various concentrations of TED, and a power of 0.45 ± 0.05 for polymerizations in the absence of TED. The initial polymerization rate exhibited a near inverse-linear relationship with the concentration of TED, with the order of dependence ranging from -0.96 ± 0.13 to -1.00± 0.14. Thus, it was found that chain transfer to TED appears to contribute significantly to the termination mechanisms in the polymerization of acrylates. It was observed that TED does not exhibit any absorbance in the visible range (400-500 nm), and hence, the dissociation of TED was eliminated in the polymerizations conducted by visible light. For these polymerizations initiated by visible light, the initial polymerization rate scaled with the initiation rate by a power of 0.84 ± 0.04 to 0.95 ± 0.05 at various TED concentrations ranging from 0.1 to 0.5 wt %. It was also observed that at a light intensity of 25 mW/cm 2 , the log-log plot of the initial polymerization rate as a function of TED concentration exhibited a slope of -1.19 ± 0.03. Thus, the dependence of polymerization rate on the TED concentration was observed to be greater than the expected inverse-linear relationship because of the dependence of the termination kinetic constant on the concentration of TED. Furthermore, it was shown that chain-transfer to TED is the dominant mechanism relative to the dissociation of TED to generate dithiocarbamate radicals, and it appears to contribute significantly to the termination reactions for both polymerizations.

Scope for Accessing the Chain Length Dependence of the Termination Rate Coefficient for Disparate Length Radicals in Acrylate Free Radical Polymerization

AbstractA method that utilizes reversible addition fragmentation chain transfer (RAFT) chemistry is evaluated on a theoretical basis to deduce the termination rate coefficient for disparate length radicals k in acrylate free radical polymerization, where s and l represent the arbitrary yet disparate chain lengths from either a “short” or “long” RAFT distribution. The method is based on a previously developed method for elucidation of k for the model monomer system styrene. The method was expanded to account for intramolecular chain transfer (i.e., the formation of mid‐chain radicals via backbiting) and the free radical polymerization kinetic parameters of methyl acrylate. Simulations show that the method's predictive capability is sensitive to the polymerization rate's dependence on monomer concentration, i.e., the virtual monomer reaction order, which varies with the termination rate coefficient's value and chain length dependence. However, attaining the virtual monomer reaction order is a facile process and once known the method developed here that accounts for mid‐chain radicals and virtual monomer reaction orders other than one seems robust enough to elucidate the chain length dependence of k for the more complex acrylate free radical polymerization.

Assessing the Importance of Diffusion‐Controlled Effects on Polymerization Rate and Molecular Weight Development in Nitroxide‐Mediated Radical Polymerization of Styrene

A previously derived kinetic model for the nitroxide‐mediated radical polymerization (NMRP) of styrene has been modified by considering diffusion‐controlled (DC) effects on the bimolecular radical termination, monomer propagation, dormant polymer activation, and polymer radical deactivation reactions. Free‐volume theory was used to incorporate the DC‐effects into the model. It was found that DC‐termination enhances the living behavior of the system, whereas DC‐propagation, DC‐activation and DC‐deactivation worsen it. Although the inclusion of overall DC‐effects into the kinetic model improved the performance of the model by slightly reducing the deviations obtained from experimental data of polymerization rate and molecular weight in the bimolecular NMRP of styrene with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and dibenzoyl peroxide (BPO), it does not seem to justify adding the extra four free‐volume parameters. In the case of the semi‐batch addition of azo‐bis‐iso‐butyronitrile (AIBN) (several single shots at definite time intervals) in the NMRP of styrene, recently reported in the literature, it was found that DC effects are more significant, but it was observed that there was a strong dependence of polymerization rate on the frequency of addition of the shots of initiator (a maximum on polymerization rate being observed at a given frequency of addition of the shots), which could not be adequately explained in terms of DC‐effects.

Photopolymerization of Acid Containing Monomers: Real-Time Monitoring of Polymerization Rates

The relationship between the polymerization rate of various acrylates and methacrylates containing acid groups and their ability to hydrogen bond has been investigated by real-time infrared spectroscopy. The polymerization rate dependence on temperature of the acid-based acrylates and methacrylates is reduced compared to traditional (meth)acrylates with no groups capable of hydrogen bonding. For two of the acid containing monomers, polymerization rates actually decreased with an increase in temperature.

Inhibicja tlenowa procesow fotopolimeryzacji i sposoby jej ograniczania

In this review the mechanism and kinetics of radical photopolymerization of unsaturated monomers carried out in the presence of atmospheric oxygen have been described. The factors influencing the oxygen inhibition value and basic methods of its suppression such as among others the use of inert gas screen, protective coatings, barriers made of transparent films or paraffin waxes, and use of high intensity light, were presented. Photopolymerization of unsaturated monomers showing decreased sensitivity to oxygen inhibition has been discussed. The mechanism of photopolymerization of the systems containing polar monomers or monomers able to form hydrogen bonds was presented as well as the dependence of polymerization rate on the monomer structure (Table 2). Basic methods of measuring of the oxygen inhibition value have also been described.

Template Polymerization of Methacrylic Acid in the Presence of Poly(N-Acetyl Iminoethylene) Macroazoinitiators

Abstract Thorough studies on the polymerization of methacrylic acid in aqueous solution in the presence of poly(N-acetyl iminoethylene), macroazoinitiators evidenced a dependence of the polymerization rate on solvent capacity to participate in hydrogen bonding interactions and on poly(N-acetyl iminoethylene) chain dimension and concentration. This behavior was ascribed to the template character of the process. The complexation ability of poly(N-acetyl iminoethylene) with carboxylcontaining vinyl monomers and polymers was demonstrated by a viscometric technique. A plot of the polymerization rate dependence on the base molar concentration of poly(N-acetyl iminoethylene) presents two maxima for [MAA]:[PNAI] ratios of 2:3 and 2:1, similar to the composition of the most stable complexes formed during block copolymerization. This characteristic is presumed to arise from a change of the matrix during the process, i.e., the poly(N-acetyl iminoethylene) template is replaced by the poly(methacrylic acid) complexed ...

Abstract of the article “study of concentration dependence of polymerization rate of monomers in an adsorbed state”

Abstract of the article “study of concentration dependence of polymerization rate of monomers in an adsorbed state”

Morphology Control of NdP5 O 14 Single Crystals Grown from Polyphosphoric Acids

Neodymium pentaphosphate single crystals are grown from polyphosphoric acids by controlling polymerization rate of the acids as a main growth parameter. Solubility of in polyphosphoric acids as well as morphology and growth rate of crystals are empirically correlated with polymerization rate, expressed by mean‐condensed rate in this study. Based on the data for epitaxial growth rates along <100>, <010>, and <001> axes, it becomes clear that morphological change of spontaneously nucleated crystals occurs because each axis growth rate shows a different polymerization rate dependence. The influence of temperature gradient given to phosphoric acid is also investigated. As a result, the shape of spontaneously nucleated crystals can be arbitrarily controlled with rather high reproducibility.

Polymerization of chlorophenylglycidyl ethers. IV. Influence of the composition of the initiator system: Aluminium isopropoxide‐zinc chloride on the polymerization of o‐chlorophenylglycidyl ether

AbstractInfluence of the composition of the initiator system employed on polymerization rate, molecular weight and structure of the polymer obtained was studied. At a zinc to aluminium ratio between 0.5 and 1, regular chain structure, and partly isotactic polymer was obtained. The dependence of polymerization rate and polymer molecular weight on the Zn/Al ratio in the initiator system was found to be of a very complex nature.

The kinetics of radiation graft polymerization of acrylic acid from the gas phase on kaolin

The main kinetic relationships of radiation graft polymerization of acrylic acid on kaolin under different reaction conditions (temperature, monomer vapour pressure, concentration of adsorbed monomer and dose rate), are investigated. The dependence of polymerization rate on dose rate is of an unusual type, both the initial rate and the rate of polymerization on a grafted layer of poly(acrylic acid) are directly proportional to dose rate. It is suggested that this unusual feature is explained by the unusually compact structure of the grafted poly(acrylic acid). After loosening of the grafted polymer layer by treatment with ammonia or successively with ammonia and hydrogen chloride, the graft polymerization rate then becomes proportional to the square root of the dose rate, as is usual in radiation graft polymerization from the gas phase.

Application of a calorimetric method in radiation-induced polymerizations—I Determination of propagation and termination rate constants for methyl methacrylate

A calorimetric method, in which a thermistor was the temperature sensitive element, has been adapted for following the non-stationary states of the polymerization of methyl methacrylate, induced by γ-rays. A polymerization rate dependence on ( dose rate) 1 2 has been found over the approximate range from 0·2 to 20 rad/sec and at temperatures between −25° and 55°. Values of the ratio of the propagation to termination rate constants have been determined in this range of temperatures by following the initial and final non-stationary states, immediately after the irradiation is abruptly started or reduced. Using values of the initiation rates, determined by means of the DPPH inhibition method, the individual values of the rate constants have been obtained. They obey closely the Arrhenius law over the range of temperature investigated.

Inverse dependence of polymerization rate on initiator concentration

Inverse dependence of polymerization rate on initiator concentration

Effect of thiourea on the radical polymerization of vinyl monomers. Part I. Polymerization of acrylonitrile with the hydrogen peroxide–thiourea catalyst system

AbstractThe polymerization of acrylonitrile (AN) was studied in aqueous solution with hydrogen peroxide (H2O2) as catalyst and thiourea (TU) as cocatalyst at 30°C. Since the polymerization was carried out at a relatively low temperature, AN was not polymerized by hydrogen peroxide alone. Upon addition of TU to the reaction system, polymerization occurred immediately, and the rate of polymerization increased with increasing TU concentration. In order to obtain the overall polymerization equation, the dependence of polymerization rate on H2O2 and AN concentration was studied kinetically. It was found that the overall polymerization rate Rp was represented by the equation: Rp = K[TU]frac12;[H2O2]frac12;[AN], where K is the rate constant. The acceleration in the presence of TU might be attributed to a redox reaction between H2O2 and TU which would produce free radicals rapidly. The effect of substituents was investigated by use of various N‐substituted derivatives of TU. The polymerization rate increased linearly with the σ* constants of the substituents as electron‐withdrawing substituents were added. The polymerization mechanism is discussed on the basis of the results.

Kinetic measurements on the cobalt-60 gamma-initiated polymerization of isobutene in the presence of zinc oxide

A dilatometric study has been made of the rate of radiolytic polymerization of isobutene in the presence of zinc oxide, samples being stirred during irradiation. Above a minimum stirring speed, polymerization rate is not dependent on stirring rate. The dependence of polymerization rate on amount of additive used, radiation intensity, and temperature, are presented. Molecular weight data for the polymer samples obtained are given, and an hypothesis of the reaction mechanism is offered.

On Co60 gamma ray‐initiated emulsion polymerization

AbstractA study has been made of the Co60 γ‐ray‐initiated polymerization of methyl methacrylate and styrene; conversion rates have been measured by a dilatometric method. The dependence of polymerization rate on monomer concentration and radiation intensity has been determined for each monomer. It has been shown that the emulsion polymerization of methyl methacrylate can be described by accepted theories of emulsion polymerization; in the case of styrene a dependence of intensity exponent on monomer concentration has been found. Such a dependence does not occur when conventional initiating systems are used, and cannot be explained without some modification of theory.

Synthesis of styrene–methyl methacrylate nonrandom copolymers in emulsion systems with cobalt‐60 gamma radiation

AbstractGraft copolymers have been prepared by the irradiation of polymer latices swollen with monomer. The latices used were prepared by radiation polymerization of emulsions to avoid the presence of initiator molecules in the second stage. Latices of polystyrene swollen with methyl methacrylate and polymethyl methacrylate swollen with styrene have been used. Polymerizations were followed dilatometrically and the dependence of polymerization rate on monomer concentration and radiation intensity obtained for both systems studied. Separation of copolymer from homopolymers has been attempted by thermal gradient elution chromatography; the method proved satisfactory when the solvent—nonsolvent system benzene—petroleum ether was used, but failed to give separations when benzene—methanol was used. This failure is thought to be due to cosolution phenomena.

The mechanism of chain termination in the free-radical polymerization of vinyl chloride by 14C-labelled initiators

G. A. RAZUVAYE~ ~ eta[. (6) On the basis of the observed dependence of polymerization rate and molecular weight on temperature the effective energy of activation for initiation was found to be 13 kcal/mole. (7) The effect of the purity of the solvent on the rate of polymerization of ethylene has been studied. In experiments in which spectroscopically pure n-heptane was used under standardized conditions for the formation of the catalyst it was possible to obtain results of satisfactory reproducibility.

Radiation‐induced ionic polymerization of isoprene

AbstractThe γ‐ray‐induced polymerization of isoprene was investigated in the temperature range of ‐78° to 40°C. The following variables were studied: the dependence of polymerization rate on temperature; the effects of DPPH and pyridine on the polymerization at various temperatures; the dependence of the polymerization rate on dose rate at ‐78° and 20°C.; and the structure of the polyisoprenes obtained at various temperatures. the following results were obtained: (1) Although the Arrhenius plot of the polymerization rate did not yield a linear relation, the total polymerization rate was successfully separated into radical and ionic contributions. (2) The polymerization rate was proportional to the square root of dose rate at 20°C., whereas it was proportional to the first power of the dose rate at ‐78°C. (3) The structure of polyisoprene prepared at ‐78°C. is closely similar to that of cationically polymerized polyisoprene. The partially ionic mechanism of the radiation‐induced polymerization of isoprene was elucidated in this investigation. It was concluded that a cationic mechanism is operative at low temperatures whereas a radical mechanism predominates at higher temperatures.

On the mechanism of emulsion polymerization of styrene. III. Polymerization initiated by oil‐soluble compounds

AbstractThis report is concerned with the kinetics of the emulsion polymerization of styrene initiated by the thermal decomposition of oil‐soluble initiators particularly cumene hydroperoxide (CHP). Only those systems are considered in which the latex particles are so small that two radicals cannot coexit for a significant length of time. Polymerization rate, particle size, and molecular weight of the polymer have been determined at 40, 50, and 70°C. as a function of initiator concentration. At low CHP concentrations the polymerization rate per particle conforms to Smith‐Ewart kinetics, i.e., on the average one polymer radical propagates during half the time in each particle. Therefore it is concluded that, although CHP may decompose into radical pairs, polymer radicals are formed one by one. It is shown that even very low rates of transfer of single radicals from the particles to the aqueous phase, or vice versa, suffice to account for the observed polymerization rates per particle. An alternative mechanism is considered in which CHP decomposes on the surface of the particle, the organic radical enters the particle, and the hydroxyl radical remains in the aqueous phase. The rate of polymerization per particle is observed to decrease with increasing CHP concentration. The fact that the transfer coefficient of this initiator is several orders of magnitude higher than that of cumene sustains the supposition that the polystyryl radical abstracts the periodic hydrogen from the peroxide. The decrease in polymerization‐rate is attributed to the inactivity of the resulting ROO·radical. The Mayo formula for the reciprocal degree of polymerization is reformulated to incorporate this kinetic feature. The dependence of polymerization rate on CHP concentration, derived from the new formula, generally agrees with experimental results. Transfer coefficients of the polystyryl radical to CHP and other organic peroxides are given. From the data it can also be concluded that the decomposition rate of CHP in emulsion polymerization is an order of magnitude larger than in styrene solution.