Apparent Rate Constant Of Propagation Research Articles

Kinetic and ESR studies on the radical polymerization. radical‐initiated copolymerization of the diethyl itaconate‐SnCl4 complex and styrene

AbstractThe copolymerization of diethyl itaconate(1) (M1) and styrene (2) (M2) with dimethyl 2,2′‐azoisobutyrate (3) was performed in benzene at 50°C, and the following copolymerization parameters were obtained: r1 = 0,34, r2 = 0,35, Q1 = 0,93 and el = +0,66. The copolymerization system was found to involve ESR1Electron spin resonance. ‐observed propagating polymer radicals at low monomer feed composition (f2) of 2. The apparent rate constant of termination increased rapidly with f2. The ESR‐determined values of the apparent propagation rate constant of the copolymerization were lower than those calculated on the basis of the Mayo‐Lewis model, suggesting a significant penultimate effect in the copolymerization. On the other hand, the copolymerization of the 1‐SnCl4 complex (M1) and 2 (M2) at 50°C yielded a nearly alternating copolymer independently of the monomer feed composition. The propagating polymer radicals were ESR‐observable even up to f2 = 0,8. The ESR‐determined apparent rate constant (kp) of propagation showed a maximum near f2 = 0,5. From the relationship between kp and f2, the rate constants of cross‐propagations of the present alternating copolymerization were evaluated as k12 = 483 and k21 = 510 L. mol−1 · s−1. Comparison of the k21 value and the reported propagation rate constant (209 L · mol−1 · s−1) of homopolymerization of 2 leads to the conclusion that the alternating copolymerization via free‐monomer propagation mechanism originates from a pronounced penultimate effect suppressing homopropagation of 2, but not from enhanced cross‐propagation.

Anionic Polymerization of Vinylsilanes III. Polymerization Behavior of Trimethylvinylsilane

Polymerization behavior of trimethylvinylsilane by sec-butyllithium was investigated in the presence or absence of N,N,N′,N′-tetramethylethylenediamine (TMEDA). In the absence of TMEDA, the elimination reaction of lithium hydride which was observed apparently at 40°C was suppressed at −10°C. In the presence of TMEDA, the chain transfer reaction to the monomer occurred even at −10°C. Initial monomer concentration was found to affect the propagation rate considerably. In the absence of TMEDA at −10°C, the apparent propagation rate constant was high at high initial monomer concentration. In the presence of TMEDA, the reverse relation was observed. The former was interpreted by the association state of the active centers and the latter by the combination of two types of propagation reaction. For the isomerization reaction, low monomer concentration and high temperature were advantageous. The content of isomerized units in the polymer increased with an increase in degree of polymerization.

An ESR study on the radical copolymerization of N-cyclohexylmaleimide and di-n-butyl itaconate in benzene

The copolymerization of N-cyclohexylmaleimide (CHMIm) (M 1 ) and di-n-butylitaconate (DBI) (M 2 ) was investigated in benzene. Monomer reactivity ratios of r 1 =0.21±0.04 and r 2 =0.34±0.04 were obtained according to the Kelen-Tudos method. The copolymerization system was found to insolve ESR-observable propagating polymer radicals, the ESR spectrum of which is inexplicable in terms of any overlapping of the spectra of poly(CHMIm) and poly(DBI) radicals observed in the corresponding homopolymerization systems. This indicates that some penultimate monomer unit causes a change in the ESR spectrum, that is, the structure of the propagating radical center. The apparent rate constants of propagation and termination were estimated

The apparent rate constant model for kinetics of radical chain copolymerization: Chemical‐controlled process

AbstractIn this article the kinetics of chemical‐controlled radical‐chain copolymerization have been reduced to pseudohomopolymerization kinetics by introducing the apparent rate constants, The methods for the determinations of the values of the apparent rate constants, mode of termination, and the methods for the calculation of molecular weights and distributions are proposed. The data required for these determinations and calculations are simply obtained by the usual steady‐state method. According to the traditional kinetics along with the definitions of the apparent rate constants, these apparent rate constants as functions of traditional rate constants, monomer compositions, and copolymer compositions are derived. Further utilizing the theoretical expressions obtained, we show that the apparent rate constants are the general rate constants for both radical chain homo‐ and copolymerizations. The bulk radical copolymerizations of methyl methacrylate and styrene at various monomer feed compositions at 60°C are used to test the proposed model. The empirical apparent rate constants obtained are described well, by the following expressions, and and the mode of termination on the combination termination is where K and K denote the apparent rate constants of propagation and termination, respectively. The term f1(= 1 − f2) stands for the mole fraction of styrene in the monomer solution fed. F1 is the copolymer composition produced at f1. β is the mode of termination.

Radiation-induced seeded copolymerization of tetrafluoroethylene with propylene. II. Kinetic analysis

The radiation-induced seeded copolymerization of tetrafluoroethylene with propylene was kinetically analyzed by assuming that growing radical in polymer particle is deactivated by degradative chain transfer to propylene and/or by recombination with newly entered radical which grows for a while before recombination. Apparent rate constant of initiation is 2.6 × 10−9 mole/liter rad independent of the monomer composition in polymer particles. Apparent rate constant of propagation lies in the range of 105 hr−1 increasing with tetrafluoroethylene fraction. Change in apparent rate constant of chain transfer with propylene fraction suggests that first-order termination by radical occlusion or radical escape to aqueous phase may occur simultaneously with the degradative chain transfer. Average number of radical in a particle is found to increase with dose rate and levelled off at the value of 0.9. The higher value above 0.5 is explained by Trommsdorff effect. The dose rate exponent of average number of radical changes from 1 to 0 with increasing dose rate. This change is consistent with the dose rate effect on the polymerization rate under the constant number of polymer particles.

Anionic polymerization of styrene in tetrahydropyran under an electric field periodically reversed

The anionic polymerization of living polystyryl di-sodium salt was investigated in tetrahydropyran (THP) at 25°, under high vacuum either in the absence or in the presence of an electric field with either constant or periodically reversed polarity over a wide range of frequencies. The application of an electric field with constant polarity increased the apparent rate constant of propagation. It increased in fact the term k p(−) K D 1 2 (where k p(−), is the rate constant of propagation of free ions and K D is the dissociation constant of ion-pairs) whereas it left unaffected the rate constant of propagation of ion-pairs k p(±). The observed effect of the field did not change appreciably if the polarity of the field was reversed with a frequency up to ca. 0.04 Hz. At frequencies of reversal above ca. 0.16 Hz, the enhancement of the polymerization rate due to the electric field became negligible. The observed field effects are interpreted in terms of electrolytic phenomena and of the possibility of growing macroanions assuming a more extended conformation in which the living ends become more accessible to the monomer.

Anionic Polymerization of Methyl Methacrylate in Tetrahydrofuran

Anionic polymerization of MMA in THF was studied by a capillary flow method with the dianion of α-methylstyrene tetramer and sodium naphthalene as initiators. From the analysis of the methanol formed, it was found that both the initiation and propagation reactions proceed without side reaction at −78°C. However, at ca. −65°C, a certain amount of initiator is consumed by carbonyl attack in the initiation step though no side reaction is observed in the propagation step. At room temperature, the carbonyl attack is found in both steps and the polymerization stops at a certain degree of polymerization. The apparent propagation rate constants were determined at −78°C and ca. −65°C. They increase with rising temperature and become too high to be determined at room temperature. The dependence of the rate constants on the propagating anion concentration revealed that the contribution of free ion to the propagation is relatively small and that the propagation rate constant of ion pair is about 1×102 l mol−1 sec−1 at these low temperatures. These data are compared with the rates of homopolymerization of styrene and the reactivities of the propagating species of the two monomers are discussed.