Kinetics of styrene homogeneous polymerization to atactic polypropylene

The rate of polymerization of styrene initiated by hydroperoxidized atactic polypropylene in a homogeneous toluene solution has been measured at 60 and 70°C. The reaction is first-order with respect to styrene concentration and independent of the polymeric hydroperoxide concentration above 2 × 10^?5N hydroperoxide. The individual rate constants, length and frequency of the grafted polystyrene chains along the polypropylene backbone have been calculated and their significance discussed. The initiation rate constant compares closely with values reported for the analogous tert-butyl hydroperoxide-initiated polymerization. The rate constant for the chain transfer termination elementary step at 70°C., however, is 18 times the value reported for the tert-butyl hydroperoxide-initiated polymerization of styrene. This high constant accounts for the relatively low rates of polymerization observed and high termination rates. Chain deactivation is presumably accelerated by increased collisions between growing styrene chains and inactive propylene hydroperoxide and polystyrene molecules. Distribution of polystyrene grafts on polypropylene is estimated from knowledge of effects of styrene concentration, polymeric hydroperoxide concentration, and temperature upon the rate of polymerization.     

Aminobutadienes. VI. Polymerization and Copolymerization of 2-Phthalimido-1,3-butadiene

2-Phthalimido-1,3-butadiene (2-PB) was polymerized either radically or thermally in bulk and in solution. While the polymer obtained by solution polymerization was soluble in some solvents such as halogenated hydrocarbons, dioxane, and dimethylformamide and had a softening point in the range of 160–170°C., that obtained by polymerization in bulk was insoluble in any solvent and only swollen on being immersed in such solvents as above. The reduced viscosity of the soluble polymer obtained by solution polymerization was approximately 1.0, and this value remained almost unchanged with varying polymerization time. Likewise the cationic polymerization in acetylene tetrachloride or in chloroform at 20°C. with the use of cationic catalysts such as boron trifluoride and stannic chloride was attempted, but no formation of polymer was observed. This monomer preferentially reacted with acrylonitrile, methyl methacrylate, styrene, and N-vinylphthalimide to form the respective copolymers; it reacted somewhat less readily with vinyl acetate. The monomer reactivity ratios in the copolymerization with styrene were calculated by the Fineman and Ross method and found to be r₁ (2-PB) = 5.2 and r₂ (styrene) = 0.11, respectively, from which the Q, e parameters were successively evaluated to be Q = 5.0 and e = ?0.05. The fact that e value is close to zero, easily explains why this monomer can copolymerize well both with acrylonitrile, which has a highly positive value of e (1.2) and with styrene, for which e is considerably negative (-0.8).     

Modeling and Experimentation of RAFT Solution Copolymerization of Styrene and Butyl Acrylate,Effect of Chain Transfer Reactions on Polymer Molecular Weight Distribution

Chain transfer reactions widely exist in the free radical polymerization and controlled radical polymerization, which can significantly influence polymer molecular weight and molecular weight distribution. In this work, the chain transfer reactions in modeling the reversible addition–fragmentation transfer (RAFT) solution copolymerization are included and the effects of chain transfer rate constant, monomer concentration, and comonomer ratio on the polymerization kinetics and polymer molecular weight development are investigated. The model is verified with the experimental RAFT solution copolymerization of styrene and butyl acrylate, with good agreements achieved. This work has demonstrated that the chain transfer reactions to monomer and solvent can have significant impacts on the number‐average molecular weight (M_n) and dispersity (Ð).     

Comments on the determination of absolute rate constants in anionic polymerization

Claims have recently been made that absolute rate constants for chain propagation of the unassociated active centers can be made in systems where a high degree of association is present. Anionic polymerization of styrene in nonpolar solvents with lithium as counterion is a typical case. The conditions required to obtain these constants (and the associated aggregate dissociation constants) are described using data from styrene polymerization with lithium and potassium as counterions and data from o-methoxystyrene polymerization. The conclusion reached must be that the k_p and K_ds values obtained for styrene with counterion lithium cannot be obtained from existing literature data and are simply artifacts of the computer analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1065–1068, 1998     

Effect of triphenyl phosphite on the radical polymerization of styrene and methyl methacrylate

The effects of triphenyl phosphite (TPP) on the radical polymerization of styrene (St) and methyl methacrylate (MMA) initiated with α,α,-azobisisobutyronitrile (AIBN) was investigated at 50°C. The rate of polymerization of St and MMA at a constant concentration of TPP was found to be proportional to the monomer concentration and the square root of the initiator concentration. The rate of polymerization and the degree of polymerization of both St and MMA increased with increasing TPP concentration. The accelerating effect was shown to be due to the decrease of the termination rate constant k_t with an increase in the viscosity of the polymerization systems. The chain transfer constant C_tr of TPP in St and MMA systems was determined from the degree of polymerization system. The C_tr of TPP was almost zero in the St system and 6.5 × 10^?5 in the MMA system.     

Investigation of the Chain Length Dependence of kp: New Results Obtained with Homogeneous and Heterogeneous Polymerization

New experimental results were collected for the free radical polymerization of styrene by pulsed laser polymerization in solution or in microemulsion. The location of the point of inflection (on the low molecular weight side) and the maximum of the first peak in the chromatograms (measured by size-exclusion chromatography) was used to extract k_p data. The extent of band broadening was determined with narrow polystyrene standards with an assumed Poisson chain length distribution. For a given experiment both k_p values (obtained via the point of inflection and the maximum) were corrected and thus became identical in most cases. Even after the correction, the effect of chain length dependence persists to a higher chain length.     

Retardation of radical polymerization by phenylacetylene and its p-substituted derivatives

Radical polymerizations of styrene and methyl methacrylate in the presence of phenylacetylene and five of its p-substituted derivatives were carried out with the use of 2,2′-azobisisobutyronitrile as the initiator at 60°C. The initial overall rates of the polymerizations of styrene and methyl methacrylate in the presence of phenylacetylene were not proportional to the square root of the initiator concentration under the experimental conditions employed. The relationship between the overall polymerization rate and the concentration of the phenylacetylenes could be expressed by the Kice equation for the rate of a radical polymerization in the presence of a terminator. From this relationship the rate constant (k_s) of the reaction of a growing polymer radical with the phenylacetylenes and the constant C_s = (k_s/k_p), where k_p is the propagation rate constant of vinyl monomers, were determined. The C_s value thus obtained agree well with that derived from the relationship between the number-average degree of polymerization and the molar ratio of the phenylacetylenes to the vinyl monomer. Therefore the mechanism of the reaction may be considered as being one in which the growing radical reacts with the ethynyl group of the phenylacetylenes to yield a comparatively stable radical which terminates mainly by reaction with the growing radical, and so apparently the phenylacetylenes retard the vinyl polymerization. The substituent effects on the reaction were discussed on the basis of the following modified Hammett equation proposed by Yamamoto and Otsu: log [C_s(p-sub. PA)/C_s(PA)] = ρσ + γE_R where PA represents phenylacetylene, σ and E_R are the Hammett polar substituent constant and resonance substituent constant, respectively, and both ρ and γ are reaction constants. The γ value for the polymerization of both styrene and methyl methacrylate was 1.7. The ρ value was 1.0 for the polymerization of styrene and approximately zero for that of methyl methacrylate. These results demonstrate that the reactivity of the phenylacetylenes with the growing chain is influenced by both polar and resonance effects of their p-substituents in the degradative copolymerization of styrene and only by the resonance effect in that of methyl methacrylate.     

Controlled radical polymerization of styrene mediated by the C‐phenyl‐N‐tert‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10^?10 mol L^?1 at 110 °C. At this temperature, the dissociation rate constant (k_d) is 3.7 × 10^?3 s^?1, the recombination rate constant (k_c) is 4.3 × 10⁶ L mol^?1 s^?1, whereas the activation energy (E_a,diss.), for the dissociation of the alkoxyamine at the chain‐end is ～125 kJ mol^?1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007     

The role of chain transfer agents in the emulsion polymerization of styrene

The effect of chain transfer agents on the nucleation and growth of polymer particles in the emulsion polymerization of styrene were examined extensively. The chain transfer agents used are carbon tetrachloride, carbon tetrabromide, and four primary mercaptans (C₂, n-C₄, n-C₇, and n-C₁₂). It is shown that with an increase in the amount of chain transfer agents charged the rate of polymerization per particle decreases progressively. The number of polymer particles formed, on the other hand, increases initially then decreases. These effects can be enhanced by using a chain transfer agent with higher values of chain transfer constant and solubility in water. It is also demonstrated that with increasing radical desorption from the particles, aided by chain transfer agents, the emulsifier dependence exponent for the number of polymer particles formed increases from 0.6 to 1.0 and the initiator dependence exponent decreases from 0.4 to 0. The effect of chain transfer agents on the nucleation and growth of polymer particles in the emulsion polymerization of styrene can be explained in terms of desorption of chain-transfered radicals from the polymer particles.     

Molecular weight development in constant-rate styrene emulsion polymerization

Continuously uniform latices were applied in an experimental study of molecular weight development in constant-rate styrene emulsion polymerization. The formulation around which this study centered exhibited Smith-Ewart, case II kinetics from zero to about 60% conversion with a constant conversion rate of 13 ± 2%/hr and a final particle diameter of 2300 Å. By utilizing an inhibitor perturbation technique, we directly confirmed that free radicals are generated from K₂S₂O₈ by a first-order process with 100% efficiency. We further confirmed that, in contrast to current theories for constant rate polymerization, both the instantaneous values of M?_n and M?_v may increase 6- to 9-fold. Little or no chain branching is evidenced. We interpret these findings to mean that radicals are not utilized with 100% efficiency in emulsion polymerization.     

Kinetics of styrene emulsion polymerization above the critical micelle concentration: Effect of the initial monomer concentration on the molecular weight

The emulsion polymerization of styrene above the critical micelle concentration has been experimentally studied from a low final polymer content up to a high polymer content (～50%). A maximum in the molecular weight (M) evolution has been observed in all cases. The presence or absence of such a maximum depends on the relative values of the rate of free‐radical entry (ρ) and the rate of chain transfer to the monomer (K_trC_Mp, where K_tr is the chain transfer to monomer rate coefficient and C_Mp is the monomer concentration in particles). If ρ ? K_trC_Mp, M is constant and equal to K_p/K_tr (where K_p is the propagation rate coefficient), except at very low particles sizes typical of the early stages of the reaction, in which the chain length is limited by the particle size. On the other hand, if ρ ? K_trC_Mp, M is determined by both C_Mp and ρ. It is proposed that ρ is determined by the sum of the entry of the oligomeric radicals formed in the aqueous phase and those contained in particles that undergo limited coagulation. This coagulative entry can become very significant; therefore, reactor hydrodynamics can play a major role in the kinetic behavior observed. Disagreement between Clay and Gilbert's model and molecular weight distribution data can be ascribed, to a lesser or greater extent, to the degree of correctness of the quasi‐steady‐state and instantaneous‐termination approaches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1963–1972, 2005     

Solvent effects on the radiation-induced graft polymerization of styrene onto poly(isobutylene oxide)

The graft polymerization of styrene onto preirradiated poly(isobutylene oxide) (PIBO) with methanol and benzene was studied. The order of grafting yield and of the number-average molecular weight of graft chains decrease in the order; undiluted styrene > styrene–methanol (1:1) solution > styrene–benzene (1:1) solution. A kinetic treatment to calculate rate constants from the rate of grafting and the molecular weight of the graft chain was proposed. The propagation rate constant k_p was 0.2–0.3 l./mole-sec and the termination rate constant k_t was 1.0–16.0 l./mole-sec. The ratio k_p/k_t in this heterogeneous system was larger than that in homogeneous system by a factor of about 10⁴–10⁵.     

Anionic polymerization of o- and p-methoxystyrene

The butyllithium-initiated polymerization of o- and p-methoxystyrene was studied in toluene at 20°C by dilatometry. Initiation of o-methoxystyrene was found to be instantaneous as evidenced by the absence of any induction period. The propagation rate proceeds by an internal first order with respect to the monomer concentration while the order with respect to the living chain ends varies from 0.67 to 0.51 over a concentration range from 4.5 × 10^?4 to 1.8 × 10^?2 mole/1. The rate may thus be expressed by the equation, where [M] and [PLi] denote concentration of monomer and poly-o-methoxystyryllithium, respectively, and n varies from 0.67 to 0.51. It is assumed that the propagation proceeds exclusively via the monomeric form of the ion-pairs in analogy with the polymerization of styrene. The variable order results from the relatively high value of the dissociation equilibrium constant of dimeric into the monomeric ion-pairs K that was evaluated graphically to be 10^?3 instead of 10^?6 for styrene. The propagation rate constant k_p was found to be equal to about 50 l./mole-min; the propagation activation energy is equal to 12 kcal/mole. No appreciable termination was found in the polymerization of o-methoxystyrene. On the contrary, no quantitative data could be obtained for the polymerization of p-methyoxystyrene due to a slow initiation and a relatively fast termination reaction with formation of a precipitate of highly branched or crosslinked polymer. It is assumed that this precipitate results from a secondary ring metallation reaction.     

Polymer effect on electron-donating character of polymeric donor. I. Formation of charge-transfer complex between polymers containing N,N-dimethylaniline group and maleic anhydride

The difference in electron-donating character between polymeric and monomeric donors in their charge-transfer-complex formation reactions was studied to clarify the so-called polymer effect in such reactions. Systems containing maleic anhydride and copolymers of N,N-dimethyl-p-aminostyrene (ASt) with styrene, which were prepared by a conventional free-radical polymerization technique, were found to be suitable for this purpose. In correlations between the mean sequence length μ_ASt of the ASt units in the copolymers and the lowest energy of their charge-transfer transition (λ_max) or the association constant of their complex formation K_CT, a bathochromic shift in λ_max and an increase in K_CT with increasing μ_ASt of copolymers are found. Moreover, there is a difference in their modes of μ_ASt dependence. It was concluded from these results that the electron-donating character of the dimethylaniline group increases with increasing number of groups attached on one polymer chain. Also, there is an interaction among neighboring functional groups on one polymer chain. The interaction may be regarded as a kind of polymer effect. In addition, the difference in μ_ASt dependence between λ_max and K_CT and also thermodynamics of the complex formation are discussed.     

Chain length‐dependent termination in pulsed‐laser polymerization. VIII. The temperature dependence of the rate coefficient of bimolecular termination in the bulk polymerization of styrene

The photosensitized polymerization of styrene in bulk was investigated in the temperature range of 25–70°C with respect to the average rate coefficient of bimolecular chain termination k̄_t, especially its chain length dependence at low conversions, by means of pulsed laser polymerization (PLP). Three methods were applied: two of them were based on equations originally derived for chain length independent termination taking the quantity k_t contained therein as an average k̄_t, while the third one consisted in a nonlinear fit of the experimental chain length distribution (CLD) obtained at very low pulse frequencies (LF‐PLP) to a theoretical equation. The exponent b characterizing the extent of chain length dependence was unanimously found to decrease from about 0.17–0.20 at 25°C to 0.08–0.11 at 70°C, slightly depending on which of the three methods was chosen. This trend toward more “ideal” polymerization kinetics with rise of polymerization temperature is tentatively ascribed to a quite general type of polymer solution behavior that consists in a (slow) approach to a lower critical solution temperature (LCST), which is associated with a decrease of the solvent quality of the monomer toward the polymer, an effect that should be accompanied with a decrease of the parameter b. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 697–705, 2000     

Radiation-induced polymerization of isoprene in aqueous solution of silver nitrate

The rate of radiation-induced polymerization of isoprene in aqueous solution of silver nitrate is 20–50 times as fast as the rate of radiation-induced polymerization of pure isoprene. The formation of a 1:2 complex of isoprene and silver nitrate was confirmed spectrometrically, and this complex seems to polymerize by attack of an active species. The equilibrium constant K_f and the extinction coefficient E of the complex were estimated to be 0.18 and 1.4, respectively. The polymerization mechanism was concluded to be a radical one, based on the effects of inhibitors. The polyisoprene obtained had a crosslinked structure, was insoluble, and did not give a distinct melting point. The 1,2 structure was the predominant polyisoprene configuration. This was interpreted on the basis of the frontier electron density of isoprene.     

Investigation of autoacceleration effects during the solution polymerization of styrene

The possibility of obtaining increases in the rate and degree of polymerization through a decrease in the termination rate in nonviscous, homogeneous solution polymerizations of styrene has been investigated. Decreases in the termination rate were achieved through decreasing segmental diffusion of the propagating macroradical by greater occlusion, on the average, of the radical in the coiled polymeric chain. Coiling of the polymeric chain was effected by polymerizing styrene in thermodynamically poor (θ) solvents near the θ temperature for polystyrene. Examples of such systems are diethyl oxalate at 51.5°C. and cyclohexane at 34.6°C. Polymerization under these conditions did lead to a decrease in the k_t/k_p² kinetic ratio; this decrease resulted in increases in the degree of polymerization, but changes in the rate of polymerization, in contrast to the marked increases noted in viscous solution or heterogeneous polymerizations, were not observed. Possible explanations for the latter observations are discussed.     

Kinetics of polymerization rate based on the dependence of termination rate on chain length

When the structure of a primary radical resembles that of the chain end of the polymer radical, the rate of the primary radical termination is approximately the same as the termination rate between the oligomer radical and the polymer radical. The rate constant of termination between polymer radicals of chain length n and s, which involve the primary radicals, is k_t,ns = const.(ns)^?a. In the polymerization of methacrylonitrile initiated by 2,2′-azobisisobutyronitrile in dimethylformamide at 60.0°C, the value of a is found to be 0.091. From data obtained previously in the bulk polymerization of styrene initiated by 1-azobis-2-phenylethane at 60.0°C, the value of a is found to be 0.167. Because such a values are so large that they are not estimated by the excluded volume, the termination rates are discussed by adding the dependence of the diffusion of the segments to that for chain length.     

Studies of the polymerization of diallyl compounds. XI. Polymerization of styrene in the presence of diallyl compounds

Radical polymerization of styrene in the presence of various diallyl compounds was carried out at 60°C, with the use of 2,2′-azobisisobutyronitrile as an initiator. The chain transfer constant C_s of the styryl radical to diallyl compounds was determined graphically by solving the Mayo equation. The C_s values of diallyl esters are quite small compared to those of diallyl acetals. The polymerization mechanism of styrene in the presence of diallyl compounds was also discussed in connection with the results obtained previously.     

Thermokinetics evaluation and simulations for the polymerization of styrene in the presence of various inhibitor concentrations

Styrene is an important commodity chemical that is globally applied in various polymerization processes. The aim of this study was to obtain integrated thermokinetics and safety parameters for polymerization of styrene. We mainly used differential scanning calorimetry (DSC), thermal activity monitor (TAM), and simulative methods to investigate thermal polymerization of styrene and styrene containing various levels of 4-tertiary-butylcatechol (TBC). The results obtained included the rate constant (k), reaction order (n), apparent activation energy (E _a), frequency factor (A), and so on, from various DSC curves and simulative methods. From DSC curves, the exothermic onset temperature (T ₀) was about 105 and 132°C for styrene and styrene containing 10 ppm TBC. On the other hand, the test results from TAM indicated that styrene polymerization displays an autocatalytic phenomenon from 50–85°C. By means of this study, the intrinsic safety of a system for styrene during transportation and storage could be established.