Anionic polymerization with alkaline-earth counterion. I. Preparation and characterization of dicarbanionic oligostyrylbarium and -strontium in tetrahydrofuran

Dicarbanionic oligostyrylbarium or -strontium, PS⁼Ba⁺⁺ and PS⁼Sr⁺⁺, were prepared by reacting styrene with finely divided barium or strontium in THF or THP. The effects of reaction temperature, monomer, and metal concentration were described. Difunctionality of these living oligomers is confirmed from calculated and observed molecular weight data and also from conductivity measurements. λ_max of carbanions is found to vary with DP . At 25°C it decreases from 368 nm for dimers to 359 nm for DP > 10. As observed for monocarbanionic polystyrylbarium (PS^?)₂Ba⁺⁺, λ_max of PS⁼Ba⁺⁺ of high DP decreases with temperature, while λ_max of PS⁼Ba⁺⁺ of low DP increases with decreasing temperature. At ?100°C the difference between the two extreme values is about 30 nm. Similar results are obtained with PS⁼Sr⁺⁺. Such unusual spectral properties are interpreted, on the basis of excitation molecular theory, in terms of ring structures for the living oligomers.     

Polymerization of polystyryl-barium in THF—I. Kinetics of mono- and α,ω-dicarbanionic mixtures

The kinetics of propagation of mixtures of mono- and bicarbanionic polystyryl-barium (PS^?)₂Ba²⁺ and (PS^2?Ba²⁺) were studied in THF and the molecular weight distribution of the resulting polystyrene was analyzed. (PS^?)₂Ba propagates much more rapidly than PS^2?Ba²⁺, each kind of chain keeping a narrow molecular weight distribution. The propagation rate of (PS^?)₂Ba²⁺ is strongly decreased by the presence of oligo PS^2?Ba²⁺. The results are explained by the formation of mixed triple ions between cyclic PS^2?Ba²⁺ and monocarbanionic (PS^?)₂Ba²⁺ and by mixed associations of ion pairs, specially important for small PS^2?Ba²⁺.     

Polymerization of mono- and α,ω-dicarbanionic polystyryl-barium—II. Effect of added lithium salt in THF

The propagation rate of polystyryl-barium was studied in THF at 20°, in the presence of small amounts of lithium chloride. These kinetic results furnish a new method for the determination of triple ion formation in both mono- and α,ω-dicarbanionic polystyryl-barium. The constant of triple ion association of monocarbanionic (PS^?)₂Ba, K_T, was found to be 3.7 × 10⁵ l M^?1, close to the value calculated from published data.

The triple ion association constant of α,ω-dicarbanionic PS^2?Ba²⁺, K_DT, is about 1.2 × 10⁶ l M^?1.

Taking into account the cyclic structure of α,ω-dicarbanionic PS^2?Ba²⁺ and a statistical factor 3 between K_T and K_DT, it is concluded that mono- and dicarbanionic polystyryl-barium have similar abilities for triple ion formation. Nevertheless, stronger associations are observed for dicarbanionic oligomers with a degree of polymerization lower than 5–7.     

Kinetics and mechanisms in carbocationic polymerization: The quest for true rate constants

This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (k_p) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, k_p = 1.35 × 10⁴ L mol^?1 s^?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k_p = 1.01 × 10⁷ L mol^?1 s^?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl₄ from various laboratories yielded of ΔH ～?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl₄ ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ～ ?40 kJ/mol, whereas H₂O/TiCl₄ in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005     

Polymerization of Cyclosiloxanes. I. Kinetic Studies on Living Polymer—Octamethylcyclotetrasiloxane Systems

The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D₄) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S^- and M represent the initiator and D₄, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k₁ = 2.3 × 10^?4 l./mole-sec., k₂ < 2.3 × 10^?5 sec.^?1, k₃ = 2.75 × 10^?2l./mole-sec. k₄ ≈ 1.17 × 10^?2 sec.^?1, K₁ > 10 l./mole and K₂ ≈ 2.35 l./mole. The rate constants k₁ and k₃ were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K₂, indicating zero ΔH and positive ΔS in the propagation reaction.     

Living Carbocationic Polymerization. LVII. Kinetic Treatment of Living Carbocationic Polymerization Mediated by the Common Ion Effect

Abstract

The effect of anion concentration on the apparent rate constant of polymerization k^A _p of isobutylene (IB) induced by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system using the CH₂Cl₂/nC₆H₁₄ (60/40 v/v) solvent system at ?40 and ?80°C was studied by the use of nBu₄NCl. Computer simulation has shown that k^A _p decreases several orders of magnitude upon the addition of even a very small amount of common anion TiCl^?- ₅ to the charge. The rate of change is reduced in the concentration range of experimental interest. It was concluded that the decrease of k^A _p with increasing TiCl ^?- ₅ concentration is mainly due to the decreasing contribution of propagation by free ions. The contribution (%) of propagation by free ions to the apparent rate of propagation was calculated.     

Kinetics and mechanism of intramolecular general base-catalyzed alkanolysis of phenyl salicylate in the presence of anionic micelles

The alkanolysis of ionized phenyl salicylate, PS^?, has been studied in the presence and absence of micelles of sodium dodecyl sulphate, SDS, at 0.05 M NaOH, 30 or 32°C and within the alkanol, ROH, (ROH = HOCH₂CH₂OH and CH₃OH) contents of 15–74 or 92%, v/v. The alkanolysis of PS^? involves intramolecular general base catalysis. At a constant concentration of SDS, [SDS]_T, the observed pseudo first-order rate constants, k_obs, for the reactions of ROH with PS^? obtained at different concentration of ROH, [ROH]_T, obey the relationship: k_obs = k[ROH]_T/(1 + K_A[ROH]_T) where k is the apparent second-order rate constant and K_A is the association constant for dimerization of ROH molecules. Both k and K_A decrease with increase in [SDS]_T. At a constant [ROH]_T, the rate constants, k_obs, show a decrease of nearly 2-fold with increase in [SDS]_T from 0.0–0.3M. These results are explained in terms of pseudo-phase model of micelle. The rate constants for alkanolysis of PS^? in micellar pseudophase are insignificant compared with the corresponding rate constants in aqueous-alkanol pseudophase. This is attributed largely to considerably low value of [ROH] in the specific micellar environment where micellar bound PS^? molecules exist. The increase in [ROH]_T decrease the value of the binding constant of PS^? with SDS micelle. The effects of anionic micelles on the rates of alkanolysis of PS^? are explained in terms of the porous cluster micellar structure.     

Criteria for living systems with a special emphasis on living cationic polymerization of alkenes

A number of new living systems have been reported in recent years. Classic anionic polymerization of nonpolar monomers allows the synthesis of well-defined high molecular weight polymers (DP > 1000), block copolymers, chains with perfect terminal functionalities and behaves as a true living system. Some new systems abuse the term “living polymerization.” A relatively modest criterion for living systems is proposed “3 X 10,000,” i.e., k_p/k_t > 10⁴ mol^-1 L, k_p/k_tr > 10⁴, 1/k_t/tr > 10⁴ s (translated to < 10% of chains deactivated at t ≈ 1000 s), which is related to a typical limit of the polymeric chain dimensions (DP ≈ 100) and standard synthetic manipulations (≈ 15 min). New living cationic systems are discussed in detail with special emphasis on exchange phenomena. © 1993 John Wiley & Sons, Inc.     

Kinetics and thermodynamics of anionic polymerization of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane

Kinetic activation parameters and thermodynamic functions describing the reversible anionic polymerization of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane (1,3-propylene methyl phosphate) were determined. Enthalpy and entropy of the anionic propagation ? depropagation equilibrium were found to be close to those found previously by the present authors for the cationic polymerization, while the activation parameters of propagation and depropagation differ substantially for both processes and reflect the differences in the involved mechanisms. Thus, data for anionic polymerization (and cationic polymerization in parentheses) are: ΔH_1s° = ?0.7 kcal/mole (?1.1); ΔS_1s° = ?2.8 cal/mole-deg (?5.4); ΔH_p^? = 26.7 kcal/mole, and ΔS_p^? = ?6.1 cal/mole-deg. The polymers obtained have low degrees of polymerization (DP _n ≤ 10) because of the extensive chain transfer, leaving cyclic end groups in macromolecules. The presence, structure and concentration of the end groups have been determined by ¹H-, ³¹P-, and ¹³C-NMR spectra.     

Reaction of tetramethyl-1,2-dioxetane with triphenylphosphine: Activation parameters for the formation of 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane

The reaction of tetramethyl-1,2-dioxetane ( 1 ) and triphenylphosphine ( 2 ) in benzene-d₆ produced 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane ( 3 ) in ?90% yield over the temperature range of 6–60°. Pinacolone and triphenylphosphine oxide ( 4 ) were the major side products [additionally acetone (from thermolysis of 1 ) and tetramethyloxirane ( 5 ) were noted at the higher temperatures]. Thermal decomposition of 3 produced only 4 and 5 . Kinetic studies were carried out by the chemiluminescence method. The rate of phosphorane was found to be first order with respect to each reagent. The activation parameters for the reaction of 1 and 2 were: Ea ? 9.8 ± 0.6 kcal/mole; ΔS^≠ = ?28 eu; k_30° = 1.8 m^?1sec^?1 (range = 10–60°). Preliminary results for the reaction of 1 and tris (p-chlorophenyl)phosphine were: Ea ? 11 kcal/mole, ΔS^≠ = ?24 eu, k_30° = 1.3 M^?1sec^?1 while those for the reaction of 1 and tris(p-anisyl)phosphine were: Ea ? 8.6 kcal/mole, ΔS^≠ = ?29 eu, k_30° = 4.9 M^?1 sec^?1.     

Kinetics of the iodine atom catalyzed gas phase geometrical isomerization of diiodoethylene. Rotation about a single bond

The spectrophotometric determination of the rate of iodine atom catalyzed geometrical isomerization of diiodoethylene in the gas phase from 502.8 to 609.1°K leads to a rate constant for the bimolecular reaction between I and trans-diiodoethylene of log k_t?c(M^?1 sec^?1) = 8.85 ± 0.12 ? (11.01 ± 0.30)/θ. Estimates of the entropy and enthalpy change for the addition of I atoms to trans-diiodoethylene (process a.b) lead to log K_a.b(M^?1) = ?2.99 ? 4.0/θ, and thus to log k_c (sec^?1) = log k_t?c – log K_ab = 11.8 ?7.0/θ for the rate constant for rotation about the single bond in the adduct radical. The theory for calculation of the rotation rate constant is presented and it is shown that while the exact value depends on the barrier height, a value of 6.8 kcal/mole for this quantity leads to log k (sec^?1) = 11.8 ?6.7/θ. The activation energy points to a better value of the group contribution to heat of formation of the group C -(I)₂(H)(C) than one based on bond additivity.     

Graft polymerization kinetics of acrylamide initiated by ceric nitrate–dextran redox systems

The kinetics of the graft polymerization of acrylamide initiated by ceric nitrate—dextran polymeric redox systems was studied primarily at 25°C. Following an initial period of relatively fast reaction, the rate of polymerization is first-order with respect to the concentrations of monomer and dextran and independent of the ceric ion concentration. The equilibrium constant for ceric ion—dextran complexation K is 3.0 ± 1.6 l./mole, the specific rate of dissociation of the complex, k_d, is 3.0 ± 1.2 × 10^?4 sec.^?1, and the ratio of polymerization rate constants, k_p/k_t, is 0.44 ± 0.15. The number-average degree of polymerization is directly proportional to the ratio of the initial concentrations of monomer and ceric ion and increases exponentially with increasing extent of conversion. The initial rapid rate of polymerization is accounted for by the high reactivity of ceric ion with cis-glycol groups on the ends of the dextran chains. The polymerization in the slower period that follows is initiated by the breakdown of coordination complexes of ceric ions with secondary alcohols on the dextran chain and terminated by redox reaction with uncomplexed ceric ions.     

Transesterification of phenyl salicylate II. Kinetics and mechanism of intramolecular general base-catalyzed cleavage of phenyl salicylate under the presence of 1,2-ethanediol and 2-ethoxyethanol

The first-order rate constants, k₁, for 1,2-ethanediolysis (within the content of 1,2-ethanediol of 5% to 90%, v/v) and 2-ethoxyethanolysis (within the 2-ethoxyethanol content of 5% to 60%, v/v) of phenyl salicylate, PSH, in alkaline aqueous mixed solvents, fit to a relationship: k₁ = k[ROH]_T/(1 + K[ROH]_T) where k and K represent the secondorder rate constant for the reaction of alkanol, ROH, with ionized phenyl salicylate, PS^?, and association constant for the dimerization of ROH, respectively, and [ROH]_T is the total concentration of ROH. Similar relationship between k₁ and [ROH]_T has been found for 1,2-ethanediolysis of PS^? studied in mixed solvents containing 1,2-ethanediol and MeCN. In the alkaline aqueous mixed solvents containing 2-ethoxyethanol, the k₁-[ROH]_T profile reveals the change in the solvent structure of the reaction medium at >60% (v/v) of ROH content. It is proposed that alkanols exist in polymeric form, (ROH)_n, and the alkanolysis of PS^? involves the pre-equilibrium formation of monomeric ROH from (ROH)_n, followed by an intramolecular general base-catalyzed nucleophilic attack at carbonyl carbon of ester. A slight negative KCl salt- and slight positive n-Bu₄NI salt-effect are obtained for 1,2-ethanediolysis while a significant positive n-Bu₄NI salt-effect is obtained for 2-ethoxyethanolysis of PS^?.     

Intermolecular chain transfer to polymer with chain scission: general treatment and determination of kp/ktr in L,L-lactide polymerization

A general kinetic treatment of the system with intermolecular chain transfer followed by fast reinitiation is given. It leads to the broadening of the molecular weight distribution (MWD), the number of growing chains being invariable. Thus, this system can be considered as a special case of living polymerization. A general method has been elaborated allowing the determination of the ratio of the rate constant of propagation (k_p) to the rate constant of the bimolecular transfer (k⁽²⁾_tr) from the dependence of the MWD on monomer conversion. Numerical values of k_p/k⁽²⁾_tr equal to ≈ 10² and 25 were thus determined for the polymerization of L , L -lactide (L , L -dilactide) initiated with aluminium tris(isopropoxide) trimer ({Al(OⁱPr)₃}₃) and tributyltin ethoxide (ⁿBu₃SnOEt), respectively.     

Polymerization kinetics of octene-1 catalyzed by metallocene methylaluminoxane investigated with attenuated total reflectance fourier transform infrared (ATR-FT-IR) spectroscopy

The kinetic parameters have been measured for octene-1 solution polymerization at 120°C catalyzed by zirconocene with the cocatalyst methylaluminoxane. The polymerizations were performed in an attenuated total reflectance (ATR) reaction cell. The progress of the reactions were followed by observing the disappearance of octene-1 using the 910 cm^?1 band measured by FT-IR spectroscopy. The dependence of the reaction rate, R_p, on catalyst concentration and cocatalyst/catalyst ratio was examined. The catalyst deactivation mechanism was studied by fitting the experimental data to mathematical models involving second-order propagation and either first or second order catalyst deactivation. Second-order catalyst deactivation provided a much better fit. The calculated deactivation rate constant, k_d, is 21 (Ms)^?1. This model is used to determine the propagation rate constant for Al/Zr = 4 × 10³ as k_p = 19.9 (M s)^?1. A decrease in Al/Zr = 3 × 10² lowered the propagation rate constant, k_p, to 9.6 (M s)^?1 indicating that less than 50% of the initial Zr is active at this Al/Zr ratio.     

Anionic copolymerization of styrene and 1,1-diphenylethylene

Kinetics of anionic copolymerization of styrene (S) and 1,1-diphenylethylene (D) were investigated in THF. The rate constant of addition of D to living polystyrene was found to be k_{1,2 ±} = 250 l./mole-sec. for , Na⁺ ion-pair, and that for the free , Na⁺ ion is k_1,2?～400,000 l./mole-sec. Both values refer to 25°C. The addition of styrene to ? D^?, Na⁺ was found to be reversible: and k_2,1 was determined by three different methods to be ～0.5–0.7 l./mole-sec. Studies performed in a stirred-flow reactor led to k-₂₁ = 13 sec. ^?1 and K₂₁ ～ 5 × 10^?2 l./mole. An alternating copolymer is obtained in the presence of a large excess of 1,1-diphenylethylene.     

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.     

Synthetic thermally reversible gel systems. IV

The polymerization kinetics in water of acrylylglycinamide (AG) initiated by K₂S₂O₈ was studied over the temperature range 40.0 to 60.0°C. Monomer concentration was varied from 7.8 × 10^?3 to 31.2 × 10^?3M and catalyst from 1.85 × to 11.10 × 10^?5M. The rate expression is ?d[M]/dt = R_p, = k_1.22[K₂S₂O₈]^0.5[M]^1.22, and the overall empirical rate constant, k_1.22 = 1.14 × 10¹¹e^?15,800/RT 1.^0.72 mole^?0.72 min^?1. To explain the dependence on monomer, a kinetic scheme which includes a bimolecular reaction (k₂) between monomer and initiator is suggested. The simplified expression which describes the initial rate of polymerization is: ?d[M]/dt = R_p, = k₄(2[I]/k₅)^1/2[M](k₁ + k₂[M])^1/2, where k₁, k₂, k₄ and k₅ are rate constants for S₂O₈ = decomposition, a bimolecular reaction between monomer and initiator, propagation, and termination, respectively. Individual bimolecular rate constants are expressed in liter/mole-min. The equation predicts a dependence on monomer concentration between 1.0 and 1.5 with 1.5 being approached a t high monomer concentrations. Plots of R_P²/[M]² versus [M] are linear, as predicted by the postulated reaction route and values for k₂ and k₄/k₅^1/2 were obtained from the slopes and intercepts of these plots. The temperature dependence of the bimolecular monomer-initiator reaction is k₂ = 5.19 × 10²¹e^?36,000/RT. Instead of the usual behavior, the k₄/k₅^1/2 ratio was found to decrease with temperature and the difference of activation energies, (E₄ ? E₅/2), is ?1.50 kcal. The temperature dependence of the propagation to square root of the termination rate constant ratio is k₄/k₅^1/2 = 6.16e^1500/RT. These rather unusual results may be related to the ability of AG polymers in water to form thermally reversible gels; even above the gel melting points, the polymers are considerably aggregated in solution. This would tend to make the bimolecular termination reaction more temperature dependent and also account for the high values (59–69) for the k₄/k₅^1/2 ratios. For similar temperatures, the overall rate constants for AG are approximately four times those for acrylamide.     

Chromocene-based catalysts for ethylene polymerization: Kinetic parameters

The chromocene catalyst for ethylene polymerization shows a high response to hydrogen which leads directly to highly saturated polyethylenes containing methyl groups as the major terminal functionality in the polymers. At a polymerization temperature of 90°C the ratio of termination rate constants for hydrogen (k_H) and ethylene (k_M) is k_H/k_M = 3.60 × 10³. The ratio of k_H to the chain propagation constant (k_p) is k_H/k_p = 4.65 × 10^?1 A simple relation that can be derived from polymerization kinetics and the Quackenbos equation exists between melt index and hydrogen–ethylene ratio. A deuterium isotope effect (k_H/k_D) = 1.2 was calculated for the termination reaction. The overall polymerization process has an apparent activation energy of 10.1 kcal/mole. Oxygen addition studies show catalyst activity is proportional to initial divalent chromium content.     

Anionic polymerization with alkaline earth counterion. III. Aging of oligo- and polystyryl-barium and -strontium in THF

The self-deactivation of polystyryl-barium and polystyryl-strontium in tetrahydrofuran (THF) results essentially from protonation by the solvent. The deactivation constant k_d of this reaction is independent of carbanion concentration, length, and functionality of chains. Relations of k_d with temperature are: polystyryl-barium: k_d = 6.25 × 10⁷ exp(-18,900/RT) sec^?1; polystyryl-strontium: k_d = 4.1 × 10⁶ exp(?16,000/RT) sec^?1. The self-deactivation of α,ω-dicarbanionic oligostyryl-barium is a nonrandomlike reaction. Residual living oligomers are left dicarbanionic even if an important deactivation occurs.