Silyl enol ethers as monomer. I. Radical copolymerizability of α-trimethylsilyloxystyrene

α-Trimethylsilyloxystyrene (TMSST), the silyl enol ether of acetophenone, was not homopolymerized either by a radical or a cationic initiator. Radical copolymerization of TMSST with styrene (ST) and acrylonitrile (AN) in bulk and the terpolymerization of TMSST, ST, and maleic anhydride (MA) in dioxane were studied at 60°C and the polymerization parameters of TMSST were estimated. The rate of copolymerization decreased with increased amounts of TMSST for both systems. Monomer reactivity ratios were found as follows: r₁ = 1.48 and r₂ = 0 for the ST (M₁)–TMSST (M₂) system and r₁ = 0.050 and r₂ = 0 for the AN (M₁)–TMSST (M₂) system. The terpolymerization of ST (M₁), TMSST (M₂), and MA (M₃) gave a terpolymer containing ca. 50 mol % of MA units with a varying ratio of TMSST to ST units and the ratio of rate constants of propagation, k₃₂/k₃₁, was found to be 0.39. Q and e values of TMSST were determined using the values shown above to be 0.88 and ?1.13, respectively. Attempted desilylation by an acid catalyst for the copolymer of TMSST with ST afforded polystyrene partially substituted with hydroxyl groups at the α-position.     

Studies of Radical Alternating Copolymerization. I. Quantitative Determination of the Relative Reactivities between Free Comonomers and a Complex between Them; A Theoretical Treatment in Terms of Frontier Molecular Orbital Interactions. Application to Radical Maleic Anhydride-Vinyl Acetate Alternating Copolymerization

A simple quantitative determination of the ratio β₁ of rate constants k_ij corresponding to the addition of a complex or a free monomer on a same growing chain in alternating copolymerization was determined. The application of this method to the case of alternating maleic anhydride (A)-vinyl acetate (D) copolymerization give for β₁ = k_AC/k_AD and for β₂ = k_DC/k_DA (C refers to the complex) the respective values of 7 and 0. A complex was more reactive than A but less reactive than D toward a growing chain. In order to explain these reactivities, a frontier molecular orbital treatment was proposed. A good qualitative correlation with experimental results was obtained.     

Characterization of novel optically active conjugated polyarylenes and poly(aryleneethnylene)s by a combination of off-line static and dynamic light scattering with gel permeation chromatography

By combining the offline static and dynamic laser light scattering (LLS) and gel permeation chromatography (GPC) results of a broadly distributed polymer sample, we were able to characterize a series of chiral binaphthyl-based polyarylenes and poly(aryleneethnylene)s in THF at 25°C. For each of the samples, we obtained not only the weight-average molar mass M_w, the second virial coefficient A₂ and the z-average translational diffusion coefficient 〈D〉, but also two calibrations: V = A + Blog(M) and D = k_D M^−αD, where V, D, and M are the elution volume, the translational diffusion coefficient and the molar mass for monodisperse polymer chains, respectively, and A, B, k_D, and α_D are four calibration constants. Using these calibrations, we estimated the molar mass distributions of these novel polymers. We showed that using polystyrene to calibrate the GPC columns could lead to a smaller M_w. Our results indicate that all the polymers studied have a rigid chain conformation in THF at 25°C and the introduction of the —NO₂ groups into the monomer can greatly promote the polymer solubility in THF.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2615–2622, 1998     

Kinetic Study of the Bromine-Catalyzed Isomerization of Maleic Acid in Aqueous Ce(IV)-Br−-H2SO4 Medium

The presence of ceric and bromide ions catalyzes the isomerization of maleic acid (MA) to fumaric acid (FA) in aqueous sulfuric acid. A kinetic study of this bromine-catalyzed reaction was carried out. The reaction between ceric ion and maleic acid is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M (adjusted by NaClO₄), and [MA]₀=(0.5–1.0)M, the observed pseudo-first-order rate constant (k₀₃) at 25° is k₀₃=7.622×10^?5 [MA]₀/(1+0.205[MA]₀). The reaction between ceric and bromide ions is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀=(0.025–0.150)M, the pseudo-first-order rate constant (k₀₂) at 25° is k₀₂= (4.313±0.095)x10^?2[Br^?]²+(2.060±0.119)x10^?3[Br^?]. The reaction of Ce(IV) with maleic acid and bromide ion is also first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [MA]₀=0.75 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀= (0.025–0.150)M, the pseudo-first-order rate constant (k₀₃) at 25° is k₀₃= (5.286±0.045)x10^?2[Br^?]²+(3.568±0.056)x10^?3[Br^?]. For [Ce(IV)]₀=5.0 × 10^?4 M, [Br^?]₀=0.050 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [MA]₀=(0.15–1.0)M at 25°, k₀₃=(2.108×10^?4+2.127×10^?4[MA]₀)/(1+0.205[MA]₀). A mechanism is proposed to rationalize the results. The effect of temperature on the reaction rate was also studied. The energy barrier of Ce(IV)—Br^? reaction is much less than that of Ce(IV)—MA reaction. Maleic and fumaric acids have very different mass spectra. The mass spectrum of fumaric acid exhibits a strong metastable peak at m/e 66.5.     

Olefin copolymerization with metallocene catalysts. II. Kinetics,cocatalyst, and additives

The kinetics of ethylene/propylene copolymerization catalyzed by (ethylene bis (indeyl)-ZrCI₂/methylaluminoxane) has been investigated. Radiolabeling found about 80% of the Zr to be catalytically active. The estimates for rate constants at 50°C are k₁₁ = 1104 (M_s)^?1, k₁₂ = 430 (M_s)^?1, k₂₂ = 396 (M_s)^?1,k₂₁ = 1020 (M_s)^?1, and k^A_tr,1 + k^A_tr.2 = 1.9 × 10^?3 s^?1. Substitution of trimethylaluminum for methylaluminoxane resulted in proportionate decrease in polymerization rate. The molecular weight of the copolymer is slightly increased by loweing the [Al]/[Zr] ratio, or addition of Lewis base modifier but at the expense of lowered catalytic activity and increase in ethylene content in the copolymer. Lowering of the polymerization temperature to 0°C resulted in a doubling of molecular weight but suffered 10-fold reduction in polymerization activity and increase of ethylene in copolymer.     

Carboxylate Catalyzed Isomerization of β,γ-Unsaturated N-Acetylcysteamine Thioesters**

We demonstrate herein the capacity of simple carboxylate salts – tetrametylammonium and tetramethylguanidinium pivalate – to act as catalysts in the isomerization of β,γ-unsaturated thioesters to α,β-unsaturated thioesters. The carboxylate catalysts gave reaction rates comparable to those obtained with DBU, but with fewer side reactions. The reaction exhibits a normal secondary kinetic isotope effect (k_1H/k_1D=1.065±0.026) with a β,γ-deuterated substrate. Computational analysis of the mechanism provides a similar value (k_1H/k_1D=1.05) with a mechanism where γ-reprotonation of the enolate intermediate is rate determining.     

Primary radical termination rate constant at high conversion in radical polymerization

A primary radical termination rate constant given by: k_ti = A_1iD_i, where A_1i is a constant and D_i is the diffusion constant of the primary radical, was examined on the basis of the variation of conversion. It was proved that this rate constant is correct at high conversion. A relationship between primary radical termination rate constant and conversion was derived. The effect of variation of conversion on the gel effect is discussed.     

Effect of diffusion on rates and molecular weights in graft polymerization

A theoretical analysis has been made of the graft polymerization process in terms of the quantitative interrelationship between the initiation rate R_i, the k_p/k_t^1/ ratio of the monomer, the equilibrium solubility M of the monomer in the polymer, the polymer film thickness L, and the diffusivity D of the monomer in the polymer. It is shown how the values of these parameters in any grafting system interact to lead to diffusion-controlled graft polymerization. Whether graft polymerization is diffusion-free or diffusion-controlled depends on the values of K_p, d, k_p/k_p^1/2, and L as gathered in the parameter A = [(K_p/k_t^1/2)R_i, D,/^1/2] L/2. When the values of the various terms are such that A is less than 0.1 (i.e., D is large while R_i, k_p, and L are small), the reaction is diffusion-free. When A is greater than 3 (i.e., D is small while R_i, k_p, and L are large), the reaction is diffusion-controlled. The derived equations showing the relationship between kinetic and diffusional parameters are theoretically applicable to all grafting systems, i.e., for all monomer-polymer combinations under all conditions of reaction temperature, radiation intensity and polymer film thickness. The theoretical analysis has been verified for the rate and degree of polymerization for the radiation-induced graft polymerization of styrene to polyethylene.     

Relationship between chain termination rate constant and conversion in radical polymerization

At low and high conversions, the chain termination rate constant for bimolecular termination between polymeric radicals given by k_t = A_tD_s, where A_t is a constant and D_s is the diffusion constant of radical chain end, is completely correct. This termination rate constant does not depend on solution viscosity, but conversion.     

Diffusion control in radiation graft polymerization with varying dependence of rate on monomer concentration

The quantitative effect of diffusion control on the rate of radiation-initiated graft polymerization has been studied theoretically for systems in which the diffusion-free reaction may show various dependencies of rate on monomer concentration other than the usual first-order dependence. The study is also very general in that it can be applied to systems involving a variety of different modes of initiation and termination. Whether the grafting process is diffusion-free or diffusion-controlled has been analyzed in terms of the interaction of the initiation rate R_i, the propagation and termination rate constants k_p and k_t, the equilibrium solubility M of the monomer in the polymer, the polymer film thickness L, the diffusivity D of the monomer in the polymer, and the diffusion-free kinetic order of dependence v of the grafting rate on monomer concentration. The dependence of the grafting rate for both the diffusion-free and diffusion-controlled reactions on these parameters is expressed both by mathematical experssions and graphically. Diffusion control is shown to occur at a critical value of the parameter A which is proportional to L(k_pR_i^w/k_t^zD)^1/2M^(ε?1)/2 where w, z, and v have different values depending on the specific modes of initiation, propagation and termination in a particular grafting system. The grafting rate is shown to vary with the value of A according to specific mathematical expressions. In comparing diffusion-free to diffusion-controlled reaction, it is shown that the former is independent of L and D while the latter is directly dependent on L and inversely on D^1/2. Further, the change from diffusion-free to diffusion-controlled reaction involves a change in the dependence of rate on monomer from v-order to [(v ? 1)/2]-order. The nonsteady-state as well as the steady-state reaction rates have been analyzed.     

The gas-phase pyrolysis of alkyl nitrites. II. s-butyl nitrite

The rate of decomposition of s-butyl nitrite (SBN) has been studied in the absence (130–160°C) and presence (160–200°C) of NO. Under the former conditions, for low concentrations of SBN (6 × 10^?5 ? 10^?4M) and small extents of reaction (～1.5%), the first-order homogeneous rates of acetaldehyde (AcH) formation are a direct measure of reaction (1) since k_3c » k₂(NO): . Unlike t-butyl nitrite (TBN), d(AcH)/dt is independent of added CF₄ (～0.9 atm). Thus k_3c is always » k₂ (NO) over this pressure range. Large amounts of NO (～0.9 atm) (130–160°C) completely suppress AcH formation. k₁ = 10^16.2–40.9/θ sec^?1. Since (E₁ + RT) and ΔH°₁ are identical, within experimental error, both may be equated with D(s-BuO-NO) = 41.5 ± 0.8 kcal/mol and E₂ = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result ΔH°_f (s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document}) = ? 16.6 ± 0.8 kcal/mol. From ΔS°₁ and A₁, k₂ is calculated to be 10^10.4 M^?1 · sec^?1, identical to that for TBN. From an independent observation that k₆/k₂ = 0.26 ± 0.01 independent of temperature, \documentclass{article}\pagestyle{empty}\begin{document}${\rm s - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}, we find E₆ = 0 ± 1 kcal/mol and k₆ = 10^9.8M^?1 · sec^?1. Under the conditions first cited, methyl ethyl ketone (MEK) is also a product of the reaction, the rate of which becomes measurable at extents of conversion >2%. However, this rate is ～0.1 that of AcH formation. Although MEK formation is affected by the ratio S/V for different reaction vessels, in a spherical reaction vessel, this MEK arises as the result of an essentially homogeneous first-order 4-centre elimination of HNO. \documentclass{article}\pagestyle{empty}\begin{document}${\rm SBN}\mathop \to \limits^{\rm 5} {\rm MEK} + {\rm HNO}$\end{document}; k₅ = 10^12.8–35.8/θ sec^?1. Sec-butyl alcohol (SBA), formed at a rate comparable to MEK, is thought to arise via the hydrolysis of SBN, the water being formed from HNO. The rate of disappearance of SBN, that is, d(MEK + SBA + AcH)/dt, is given by k_global = 10^15.7–39.6/θ sec^?1. In NO (～1 atm) the rate of formation of MEK was about twice that in the absence of NO, whereas the SBA was greatly reduced. This reaction was also affected by the ratio S/V of different reaction vessels. It was again concluded that in a spherical reaction vessel, the rate of MEK formation was essentially homogeneous and first order. This rate is given by k_obs = 10^12.9–35.4/θ sec^?1, very similar to k₅. However, although it is clear that the rate of formation of MEK is doubled in the presence of NO, the value for k_obs makes it difficult to associate this extra MEK with the disproportionation of s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document} and NO: s-\documentclass{article}\pagestyle{empty}\begin{document}$s{\rm - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}. NO at temperatures of 130–160°C completely suppresses AcH formation. AcH reappears at higher temperatures (165–200°C), enabling k_3c to be determined. Ignoring reaction (6), d(AcH)/dt = k₁k₃ (SBN )/[k_3c + k₂(NO)]; k_3c = 10^14.8–15.3/θ sec^?1. Inclusion of reaction (6) into the mechanism makes very little difference to the result. Reaction (3c) is expected to be a pressure-dependent process.     

Studies of Radical Alternating Copolymerization. III. Kinetics of the Copolymerization of Citraconic Anhydride and Vinyl Acetate: A New Method of Evaluating the Kinetics Constant

We show that the copolymerization of citraconic anhydride and vinyl acetate is an alternating one. The two monomers form a charge transfer complex, and we propose a new strategy to determine the value of the velocity constants β₁ = K_AC/K_AD and β₂ = K_DC/K_DA involving the acceptor A, the donor D, and their charge transfer complex C. We obtained β₁ = 9.9 and β₂ = 3.6. The complex exhibits a greater reactivity than the monomer in the propagation reactions.     

Synthesis of poly(dimethylsiloxane)‐containing diblock and triblock copolymers by the combination of anionic ring‐opening polymerization of hexamethylcyclotrisiloxane and nitroxide‐mediated radical polymerization of methyl acrylate,isoprene, and styrene

Poly(dimethylsiloxane)‐containing diblock and triblock copolymers were prepared by the combination of anionic ring‐opening polymerization (AROP) of hexamethylcyclotrisiloxane (D₃) and nitroxide‐mediated radical polymerization (NMRP) of methyl acrylate (MA), isoprene (IP), and styrene (St). The first step was the preparation of a TIPNO‐based alkoxyamine carrying a 4‐bromophenyl group. The alkoxyamine was then treated with Li powder in ether, and AROP of D₃ was carried out using the resulting lithiophenyl alkoxyamine at room temperature, giving functional poly(D₃) with M_w/M_n of 1.09–1.16. NMRPs of MA, St, and IP from the poly(D₃) at 120 °C gave poly(D₃‐b‐MA), poly(D₃‐b‐St), and poly(D₃‐b‐IP) diblock copolymers, and subsequent NMRPs of St from poly(D₃‐b‐MA) and poly(D₃‐b‐IP) at 120 °C gave poly(D₃‐b‐MA‐b‐St) and poly(D₃‐b‐IP‐b‐St) triblock copolymers. The poly(dimethylsiloxane)‐containing diblock and triblock copolymers were analyzed by ¹H NMR and size exclusion chromatography. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6153–6165, 2005     

Kinetics of high-intensity electron-beam copolymerization of a divinyl urethane and 2-hydroxyethyl methacrylate

The kinetics of the electron-beam-induced copolymerization of di(2′-methacryloxyethyl)-4-methyl-m-phenylenediurethane (DVU) with 2-hydroxyethyl methacrylate (HEMA) were studied. Monomer mixtures containing 1.96–82.8% DVU have been described at dose rates of 1.7–17 Mrad/sec with the use of 270-kV electrons. Based on rates of conversion, gel formation, and intensity-rate data, a kinetic scheme is proposed in accord with a model which undergoes unimolecular termination and for which the copolymerization and gel formation take place in a crosslinked network swollen with monomers. The rate of gel formation is: In[(1 + g)/(1 ? M₂g)] = A (1 + M₂)t, where g is the gel fraction, M₂ is the mole fraction of DVU in the monomer charge, and A is k_pk_i/k_t. Up to 55% conversion, the rate of disappearance of unsaturation for concentrated DVU solutions (M₂ > 0.03) is: In[M_o/M(1 ? M₂g)] = A (1 + M₂t), where M is the total unsaturation. For dilute solutions of DVU, the rate expression for pregel copolymerization simplifies to: In(M_o/M) = A (1 + M₂)t. These results show that at a certain optimum concentration of monovinyl monomer—70% in the present system—both rapid reaction rates and complete copolymerization occur. Because of the inability of gel bonds to undergo polymerization, a limiting conversion is reached for copolymerizing mixtures containing insufficient monovinyl monomer.     

Kinetics of cerium (IV) oxidation of mandelic acid. Ionic strength and specific cation effects

The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H₂SO₄? MClO₄ (M⁺ = H⁺, Li⁺, Na⁺) and H₂SO₄? MHSO₄ (M⁺ = Li⁺, Na⁺, K⁺) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k₁ + k₂/(1 + a)²[HSO₄^?]² = k₁ + k₂/(1 + 1/a)²[SO₄^2?]², a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H⁺ ? Li⁺ < Na⁺ < K⁺. The observed negative cation effects on the rate constant k₁ are in the order Na⁺ < Li⁺ < H⁺, whereas the order is in reverse for k₂, namely, H⁺ ? Li⁺ < Na⁺. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters.     

Electronic Spectroscopic Studies of the Charge Transfer Complex of N,N , N ′, N ′-Tetramethyl-4-4′-Diamino-Benzophenone with Iodine in Methanol

The UV-visible absorption bands of the charge transfer (CT) complex of N, N, N', N'-tetramethyl-4,4'-diamino-benzophenone with iodine in methanol at 30°C have been studied. The value of K^AD , ?^AD and E _CT were calculated for this complex. The value of the equilibrium constant, K^AD , for the above complex reaction was calculated as 28.85m³·mol^?1. The value of the molar extinction coefficient of the CT complex, ?^AD , was also calculated as 1171m²·mol^?1 for λ_max = 602 nm and the absorption band energy E _CT of the complex was found to be 2.06 e.v. The ionization potential of the electron donor was also obtained spectroscopically and found to be 6.284 e.v. The rate constant obtained for the forward reaction is 3.624 x 10^?5M^1/2s^?1 and for the reverse reaction is 1.256 x 10^?6s^?1. Finally, the half-life value for the above reaction was graphically calculated and shown to be 1.549 day. The kinetics of the above reaction were studied showing the reaction to be a half-order reaction. The values of rate constants and half-life were calculated.     

Diffusion-controlled reaction. V. Effect of concentration-dependent diffusion coefficient on reaction rate in graft polymerization

The effect of diffusion on radiation-initiated graft polymerization has been studied with emphasis on the single- and two-penetrant cases. When the physical properties of the penetrants are similar, the two-penetrant problem can be reduced to the single-penetrant problem by redefining the characteristic parameters of the system. The diffusion-free graft polymerization rate is assumed to be proportional to the v power of the monomer concentration C, in which the proportionality constant a = k_pR/k, where k_p and k_t are the propagation and termination rate constants, respectively, and R_i is the initiation rate. The values of v, w, and z depend on the particular reaction system. The results of our earlier work were generalized by allowing a non-Fickian diffusion rate, obtained from an extension of the Fujita free-volume theory, which predicts an essentially exponential dependence on the monomer concentration of the diffusion coefficient, D = D₀ [exp(δC/M)], where M is the saturation concentration. It was shown that a reaction system is characterized by the three dimensionless parameters v, δ, and A = (L/2)[aM^(v?1)/D₀]^1/2, where L is the polymer film thickness. Graft polymerization tends to become diffusion controlled as A increases. Larger values of δ and v cause a reaction system to behave closer to the diffusion-free regime. The transition from diffusion-free to diffusion-controlled reaction involves changes in the dependence of the reaction rate on film thickness, initiation rate, and monomer concentration. Although the diffusion-free rate is w order in initiation rate, v order in monomer, and independent of film thickness, the diffusion-controlled rate is w/2 order in initiator rate and inverse first-order in film thickness. The dependence of the diffusion-controlled rate on monomer is dependent in a complex manner on the diffusional characteristics of the reaction system.     

Determination of propagation and termination rate constants for some methacrylates in their radical polymerizations

Rotating sector determinations of k_p and 2k_t for ten methacrylates undergoing radical polymerization were carried out at 30°C. Ester groups in the monomers were: isopropyl, ethyl, β-cyclohexylethyl, methyl, γ-phenylpropyl, β-phenylethyl, β-methoxyethyl, benzyl, β-chloroethyl, and phenyl. Values of k_p obtained were 121, 126, 1190, 141, 149, 228, 249, 1250, 254, and 411 l./mole-sec., respectively; values of 2k_t × 10^?6 were 4.52, 7.35, 32.8, 11.6, 0.813, 1.88, 9.30, 41.9, 6.71, and 11.9 l./mole-sec., respectively. Omitting the data for the β-cyclohexylethyl and benzyl esters, a Taft correlation, log k_p = (0.70 ± 0.18)σ* + 2.2, was established, where σ* denotes Taft's polar substitutent constants for the above-mentioned ester groups. The steric substituent constants E_s were found to have no influence on k_p. Combination of k_p with r₂ data from copolymerization studies with styrene or methyl methacrylate as M₁ comonomer revealed that the more reactive monomer gave rise to the more reactive polymer radical. Monomer viscosities and molar volumes of the ester groups were found to correlate with 2k_t.     

Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L‐ascorbic acid

The reduction of Fe(CN)₅L^2? (L = pyridine, isonicotinamide, 4,4′‐bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1–7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H₂A(k₀), HA^?(k₁), and A^2? (k₂), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka₁ and Ka₂, the rate constants are k₀ = 1.8, 7.0, and 4.4 M^?1 s^?1; k₁ = 2.4 × 10³, 5.8 × 10³, and 5.3 × 10³ M^?1 s^?1; k₂ = 6.5 × 10⁸, 8.8 × 10⁸, and 7.9 × 10⁸ M^?1 s^?1 for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO₄/LiClO₄, T = 25°C. The kinetic results are compatible with the Marcus prediction. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 126–133, 2005     

A theoretical approach to the kinetics of polymer degradation in solution

After main-chain scission in a polymer, the frequency of encounter between segments in the different fragments is related to the separating process between the fragments. The relationship obtained shows that the separating time is proportional to M ^½, where M is the molecular weight, when the excluded volume disappears. When good solvent is used, the half-time for the separation is obtained as τ_½ = const. M ^0.16–0.22, which is approximated to the experimental data obtained previously (τ_½ = const. M ^0.34 and τ_½ = const. M ^0.22) for the degradations of polyisobutene and poly(phenyl vinyl ketone), respectively. The increase of the half-time with increasing coil density can be explained by the excluded volume. The inverse proportionality of the diffusion of segments to solvent viscosity explains the proportionality of the half-time to microviscosity. The above separating process reverses the reaction between polymer radicals. From their dependence on the chain length, τ_½/k_D = const. M ^½ (where k_D is the specific rate for the reaction), is estimated. Such an approximation holds, regardless of the type of solvent.