Homopolymerization and copolymerization of isocyanatoethyl methacrylate

This article describes the homopolymerization of isocyanatoethyl methacrylate (IEM) and its copolymerization with methyl methacrylate (MMA) in acetonitrile in the presence of 2,2′‐azobisisobutyronitrile. The constant characteristic of IEM polymerizability (k_p²/k_te = 128 × 10^?3 L mol^?1 s^?1, where k_p is the propagation constant and k_te is the termination constant) was determined. The study of IEM reactivity toward MMA gave ratios of 0.88 and 1.20 for IEM and MMA, respectively. The physicochemical properties of the IEM homopolymer and IEM/MMA copolymers were also studied. The glass‐transition temperature of poly(isocyanatoethyl methacrylate) was found to be 47 °C. From the thermogravimetric analysis of the weight‐loss percentage corresponding to the first wave of the thermogram, it was shown that the degradation mechanism of the IEM/MMA copolymers started from the isocyanate group. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4762–4768, 2006     

Laser‐induced decomposition of 2,2‐dimethoxy‐2‐phenylacetophenone and benzoin in methyl methacrylate homopolymerization studied via matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Pulsed laser polymerization (PLP) experiments were performed on the bulk polymerization of methyl methacrylate (MMA) at ?34 °C. The aim of this study was to investigate the polymer end groups formed during the photoinitiation process of MMA monomer using 2,2‐dimethoxy‐2‐phenylacetophenone (DMPA) and benzoin as initiators via matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Analysis of the MALDI‐TOF spectra indicated that the two radical fragments generated upon pulsed laser irradiation show markedly different reactivity toward MMA: whereas the benzoyl fragment—common to both DMPA and benzoin—clearly participates in the initiation process, the acetal and benzyl alcohol fragments cannot be identified as end groups in the polymer. The complexity of the MALDI‐TOF spectrum strongly increased with increasing laser intensity, this effect being more pronounced in the case of benzoin. This indicates that a cleaner initiation process is at work when DMPA is used as the photoinitiator. In addition, the MALDI‐TOF spectra were analyzed to extract the propagation‐rate coefficient, k_p, of MMA at ?34 °C. The obtained value of k_p = 43.8 L mol^?1 s^?1 agrees well with corresponding numbers obtained via size exclusion chromatography (k_p = 40.5 L mol^?1 s^?1). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 675–681, 2002; DOI 10.1002/pola.10150     

Addition–fragmentation chain transfer: Molecular weight distributions and retardation in the system methyl methacrylate/methyl α‐(bromomethyl)acrylate

A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (k_add) over 60–120 °C resulted in E_add = 21.7 kJ mol^?1 and A_add = 2.18 × 10⁶ M^?1 s^?1 and a very weak temperature dependence of the chain‐transfer constant (E_add ≈ E_p). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as k_f ≈ 39 s^?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004     

Mechanism and kinetics of the imidazolidinone nitroxide‐mediated free‐radical polymerization of styrene

Styrene radical polymerizations mediated by the imidazolidinone nitroxides 2,5‐bis(spirocyclohexyl)‐3‐methylimidazolidin‐4‐one‐1‐oxyl (NO88Me) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) were investigated. Polymeric alkoxyamine (PS‐NO88Bn)‐initiated systems exhibited controlled/living characteristics at 100–120 °C but not at 80 °C. All systems exhibited rates of polymerization similar to those of thermal polymerization, with the exception of the PS‐NO88Bn system at 80 °C, which polymerized twice as quickly. The dissociation rate constants (k_d) for the PS‐NO88Me and PS‐NO88Bn coupling products were determined by electron spin resonance at 50–100 °C. The equilibrium constants were estimated to be 9.01 × 10^?11 and 6.47 × 10^?11 mol L^?1 at 120 °C for NO88Me and NO88Bn, respectively, resulting in the combination rate constants (k_c) 2.77 × 10⁶ (NO88Me) and 2.07 × 10⁶ L mol^?1 s^?1 (NO88Bn). The similar polymerization results and kinetic parameters for NO88Me and NO88Bn indicated the absence of any 3‐N‐transannular effect by the benzyl substituent relative to the methyl substituent. The values of k_d and k_c were 4–8 and 25–33 times lower, respectively, than the reported values for PS‐TEMPO at 120 °C, indicating that the 2,5‐spirodicyclohexyl rings have a more profound effect on the combination reaction rather than the dissociation reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 327–334, 2003     

Influence of nitroxide structure on the 2,5‐ and 2,6‐spirodicyclohexyl substituted cyclic nitroxide‐mediated free‐radical polymerization of styrene

The 2,6‐spirodicyclohexyl substituted nitroxide, cyclohexane‐1‐spiro‐2′‐(3′,5′‐dioxo‐4′‐benzylpiperazine‐1′‐oxyl)‐6′‐spiro‐1″‐cyclohexane (BODAZ), was investigated as a mediator for controlled/living free‐radical polymerization of styrene. The values of the number‐average molecular weight increased linearly with conversion, but the polydispersities were higher than for the corresponding 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) mediated systems at approximately 2.2 and 1.6 at 100 and 120 °C, respectively. These results were reflected in the rate coefficients obtained by electron spin resonance spectroscopy; at 120 °C, the values of the rate coefficients for polystyrene‐BODAZ alkoxyamine dissociation (k_d), combination of BODAZ and propagating radicals (k_c), and the equilibrium constant (K) were 1.60 × 10^?5 s^?1, 5.19 × 10⁶ M^?1 s^?1, and 3.08 × 10^?12 M, respectively. The value of k_d was approximately one and two orders of magnitude lower, and that of K was approximately 20 and 7 times lower than for the NO88Bn and TEMPO adducts. These results are explained in terms of X‐ray crystal structures of BODAZ and NO88Bn; the six‐membered ring of BODAZ deviates significantly from planarity as compared to the planar five‐membered ring of NO88Bn and possesses a benzyl substituent oriented away from the nitroxyl group leading to a seemingly more exposed oxyl group, which resulted in a higher k_c and a lower k_d than NO88Bn. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3892–3900, 2003     

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     

Initiator efficiency of 2,2′‐azobis(isobutyronitrile) in bulk dodecyl acrylate free‐radical polymerizations over a wide conversion and molecular weight range

An Erratum has been published for this article in J. Polym. Sci. Part A: Polym. Chem. (2004) 42(21) 5559 . The initiator efficiency, f, of 2,2′‐azobis(isobutyronitrile) (AIBN) in dodecyl acrylate (DA) bulk free‐radical polymerizations has been determined over a wide range of monomer conversion in high‐molecular‐weight regimes (M_n ? 10⁶ g mol^?1 [? 4160 units of DA)] with time‐dependent conversion data obtained via online Fourier transform near infrared spectroscopy (FTNIR) at 60 °C. In addition, the required initiator decomposition rate coefficient, k_d, was determined via online UV spectrometry and was found to be 8.4 · 10^?6 s^?1 (±0.5 · 10^?6 s^?1) in dodecane, n‐butyl acetate, and n‐dodecyl acetate at 60 °C. The initiator efficiency at low monomer conversions is relatively low (f = 0.13) and decreases with increasing monomer to polymer conversions. The evolution of f with monomer conversion (in high‐molecular‐weight regimes), x, at 60 °C can be summarized by the following functionality: f^{60 °C} (x) = 0.13–0.22 · x + 0.25 · x² (for x ≤ 0.45). The reported efficiency data are believed to have an error of >50%. The ratio of the initiator efficiency and the average termination rate coefficient, 〈k_t±, (f/〈k_t〉) has been determined at various molecular weights for the generated polydodecyl acrylate (M_n = 1900 g mol^?1 (? 8 units of DA) up to M_n = 36,500 g mol^?1 (? 152 units of DA). The (f/〈k_t〉) data may be indicative of a chain length‐dependent termination rate coefficient decreasing with (average) chain length. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5170–5179, 2004     

Modeling the reversible addition–fragmentation chain transfer process in cumyl dithiobenzoate‐mediated styrene homopolymerizations: Assessing rate coefficients for the addition–fragmentation equilibrium

A full kinetic scheme for the free‐radical reversible addition–fragmentation chain transfer (RAFT) process is presented and implemented into the program package PREDICI®. With the cumyl dithiobenzoate‐mediated bulk polymerization of styrene at 60 °C as an example, the rate coefficients associated with the addition–fragmentation equilibrium are deduced by the careful modeling of the time‐dependent evolution of experimental molecular weight distributions. The rate coefficient for the addition reaction of a free macroradical to a polymeric RAFT species (k_β) is approximately 5 · 10⁵ L mol^?1 s^?1, whereas the fragmentation rate coefficient of the formed macroradical RAFT species is close to 3 · 10^?2 s^?1. These values give an equilibrium constant of K = k_β/k_?β = 1.6 · 10⁷ L mol^?1. Conclusive evidence is given that the equilibrium lies well on the side of the macroradical RAFT species. The high value of k_β is comparable in size to the propagation rate coefficients reported for acrylates. The transfer rate coefficient to cumyl dithiobenzoate is close to 3.5 · 10⁵ L mol^?1 s^?1. A careful sensitivity analysis was performed, which indicated that the reported rate coefficients are accurate to a factor of 2. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1353–1365, 2001     

Free‐radical copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate studied by 1H NMR kinetic experiments

The free‐radical copolymerization of m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) and styrene was studied with ¹H NMR kinetic experiments at 70 °C. Monomer conversion vs time data were used to determine the ratio k_p × k_t^?0.5 for various comonomer mixture compositions (where k_p is the propagation rate coefficient and k_t is the termination rate coefficient). The ratio k_p × k_t^?0.5 varied from 25.9 × 10^?3 L^0.5 mol^?0.5 s^?0.5 for pure styrene to 2.03 × 10^?3 L^0.5 mol^?0.5 s^?0.5 for 73 mol % TMI, indicating a significant decrease in the rate of polymerization with increasing TMI content in the reaction mixture. Traces of the individual monomer conversion versus time were used to map out the comonomer mixture composition drift up to overall monomer conversions of 35%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed was observed. This depletion became more pronounced at higher levels of TMI in the initial comonomer mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1064–1074, 2002     

Changes in superstructure and mechanical properties of poly(ethylene‐2,6‐naphthalate) fibers with critical necking tension

Poly(ethylene‐2,6‐naphthalate) fibers were zone‐drawn under a critical necking tension (σ_c) defined as the minimum tension needed to generate a necking at a given drawing temperature (T_d). In the zone drawing under σ_c, the neck was observed from 110 to 160 °C. The superstructure in a neck zone induced at each T_d was studied. The σ_c value decreased exponentially with increasing T_d and dropped to a low level at a higher T_d. The draw ratio increased rapidly with T_d increasing above 90 °C, but the birefringence and degree of crystallinity decreased gradually. To study the molecular orientation in the neck zone, we measured a dichroic ratio (A_‖/A_?) of a C? O band at 1256 cm^?1 along a drawing direction in the neck zone with a Fourier transform infrared microscope. A_‖/A_? at T_d = 110 °C increased rapidly in the narrow neck zone, and that at T_d = 140 °C increased in the edge of the wide neck zone. Wide‐angle X‐ray diffraction patterns of the fibers obtained at T_d = 130 °C and lower showed three reflections due to an α form, but those at T_d = 140 and 150 °C had reflections due to the α form and a β form. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1629–1637, 2001     

β‐Hydrogen transfer from poly(methyl methacrylate) propagating radicals to the nitroxide SG1: Analysis of the chain‐end and determination of the rate constant

Methyl methacrylate (MMA) was polymerized in bulk at 70 °C in the presence of an alkoxyamine initiator with low dissociation temperature (the so‐called BlocBuilder?) and increasing amounts of free N‐tert‐butyl‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl) nitroxide (SG1). Low final monomer conversions were reached, indicating a loss in radical activity due to side reactions such as irreversible homoterminations between the propagating radicals and β‐hydrogen transfer (also called disproportionation) from a propagating radical to a free‐SG1 nitroxide. Proton NMR and MALDI‐TOF mass spectrometry were used to analyze the polymer chain‐ends and to clearly identify the main mechanism of irreversible termination. In particular, it was shown that all polymer chains were terminated by an alkene function in the presence of a large excess of free SG1, meaning that β‐hydrogen transfer from PMMA propagating radicals to the nitroxide SG1 was the major chain‐stopping event. On the other hand, for a low excess of free SG1, the two termination modes coexisted. Kinetic modeling was then performed using the PREDICI software, and the rate constant of β‐hydrogen transfer, k_βHtr, was estimated to be 1.69 × 10³ L mol^?1 s^?1 at 70 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6333–6345, 2008     

Atom transfer radical polymerization of methyl methacrylate by copper(I)‐pyridine‐2‐carboximidate catalysts

Pyridine‐2‐carboximidates [methyl ( 1a ), ethyl ( 1b ), isopropyl ( 1c ), cyclopentyl ( 1d ), cyclohexyl ( 1e ), n‐octyl ( 1f ), and benzyl ( 1g )] were prepared from the reaction of 2‐cyanopyridine with the corresponding alcohols. Cyclopentyl‐substituted 1d was found to be a highly effective ligand for copper‐catalyzed atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). For example, the observed rate constant for a CuBr/ 1d catalytic system was found to be nearly twice as high as the cyclohexyl‐substituted CuBr/ 1e catalytic system [k_obs = (1.19 vs 0.56) × 10^?4 s^?1). The effects of the solvents, temperature, catalyst/initiator, and solvent/monomer ratio on the ATRP of MMA were studied systematically for the CuBr/ 1d catalytic system. The optimum condition for the ATRP of MMA was found to be a 1:2:1:400 [CuBr]_o/[ 1d ]_o/[ethyl 2‐bromoisobutyrate]_o/[MMA]_o ratio at 60 °C in veratrole solution, which yielded well‐defined poly(MMA) with a narrow molecular weight distribution of 1.14. The catalytically active copper complex 2d was isolated from the reaction of CuBr with 1d . Narrow molecular weight distributions as low as 1.06 were achieved for the CuBr/ 1d catalytic system by employing 10% of the deactivator CuBr₂. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2747–2755, 2004     

Solvation effect in the thermal decomposition of 2,2′‐azoisobutyronitrile in the three‐component system

The thermal decomposition rate constant (k_d ) of 2,2′‐azoisobutyronitrile in acrylonitrile (AN; monomer A)–methyl methacrylate (MM; monomer B) comonomer mixtures in N,N‐dimethylformamide (DMF) as a function of the comonomer mixture composition and its concentration in the solvent at 60 °C was studied. The dependences k_d = f(x_A ,C) [x_A (mole fraction of A in the comonomer mixture) = A/(A + B) = A/C, where C is the comonomer mixture concentration] have a different course as a function of C: from a curve k_d = f(x_A ) approaching the straight line (C = 2 mol · dm⁻³) to a convex curve possessing a maximum at a point x_A = 0.7 (C = 4 mol · dm⁻³) to a curve with a flattened wide maximum within the range of x_A = 0.2–0.8 (C = 7 mol · dm⁻³) to a curve with the shape of a lying s (C = 9 mol · dm⁻³). All the courses of the experimental dependences k_d = f(x_A ,C) can be explained with a hypothesis of initiator solvation by the comonomers AN and MM and the solvent DMF. The existing solvated forms, their relative stability constants, the thermal decomposition rate constants, and the relative contents in the system were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2156–2166, 2000     

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate,ethyl 1‐methylpiperidine‐3‐carboxylate,and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

The gas‐phase elimination kinetics of the above‐mentioned compounds were determined in a static reaction system over the temperature range of 369–450.3°C and pressure range of 29–103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3‐(piperidin‐1‐yl) propionate, log k₁(s^?1) = (12.79 ± 0.16) ? (199.7 ± 2.0) kJ mol^?1 (2.303 RT)^?1; ethyl 1‐methylpiperidine‐3‐carboxylate, log k₁(s^?1) = (13.07 ± 0.12)–(212.8 ± 1.6) kJ mol^?1 (2.303 RT)^?1; ethyl piperidine‐3‐carboxylate, log k₁(s^?1) = (13.12 ± 0.13) ? (210.4 ± 1.7) kJ mol^?1 (2.303 RT)^?1; and 3‐piperidine carboxylic acid, log k₁(s^?1) = (14.24 ± 0.17) ? (234.4 ± 2.2) kJ mol^?1 (2.303 RT)^?1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six‐membered cyclic transition state type of mechanism. The intermediate β‐amino acids decarboxylate as the α‐amino acids but in terms of a semipolar six‐membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106–114, 2006     

Dark‐cure studies of cationic photopolymerizations of epoxides: Characterization of the active center lifetime and kinetic rate constants

We have characterized the effective rate constants for termination/trapping (k_t/t) and propagation (k_p) for solvent‐free cationic photopolymerizations of phenyl glycidyl ether for conversions up to 50%. We have performed dark‐cure experiments in which active centers are produced photochemically for a specified period of time until the initiating light is shuttered off, and then the polymerization rate is monitored in the dark. This method is especially well suited for characterizing cationic polymerizations because of the long active center lifetimes. Our analysis provides profiles of the instantaneous kinetic rate constants as functions of conversion (or time). For photopolymerizations of phenyl glycidyl ether initiated with iodonium photoinitiators, k_t/t and k_p remain essentially invariant for conversions up to 50%. For the photoinitiator (tolycumyl) iodonium tetrakis (pentafluorophenyl) borate (IPB), the values of k_t/t at 50 and 60 °C are 0.027 and 0.033 min^?1, respectively. The corresponding values of k_t/t for diaryliodonium hexafluoroantimonate (IHA) are 0.041 and 0.068 min^?1. The values of k_p at 50 °C for IPB and IHA are 0.6 and 0.4 L mol^?1 s^?1, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2064–2072, 2003     

Incubation period in the 2,2,4,4‐tetramethyl‐1‐piperidinyloxy‐mediated thermal autopolymerization of styrene: Kinetics and simulations

Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide‐mediated autopolymerization of styrene are discussed. At 120–125 °C and moderate 2,2,4,4‐tetramethyl‐1‐piperidinyloxy (TEMPO) concentrations (0.02–0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (k_h)]. At higher TEMPO concentrations ([N?] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition k_ad, also becomes relevant. From previous experimental data and simulations, initial estimates of k_h ≈ 1 and k_ad ≈ 6 × 10^?7 L mol^?1 s^?1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction‐period conditions, the simulations confirm the validity of the quasi‐steady‐state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well‐known expression k_th[M]³ (where [M] is the monomer concentration and k_th is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962‐6979, 2006     

Kinetics and mechanism of photochemical reactions of peroxomonosulfate in the presence and absence of 2-propanol

The photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2-propanol at 25°C was found to obey an overall first-order rate – d[PMS]/dt = k_?[PMS]. In the absence of 2-propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] > 2 × 10^?M, and is independent of concentration at [PMS] > 2 × 10^?2M. The quantum yield in the presence of 2-propanol was found to be 3.03 at [PMS] = 1 × 10^?2M and 4.45 at higher concentrations of PMS. In the pH range of 2–9.0 the quantum yield was found to be independent of pH, and the overall rate constant k_? was found to be 6.49 × 10^?3 s^?1 and 1.68 × 10^?3 s^?1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.     

Kinetic analysis of styrene atom transfer radical polymerization: Extraction of radical‐radical termination rate coefficients

Kinetic studies of the atom transfer radical polymerization (ATRP) of styrene are reported, with the particular aim of determining radical‐radical termination rate coefficients (<k_t>). The reactions are analyzed using the persistent radical effect (PRE) model. Using this model, average radical‐radical termination rate coefficients are evaluated. Under appropriate ATRP catalyst concentrations, <k_t> values of approximately 2 × 10⁸ L mol^?1 s^?1 at 110 °C in 50 vol % anisole were determined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5548–5558, 2004     

Kinetic study of the reactions of atomic chlorine with several volatile organic compounds at 240–340 K

The rate constant for the reactions of atomic chlorine with 1,4‐dioxane (k₁), cyclohexane (k₂), cyclohexane‐d₁₂(k₃), and n‐octane (k₄) has been determined at 240–340 K using the relative rate/discharge fast flow/mass spectrometer (RR/DF/MS) technique developed in our laboratory. Essentially, no temperature dependence for these reactions was observed over this temperature range, with an average of k₁ = (1.91 ± 0.20) × 10^?10 cm³ molecule^?1 s^?1, k₂ = (2.91 ± 0.31) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.73 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1, and k₄ = (3.22 ± 0.36) × 10^?10 cm³ molecule^?1 s^?1, respectively. The kinetic isotope effect of the reaction of cyclohexane with atomic chlorine has also been determined to be 1.14 by directly monitoring the decay of both cyclohexane and cyclohexane‐d₁₂ in the presence of chlorine atoms, which is consistent with the literature value of 1.20. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 386–398, 2006     

A novel tridentate nitrogen donor as ligand in copper catalyzed ATRP of methyl methacrylate

A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, Cu^IBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities M_w/M_n ≤ 1.23. The rate of polymerization follows first‐order kinetics, k_app = 3.4 × 10^?5 s^?1, indicating the presence of low radical concentration ([P*] ≤ 10^?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (M_n,SEC) increased linearly with conversion and were found to be higher than predicted molecular (M_n,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (M_n = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (M_n = 10,300), which is achieved in 23 h. The plot of lnk_app versus 1/T gave an apparent activation energy of polymerization as (ΔE^≠_app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH⁰_eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005