Living carbocationic copolymerization of isobutylene with styrene

The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2‐chloro‐2,4,4‐trimethylpentane/TiCl₄ in 60/40 (v/v) methyl chloride/hexane at ?90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and M_n–conversion plots) were found, provided that the St concentration was above a critical value ([St]₀ ～ 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching M_w/M_n ～ 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with M_n = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric–NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778–1787, 2007     

Living carbocationic polymerization of isobutyl vinyl ether and the synthesis of poly[isobutylene-b-(isobutyl vinyl ether)]

The MeCH(O-i-Bu)Cl/TiCl₄/MeCONMe₂ initiating system was found to induce the rapid living carbocationic polymerization (LC^⊕Pzn) of isobutyl vinyl ether (IBuVE) at ?100°C. Degradation by dealcoholation which usually accompanies the polymerization of alkyl vinyl ethers by strong Lewis acids is “frozen out” at this low temperature and poly(isobutyl vinyl ether)s (PIBuVEs) with theoretical molecular weights up to ca. 40,000 g/mol (calculated from the initiator/monomer input) and narrow molecular weight distributions (M?_w/M?_n ≤ 1.2) are readily obtained. According to ¹³C-NMR spectroscopy, PIBuVEs prepared by living polymerization at ?100°C are not stereoregular. The MeCH(O-i-Bu)Cl/TiCl₄ combination induces the rapid LC^⊕Pzn of IBuVE even in the absence of N,N-dimethylacetamide (DMA). The addition of the common ion salt, n-Bu₄NCl to the latter system retards the polymerization and meaningful kinetic information can be obtained. The kinetic findings have been explained in terms of TiCl₄. IBuVE and TiCl₄ · IBuVE and TiCl₄ · PIBuVE complexes. The HCl (formal initiator)/TiCl₄/DMA combination is the first initiating system that can be regarded to induce the LC^⊕Pzn of both isobutylene (IB) and IBuVE. Polyisobutylene (PIB)–PIBuVE diblocks were prepared by sequential monomer addition in “one pot” by the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl₄/DMA initiating system. Crossover efficiencies are, however, below 35% because the PIB^⊕ + IBuVE → PIB-b-PIBuVE^⊕ crossover is slow. © 1993 John Wiley & Sons, Inc.     

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     

Details of the emulsion polymerization of styrene using a reaction calorimeter

An automated reaction calorimeter was used to directly monitor the rate of emulsion polymerization of styrene using different emulsifier (sodium lauryl sulfate) and initiator (potassium persulfate) concentrations. By using this technique in conjunction with off-line measurements of the evolution of the particle size distributions, important details of the process were observed. The classical constant rate period (Interval II) often reported for the batch emulsion polymerization of styrene was not seen in this work. Instead, the experimental results suggest that the end of nucleation and the disappearance of monomer droplets take place at approximately the same conversion (36–40%). From the polymerization rate data, important parameters such as the monomer concentration in the polymer particles and the average number of radicals per particle were calculated. © 1996 John Wiley & Sons, Inc.     

Reactive surfactants in heterophase polymerization. Part XXI—kinetics of styrene dispersion polymerization stabilized with poly(ethylene oxide) macromonomers

The kinetics of styrene dispersion polymerization, using poly(ethylene oxide) macromonomers as precursors for the stabilization, has been studied. The conversions of both styrene and macromonomers have been determined. The effects of various parameters such as the polarity of the medium, the nature and the amount of macromonomer and the concentrations of the reactants have been studied. A strong gel effect was observed, the main polymerization process taking place inside the particles where the average number of radicals per particle may be more than a thousand. © 1997 John Wiley & Sons, Ltd.     

Effect of temperature on styrene emulsion polymerization in the presence of sodium dodecyl sulfate. II

The batch emulsion polymerization kinetics of styrene initiated by a water‐soluble peroxodisulfate at different temperatures in the presence of sodium dodecyl sulfate was investigated. The curves of the polymerization rate versus conversion show two distinct nonstationary‐rate intervals and a shoulder occurring at a high conversion, whereas the stationary‐rate interval is very short. The nonstationary‐state polymerization is discussed in terms of the long‐term particle‐nucleation period, the additional formation of radicals by thermal initiation, the depressed monomer‐droplet degradation, the elimination of charged radicals through aqueous‐phase termination, the relatively narrow particle‐size distribution and constant polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The maximum rate of polymerization (or the number of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymerization. The low activation energy of polymerization is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the additional formation of radicals by thermally induced initiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1477–1486, 2000     

Novel substituted epoxide initiators for the carbocationic polymerization of isobutylene

This article presents the first detailed account of the discovery that substituted epoxides can initiate the carbocationic polymerization of isobutylene. α‐Methylstyrene epoxide (MSE), 2,4,4‐trimethyl‐pentyl‐epoxide‐1,2 (TMPO‐1), 2,4,4‐trimethyl‐pentyl‐epoxide‐2,3 (TMPO‐2), and hexaepoxi squalene (HES) initiated isobutylene polymerization in conjunction with TiCl₄. MSE, TMPO‐2, and HES initiated living polymerizations. A competitive reaction mechanism is proposed for the initiation and propagation. According to the proposed mechanism, initiator efficiency is defined by the competition between the S_N1 and S_N2 reaction paths. A controlled initiation with external epoxides such as MSE should yield a primary hydroxyl head group and a tert‐chloride end‐group. The presence of tert‐chloride end‐groups was verified by NMR spectroscopy, whereas the presence of primary hydroxyl groups was implied by model experiments. Multiple initiation by HES was verified by diphenyl ethylene end‐capping and NMR analysis; the resulting star polymer had an average of 5.2 arms per molecule. A detailed investigation of the reaction mechanism and the characterization of the polymers are in progress. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 444–452, 2000     

On the emulsion polymerization of styrene in the presence of a nonionic emulsifier

The batch emulsion polymerization kinetics of styrene (St) initiated by a water-soluble peroxodisulfate in the presence of a nonionic emulsifier was investigated. The polymerization rate versus the conversion curves showed two nonstationary rate intervals, two rate maxima, and Smith–Ewart Interval 2 (nondistinct). The rate of polymerization and number of nucleated polymer particles were proportional to the 1.4th and 2.4th powers, respectively, of the emulsifier concentration. Deviation from the micellar nucleation model was attributed to the low water solubility of the emulsifier, the low level of the micellar emulsifier, and the mixed modes of particle nucleation. In emulsion polymerizations with a low emulsifier concentration, the number of radicals per particle and particle size increased with increasing conversion, and the increase was more pronounced at a low conversion. By contrast, in emulsion polymerizations with a high emulsifier concentration, the number of radicals per particle decreased with increasing conversion. This is discussed in terms of the mixed models of particle nucleation, the gel effect, and the pseudobulk kinetics. The formation of monodisperse latex particles was attributed to coagulative nucleation and droplet nucleation for the polymerizations with low and high emulsifier concentrations, respectively. The effects of the continuous release of the emulsifier from nonmicellar aggregates and monomer droplets, the close-packing structure of the droplet surface, and the hydrophobic nature of the emulsifier on the emulsion polymerization of St are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4422–4431, 1999     

Alkoxyamine‐mediated “living” radical polymerization: MS investigation of the early stages of styrene polymerization initiated by cumyl‐TEISO

A new series of 1,1,3,3‐tetraethylisoindoline‐2‐oxyl (TEISO)‐based alkoxyamines was prepared. The half‐lives for thermal dissociation indicated that the most sterically congested cumyl‐TEISO alkoxymine had the greatest potential as an initiator for the polymerization of monomers at lower temperatures. The polymerization of styrene at 110 °C gave a linear evolution of M_n with conversion in the early stages. Further evidence for the “living” nature was given by the polydispersities of the polymers that remained low (M_w/M_n = 1.13–1.27) throughout the polymerization (up to 80% conversion). No polymer was formed for the styrene system in a reasonable time below 100 °C. High‐performance liquid chromatographic/mass spectrometric investigations of the distribution of trapped oligomers containing one to nine monomer units formed at 60 °C revealed that the trapping of oligomeric cumyl–styryl radicals by TEISO is irreversible at this temperature. Methyl methacrylate polymerized with cumyl‐TEISO at 60–70 °C, although the initial high rates of polymerization soon decreased to zero at low conversions (10–15%), and the high polydispersities (M_w/M_n = 1.42–1.73) indicated significant side reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1232–1241, 2001     

The common ion effect in sulfenylhalogenation of alkenes in formic acid

The reactions of 2,4-dinitrobenzenesulfenyl chloride with cyclohexene and allylbenzene in formic acid were studied. In this solvent, the reaction yields solvo-adducts and the products of addition of the reagent to the double bond. The reaction follows kinetics of the second order, first order with respect to each reagent. The hydrogen chloride evolved in the reaction has no effect on the overall rate of the process but sharply decreases the rate of accumulation of solvo-adducts due to the common ion effect. In the reaction with allylbenzene, the yield of the solvo-adduct can vary under the action of HCl from 88% at low degrees of reagent conversion to 30% when the reaction is complete. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 95–100, January, 1997.     

Living polymerization of styrene initiated by mercaptan/ε‐caprolactam

The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, ¹H NMR, and ¹³C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004     

Living cationic polymerization of p-alkoxystyrenes by free ionic species

In contrast to the common view, living cationic polymerization of p-methoxy- and p-t-butoxystyrenes proceeded in polar solvents such as EtNO₂/CH₂Cl₂ mixtures, and involvement of free ionic growing species therein was examined. For example, the two alkoxystyrenes were polymerized with the isobutyl vinyl ether-HCl adduct/ZnCl₂ initiating system at −15°C in such polar solvents as CH₂Cl₂ or EtNO₂/CH₂Cl₂ [1/1 (v/v)], as well as toluene. The number average molecular weight (M̄_n) of the polymers increased in direct proportion to the monomer conversion, even after sequential monomer addition, and the molecular weight distribution (MWD) stayed very narrow throughout the reaction. In addition, the M̄_n agreed with the calculated values, assuming that one adduct molecule generates one living polymer chain. In these polar media the addition of a common ion salt retarded the polymerization, indicating that dissociated ionic species are involved in the propagating reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3694–3701, 1999     

On the kinetics of styrene emulsion polymerization above CMC. I. A mathematical model

A detailed mathematical model of the kinetics of styrene emulsion polymerization has been proposed. Its main features/assumptions are compartmentalization, micellar and homogeneous nucleation, particle formation by both initiator‐derived and desorbed radicals, dependence on the particle size of the rate coefficients, thermodynamic considerations, and aqueous phase kinetics. The model predicts that micellar nucleation dominates over homogeneous nucleation and that the evolution of the nucleation rate reaches a maximum, where desorbed radicals have an important contribution. Initiator‐derived radicals with only one monomeric unit have also a significant contribution on the rate of capture in particles. The results suggest that the correctness of the instantaneous termination approach depends not only on the size of the particle, but also on the type of entering radical (initiator‐derived or monomeric). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2201–2218, 2000     

Living/controlled radical polymerization of styrene with a new initiating system: DCDPS/FeCl3/PPh3

The living/controlled radical polymerization of styrene was investigated with a new initiating system, DCDPS/FeCl₃/PPh₃, in which diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS) was a hexa‐substituted ethane thermal iniferter. The polymerization mechanism belonged to a reverse atom transfer radical polymerization (ATRP) process. The polymerization was controlled closely in bulk (at 100 °C) or in solution (at 110 °C) with a high molecular weight and quite narrow polydispersity (M_w/M_n = 1.18 ∼ 1.28). End‐group analysis results by ¹H NMR spectroscopy showed that the polymer was ω‐functionalized by a chlorine atom, which also was confirmed by the result of a chain‐extension reaction in the presence of a FeCl₂/PPh₃ or CuCl/bipy (2,2′‐bipyridine) catalyst via a conventional ATRP process. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 101–107, 2000     

Dispersion polymerization of styrene in alcohol media: Effect of initiator concentration,solvent polarity,and temperature on the rate of polymerization

The effects of three different variables (initiator concentration, polarity of the solvent and reaction temperature) on the rate of dispersion polymerization of styrene in alcohols have been investigated. It was found that the rate of polymerization increases with the initiator (AIBN) concentration at the 0% conversion level and becomes independent of it at higher monomer conversions. More significant was the result that the rate was also found to increase with solvent polarity. This is consistent with thermodynamic equilibrium calculations which account for the partitioning behavior of monomer and solvent in both the solution and the particle phases. The results further suggest the existence of two different kinetic regions: one at low conversions, where the reaction takes place primarily in the solution phase, and one at high conversions, where the reaction takes place primarily in the particle phase. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2907–2915, 1997     

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     

Kinetics of the microemulsion polymerization of styrene with short‐chain alcohols as the cosurfactant

The kinetics of styrene microemulsion polymerization stabilized by sodium dodecyl sulfate (SDS) and a series of short‐chain alcohols (n‐C_iH_2i+1OH, abbreviated as C_iOH, where i = 4, 5, or 6) at 60 °C was investigated. Sodium persulfate was used as the initiator. The microemulsion polymerization process can be divided into two intervals: the polymerization rate (R_p) first increases to a maximum at about a 20% conversion (interval I) and thereafter continues to decrease toward the end of the polymerization (interval II). For all the SDS/C_iOH‐stabilized polymerization systems, R_p increases when the initiator or monomer concentration increases. The average number of free radicals per particle is smaller than 0.5. The molecular weight of the polymer produced is primarily controlled by the chain‐transfer reaction. In general, the reaction kinetics for the polymerization system with C₄OH as the cosurfactant behaves quite differently from the kinetics of the C₅OH and C₆OH counterparts. This is closely related to the different water solubilities of these short‐chain alcohols and the different concentrations of the cosurfactants used in the preparation of the microemulsion. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 898–912, 2001     

Polyisobutylene-containing block polymers by sequential monomer addition. IV. New triblock thermoplastic elastomers comprising high Tg styrenic glassy segments: Synthesis,characterization and physical properties

New linear triblock thermoplastic elastomers (TPEs) comprising a rubbery polyisobutylene (PIB) midblock flanked by two glassy endblocks of various styrenic polymers have been synthesized by living carbocationic polymerization by sequential monomer addition. First isobutylene (IB) was polymerized by a bifunctional tert-ether (dicumyl methyl ether) initiator in conjunction with TiCl₄ coinitiator in CH₃Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at ?80°C. After the living narrow molecular weight distribution PIB midblock ( = 1.1–1.2) has reached the desired molecular weight, the styrenic monomers together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to start the blocking of the glassy segments from the living ⊕PIB⊕ chain ends. While p-methylstyrene (pMeSt), p-t-butylstyrene (ptBuSt) and indene (In) gave essentially 100% blocking to the corresponding glassy endblocks, the blocking of 2,4,6-trimethylstyrene (TMeSt) and α-methylstyrene (αMeSt) were ineffective. Uncontrolled initiation by protic impurities was prevented by the use of DtBP. In the simultaneous presence of DtBP and the strong ED N,N-dimethylacetamide (DMA), TPEs with good mechanical properties (10–20 MPa tensile strength, 300–600% elongation) were prepared. The products exhibit a low and a high temperature T_g characteristic of phase separated rubbery and glassy domains. The service temperature of these new TPEs exceeds that of PSt–PIB–PSt triblock copolymers due to the higher T_gs (PpMeSt = 108, PptBuSt = 142 and PIn = 220–240°C) of the outer blocks. The T_g of the glassy blocks can be regulated by copolymerizing two styrene derivatives; a triblock copolymer with outer blocks of poly(pt-butylstyrene-co-indene) showed a single glassy transition T_g = +165°C, i.e., in between that of PptBuSt and PIn. Virgin TPEs have been repeatedly compression molded without deterioration of physical properties. The high melt flow index obtained with a TPE containing PptBuSt endblocks suggests superior processability relative to those with PSt end-blocks. The tensile strength retention at 60°C of the former TPE is far superior to that of a PSt–PIB–PSt triblock of similar composition.