Free radical polymerization in ionic liquids—Influence of the IL-concentration and temperature

The influence of the ionic liquid (IL) 1-ethyl-3-methylimidazoliumethylsulfate ([EMIM]EtSO₄) on the polymerization kinetics of methyl methacrylate was investigated. ILs are liquids with relatively high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t of polymerizations carried out in ILs. The rate constant of termination k_t decreases when the concentration of ionic liquid, and thus the viscosity is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of ILs can be varied by either working with mixtures of ILs with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with dimethyl formamide (DMF) – or by variation of the temperature. The studies were carried out to determine the influence of the viscosity on the propagation and the termination reaction as well as the molecular weight distribution.     

Absolute rate constants for radical-monomer reactions

Summary A method is described for determining the absolute rate constants for the first few propagation steps in radical polymerization. The procedure involves a product analysis of the oligomeric alkoxyamines formed when an initiator is decomposed in monomer containing a very low concentration of a nitroxide radical scavenger. The method is illustrated with analysis of data for methyl acrylate. The rate constants for the first two propagation steps for polymerization of this monomer,k _p(1) andk _p(2), are at least an order of magnitude greater thank _p(average). Values of the absolute rate constants for reactions of phenyl and primary alkyl radicals with methyl acrylate are also estimated.     

Termination kinetics of free-radical polymerization in ionic liquids

Termination rate coefficients, k_t, for free-radical polymerization of 15 vol.-% methyl methacrylate (MMA) dissolved in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide and in 1-butyl-3-methylimidazolium tetrafluoroborate were measured at 10 °C via the single pulse − pulsed laser polymerization − electron paramagnetic resonance (SP-PLP-EPR) technique. Whereas absolute k_t in ionic liquid solution is by about one order of magnitude below the associated bulk MMA value, the chain-length dependence of k_t is very similar in both liquid environments.     

Real‐time monitoring of ring‐opening polymerization of tetrahydrofuran via in situ Fourier Transform Infrared Spectroscopy

The polymerization of tetrahydrofuran (THF) was carried out in CH₂Cl₂ by using phosphotungstic heteropolyacid as initiator and epichlorohydrin as promoter. This cationic ring‐opening polymerization process was monitored by in situ mid‐infrared spectroscopy system (ReactIR) to further study the thermodynamics and kinetics of THF polymerization. It was observed that the sharp infrared peak of C? O? C stretching vibrations will shift from about 1068 to 1109 cm^?1 in THF ring‐opening step. The changes in absorbance intensity of the two characteristic peaks were used for determining instantaneous concentration of linear polymer and ring monomer. The experimental results demonstrated that the kinetics of THF polymerization proved to be typically first‐order. Thermodynamic parameters were determined from the temperature dependence of the monomer equilibrium concentration [M]_e over the range from ?5 to 25°C. The values of k_app were obtained via the plots of ln{([M]₀?[M]_e)/([M]_t?[M]_e)} vs reaction time, for polymerization under specific conditions. The apparent activation energy (E_a) and frequency (A) were determined from the Arrhenius plot of k_app vs. T^?1. Besides, the in situ kinetic investigation revealed that more chain‐transfer occurred at higher temperatures, leading to a reduction in propagation species concentration and a deviation from first‐order propagation at the later stage of polymerization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40503.     

Reactivity and mechanism in the cationic polymerization of isobutyl vinyl ether

The cationic polymerization of isobutyl vinyl ether initiated by triphenyl methyl and tropylium hexachloroantimonates, and by triphenyl methyl tetrafluoroborate, has been studied in detail. Initiation was rapid and complete, termination was shown to be insignificant, polymerization half lives were of the order of 5–10 s and reaction rates were measured by an adiabatic calorimetric technique. Catalyst concentrations employed were sufficiently low that essentially complete dissociation into free ions is indicated by ion-pair dissociation constants, and this permits estimation of the rate coefficient for propagation by free cations (k_p). At 0°C in methylene dichloride k_p ∼ 5 × 10³ M⁻¹ s⁻¹, in substantial agreement with values obtained by radiation induced polymeirzation of bulk monomer. Molecular weights of the poly(isobutyl vinyl ether) samples fell in the range 2000–5000 on account of monomer transfer processes. Detailed mechanisms for initiation, propagation, transfer and termination reactions are considered.     

Estimation of the chain propagation rate constants of propylene polymerization and ethylene-1-hexene copolymerization catalyzed with MgCl2-supported Ziegler–Natta catalysts

In olefin polymerization with MgCl₂-supported Ziegler–Natta (Z–N) catalysts, the apparent propagation rate constant (k_p)_a calculated by R_p = (k_p)_a [C*] C_Me (C_Me is equilibrium monomer concentration in the reaction system) declines with reaction time for gradually developed monomer diffusion limitation in the polymer/catalyst particles. In this work, a simplified multi-grain particle model was proposed to build correlation between (k_p)_a and other kinetic parameters that can be determined experimentally. Rate profiles of propylene polymerization and ethylene-1-hexene copolymerization by three MgCl₂-supported Z–N catalysts were determined, and the (k_p)_a data was calculated using [C*] determined by quench-labelling the propagation chains with acyl chloride. Decline of (k_p)_a in each polymerization process was precisely fitted by the linear correlation between lg(k_p)_a and [(ρ_catm_p)/(ρ_pm_cat) + 1]^1/3 developed on the particle model. Real propagation rate constant (k_p) was estimated by extrapolating the fitting line to the starting point of polymerization, where no concentration gradient exists. According to the particle model, the slope of the lg(k_p)_a versus [(ρ_catm_p)/(ρ_pm_cat) + 1]^1/3 line (lgd) represents the degree of monomer diffusion limitation. Variations of parameter d found in the studied reaction systems can be reasonably explained based on the knowledge of olefin diffusion in the polymer phase.     

Preparation of deuterated methyl 6,9,12-octadecatrienoates and methyl 6,9,12,15-octadecatetraenoates

Methyl 6,9,12-octadecatrienoate-15,15,16,16-d ₄ was obtained by Wittig coupling between 6,6,7,7-tetradeutero-3-nonenyltriphenylphosphonium iodide, 8, and the aldehyde ester, methyl 9-oxo-6-nonenoate. Methyl 6-oxohexanoate, obtained by ozonolysis of cyclohexene, was coupled in a Wittig reaction with [2-(1,3-dioxan-2-yl)ethyl]triphenylphosphonium bromide to give methyl 8-dioxanyl-6-octenoate. This compound was transacetalized to methyl 9,9-dimethoxy-6-nonenoate, which was then hydrolyzed to the aldehyde ester. For the preparation of compound 8, the tetrahydropyranyl ether of 2-pentynol was deuterated with deuterium gas and tris-(triphenylphosphine)chlororhodium. The tetradeuterated tetrahydropyranyl ether was converted to the bromide with triphenylphosphine dibromide, and the bromide was coupled with 3-butynol by means of lithium amide in liquid ammonia to give 3-nonynol-6,6,7,7-d ₄. Hydrogenation over Lindlar's catalyst converted the deuterated alkynol to 3-nonenol-6,6,7,7-d ₄. This deuterated alkenol was converted to the bromide with triphenylphosphine dibromide, then to the iodide with sodium iodide in acetone, and finally to 8 with triphenylphosphine in acetonitrile. Methyl 6,9,12,15-octadecatetraenoate-12,13,15,16-d ₄ was obtained by Wittig coupling between methyl 9-oxo-6-nonenoate and 3,4,6,7-tetradeutero-3,6-nonadienyltriphenylphosphonium iodide, 15. For the preparation of compound 15, the bromide obtained from the reaction of 2-pentynol with triphenylphosphine dibromide was coupled with 3-butynol with lithium amide in liquid ammonia. The resulting 3,6-nonadiynol was deuterated with deuterium gas in the presence of P-2 nickel, and the resultant deuterated nonadienol was converted to 15 through the bromide and iodide. The final products were separated from isomers formed during the synthetic sequences by silver resin chromatography.     

Cationic polymerization of 5-methyl-2-oxazoline and alkaline hydrolysis of product polymer to linear poly(propylenimine)

Summary A new monomer of 5-methyl-2-oxazoline(5-MeOZO) was prepared. It was found that 5-MeOZO underwent the cationic ring-opening isomerization polymerization to produce poly(N-formylpropylenimine) 1 of waxy or powdery materials. Alkaline hydrolysis of 1 gave linear poly(propylenimine) 2. Polymers 1 and 2 are the same as the respective polymers derived from 4-methyl-2-oxazoline.     

Effects of dual-crosslinking networks on shape memory performance of polynorbornene

In this article, Polynorbornene (PNB)/Zinc dimethacrylate (ZDMA)/Dicumyl peroxide (DCP) composites can form dual-crosslinking networks, which contain an ionic crosslinking network, and a part of the C─C covalent crosslinking network. DCP was used to initiate the polymerization of ZDMA to form ionic crosslinking bonds. With the increase of ZDMA, the total crosslink density (V_r) and ionic crosslink density (V_r2) increased. DCP was consumed in ZDMA polymerization, which made the PNB reduce the covalent crosslinking networks. Leading to the covalent crosslink density (V_r1) decreased. Compared with covalent crosslinking network, the dual-crosslinking networks stored more energy when deformed, provided better restoring force and a higher shape recovery ratio for materials. When ZDMA exceeded 3.9 wt%, the ZDMA aggregates hindered the movement of molecular chains leading to the shape recovery ratio slightly decreased. When ZDMA was 2.4 wt%, the composite had an optimum shape fixing and shape recovery ratio. This article provided the experimental basis for the research of PNB dual-crosslinking networks, also widened the research of PNB shape memory materials. © 2020 Wiley Periodicals Inc. J. Appl. Polym. Sci. 2020 , 137, 48955.     

Morphology of latex particles formed by poly(methyl methacrylate)-seeded emulsion polymerization of styrene

Poly(methyl methacrylate)–polystyrene composite particle latexes were prepared by poly(methyl methacrylate)-seeded emulsion polymerization of styrene employing batch, swelling-batch, and semibatch methods. The changes in particle morphology taking place during the polymerization reaction were followed by electron microscopy. Anchoring effect exerted by ionic terminal groups introduced by ionic initiator was found to be the main factor in controlling the particle morphology. The polymer particles obtained by oil-soluble hydrophobic initiators such as azobisisobutyronitrile and 4,4′-azobis-(4-cyanovaleric acid) gave the inverted core-shell morphology. Water-soluble hydrophilic initiator, K₂S₂O₈, also gave the inverted core-shell morphology. However, in this case the occurrence of the halfmoonlike, the sandwichlike, and the core-shell morphologies were also observed depending upon the polymerization conditions. The distribution of terminal ? SO groups on the surface area of polystyrene particles could be controlled by initiator concentration and polymerization temperature. Viscosity of polymerization loci dictated the movement of polymer molecules, thus causing the unevenness of particle shape and phase separation at high viscosity state. Viscosity was controlled by the styrene/poly(methyl methacrylate) ratio, the addition of a chain transfer agent or a solvent which is common to polystyrene and poly(methyl methacrylate).     

Controlled radical polymerization catalyzed by CuCl/BDE complex in water medium. II. Polymerization of methyl methacrylate and formation of PMMA with bimodal molecular weight distribution

The emulsion polymerization of MMA was explored for the BDE/CuCl coordinated catalyst. The M_n of PMMA linearly increased both with increasing the monomer conversion and the proceeding polymerization time, which means that the MMA polymerized in “living”/controlled characters with zero order kinetics under BDE/CuCl‐catalyzed emulsion conditions. The apparent polymerization rate constants of MMA were k = 0.765 mol/min, k = 0.760 mol/min at 80°C, while k = 0.228 mol/min at 50°C, respectively. Slight differences of polymerization results were obtained when emulsifier lauryl phosphate (ADP) and Polyoxyethylene nonyl phenyl ether (OP‐10) were adapted in the polymerization. Based on the “coordinated radical cage” mechanism proposed particularly to the BDE/CuCl catalyzed polymerization, reversible equilibrium between common free radical and the coordinated “living” species should exist in this system. Increasing the amount of catalyst must affect the fast equilibrium between those two species, thus, also affecting the relative content in the emulsion circumstance. Therefore, PMMA, with bimodal molecular weight distribution, was achieved through this approach. The formation of PMMA with bimodal distribution was affected by concentration of catalyst and polymerization temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3076–3081, 2002; DOI 10.1002/app.2336     

Synthesis of Sodium (+)-(12S,13R)-Epoxy-cis-9-octadecenyl Sulfonate from Vernonia Oil

A water-soluble, foaming epoxyalkene sulfonate, sodium (+)-(12S,13R)-epoxy-cis-9-octadecenyl sulfonate, was synthesized from vernonia oil (VO) by a series of simple reactions that include transesterification, metal hydride reduction, tosylation, and S_N2 reactions. Conversion of VO into vernonia oil methyl esters (VOME) using sodium methoxide was quantitative. Subsequent reduction of VOME with lithium aluminum hydride yielded (+)-(12S,13R)-epoxy-cis-9-octadecenol (94%), along with minor amounts of hexadecenol, octadecenol, cis-9-octadecenol, and cis-9,12-octadecandienol. The (+)-(12S,13R)-epoxy-cis-9-octadecenol, was tosylated with p-toluenesulfonyl chloride to give (+)-(12S,13R)-epoxy-cis-9-octadecenyl tosylate at 96% yield. Iodination of the tosylate with sodium iodide and subsequent S_N2 reaction with sodium sulfite afforded (+)-(12S,13R)-epoxy-cis-9-octadecenyl sulfonate (63% yield). This study demonstrates the ability to produce an epoxyalkenyl sulfonate, belonging to a class of anionic surfactants, from VO without destroying the epoxy functionality in the (+)-(12S,13R)-epoxy-cis-9-octadecenyl moiety of VO. The critical micelle concentration of the synthesized sulfonate was also determined.     

Kinetics of graft copolymerization of methyl methacrylate in wool fibers

The graft copolymerization of methyl methacrylate in wool fibers was investigated in the aqueous LiBr–K₂S₂O₈ system without homopolymer. The rate of grafting and the degree of polymerization of graft polymer were determined on varying the extent of reduction of wool fibers and the concentration of monomer. From the graft copolymerization behavior observed at a given concentration of redox catalysts (LiBr and K₂S₂O₈), the thiol groups in wool fibers were considered to play a role as a sort of catalyst of polymerization, not as the chain transfer agent, and also to give the grafting sites. So, the initiation process of grafting was assumed to be started by d[S·]/dt = k_i[SH]_eff, and the kinetic consideration was found to lead to the following expression in agreement with the experimental results: 1/DP = (k_t/k_p²[M]_fib²)R_p, where d[S·]/dt is the rate of formation of thiol radicals by radicalotropy to ? SH from SO₄^?., OH·, or Br·; k_i, k_p, and k_t are the rate constants of initiation, propagation, and termination, respectively; [SH]_eff and [M]_fib are the concentration of the effective thiol groups and the MMA monomers within the wool fibers, respectively; DP is the average degree of polymerization of graft polymers, and R_p the overall rate of grafting.     

Synthesis of end-group functionalized poly(octadecyl vinyl ether)

The cationic polymerization of octadecyl vinyl ether (ODVE) initiated by trimethylsilyl iodide and 1,1-diethoxyethane in the presence of ZnI₂ in toluene at 0°C and 10°C has been investigated. For molecular weights lower than 6000, a linearity of M̄_n with conversion was observed, but for higher molecular weights a strong deviation from calculated values, assuming a living mechanism, was found. Kinetic analysis of the polymerization and the variation of molecular weight as a function of conversion was in agreement with a transfer to monomer with k_tr/k_p ≌ 0.006 at 10°C. Analysis of the polymers obtained by termination with methanol provided evidence that the alkenyl ether end-groups formed by the transfer reaction lead to the same acetal end-groups as the active species. As a consequence, it is possible to prepare functionalized polyODVE polymers by end-capping with alcohols. This was confirmed by the synthesis of polyODVE macromonomers by end-capping with 2-hydroxyethyl methacrylate.     

Cationic polymerization of 2,4,4-trimethyl-2-oxazoline

Summary The cationic homopolymerization of 2,4,4-trimethyl-2-oxazoline using BF₃Et₂O as initiator at different initiator concentrations, temperatures, times and solvents of polymerization were carried out. The effect of these variables on the polymerization yield and viscosity of the polymers were studied. Polymers were characterized by IR.¹H NMR and¹³C NMR which support that the polymerization reaction occurs by ring opening of oxazoline through oxazolinium intermediates.     

Electrochemical properties of lithium ionic conductors of the type: LiJ · xC9H15NO3 · CH3J

A series of lithium ionic conductors of the type: LiJ · xC₉H₁₅NO₃ · CH₃J (N-methylammonium iodide of 2,6,10-tri-oxa-13-azatricyclo[7,3,1,0^5,13]tridecane) was investigated. The ionic conductivity of these compounds is higher than that of pure lithium iodide and comparable to that of doped lithium iodide or lithium iodide alumina mixtures. This effect is obviously due to a softening of the substances at elevated temperatures. The electrochemicl properties were checked by cyclic voltammograms at elevated temperatures. Cells of the type Li/electrolyte/AgJ (mixt) and Le/electrolyte/J₂ were discharged and voltammograms of the AgJ (mixt) electrode were recorded.     

Reverse atom transfer radical polymerization of MMA via immobilized catalysts in imidazolium ionic liquids

Reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) employing immobilized catalyst was approached at 50 and 60°C in [C₈mim]PF₆, and compared with the polymerization of MMA DMF as solvent. Other ionic liquids, [C₆mim]BF₄, [C₈mim]BF₄, and [C₁₂mim]BF₄, were used as solvents to perform the RATRP of MMA. By comparison, we found that the [C₈mim]PF₆ was the best solvent in this immobilized catalyst system and the polymerization was best controlled. In addition, the immobilized catalyst spherules can easily separate from the reaction mixture, which avoids the prevalent problem of the catalyst residual in RATRP and also gives us a possibility to recycle the catalyst system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3915–3919, 2007     

Simulation of reversible chain transfer catalyzed polymerization (RTCP): effect of different iodide based catalysts

Monte Carlo kinetic simulation method was performed to study the reversible chain transfer catalyzed polymerization (RTCP) of styrene in 80°C. The effect of different iodide based catalysts (AI) was investigated on RTCP systems by simulating the chain length distribution, the depletion rate of polymerization ingredients, average molecular weights and the monomer conversion. In RTCP systems a narrow distribution was obtained compared to iodide-mediated polymerization. Superior reversible chain transfer reaction constants (k_a and k_da) led to a more uniform chain length distribution and a faster PDI decrement. In each RTCP system k_da/k_a ratio, designates the concentration of A* by dictating the dominant side of exchange equilibriums which specifies the number of cross-termination reactions. Addition of cross-termination reactions to the iodide-mediated polymerization system decreases the number of combination reactions leading to lower average molecular weights. Higher k_da/k_a ratios also consequences in faster catalyst depletions and lessen monomer conversions. On the other hand, PhE-I was found to deplete rapidly in RTCP systems, changing the nonlinear increase of the number average molecular weight to a linear pattern. The Monte Carlo simulation results were in a fine agreement with experimental data which were obtained from different RTCP systems.     

Free-radical propagation rate coefficients

The pulsed laser polymerization-size-exclusion chromatography (PLP-SEC) technique has become the International Union of Pure and Applied Chemistry (IUPAC)-recommended method for the accurate determination of propagation rate coefficients, k_p, for radical polymerization. The fundamental insight provided by Heuts, Gilbert, and Radom into the relevance of transition state dynamics allows for an adequate understanding of the dependence of k_p on radical chain length, solvent environment, and monomer conversion. The associated entropic effects are particularly pronounced in aqueous solution, but are also found in less polar media and with non-polar monomers. Moreover, these arguments are applicable towards the interpretation of copolymerization reactivity ratios. The addition of sodium hydroxide to aqueous solutions of (meth)acrylic acid yields partially and even fully ionized systems with clearly reduced k_p, which indicates the action of repulsive forces between the equally charged monomer and radical species. Increasing the concentration of monomer as well as the addition of salts may reverse this effect and increase k_p due to counterion activity.