Synthesis of a well-defined cyclic polystyrene via α-carboxyl, ω-amino heterodifunctional polystyrene

Living anionic polymerization of styrene was carried out in benzene at room temperature using 1-(3-lithiopropyl)-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane and 2,2,5,5-tetramethyl-1-(3-bromopropyl)-1-aza-2,5-disilacyclopentane as an initiator and terminator, respectively, to obtain α-2,2-bis(hydroxymethyl)propoxycarbonyl, ω-amino heterodifunctional polystyrene. It was hydrolyzed to α-carboxyl, ω-amino heterodifunctional polystyrene which gave a well-defined cyclic polystyrene by the intramolecular cyclization under high dilution conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2027–2033, 1999     

Arene complexes of beta-diketiminato supported organoscandium cations: mechanism of arene exchange and alkyne insertion in solvent separated ion pairs

A family of isolable solvent separated organoscandium methyl cations stabilized by beta-diketiminato ligands (Ar)NC(CH3)CHC(CH3)N(Ar) (Ar=2,6-iPr-C6H3, LMe) has been prepared by reaction of LMeScR2 with [CPh3][B(C6F5)4] in the presence of an arene solvent. Arenes such as bromobenzene, benzene, toluene, para-xylene and mesitylene bind the scandium center in an eta6-bonding mode, yielding cations 1 a-e. Their solution and solid-state structures have been explored using multinuclear NMR spectroscopy and X-ray crystallography. Mechanistic studies on arene exchange reactions and the insertion of diphenylacetylene indicate that these processes occur via arene intermediates of lower hapticity, followed by binding of the incoming reagent. Which of the two steps is rate limiting depends on the arene being displaced and/or the nature of the incoming substrate. The experiments present a unified view of these mechanisms, which have relevance to propagation processes in olefin polymerizations mediated by such cations.     

Historical perspectives on living anionic polymerization

A brief overview of the role that Dr. Michael Szwarc has played in unraveling the mechanism of living anionic polymerization is presented. Emphasis is placed on the different ionic species that control the propagation reaction in ether-type solvents. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2101–2107, 2002     

Polystyrene with dendritic branching by convergent living anionic polymerization. II. Approach using vinylbenzyl chloride

Vinylbenzyl chloride (VBC) has been used as a coupling agent in Convergent Living Anionic Polymerization to produce polymers with dendritic branching. The slow addition of a stoichiometric amount of VBC to living polystyrene chains allows the coupling to proceed through macromonomer formation followed by vinyl addition. Changing the reaction conditions produced two types of structures. Star‐shaped polymers with a hyperbranched core were made by the continuous slow addition of VBC alone, and chain‐extended hyperbranched structures with varied molecular weight between branch points were produced by the slow addition of VBC mixed with different amounts of styrene monomer. The extent of growth of the two different types of structures ranged from 2.4 to 2.6 generations for the case of VBC added alone, corresponding to an average of 5.3 to 6.1 arms attached to the hyperbranched core, and from 3.2 to 4.2 generations for polymers produced from the addition of VBC mixed with styrene. Relatively low polydispersities were obtained for all samples. The highly branched nature of the polymers was reflected in the low intrinsic viscosity relative to linear polystyrene and in the dependence of glass‐transition temperature on the molecular weight relative to the number of end groups. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4289–4298, 2000     

Photoinduced electron transfer in ion pairs of cation-anion polymethine dyes

Photoinduced electron transfer in ion pairs of cation-anion polymethine dyes was studied by flash photolysis. The formation of radicals, which are the products of photoinduced transfer of an electron from an anion to a cation in the ion pairs, was observed during photoexcitation of a number of cation-anion dyes in nonpolar and some weakly polar solvents (in particular, in toluene and chloroform). Photoinduced electron transfer is also observed during triplet sensitization of ion pairs of the cation-anion dyes. The redox potentials of the cations and anions constituting the dyes were measured; the radical yields were compared with the free energies of photoinduced electron transfer. Photoinduced electron transfer in the systems under study was compared with similar process in cyanineborate ion pairs.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 878–884, May, 1995.The authors thank I. Ya. Levitin for help in measuring redox potentials.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4217).     

Anionic polymerization of methacrylates by samarium (III) enolate on networked polystyrene: Effects of its sterically confined environment on polymerization behavior

Anionic polymerization of methacrylates under sterically confined environment in a spherical beads‐shaped networked polystyrene (NwPS) matrix is described. The initiator used herein is a samarium (Sm) (III) enolate, which was formed by treatment of 2‐bromoisobutylate immobilized in the side chain of NwPS with Sm (II) iodide. By using this NwPS‐bound initiator, polymerization of a series of methacrylates (=solid‐supported polymerization) was studied to find its two aspects: (1) In the early stages, the rate constant for each methacrylate was comparable to that for its conventional solution‐phase polymerization using a Sm (III) enolate, suggesting that methacrylate can be efficiently supplied to the propagating end by its free permeation without any interference by the networked structure of the matrix. (2) After the early stages, the rate constant decreased remarkably, implying that permeation of methacrylate was sterically interfered by the formed poly(methacrylate) that filled the confined space in NwPS, as supported by a SEM image of the resulting beads, of which pores were filled with the formed polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1510–1521, 2009     

Isomerization of ion pairs of symmetrical indopolycarbocyanine dyes

It was shown that from a polar solvent to a nonpolar solvent the rate constant of cis-trans isomerization of the dyes studied decreases sharply (by a factor of 10) on account of the formation of ion pairs (between the dye cation and anion in a nonpolar solvent). This is explained by an increase in the order of the bond of the polymethine chain of the dye, around which isomerization occurs. The formation of ion pairs was found to have virtually no effect on the lifetime of the triplet state of dyes; the sharp increase in the decay rate of the triplet state for dye 6 is due to the heavy-atom effect (the I^– anion).N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 107–113, January, 1992.     

Anionic High Impact Polystyrene: A New Process for Low Residual and Low Cost HIPS

BASF has developed a new process for the manufacturing of High Impact Polystyrene (HIPS) via an anionic route: the so-called A-HIPS process. The driving forces were the development of a product with a low content of residuals and improved cost performance compared to the radical state of the art HIPS. The production of A-HIPS includes the synthesis of the rubber, a styrene-butadiene block copolymer. To overcome the main challenges of anionic polymerization such as reactivity control, solvent purity and initiator costs, BASF has developed its own proprietary technology, the Retarded Anionic Polymerization (R.A.P.) which allows styrene polymerization to 100% conversion under similar reaction conditions as the radical polymerization. A new low cost anionic initiator system (BuLi-free), based on sodium hydride and triethylaluminum, has been developed for perfect reactivity control over a broad temperature and concentration range even up to bulk conditions.     

Living carbocationic polymerization. LXII. Living polymerization of styrene,p-methylstyrene and p-chlorostyrene induced by the common ion effect

The effect of common anion producing salt, tetrabutylammonium chloride (n-Bu₄NCl), on the livingness and kinetics of styrene (St), p-chlorostyrene (pClSt), and p-methylstyrene (pMeSt) polymerization initiated by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ system has been investigated. Uncontrolled (conventional) carbocationic polymerization of St and p MeSt can be converted to living polymerization by the use of n-Bu₄NCl. Under similar conditions the polymerization of p ClSt is living even in the absence of n-Bu₄NCl, although the molecular weight distribution (MWD) of the polymer becomes narrower in the presence of this salt. The apparent rates of polymerizations decrease in the presence of n-Bu₄NCl in proportion with the concentration of the salt. The rate of living polymerization of p ClSt is noticeably lower than that of St, while that of p MeSt is higher. The apparent rate constants, k_p^A, of these polymerizations have been determined, and the effects of the electron donating p Me- and electron withdrawing p Cl-substituents relative to the rate of St polymerization have been analyzed. [For part LXI, see J. Si and J. P. Kennedy, Polym. Bull., 33 , 651 (1994)]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3341–3347, 1997     

The origin of living polymerization with an o-fluorinated catalyst: NMR spectroscopic characterization of chain-carrying species

To characterize the origin of living polymerization with nonmetallocene titanium-based catalysts containing o-fluoroaryl substituents, ethene polymerization by an o-fluorinated bis(enolatoimine) titanium catalyst and its nonfluorinated counterpart has been studied by multinuclear NMR spectroscopy by using methylaluminoxane (MAO) or AlMe(3)/CPh(3)B(C(6)F(5))(4) as activators. Formation of ion pairs of the type [TiL(2)Me][MeMAO] and [TiL(2)Me][B(C(6)F(5))(4)] has been observed for both catalysts. These ion pairs react with ethene to afford the chain-propagating species [TiL(2)P][MeMAO] and [TiL(2)P][B(C(6)F(5))(4)], respectively (P = growing polymeryl chain). For the o-F-substituted catalyst species of the second type, NMR spectroscopy provides evidence that the o-F substituents interact with the metal center. This interaction is proposed to keep the polymerization catalysis living by suppressing chain transfer to AlMe(3) and β-hydrogen transfer processes.     

Amphiphilic organic ion pairs in solution: a theoretical study.

The macroscopic manifestation of hydrophobic interactions for amphiphilic organic ion pairs (tetraalkylammonium-anion) has been shown experimentally by measuring their association constants and their affinity with the organic phase. Beyond a certain size, there is a direct relation between association constants and chain lengths in tetraalkylammonium ions. We propose to cast a bridge between these results and geometrical properties considered at the level of a single ion pair by means of quantum chemistry calculations performed on model systems: trimethylalkylammonium-pentyl sulfate instead of tetraalkylammonium-dodecyl sulfate. Two limiting cases are considered: head-to-head configurations, which yield an optimal electrostatic interaction between polar heads, and parallel configurations with a balance between electrostatic and hydrophobic interactions. All properties (geometries, complexation energies, and atomic charges) were obtained at the MP2 level of calculation, with water described by a continuum model (CPCM). Dispersion forces link hydrocarbon chains of tetraalkylammonium ions and pentyl sulfate, thus yielding (for the largest ion pairs) parallel configurations favored with respect to head-to-head geometries by solute-solvent electrostatic interactions. Given the small experimental association energies, we probe the accuracy limit of the MP2 and CPCM methods. However, clear trends are obtained as a function of chain length, which agree with the experimental observations. The calculated monotonic stabilization of ion pairs when the hydrocarbon chain increases in length is discussed in terms of electrostatic interactions (between ions and between ion pairs and water), dispersion forces, and cavitation energies.     

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     

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 Anionic Polymerization of 2‐Methyl‐4‐ phenyl‐1‐buten‐3‐yne

The anionic polymerization behavior of 2‐methyl‐4‐phenyl‐1‐buten‐3‐yne (2) was investigated to get information on the effect of substituent at the 2‐position. The polymerization of 2 did not proceed in tetrahydrofuran at –78°C by lithium initiators, while sodium initiators can conduct the polymerization smoothly to give polymers consisting of a specific 1,2‐polymerized unit. The living nature of the polymerization of 2 by diphenylmethylsodium was supported by the post‐polymerization experiment.     

Mechanism of coupling reactions of polystyryllithium with dihalomethanes

We report here an in‐depth analysis of the reaction mechanisms involved in the formation of polymer dimers formed by the coupling of polystyryllithium (PSLi) with dichloromethane (DCM), dibromomethane (DBM), and diiodomethane (DIM) in tetrahydrofuran at ?78 °C. The DBM‐mediated reactions give a high degree of coupling but generate 1,2‐diphenyl linkages in addition to the expected 1,3‐diphenyl linkages and small amounts of β‐substituted styrenic end groups that are detectable by fluorescence measurements. This is consistent with the formation of bromobenzyl end groups by lithium–bromine exchange and PSLi‐mediated elimination. The formation of α‐substituted styrenic end groups by conventional displacement and elimination is also possible. Although reactions of PSLi with DCM show no coupling at all, DIM is a much better coupling agent than DBM, significantly suppressing side reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1081–1091, 2002