Optical anisotropy of polyisobutylene: Strain birefringence

Strain birefringence measurements on crosslinked polyisobutylene (butyl rubber) confirm earlier work of Stein and Tobolsky on the linear polymer indicating the optical anisotropy to be much greater than should have been expected from the structural symmetry of the polyisobutylene (PIB) chain. The configuration–optical anisotropy parameter Δa for PIB at 25°C is 4.1(±0.1) × 10^?24 cm³, or about half the value for crosslinked polymethylene, both polymers being undiluted and amorphous. Swelling with cyclohexane, CCl₄, and CBrCl₃ lowers Δa to values of 3.8, 3.4, and 2.8 × 10^?24 cm³, respectively. Contributions from intermolecular correlations in the bulk polymer and from form anisotropy in the diluted systems are small, if not negligible. Temperature coefficients measured isometrically yield d In Δa/dT ≈ 0.2 × 10^?3 deg^?1. Both Δa and its temperature coefficient are much greater than calculated from rotational isomeric state theory assuming additivity of bond polarizabilities. The disparity (more than tenfold for Δa) cannot be relieved by any rational adjustment of the structural parameters. It is suggested that the severe crowding of groups in the PIB chain may affect the anisotropies of group polarizabilities.     

聚醚砜酮的磺化及其在异丁烯低聚反应中的应用

Concentrated homogeneous mineral acids have been widely used as catalysts in industrial processes for several decades. These catalysts are corrosive to the apparatus, and there are large volumes of chemically reactive waste stream that are difficult to deal with[1]. In order to solve these problems, investigators have replaced these mineral acids with solid acid catalysts. Besides inorganic solid acid catalysts such as zeolite, solid organic polymeric resins containing acid groups, especially sulfuric acid resins such as Amberlyst[2], have attracted much attention. Compared with most inorganic acid catalysts, they have the advantages of their potentially high acidity, controllable surface area and porosity[3]. This article reports a novel sulfonated poly(phthalazinone ether sulfone ketone) (S-PPESK) resin and its application to isobutene oligomerization. S-PPESK exhibits high catalytic activity and excellent dimerization selectivity.     

Synthesis of triphenylsilyl- and triphenylmethyl-telechelic polyisobutylene: An approach to the synthesis of multi-ion telechelic ionomers

Triphenylsilyl- and triphenylmethyl-telechelic polyisobutylene (PIB) were prepared by lithiation of three-arm star PIBs carrying either olefinic or tert-alkyl chloride end groups, followed by reaction with triphenylsilyl chloride or triphenylcarbenium ion, respectively. Since the lithiated intermediate is a substituted allylic carbanion, the chain end also possesses a double bond which is located β-γ relative to the silyl or triphenylmethyl group. The phenyl groups were incorporated into the polymers to provide extra sites for sulfonation, in addition to the double bond, to enable the synthesis of multi-ion telechelic ionomers. ¹H- and ¹³C-NMR spectroscopy showed that triphenylsilylation and triphenylmethylation were essentially quantitative when applied under the prescribed conditions to either the model compound, 2,4,4-trimethyl-1-pentene, or to the telechelic PIBs. It was observed that exhaustive sulfonation of these materials using acetyl sulfate or chlorosulfonic acid yielded only about 50% sulfonation of the available sites. This suggests that sulfonation of closely adjacent, multiple sites within the same molecule fails due to deactivation of the remaining sites after one or perhaps two sulfonations. However, the triphenylsilyl- and triphenylmethyl-telechelic PIBs represent novel prepolymers which can perhaps be derivatized by some method other than sulfonation, and the general concept for producing telechelic ionomer precursors with multiple sulfonation sites may prove successful with other moieties containing spacer groups between sites. © 1993 John Wiley & Sons, Inc.     

Iridium-catalyzed addition of aroyl chlorides and aliphatic acid chlorides to terminal alkynes

Iridium complexes show high catalytic activity in intermolecular additions of acid chlorides to terminal alkynes to afford valuable (Z)-β-chloro-α,β-unsaturated ketones. Ligands in the catalytic system play a crucial role in this reaction. An N-heterocyclic carbene (NHC) is an efficient ligand for the addition of aroyl chlorides, while dicyclohexyl(2-methylphenyl)phosphine (PCy(2)(o-Tol)) is indispensable for the reaction of aliphatic acid chlorides. The addition reactions proceed regio- and stereoselectively with suppression of decarbonylation and β-hydrogen elimination, which have been two major intrinsic problems in transition-metal-catalyzed reactions. Stoichiometric reactions of active iridium catalysts with aroyl chlorides and aliphatic acid chlorides are carried out to gain insights into the reaction mechanisms.     

Addition of alkanesulfenyl chlorides to N-allylphthalimide

Russian Chemical Bulletin -     

Thermal decomposition mechanisms of tert-alkyl peroxypivalates studied by the nitroxide radical trapping technique

The thermolysis of a series of tert-alkyl peroxypivalates 1 in cumene has been investigated by using the nitroxide radical-trapping technique. tert-Alkoxyl radicals generated from the thermolysis underwent the unimolecular reactions, beta-scission, and 1,5-H shift, competing with hydrogen abstraction from cumene. The absolute rate constants for beta-scission of tert-alkoxyl radicals, which vary over 4 orders of magnitude, indicate the vastly different behavior of alkoxyl radicals. However, the radical generation efficiencies of 1 varied only slightly, from 53 (R = Me) to 63% (R = Bu(t)()), supporting a mechanism involving concerted two-bond scission within the solvent cage to generate the tert-butyl radical, CO(2), and an alkoxyl radical. The thermolysis rate constants of tert-alkyl peroxypivalates 1 were influenced by both inductive and steric effects [Taft-Ingold equation, log(rel k(d)) = (0.97 +/- 0. 14)Sigmasigma - (0.31 +/- 0.04)SigmaE(s)(c), was obtained].     

An efficient system for the Pd-catalyzed cross-coupling of amides and aryl chlorides

A catalyst based on a new biarylphosphine ligand (3) for the Pd-catalyzed cross-coupling reactions of amides and aryl chlorides is described. This system shows the highest turnover frequencies reported to date for these reactions, especially for aryl chloride substrates bearing an ortho substituent. An array of amides and aryl chlorides were successfully reacted in good to excellent yields.     

Access to "Friedel-Crafts-restricted" tert-alkyl aromatics by activation/methylation of tertiary benzylic alcohols

Herein we describe a two-step protocol to prepare m-tert-alkylbenzenes. The appropriate tertiary benzylic alcohols are activated with SOCl(2) or concentrated HCl and then treated with trimethylaluminum, affording the desired products in 68-97% yields (22 examples). This reaction sequence is successful in the presence of a variety of functional groups, including acid-sensitive and Lewis-basic groups. In addition to t-Bu groups, 1,1-dimethylpropyl and 1-ethyl-1-methylpropyl groups can also be installed using this method.     

Incompatibility of polymer solutions. III. Critical opalescence in the system polystyrene + polyisobutylene + toluene

The angular dependence of light scattering from the homogeneous ternary system polystyrene + polyisobutylene + toluene was measured at a fixed (critical) concentration as a function of temperature. On approaching the critical temperature the scattering becomes very large and strongly angle-dependent. The experiments show that the interaction range r_G is of the same order of magnitude as the molecular radius of gyration of the polymer, but cannot be set equal to it as in the case of a binary system of one polymer in a single solvent. The temperature dependence of the various interaction parameters does not depend on the molecular weights of the polymers.     

The addition of perfluoroalkanesulfinyl chlorides to alkoxyallenes

The addition reaction of perfluoroalkanesulfinyl chlorides to alkoxyallenes was achieved under mild conditions. Two kinds of perfluoroalkyl alkenyl sulfoxides, β-alkoxyvinyl perfluoroalkyl sulfoxides and α-perfluoroalkanesulfinyl enones or enals, were obtained selectively depending on the structure of alkoxyallenes.     

Addition of sulfenyl chlorides to α-fluoroacrylates

Conclusions -Fluoroacrylates add sulfenyl chlorides in such a manner that the methylthio group adds exclusively, and the phenylthio group adds predominantly, to the-carbon atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1412–1414, June, 1973.     

Solvent-free synthesis of glycosyl chlorides based on the triphenyl phosphine/hexachloroacetone system

Glycosyl chlorides, useful as glycosyl donors in glycoside synthesis and precursors in organic synthesis, can be easily prepared under solvent-free conditions by exposing a sugar hemiacetal to an equimolar mixture of PPh₃ and hexachloroacetone at 70 °C. The reaction affords products in high yields and short times, and is tolerant of a wide range of commonly adopted protecting groups.     

Functionalization of living polyisobutylene: Preference for reduction over electrophilic addition

Polyisobutylene was synthesized using 2-chloro-2,4,4-trimethylpentane (TMPCl) as an initiator and TiCl₄ as a coinitiator. After taking a base sample, the living cation was reacted with 5 equivalents of (4-vinylphenyl)dimethylsilane (VPDMSi). It was observed that the cation preferred reduction by hydride elimination from VPDMSi compared to electrophilic addition of even a single vinyl group. It was postulated that the reduction of the cation in presence of strong Lewis acid such as TiCl₄ occurs readily before addition of cation to vinyl group. Thus saturated polyisobutylene was obtained with a terminal hydrogen group instead of chlorine group which is produced by conventional cationic polymerization.