Abstract

Abstract

Summary: An H-shaped poly(tetrahydrofuran), poly(THF), having four terminal allyl groups was prepared through the covalent conversion of an ionically linked polymer assembly, comprised of four units of cationic poly(THF) having a pyrrolidinium salt and an allyl end group, and one unit of anionic poly(THF) having two dicarboxylate end groups. A pair of polymeric topological isomers, having double-cyclic, manacle, and θ-shaped constructions, was subsequently produced under dilution through the intramolecular double metathesis condensation of four terminal allyl groups of the H-shaped precursor.

A collection of recent developments in topological polymer chemistry is presented. First, topological isomerism occurring on randomly coiled, flexible polymer molecules having cyclic and linear structures is discussed. Second, an electrostatic self-assembly and covalent fixation strategy has been developed for the synthesis of polymeric topological isomers. These isomers have double cyclic, manacle-, and θ-shaped constructions, and are prepared by using either linear or star telechelic polymer precursors having moderately strained cyclic ammonium salt groups, which carry multifunctional carboxylate counteranions. A technique of reversed-phase chromatography (RPC) is demonstrated as an effective means to separate polymers with different topologies, especially polymeric topological isomers. A further extension of topological polymer chemistry has been observed by dynamic selection from electrostatic polymer self-assembly to enable the effective formation of tadpole-shaped, cyclic-linear hybrid topologies. © 2005 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 5: 17–26; 2005: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20029

Summary: A pair of macromolecular constitutional isomers having topologically distinctive, dicyclic constructions, that is, θ-shaped and manacle-shaped polymers, has been synthesized from a polymer self-assembly, comprised of three-armed star poly(tetrahydrofuran) [poly(THF)] having N-phenylpyrrolidinium salt end groups carrying dicarboxylate counteranions (1S/2d). The presence of the two constitutional polymeric isomers was confirmed by means of a reversed-phase liquid chromatography (RPC) technique. Moreover, size exclusion chromatography (SEC) showed that a major component possesses notably larger hydrodynamic volume than the others, and is assignable as a manacle-shaped isomer while a minor component is assigned as a θ-shaped isomer. The statistics of the covalent-linking process of 1S/2d were consistent with the other experimental results.

Recent developments in topological polymer chemistry are outlined. First, nonlinear polymer topologies are systematically classified on the basis of topological considerations of constitutional isomerism in a series of alkanes (C_nH_2n+2), monocycloalkanes (C_nH_2n), and polycycloalkanes (C_nH_2n−2, C_nH_2n−4, etc.). Various pairs of topological isomers are identified in randomly coiled, flexible polymer molecules with cyclic and branched structures. An electro- static self-assembly and covalent fixation strategy has subsequently been developed for the efficient synthesis of a variety of topologically unique polymers, including monocyclic and polycyclic polymers, topological isomers, and topological block copolymers. In this process, new telechelics with moderately strained cyclic onium salt groups carrying multifunctional carboxylate counteranions have been designed as key polymeric precursors. Further extensions of topological polymer chem- istry have been achieved by the use of cyclic telechelics (kyklo-telechelics) and cyclic macromonomers, obtainable also by means of the electrostatic self-assembly and covalent fixation process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2905–2917, 2003

A novel and unusual polymer topology, i.e. a-ring-with-two-branches, has been constructed efficiently by making use of an interiorly functionalized poly(tetrahydrofuran) (poly(THF)) having two pyrrolidinium groups. The dicarboxylate counterion, i. e. terephthalate, was then introduced by an ion-exchange reaction of the interiorly located pyrrolidinium group. Subsequent heat treatment under appropriate dilution caused an efficient polymer cyclization to produce an a-ring-with-two-branches polymer topology in high yield through the selective and quantitative ring-opening of the pyrrolidinium groups by the dicarboxylate counterion.

A novel methodology (electrostatic self-assembly and covalent fixation) has been proposed for designing various nonlinear polymer topologies, including monocyclic and polycyclic polymers, cyclic macromonomers and cyclic telechelics (kyklo-telechelics), a-ring-with-a-branch topology polymers and polymeric topological isomers, as well as branched model polymers, such as star polymers and polymacromonomers. Thus, new telechelic polymer precursors having a moderately strained cyclic onium salt group as single or multiple end groups and carrying multifunctional carboxylates as the counterions were prepared through an ion-exchange reaction. A variety of electrostatic self-assemblies of these polymer precursors, formed particularly in dilute organic solution, was then subjected to heat in order to convert the ionic interactions into covalent linkages by ring-opening reaction, and to produce topologically unique, nonlinear polymer architectures in high efficiency.

Mono-, bis-, and tris(trifluoromethanesulfonate ester)s ((triflate ester)s) were prepared by the reaction of benzyl alcohol (1), 1,4-bis(hydroxymethyl)benzene (2) and 1,3,5-tris(hydroxymethyl)benzene (3) with trifluoromethanesulfonic anhydride in the presence of 2,6-di-tert-butylpyridine. These benzylic triflate esters were applied in-situ for the living polymerization of tetrahydrofuran (THF). The subsequent end-capping reaction with a suitable nucleophile proceeded quantitatively to produce mono, bi- and, in particular, novel trifunctional telechelic poly(THF)s, respectively.