Topological polymer chemistry

Recent developments in designing non-linear polymer topologies comprising cyclic and branched segments are reviewed. Thus first, a systematic classification of non-linear polymer topologies is presented by reference to constitutional isomerism in a series of alkanes (CnH2n+2), monocycloalkanes (CnH2n) and polycycloalkanes (CnH2n-2, CnH2n-4, etc.). A special emphasis is placed on constitutional isomerism as well as stereoisomerism occurring uniquely in such non-linear polymer molecules as cyclics, knots and catenanes. Secondly, a novel strategy based on an 'electrostatic self-assembly and covalent fixation' process is described to realize a variety of topologically unique polymer architectures. Those include monocyclic and polycyclic polymers, polymeric topological isomers, cyclic macromonomers and cyclic telechelics (kyklo-telechelics) and 'a ring with a branch' topology polymers, as well as such model branched polymers as star polymers and polymacromonomers. In this process, new telechelic polymer precursors having a moderately strained cyclic onium salt group as single or multiple end groups carrying multifunctional carboxylate counteranions have been prepared through an ion-exchange reaction. The unique electrostatic self-assembly directed by these polymer precursors, particularly in a diluted organic solution, is transformed into the covalent product by the heat treatment of the polymer precursor, causing the ring-opening reaction to produce a variety of topologically unique, non-linear polymer architectures in high efficiency. (C) 2002 Elsevier Science Ltd. All rights reserved.