CONTROLLED SYNTHESIS OF TOPOLOGICALLY TEMPLATED CATENANE AND KNOTTY POLYMER

The topologically interesting structure of polymer catenanes and knotty polymers are of high interest for their unique chemical and physical properties. However, the practical applications of these materials have not been explored well due to synthetic obstacles in obtaining high yields. Chapter 1 reviews template directed synthesis of low molecular weight catenanes and the trefoil knot. In addition, recent advances in synthesis of topologically similar cyclic polymer via end-to-end cyclization of linear analogue or ring-expansion polymerization from cyclic catalyst/initiator are also discussed. Chapter 2 demonstrates a novel route for the synthesis of polymer catenanes using supramolecularly templated Atom Transfer Radical Polymerization (ATRP) initiator for polymerization and subsequent closing of the resulting four-armed type polymer template by Atom Transfer Radical Coupling (ATRC). Direct visualization of the interlocked topology of polymer catenane was achieved by Atomic Force Microscopy (AFM) imaging technique. Chapter 3 reports an important extension of the above mentioned methodology to obtain a catenated block copolymer. The four-armed type homopolymer template was used as macroinitiator to polymerize another monomer by ATRP. The resulting block copolymer template was subjected to template-closing via slightly modified ATRC method. Chapter 4 demonstrates another novel approach to synthesize polymer catenanes by first grafting a preformed alkyne-functionalized linear polymer to an azide-functionalized supramolecular template, followed by ATRC of the resulting polymer template. Detailed analysis of AFM image reveals important information about the side products of ATRC such as inter-molecular coupling and other isomer formation. Chapter 5 reports on a preliminary study of thermally initiated ring-expansion Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization from cyclic RAFT initiator. A novel dixanthate type cyclic RAFT initiator was synthesized and used in a thermally initiated free radical polymerization of N-vinylcarbazole. The cyclic topology of the resulting polyvinylcarbazole was confirmed by Gel Permeation Chromatography (GPC) and AFM analysis. Chapter 6 demonstrates for the first time the synthesis of trefoil knot polymer (knotty polymer) via grafting of an alkyne-functionalized polymer to azide-functionalized double helical type supramolecular template. A well-defined knotty polymer was then obtained by closing the polymer template via ATRC method. Finally in Chapter 7, conclusions, perspectives, and future work on these topics are discussed.