title: Cyclic polymers from alkynes.
abstract: Cyclic polymers have dramatically different physical properties compared with those of their equivalent linear counterparts. However, the exploration of cyclic polymers is limited because of the inherent challenges associated with their synthesis. Conjugated linear polyacetylenes are important materials for electrical conductivity, paramagnetic susceptibility, optical nonlinearity, photoconductivity, gas permeability, liquid crystallinity and chain helicity. However, their cyclic analogues are unknown, and therefore the ability to examine how a cyclic topology influences their properties is currently not possible. We have solved this challenge and now report a tungsten catalyst supported by a tetraanionic pincer ligand that can rapidly polymerize alkynes to form conjugated macrocycles in high yield. The catalyst works by tethering the ends of the polymer to the metal centre to overcome the inherent entropic penalty of cyclization. Gel-permeation chromatography, dynamic and static light scattering, viscometry and chemical tests are all consistent with theoretical predictions and provide unambiguous confirmation of a cyclic topology. Access to a wide variety of new cyclic polymers is now possible by simply choosing the appropriate alkyne monomer.
authors.affiliation: Department of Chemistry, University of Florida, Center for Catalysis, PO Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Roland
authors.affiliation: Department of Chemistry, University of Florida, Center for Catalysis, PO Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of Florida, Center for Catalysis, PO Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Khalil A
authors.initials: KA
authors.lastname: Abboud
authors.affiliation: Department of Chemistry, University of Florida, Center for Catalysis, PO Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Wagener
authors.affiliation: Department of Chemistry, University of Florida, Center for Catalysis, PO Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Veige