While conjugated polymers can be prepared by many means, chain growth polymerization techniques allow for high-molecular weight polymers and good control over the polymerization itself. The metathesis-based cyclopolymerization of 1,6-heptadiynes and 1,7- octadiynes offers a unique access to poly(acetylene)-type polymers with excellent solubility and stability. During the last decade, the fundamental aspects of both regio- and stereoselectivity in cyclopolymerization have been successfully addressed, allowing for a precise control of the final polymer structure.1-6 The switch from Schrock- to Grubbs-type initiators was not only a change of paradigm in initiator reactivity and selectivity, but also opened the door to more robust polymerization setups, allowing for the synthesis of poly(ene)s and poly(ene)-based materials under ambient conditions or in water. This talk will address the fundamentals of cyclopolymerization with both Mo- and Ru-based alkylidenes and the structural prerequisites of both the initiators and the monomers to accomplish high regio- and stereoselectivity. Back-up by DFT calculations will be provided. Selected structure-dependant properties will be outlined where applicable. Finally, the use of the thus prepared poly(ene)s, e.g., as conductive supports for heterogeneous electrocatalysis or conductive fibers will be presented.4-18

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