For decades, cyclopolymerization of α,ω-diyne derivatives has been an effective method to synthesize various soluble polyacetylenes containing fiveto seven-membered rings in the backbone. However, cyclopolymerization to form fourmembered carbocycles was considered impossible due to their exceptionally high ring strain (∼30 kcal/mol). Herein, we demonstrate the successful cyclopolymerization of rationally designed 1,5-hexadiyne derivatives to afford various polyacetylenes containing highly strained cyclobutenes in each repeat unit. After screening, Ru catalysts containing bulky diisopropylphenyl groups promoted challenging four-membered ring cyclization efficiently from various monomers, enabling the synthesis of high molecular weight (up to 40 kDa) polyacetylenes in a controlled manner. Furthermore, living polymerization allowed for block copolymer synthesis by combining with ring-opening metathesis polymerization as well as block copolymerization of two different 1,5hexadiyne monomers to give a fully conjugated polyacetylene. These new polymers unexpectedly showed much narrower band gaps than conventional substituted polyacetylenes by >0.2 eV. Interestingly, computational studies showed much smaller bond length alternation in the conjugated backbone containing cyclobutenes, resulting in highly delocalized π electrons along the polymer chain and lower band gaps.

Doubly grafted polymers bearing two different macromolecular side groups in each repeat unit of the polymer backbone have received considerable attention because of their unique molecular structures and properties. However, the preparation of these polymers is challenging because of the synthetic difficulty arising from their steric crowding and structural complexity. Here, based on the diversity-oriented polymerization concept, we report the synthesis of well-defined doubly grafted polymers at 30 °C using a one-shot Cu-catalyzed multicomponent grafting strategy using readily accessible precursor polymers possessing sulfonyl azides and alkyne and amine macromonomers. Based on this strategy, we prepared 35 doubly grafted polymers. Detailed 1 H NMR and SEC analyses revealed high grafting efficiency (79−99%) and narrow-to-moderate dispersities of the welldefined doubly grafted polymers.

Sol-gel coating that is commonly used in photocatalyst immobilization has low binding capacity with supporting materials and low photocatalytic efficiency due to reduction of surface area of catalysts. In addition, the recombination of electrons and holes is an important reason of low efficiency in photocatalytic reaction. To solve such problems, our study devised a TiO