Molecular design of novel network polymers

Cationic, anionic, and radical ring‐opening polymerization of spiro and bicyclic monomers, and their application to network polymers have been developed. Bicyclo orthoesters (BOEs), spiro orthoesters (SOEs), and spiro orthocarbonates (SOCs) were polymerized by cationic double ring‐opening. Bicyclobis(γ‐butyrolactone)s and spirobis(γ‐butyrolactone)s were copolymerized with epoxides by anionic alternating ring‐opening. Polymers from SOCs bearing exomethylene groups consisted of ring‐opened and vinyl polymerized units. The degree of ring‐opening of SOCs depended upon the number of rings and steric hindrance. The radical polymerization of vinylcyclopropanone cyclic acetals depended on the ring‐size. With the monomers bearing 5‐ and 6‐membered acetal rings, single ring‐opened polymers were obtained. With the monomer bearing 7‐membered acetal ring, the polymer mainly consisted of double ring‐opened unit. These monomers could be crosslinked by bifunctionalization. Poly(cyclic orthoester)s linked by covalent bonds with dithiols to bifunctional SOEs were crosslinked by acid catalysts, and the reversible crosslinking‐depolymerization system could be controlled by temperature.