Ring-chain interconversion in high-performance polymer systems.: 1.: [Poly(oxy-4,4′-biphenyleneoxy-1,4-phenylenesulfonyl-1,4-phenylene)] (Radel-R)

At a polymer concentration of 1 wt % in dimethylacetamide, fluoride-promoted cleavage of ether linkages in Radel-R (an industrially important aromatic poly(ether sulfone) derived from 4,4'-biphenol) leads to ring-closing depolymerization. A high molar mass poly(ether sulfone) is thus converted in good yield to a family of macrocycles containing from eight up to at least sixty aromatic rings. Detailed analyses of the reaction products indicate a linear oligomer content of less than 4 wt %. Individual macrocycles containing eight, twelve, sixteen, and twenty aromatic rings have been isolated and characterized as pure, monodisperse oligomers (the first two by single-crystal X-ray analysis). The cyclic dimer and trimer both adopt open, flattened conformations with substantial free pathways through the ring centers, and the cyclic dimer packs to give a continuous-channel structure in the solid state. These macrocyclic oligomers undergo efficient ring-opening polymerization in the presence of phenoxide and especially thiophenoxide initiators to regenerate high-molar-mass polymer, demonstrating for the first time that the chemical recovery and recycling of high-performance aromatic polymers is-in principle- entirely feasible.