Mechanically Linked Poly(ethylene terephthalate)

Abstract

The synthesis, by solid-state copolymerization, and properties of poly(ethylene terephthalate) (PET) copolymers containing various amounts of [2] catenane mechanical linkages are described. Polymers end-capped by the corresponding noninterlocked macrocycle as well as a copolymer with a rigid fluorene monomer unit were also prepared as reference systems. Size exclusion chromatography and H-1 NMR indicate that the catenane is quantitatively incorporated during synthesis but that a small fraction ring-opens to form noninterlocked macrocycles, incorporated as either chain ends or branching points. Catenanes induce a smaller increase in the glass transition temperature than the macrocycle at the same weight content. This is probably due to the suppression of interchain hydrogen bonds upon interlocking and points to a specific effect of the mechanical linkage on properties. The crystallization and melting temperatures of catenane copolymers are only slightly depressed compared to those of PET homopolymer, further demonstrating significant flexibility of the catenane rings. SAXS results show that the amorphous interlayer between lamellae increases with increasing catenane content at constant lamellar thickness, confirming that the uncrystallizable catenane units concentrate in the amorphous phase during solid-state polymerization.