A study on properties of PEG bent double chain stranded polypseudorotaxanes with γ-cyclodextrins

Recently a variety of cyclodextrin (CD)-based polypseudorotaxanes (PPRs) and polyrotaxanes (PRs) have attracted trememdous attention as building blocks for hierarchical nanostructured materials. γ-CDs are known to include two chains of poly (ethylene glycol) (PEG) into their cavity, either bent double chains or two parallel chains to create PPRs or PRs. A distal 2-bromoisobutyryl end-capped PEG (M_n=4000) was found to self-assemble with γ-CDs to form PEG bent double chain stranded PPRs which are stable enough to further initiate the bulk atom transfer radical polymerization (ATRP) of n-butyl methacrylate (BMA) to give rise to the same conformational PPR-based block copolymers. As attached PBMA possesses good processing and mechanical properties, the resulting copolymers were soluble in chloroform to be cast into films. Due to added γ-CDs in the conformation of PEG bent double chain remaining the characteristic channel-type crystal structure, the higher mechanical strength was noted in the copolymers, while the elongation ratio was remarkedly got down. The static contact angle was substantially decreased as compared to the homopolymer PBMA, but was slightly enhanced with regard to the triblock copolymer PBMA-PEG-PBMA. Furthermore, they were electrospun into uniform non-woven fibers in a solution of dichloromethane, and morphology of fibers was affected by the polymer solution concentration.