Preparation and Characterization of Polypseudorotaxanes Based on Biodegradable Poly(l-lactide)/Poly(ethylene glycol) Triblock Copolymers

Abstract

A variation of A−B−A-type triblock copolymers consisting of poly(l-lactide) (PLLA) and poly(ethylene glycol) (PEG) was synthesized and examined for complexation with α-cyclodextrins (α-CDs). Although the PLLA block has bulky methyl groups as side chains, stable polypseudorotaxanes of PLLA−PEG−PLLA triblock copolymers as well as PLLA were obtained and confirmed by 1H NMR, solid-state 13C CP/MAS NMR, FT-IR, and X-ray spectroscopies. From the results, it was hypothesized that the guest molecules threaded into the hydrophobic CD cavities, and they form stable pseudorotaxanes in both PEG and PLLA blocks. The α-CDs slide over the flanking bulky PLLA blocks to form an inclusion complex with PEG block; in addition, they form very stick pseudorotaxanes with the end-blocks of PLLA parts. The copolymers confined to the CD channels lost their original crystalline properties but formed a channel-type hydrophobic crystalline structure with CDs due to long chain nature of the copolymers. Such a polymeric inclusion compl...