Preparation and characterization of polypseudorotaxanes based on biodegradable poly(L-lactide)/poly(ethylene glycol) triblock copolymers

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 alpha-cyclodextrins (alpha-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 H-1 NMR, solid-state C-13 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 a-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 complex can have an important role for constructing supramolecular architectures such as polyrotaxanes and molecular tubes for the use of the bioactive agent delivery system.