INCLUSION COMPLEXES BETWEEN CYCLODEXTRINS AND TRIBLOCK COPOLYMERS IN AQUEOUS-SOLUTION - A DYNAMIC AND STATIC LIGHT-SCATTERING STUDY

Simultaneous static and dynamic light experiments have been made on va rious cyclodextrins and cyclodextrin derivatives, as well as the inclu sion complexes formed between different polyethylene oxide/polypropyle ne oxide triblock copolymers (PEO-PPO-PEO) (pluronics) and dimethyl-be ta-cyclodextrin (DIMEB). The inclusion complexes formed between DIMEB and pluronics are highly soluble, in contrast to the insoluble complex es formed between beta-cyclodextrin and the same substances. The stati c light-scattering (LS) data show that approximately 11 DIMEB molecule s thread onto the copolymer chains and are located on the PPO block. W ith the inverse structure (PPO-PEO-PPO), about seven DIMEB molecules a re present in the complex. NMR measurements are used to substantiate c omplex formation by means of characteristic changes in the proton sign als. Hydrodynamic radii obtained from the dynamic LS data at infinite dilution for the cyclodextrins correspond well with dimensions determi ned using X-ray methods. Inverse Laplace transformation (ILT) allowed resolution of the relaxational modes from the cyclodextrin/pluronic co mplex and the excess cyclodextrin. The complexes formed with the DIMEB are shown to be significantly larger than the copolymer unimers, whic h may be due to accentuation of steric hindrance to flexing in the PPO block. With the inverse pluronic structure, on the other hand, the co mplex is smaller in radius than the unimer. At temperatures above whic h the copolymer forms micelles, addition of DIMEB inhibits both cluste r formation and micellization of the pluronics and also prevents netwo rk formation with the inverse pluronic, whereas the trimethyl analogue (TRIMEB) does not have this effect.