Preparation and characterization of inclusion complexes of poly(dimethylsiloxane)s with cyclodextrins

beta -Cyclodextrin (beta -CD) and gamma -cyclodextrin (gamma -CD) formed inclusion complexes with poly(dimethylsiloxane)s (PDMS) of various molecular weights to give crystalline compounds. However, a-cyclodextrin (alpha -CD) did not form complexes with PDMS of any molecular weight. The yields of the beta -CD-PDMS inclusion complexes decreased with increasing molecular weight of PDMS. In contrast, the yields of the gamma -CD-PDMS inclusion complexes increased with increasing molecular weight, reached a maximum at molecular weight of around 760, and gradually decreased at higher molecular weight. The chain-length selectivity is reversed between beta -CD and gamma -CD. The P-CD-PDMS inclusion complexes are stoichiometric 1:1 compounds when the molecular weights of PDMS are low. The gamma -CD-PDMS inclusion complexes are stoichiometric 2:3 (cyclodextrin:monomer unit of PDMS) compounds. The complexes were isolated and characterized by H-1 NMR, C-13 CP/ALAS NMR, and X-ray diffraction studies. The inclusion modes are discussed.