Preparation and Characterization of Inclusion Complexes of Poly(dimethylsiloxane)s with Cyclodextrins

β-Cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) formed inclusion complexes with poly(dimethylsiloxane)s (PDMS) of various molecular weights to give crystalline compounds. However, α-cyclodextrin (α-CD) did not form complexes with PDMS of any molecular weight. The yields of the β-CD−PDMS inclusion complexes decreased with increasing molecular weight of PDMS. In contrast, the yields of the γ-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 β-CD and γ-CD. The β-CD−PDMS inclusion complexes are stoichiometric 1:1 compounds when the molecular weights of PDMS are low. The γ-CD−PDMS inclusion complexes are stoichiometric 2:3 (cyclodextrin:monomer unit of PDMS) compounds. The complexes were isolated and characterized by 1H NMR, 13C CP/MAS NMR, and X-ray diffraction studies. The inclusion modes are discussed.