Aggregation of hydrophobic substituents of poly(acrylate)s and their competitive complexation by β- And γ-cyclodextrins and their linked dimers in aqueous solution

Competition between the aggregation of the octadecyl substituents of 3% randomly substituted poly(acrylate), PAAC18, and of the dodecyl substituents of the PAAC12 analogue, and their complexation by β-cyclodextrin, βCD, the linked dimers, N,N′-bis(6^A-deoxy-6^A-β- cyclodextrin)urea, 66βCD₂ur, and N,N′-bis(6 ^A-deoxy-6^A-β-cyclodextrin)succinamide, 66βCD₂su, and γ-cyclodextrin, γCD, and the analogous dimers 66γCD₂ur and 66γCD₂su have been studied in aqueous solution. The zero-shear viscosities of 3.3 wt % aqueous solutions of PAAC18, decreases in the presence of βCD, 66βCD ₂ur, 66βCD₂su and γCD, is little changed in the presence of 66γCD₂ur, and increases in the presence of 66γCD₂su. In contrast, the zero-shear viscosities of aqueous solutions of PAAC12 increase in the presence of βCD, γCD, and their dimers but they are much less than those of the corresponding PAAC18 solutions. These macroscopic variations are due to host-guest complexation of the octadecyl and dodecyl substituents by βCD, γCD, and their dimers (as shown by 2D ¹H NOESY NMR spectroscopy) competing with aggregation of the octadecyl and dodecyl substituents where differences in substituent length and cyclodextrin annular size are dominant factors.