Properties of polymer-cyclodextrin-inclusion compounds

The dipolar interactions between polar host CDs and included guests with permanent dipole moments are considered to affect at least the conformations and structures of soluble small-molecule guest/host CD-ICs.Our observations of the preference for inclusion of poly (e-caprolactone) (PCL) over poly(L-lactic acid) (PLLA) chains in both dissolved and crystalline suspended a-CD (a-CDcs), as well as the displacement of PLLA chains by PCL from PLLA-a-CD-ICs when suspended in PCL solution, indicate that dipole-dipole electrostatic interactions may not be critical to the formation of polymer-CD-ICs. If they were, then we might expect PLLA to be preferentially included in a-CD compared to PCL, because two PLLA repeat units and two ester group dipoles occupy each a-CD, while only single PCL 

Because both aliphatic polyesters likely adopt nearly fully extended all-trans conformations when included in their a-CD-lCs/ the dipole moments in neighboring repeat units point in approximately opposite directions. This might cause partial cancellation of the net PLLA dipole moment in each a-CD, because two PLLA repeat units occupy each host a-CD, while only a single PCL ester group is included. Aside from this potential caveat, and because purely non-polar hydrocarbon polymers may be included in CDs, it is likely that dipolar electrostatic interactions do not play a major role in the nano-threading and subsequent formation of polymer-CD-lCs. 

Liu and Guo concluded that van der Waals interactions are a major driving 

Because PCL is less polar than PLLA, with an increased potential for hydrophobic interactions, we conclude that hydrophobic interactions may be important in the formation of polymer-CD-lCs, because, compared with PLLA, PCL is preferentially included by a-CD. In addition, the observed competitive preference for the solution inclusion of bisphenol-A polycarbonate (PC) in y-CD in the presence of poly(methyl methacrylate) and/or poly(vinyl acetate) further strengthens this conclusion, because PC is more hydrophobic than the other two polymers. 

Once again the preference of PCL over PLLA inclusion and the fact that all hydrocarbon polyolefins can form CD-lCs imply that hydrogen-bonding between included guest polymers and host CDs is not likely crucial in the formation of polymer-CD-ICs. 

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