A new story of cyclodextrin as a bulky pendent group causing uncommon behaviour to random copolymers in solution

A series of random copolymers poly[(N-isopropyl acrylamide)-co-(aminoethyl methacrylate β-cyclodextrin)] (PNiCD) were synthesized by free radical polymerization, followed by examination of their physical properties to measure , , Mw and A2 using dynamic and static light scattering (DLS and SLS). The cyclodextrin (CD) moiety attached to the main chain plays two roles. As supramolecular host moieties, CDs form inclusion complexes with guest-ended polymers, leading to “graft-like” copolymers. As bulky hydrophilic moieties, CDs stabilize the micelles induced by the “coil-to-globule” transition of NIPAM segments as temperature increases. The studies of heating rate dependency of this self-assembly of PNiCD are performed by a combination of DLS, SLS, AFM and TEM. Based on tracing the evolution of the size distributions of the aggregates of PNiCD at different heating rates and AFM observations, two mechanisms for the aggregation have been proposed as follows: in slow heating, the copolymer chains form unimolecular micelles first and then second aggregation of the micelles takes place leading to a large but loose aggregates; in fast heating, random aggregation occurs directly leading to small and compact aggregates. The formation of the unimolecular micelles as building blocks for the following aggregation, which was observed exclusively in slow heating process, was not reported before for PNIPAM and the corresponding copolymers. This can be attributed to the presence of the pendent bulky CD groups making the copolymer chains rigid, which has been addressed.