Effect of macrocycles on the temperature-responsiveness of poly[(methoxy diethylene glycol methacrylate)-graft-PEG]

A homopolymer of 2-(2′-methoxyethoxy)ethyl methacrylate (DM) dissolved in pure water demonstrated an abrupt increase in its turbidity at a critical temperature (LCST). Meanwhile, the LCST for a copolymer of DM and ω-methoxy(oligoethyleneoxy)ethyl methacrylate (P_aM) (PDMP _aM) significantly increased with increasing content of P_aM residue. Furthermore, the addition of macrocycles such as hexasodium calix[6]arenehexasulfonic acid (SCX₆), α-cyclodextrin (α-CD) and 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) changed the LCST. SCX₆ raised the LCST significantly, DM-β-CD slightly raised the LCST and α-CD slightly lowered it. These phenomena could be attributed to the formation of an inclusion complex (polypseudorotaxane) at the grafted PEG chain of the copolymer. ROESY, fluorescence measurements and the viscosity behavior of the SCX₆-PEG dimethylether (PEG-DME) mixture supported the theory of the complexation of SCX⁶ with the PEG chain. The apparent association constants (K_app) of PEG-DME or grafted PEG with SCX₆ and α-CD were determined using fluorescence and UV-vis absorption measurements, respectively. The complexation of the SCX ₆-polymer conjugate with PDMP_aM was also examined by time-evolution measurements of the turbidity. The effect of the structure of guest and host molecules on the LCST for the copolymer was discussed in detail.