Supramolecular chemistry with macromolecules: New self-assembly based main chain polypseudorotaxanes and their properties

A new class of main chain polypseudorotaxanes, 8, was prepared by self-assembly of a poly(ester crown ether), poly[bis(5-methylene-1,3 -phenylene)-32-crown-10 sebacate] (5), and N,N'-bis(beta-hydroxyethyl)-4,4'-bipyridinium bis(hexafluorophosphate) (6). The equilibrium constant (K = 58.0 M-1 at 21.8 degrees C), Delta H (-26.5 kJ/mol) and Delta S (-56.4 J/mol deg)(all averages from several iterative methods) for the formation of 8 were measured by proton NMR spectroscopy. Compared to those (K = 247 M-1 at 21.8 degrees C, Delta H = -44.7 kJ/mol, Delta S = -106 J/mol deg) for the model system, bis(5-acetoxymethyl-m-phenylene)-32-crown-10 (4) and 6, the enthalpy term is less favorable for the polymeric system, while the entropy term is less unfavorable. The measured values enabled us to design polypseudorotaxanes with targeted degrees of threading (m/n, the fraction of the cyclic moieties threaded with linear species). The solubility of polypseudorotaxane 8 was different from both starting materials 5 and 6, and depended on the min value. Polypseudorotaxanes 8 with higher min had higher viscosities because of increased hydrodynamic volume in solution and were more rigid as manifested by higher glass transition temperatures (T-g) in the solid state. Dethreading (decomplexation) took place above T-g in the solid state, causing loss of color (orange), a process potentially useful for temperature sensors.