Threading/dethreading exchange rates as structural probes in polypseudorotaxanes

First, the complexation of rigid bis(paraquat)-based cyclophane host 1 with linear MDI-based polyurethane guests 2-5 prepared from tetra(ethylene glyc ol) was studied. Through detailed analysis of H-1 NMR data, we have shown a relationship between the length of the linear polyurethanes and the fracti on of all threaded cyclophanes rapidly exchanging with solution upon the H- 1 NMR time scale. Ln other words, the molecular weight of the polymer can b e estimated from the proportion of cyclic threaded but exchanging rapidly, i.e., those near the ends, versus those that are threaded but exchanging sl owly because they do not have ready access to the ends of the macromolecule ; this is essentially an end group analysis. And then in a similar study of branched polyurethanes 7-11 derived from tetra(ethylene glycol) and glycer ol, it was shown that the cyclophane can be used to determine the (accessib le) fraction of the polymer between a branch point and a terminus and the a verage length between a branch point and a terminus. Third, inclusion of bi sphenol A diethoxylate units in linear polyurethanes 12-16 provides effecti ve barriers to room-temperature threading and dethreading, allowing a "slip page" method for polyrotaxane synthesis at elevated temperature (60 or 90 d egrees C), yielding polyrotaxanes stable for extended periods in solution a t room temperature.