Main chain polyrotaxanes by threading crown ethers onto a preformed polyurethane: Preparation and properties

摘要

A new method for preparation of crown ether-based polyrotaxanes is described; stirring a solution of the melt of an aliphatic crown ether and a polyurethane afforded the corresponding polypseudorotaxane with hydrogen bonding between the NH groups of the polymer and the ether oxygen atoms of the cyclic species as the driving force. The degree of threading (m, the average number of cyclics per repeat unit) increased with increasing molar feed ratio of crown ether to polymeric NH groups. The degree of threading was reduced by simple dilution with a cosolvent, or threading was prevented by use of a competitive hydrogen-bonding solvent such as DMSO. The polyrotaxanes had higher intrinsic viscosities but lower shape-dependent Huggins constants than the backbone; this was attributed to their greater hydrodynamic volumes and more expanded chain conformations. Moreover, all the polyrotaxanes had only one glass transition temperature; the values depending on m agreed with the Fox equation using a T-g of -22 degrees C for threaded crown ether instead of using the T-g (-68 degrees C) of the free counterpart. [References: 42]