MAIN-CHAIN POLYROTAXANES BY THREADING CROWN-ETHERS ONTO A PREFORMED POLYURETHANE - PREPARATION AND PROPERTIES

A new method for preparation of crown ether-based polyrotaxanes is des cribed; stirring a solution of the melt of an aliphatic crown ether an d a polyurethane afforded the corresponding polypseudorotaxane with hy drogen bonding between the NH groups of the polymer and the ether oxyg en atoms of the cyclic species as the driving force. The degree of thr eading (m/n, 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 cosolv ent, or threading was prevented by use of a competitive hydrogen-bondi ng solvent such as DMSO. The polyrotaxanes had higher intrinsic viscos ities but lower shape-dependent Huggins constants than the backbone; t his was attributed to their greater hydrodynamic volumes and more expa nded chain conformations. Moreover, all the polyrotaxanes had only one glass transition temperature; the values depending on m/n agreed with the Fox equation using a T-g of -22 degrees C for threaded crown ethe r instead of using the T-g (-68 degrees C) of the free counterpart.