POLYROTAXANES BASED ON POLYURETHANE BACKBONES AND CROWN-ETHER CYCLICS.1. SYNTHESIS

Polymeric rotaxanes, consisting of crown ether macrocycles threaded on to a polyurethane backbone, were synthesized by allowing the crown eth er to equilibrate with tetrakis(ethylene glycol) prior to its reaction with bis(p-isocyanatophenyl)methane (MDI). Use of 18-crown-6, which i s too small to be threaded, demonstrated that (1) free macrocycles wer e easily removed by reprecipitation and (2) no ring opening or other s ide reactions of the crown ether took place. The threading efficiency, as measured by x/n, the mole ratio of the cyclics per repeat unit, in creased linearly with ring size from 36- to 60-membered crown ethers a nd at constant ring size nonlinearly with the ratio of the cyclic to l inear components in neat reactions. Up to 63% by mass of macrocycle wa s incorporated. The rotaxane structures were demonstrated after repeat ed precipitation to constant composition as determined by proton NMR u sing GPC analyses to establish the absence of free macrocycles. The po lyrotaxanes have solution and solid-state behaviors that differ from t hose of the model backbone polyurethane. In solution the interactions of the crown ethers with solvent alter the hydrodynamic volume of the polymers, leading to changes that depend on the size of the crown and the proportion incorporated. In the solid state the glass transition t emperature varies with crown content, and at sufficiently high loading s, crystallization of the macrocycle occurs without dethreading. These physically linked analogs of conventional covalent copolymers thus of fer new avenues for control of the behavior and properties of polymeri c materials.