POLY(URETHANE CROWN ETHER ROTAXANE)S WITH SOLVENT SWITCHABLE MICROSTRUCTURES/

Poly(urethane/crown ether rotaxane)s 7c-g were prepared from l)bis[p-( 2-(2'-hydroxyethoxy)ethoxy)phenyl]methane (diol BG 4), tetrakis(ethyle ne glycol) (5) and 4,4'-methylenebis(phenyl isocyanate) (MDI) (6) usin g 30-crown-10 (30C10) as solvent. It was found that threading efficien cies (min value, average number of cyclics per repeat unit) of 7c-g in creased with the feed proportion of diol BG 4. Compared to poly(ester rotaxane)s in which the crown ethers can freely move along the backbon e, the dethreading rate during polymerization is slow due to the H-bon ds between in-chain NH groups and threaded crown ethers. In poly(ureth ane rotaxane)s, crown ethers are localized at the NH sites by H-bondin g in chloroform, locked translationally and perhaps rotationally, to a fford a well-defined microstructure. However, the cyclics tend to be i n the vicinity of BG units in DMSO, which disrupts the H-bonding. Indu ction of shuttling between the two sites is caused by the use of mixtu res of DMSO and CHCl3. Therefore, 7c-g are considered to be the first polymeric molecular switches reported so far. Threaded 30C10 has much shorter relaxation time than its free counterpart; this is a novel and easy method to characterize the formation of polyrotaxanes. The glass transition temperatures of 7c-g increase with the amount of BG units in the polymers, an easy approach to adjust T-g's of polyurethanes.