Caiguo Gong and, H. Gibson
Sep 17, 1997
Citations
0
Influential Citations
72
Citations
Quality indicators
Journal
Journal of the American Chemical Society
Abstract
Compared to that of model polyurethane 8 from the reaction of tetra(ethylene glycol) (6) and 4,4‘-methylenebis(p-phenyl isocyanate) (7) under the same polymerization conditions, polydispersities (PDI) of copolyurethanes 9−11 incorporating bis(5-(hydroxymethyl)-1,3-phenylene)-32-crown-10 (5) as comonomer were significantly higher; for these branched polymers, the PDI increased with feed ratio of 5 vs 6 up to Mw/Mn = 24 for 75% of 5. This constitutes an original method to control branching. The branching units in 9−11 are main chain rotaxanes formed with H-bonding between the ether moieties of macrocycle 5 and −OH groups as a driving force and thus are mechanically linked, as directly proven by 1H NMR spectra, NOESY, and complexation studies with a bipyridinium salt. The cavity of 5 acts as a “topological functionality”. Since solvent can either allow or disfavor such H-bonding, polymeric topology, branched or linear, can be controlled by the proper choice of solvent. Indeed, although homopolyurethanes were...