NOVEL POROUS POLYURETHANE FILMS

Polyurethane films treated in a two-stage process with aqueous bromine and ammonia solutions underwent significant modifications in crystall ine and surface structure as well as in mechanical and physical proper ties. Bromine was sorbed on the film and formed several charge transfe r complexes with the soft and hard segments of the polyurethane as wel l as bridges between adjacent chains. In the second stage, ammonia rea cted with the sorbed bromine producing gaseous nitrogen and ammonium b romide. The expansion of the gas resulted in a repacking of the polyme ric chains and the formation of a porous structure. The bromine concen trations used and the times of contact between the films and the bromi ne were 0.02-0.06 normal and 1-10 min, respectively. The contact angle of the pms decreased, depending on treatment conditions, from 73 to 2 0. The water vapor permeability increased three-fold. The treatment ap peared to bring about a crystallization in the hard as well as in the soft segments of the PU as shown by differential scanning calorimetry measurements. Possible applications of the treated films for wound dre ssing are discussed. (C) 1998 John Wiley & Sons, Ltd.