Novel porous polyurethane films

Polyurethane films treated in a two-stage process with aqueous bromine and ammonia solutions underwent significant modifications in crystalline and surface structure as well as in mechanical and physical properties. Bromine was sorbed on the film and formed several charge transfer complexes with the soft and hard segments of the polyurethane as well as bridges between adjacent chains. In the second stage, ammonia reacted with the sorbed bromine producing gaseous nitrogen and ammonium bromide. The expansion of the gas resulted in a repacking of the polymeric chains and the formation of a porous structure. The bromine concentrations used and the times of contact between the films and the bromine 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 20. The water vapor permeability increased three-fold. The treatment appeared 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 dressing are discussed. (C) 1998 John Wiley & Sons, Ltd.