Organized structures obtained from urethane/urea elastomers

In this work we address new results obtained with free thin flexible films (60-100 μm) of urethane/urea elastomers related to the formation of micro- and nano-patterns. The samples were synthesised from a polypropylene oxide-based prepolymer with three isocyanate terminal groups (PU) and polybutadienediol (PBDO) with different PBDO content of 30, 40 and 60 wt.% After casting and curing the films were exposed to UV radiation (λ=254 nm) and extracted with toluene. The dried films were studied by polarising optical microscopy (POM), small angle light scattering (SALS) and the surfaces exposed to UV radiation were analysed by means of atomic force microscopy (AFM). Before extraction with toluene a nanometer-flat surface, characterized by a mean roughness value R_a = 0.59 nm, was obtained. The sample with 40 wt.% of PBDO, after exposed to UV and extracted with toluene shows a corrugated surface, with features μm-sized in all axes, resulting in a dramatic increase of the overall mean roughness. As the PBDO concentration decreases the free films surfaces show an increasing density of the structures observed and a decreasing characteristic peak-to-valley height. This work suggests that the PBDO/PU samples exposed to UV radiation can be nano to micromodulated by tuning the PBDO/PU relative content. These structures can be revealed with toluene from the original nanometer-flat surface.