Honeycomb-like polymeric films from dendritic polymers presenting reactive pendent moieties

In this paper we describe the fabrication of honeycomb-shaped polyurethane films from dendritic side-chain polymers presenting reactive pendent units. Two novel functional polyurethanes, poly(urethane-co-acylurea) (PU-PACY) and polyurethane-co-azetidine-2,4-dione containing polyurethane (PU-PAZ), were synthesized. The waxy dendrons featured focal urea/malonamide linkages favorable for hydrogen bonding and peripheral alkyl chains. These intermolecular forces caused two functional PUs to undergo phase separation and self-assembly. This resulted in honeycomb-like films with well-controlled surface roughness characterized in terms of the ratio of rim width (W) to the pore size (D), i.e. W/D. The PU-PAZ film had a higher contact angle (CA) and a lower value of W/D than did the PU-PACY analogue, due to the presence of relatively more hydrophobic azetidine-2, 4-dione functionalities in the former film. Subsequent chemical modification of the PU-PAZ films through reaction with a hydrophobic poly(oxyalkylene)amine enhanced the CA from 113 to 134°. Further physical modification through a peeling-off process rendered the film surface with a three-dimensional (3D) rod-co-valley-structure having feature dimensions on a submicrometer scale. The 3D rod-co-valley–like film exhibited superhydrophobicity with a CA of 151°. The films also displayed excellent solvent-resistance after crosslinking with a diamine. Through hydrophobic or hydrophilic chemical modification, we could readily manipulate the surface properties of these honeycomb-like films with controllable surface roughnesses and reactive functionalities.