Chain and mirophase-separated structures of ultrathin polyurethane films

Measurements are presented how chain and microphase-separated structures of ultrathin polyurethane (PU) films are controlled by the thickness. The film thickness is varied by a solution concentration for spin coating. The systems are PUs prepared from commercial raw materials. Fourier-transform infrared spectroscopic measurement revealed that the degree of hydrogen bonding among hard segment chains decreased and increased with decreasing film thickness for strong and weak microphase separation systems, respectively. The microphase-separated structure, which is formed from hard segment domains and a surrounding soft segment matrix, were observed by atomic force microscopy. The size of hard segment domains decreased with decreasing film thickness, and possibility of specific orientation of the hard segment chains was exhibited for both systems. These results are due to decreasing space for the formation of the microphase-separated structure.