Study on phase separation in an ultra-thin poly(methyl methacrylate)/poly(4-vinyl phenol) film by infrared reflection absorption spectroscopy

Abstract The phase separation of poly(methyl methacrylate) (PMMA)/poly(4-vinyl phenol) (PVPh) (50/50 wt%) ultra-thin films was investigated by infrared reflection absorption spectroscopy (IR-RAS). Of particular note is that we succeeded in measuring the IR-RAS spectra of ultra-thin films of PMMA/PVPh (50/50 wt%) polymer blend with a film thickness of only 2.14 nm. It was found from the present study that the PMMA/PVPh polymer blends were clearly separated as the film thickness was thinner than the radius of gyration of PMMA. The IR-RAS spectra reveal that the hydrogen bond between the C=O group of PMMA and the OH group of PVPh is broken upon the phase separation in the ultra-thin film. In the spectra, many peaks are observed in the OH stretching region of the ultra-thin PMMA/PVPh films, indicating the existence of several weak hydrogen bonds with slightly different interactions, presumably due to the quasi-stable molecular chain configurations resulting from the strong confinement. This is in sharp contrast to the corresponding bulk sample for which a broad band is usually observed in this region because of the continuous distribution of the hydrogen bonding, which is typical for the blends.