Sum frequency vibrational spectroscopy of the comb copolymer cetyl dimethicone copolyol

The sum frequency (SF) vibrational spectrum in the C-H stretching region of a comb copolymer, cetyl dimethicone copolyol (CDC), consisting of a poly(dimethylsiloxane) backbone and grafted poly(ethylene oxide) (PEO) and cetyl side chains has been recorded after deposition on a gold-coated substrate. Resonant assignment of the SF spectrum of CDC has been achieved by examining the spectra of several structural analogues of the polymer. Since sum frequency generation is dependent upon both infrared and Raman activity, assignment of the SF spectrum of CDC was aided by recording complementary infrared and Raman spectra. Sum frequency resonances attributable to the methyl groups of the polymer backbone and the cetyl side chains of the polymer were observed, implying conformational order of these moieties. Further, it was concluded from the phase of the cetyl resonances that the grafted alkyl chains were oriented away from the polymer/air interface. Conversely, the PEO side chains of CDC were found to be SF inactive.