Determination of the Distribution of Poly(dimethylsiloxane) Segment Lengths at the Surface of Poly[(dimethylsiloxane)−urethane]-Segmented Copolymers by Time-of-Flight Secondary Ion Mass Spectrometry

Abstract

Time-of-flight secondary ion mass spectra were recorded from submonolayer thin films of aminopropyl end-capped poly(dimethylsiloxane) (PDMS) and from thick films (ca. 50 μm) of poly[(dimethylsiloxane)−urethane] (PU−DMS)-segmented copolymers. Ions detected and assigned to fragments in the low-mass range (m/z ≤ 300) provided structural information about the repeat units and the end groups. The high-mass spectrum of the PDMS homopolymer yielded a series of ions assigned to Ag+-cationized oligomers; this enabled determination of the molecular weight distribution in comparison with GPC measurement. In the high-mass (m/z = 800−3500) spectra of thick PU−DMS films, the peak series was assigned to a simple fragmentation process. That process would yield ions where the intact PDMS segment is present; it therefore can be used to evaluate the PDMS segment length distribution at the surface of the copolymer. It was found that the distribution of PDMS segment lengths segregated at the surface of the thick film was almo...