A method has been developed to measure the relative secondary ion yields of polymers. Parameters affecting secondary ion yield include primary ion current, detector efficiency, mole concentrations of oligomers, and the extent of oligomer fragmentation. All of these factors are considered in the measurement protocol. Two specific homopolymers were investigated: poly(dimethylsiloxane) and poly(methylphenylsiloxane). The relative secondary ion yields measured for PMPhS/PDMS were in the range of 0.29-0.35, depending on the polymer ratio. Transformation probabilities also were measured for the two polymers, and the PMPhS/PDMS ratio was 0.57. The results of the study indicate that the pendant groups on the siloxane side chain have a significant effect on polymer ion yield and that measurement of relative ion yields for polymer mixtures represents a valid yield comparison.