END-FUNCTIONALIZED POLYMERS .2. QUANTIFICATION OF FUNCTIONALIZATION BY TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY

The applicability of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for quantification of functionalization is demonstrated using five 1.0 x 10(3) g/mol polystyrene samples which were synthesized by living anionic polymerization. The polymerizations were functionally terminated to various extents (0, 25,50,75, and 100 %) by using sequential termination techniques with chlorodimethylphenylsilane and methanol. Two distinct molecular weight distributions of intact oligomer signals are resolved in the TOF-SIMS spectra resulting from the functionalized and unfunctionalized (protonated) oligomer species in each sample. Through direct comparison of the signal intensities of the two types of oligomers, the extent of functionalization is determined at each degree of polymerization and agrees well with expected values. The results are substantiated using physical mixtures of dimethylphenylsilyl (100% functionalized) and proton (0% functionalized) terminated polymers. The relative oligomer intensities for the physical mixture of polymers corresponds well to the ratio in which they were initially combined. Sputter yield, extent of fragmentation, and ionization and detection probabilities are determined to be very similar for the proton- and dimethylphenylsilyl-functionalized oligomers. Thus, quantification of end groups can be achieved without standards calibration. Analysis by gel permeation chromatography (GPC) shows a systematic shift to higher [M(n)] values as the extent of functionalization of the polystyrene samples is increased from 0 to 100%. [M(n)] values calculated from TOF-SIMS analysis for the oligomers agree well with GPC results. The [M(n)] values for the functionalized and unfunctionalized components in each sample can also be determined by TOF-SIMS and are distinct for each oligomer type.