TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY OF POLYBUTADIENES

High resolution time-of-flight secondary ion mass Spectrometry was used to study a series of polybutadienes with molecular weights between 400 and 170000 Da. The number-averaged and weight-averaged molecular weights of polybutadienes with molecular weights of <5000 Da were determined and showed reasonable agreement with values obtained by conventional methods. Samples with molecular weights of >5000 Da showed primarily fragments in the mass range 500-4000 Da, resulting from main chain cleavage of C-C single bonds. A fragmentation model based on simple statistical chain cleavage was used to explain the fragmentation patterns observed in the spectra. These fragmentation patterns contained R(n), +DELTA, +2DELTA and -DELTA species, where R(n) represents an integral number (n) of repeat units and DELTA is a methylene group. The relative intensities of these clusters as a function of sample molecular weight and cluster size were studied, and were the same regardless of polymer size. The fine structure of the fragment clusters was also examined, and the mechanisms responsible for their formation are discussed.