MALDI-TOF/TOF CID Study of Polystyrene Fragmentation Reactions

Abstract

MALDI-TOF/TOF CID experiments were conducted on a variety of hydroxylated polystyrene precursor ions (m/z 1249.6 (n = 10), 1769.9 (n = 15), 2290.2 (n = 20), 2810.5 (n = 25), and 3330.8 (n = 30)) to examine the influence of molecular weight and collision kinetic energy on the degradation mechanisms. Our study indicates that polystyrene free radicals are formed initially through multiple chain breaks and subsequently undergo a variety of secondary depolymerization reactions to yield predominantly monomer, dimer, and trimer species; the intensity of each species depends on the kinetic energy selected for the CID process. Long-chain “unzipping” is not a major pathway for any of the experimental conditions. Each depolymerization mechanism is presented in detail with experimental and computational data to justify/rationalize its process and kinetic energy dependence. These processes show the complex interrelationships between the various pathways along with preferred production of secondary radicals (which suppresses the appearance of primary radicals). Additionally, Py-GC/MS experimental data are presented, for comparison of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS.