Interchain ion formation in secondary ion mass spectrometry resulting fromthe double-helical structure of isotactic poly(methyl methacrylate) in adsorbed monolayers

Results from time-of-flight secondary ion mass spectra (TOF-SIMS) of Langmu ir-Blodgett monolayers of various isomers (isotactic and syndiotactic) of p oly(methpl methacrylate) (PMMA) are reported. A detailed analysis of the re peating pattern of fragment ion clusters yields very different patterns for isotactic PMMA LB layers than for the syndiotactic and atactic forms. This is attributed to the resulting double-helical tertiary structure of isotac tic. PMMA, a structure that does not form for the syndiotactic and atactic PMMA polymer monolayers. The double-helical structure of isotactic PMMA mon olayers is verified using reflection absorption Fourier transform infrared spectroscopy. The repeating patterns of cluster ions in syndiotactic and at actic PMMA monolayers can be explained using statistical chain-breaking mod els for fragmentation of single isolated polymer chains. The repeating ion patterns from the TOF-SIMS of the isotactic PMMA monolayers are analyzed by considering bond breaking and ion formation between adjacent polymer chain s, resulting in a newly proposed ion formation model due to the tertiary st ructure of the double-helical form. PI rearrangement mechanism consistent w ith all ions that are formed is proposed.