Results from time-of-flight secondary ion mass spectra (TOF-SIMS) of Langmuir-Blodgett monolayers of various isomers (isotactic and syndiotactic) of poly(methyl methacrylate) (PMMA) are reported. A detailed analysis of the repeating 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 isotactic PMMA, a structure that does not form for the syndiotactic and atactic PMMA polymer monolayers. The double-helical structure of isotactic PMMA monolayers is verified using reflection absorption Fourier transform infrared spectroscopy. The repeating patterns of cluster ions in syndiotactic and atactic PMMA monolayers can be explained using statistical chain-breaking models 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 chains, resulting in a newly proposed ion formation model due to the tertiary structure of the double-helical form. A rearrangement mechanism consistent with all ions that are formed is proposed.
Advances in the development of techniques for the energy and mass analysis of ejected particles, form the basis of their use as surface analytical spectroscopies. Methods such as X-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion-scattering spectroscopy (ISS), and secondary ion mass spectrometry (SIMS) are becoming more widely applicable to problems in the chemical analysis of coatings surfaces and interfaces. In this paper a brief review of instrumentation and theory allows projection of new capabilities for the method. Recent progress in the analysis of homopolymer and multicomponent polymer interfaces is described.
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