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Two-dimensional polymer characterization is used for a simultaneous analysis of molar masses and chemical heterogeneities (e.g., end groups, copolymer composition, etc.). This principle is based on coupling of two different chromatographic modes. Liquid adsorption chromatography at critical conditions (LACCC) is applied for a separation according to the chemical heterogeneity, whereas in the second-dimension fractions are analyzed with regard to their molar mass distribution by means of size exclusion chromatography (SEC). Because appropriate standards for a calibration of the SEC are seldom available, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was used to substitute the SEC. The LACCC-MALDI MS coupling enables acquiring additional structural information on copolymer composition, which can considerably enhance the performance of this coupled method.
Untersuchungen zur Charakterisierung des Abbaus von Polylactiden mittels 2D-HPLC und MALDI-TOF-MS
(1995)
The role of 1,1-diphenylethylene (DPE) in radical emulsion polymerization of methyl methacrylate is investigated. The presence of DPE causes a strong decrease in both the rate of polymerization and the molecular weight. According to the results of structure analysis by means of MALDI-TOF mass spectrometry, UVvis spectroscopy, and 1HNMR spectroscopy, DPE is incorporated in the copolymer chain exclusively as a reactive recombinant ?,p-dimer, underlining the peculiar role of DPE in radical polymerizations.
A novel family of air-stable dendrimers with a N-Si-C framework has been prepared up to the fourth generation. The divergent synthesis starts with the hydrosilylation of the trisilazane N(SiMe2vinyl)3 [0-G(vinyl)] by HSiMe2Cl, which gives the three-directional core molecule N(SiMe2CH2CH2SiMe2Cl)3 [0-G(Cl)]. A 1-to-2 branching achieved by reacting the core molecule [0-G(Cl)] with 3 equiv of KN(SiMe2vinyl)2 affords the first generation dendrimer [1-G(vinyl)]. By repeating the above two steps, the second [2-G(vinyl)], third [3-G(vinyl)], and fourth generation [4-G(vinyl)] can be obtained. The compounds have been characterized by 1H, 13C, and 29Si NMR spectroscopy, by elemental analysis, and up to the third generation by MALDI-TOF mass spectrometry. Gel permeation chromatography was used to prove the fourth generation [4-G(vinyl)].