Book Description

The matrix-assisted laser desorption ionization time-of-flight/time-of-flight mass spectrometry (MALDI-ToF/ToF MS) characteristics of different polystyrenes and polybutadienes are discussed in this dissertation. The compounds examined include linear, cyclic, in-chain substituted, and star-branched polymers as well as copolymers of styrene and either para-dimethylsilyl styrene (p-DMSS) or meta-dimethylsilyl styrene (m-DMSS). Chapter IV describes the differentiation of cyclic and linear polymers by 2D-mass spectrometry. The silverated quasimolecular ions from cyclic and linear polystyrenes and polybutadienes, formed by MALDI, give rise to significantly different fragmentation patterns in tandem mass spectrometry (MS2) experiments. With both architectures, fragmentation starts with homolytic cleavage at the weakest bond, usually a C-C bond, to generate two radicals. From linear structures, the separated radicals depolymerize extensively by monomer losses and backbiting rearrangements, leading to low-mass radical ions and much less abundant medium- and high-mass closed-shell fragments that contain one of the original end groups, along with internal fragments. With cyclic structures, depolymerization is less efficient, as it can readily be terminated by intramolecular H-atom transfer between the still interconnected radical sites (disproportionation). These differences in fragmentation reactivity result in substantially different fragment ion distributions in the MS2 spectra. Simple inspection of the relative intensities of low- vs. high-mass fragments permits conclusive determination of the macromolecular architecture, while full spectral interpretation reveals the individual end groups of the linear polymers or the identity of the linker used to form the cyclic polymer. Chapter V presents the first sequence analysis of styrenic copolymers by tandem MS. Copolymers of para-dimethylsilyl styrene (p-DMSS) or m-DMSS with styrene were prepared by living anionic polymerization. The MALDI-MS2 results for p-DMSS indicate that a block copolymer is formed, with the para-substituted styrene incorporated near the initiator. On the other hand, the MS2 results of m-DMSS reveal that a random copolymer is formed, consistent with comparable reactivities for m-DMSS and styrene. These findings suggest that p-DMSS is more reactive than m-DMSS. The single-stage (1D) MALDI-MS results further show that linear and 2-armed architectures are formed with both the m-DMSS and the p-DMSS comonomers. The last Chapter, VI, focuses on the differentiation of linear in-chain substituted, cyclic, and star-branched polystyrene (PS) by tandem mass spectrometry. The in-chain functionalized PS gives a MS2 fragmentation pattern that is different from the one observed for cyclic PS with two linker units and, again, with a simple inspection of the tandem mass spectra, these architectures can easily be distinguished. The four-arm star-branched polymer investigated mainly breaks down by losing arms under MALDI-MS2 conditions. Overall, this dissertation documents the usefulness of combined 1D and 2D mass spectrometry experiments for the identification of polymer substituents and their location, for distinguishing polymer architectures, and for determining copolymer sequences.The results presented in this dissertation have been published or are pending for publication in the following journals. 1. Quirk, R. P.; Wang, S-F.; Foster, M. D.; Wesdemiotis, C.; Yol, A. M. "Synthesis of Cyclic Polystyrenes Using Living Anionic Polymerization and Metathesis Ring-Closure" Macromolecules 2011, 44, 7538-7545. 2. Liu, B.; Quirk, R. P.; Wesdemiotis, C.; Yol, A. M.; Foster, M. D. "Precision Synthesis of [omega]-Branch, End-Functionalized Comb Polystyrenes Using Living Anionic Polymerization and Thiol-Ene 'Click' Chemistry" Macromolecules 2012, 45, 9233-9242. 3. Yol, A. M.; Dabney, D. E.; Wang, S-F.; Laurent, B. A.; Foster, M. D.; Quirk, R. P.; Grayson, S. M.; Wesdemiotis, C. "Differentiation of Linear and Cyclic Polymer Architectures by MALDI Tandem Mass Spectrometry (MALDI-MS2)" J. Am. Soc. Mass Spectrom. 2013, 24, 74-82. 4. Quirk, R.P.; Chavan, V.; Janoski, J.; Yol, A.; Wesdemiotis, C. "General Functionalization Method for Synthesis of [alpha]-Functionalized Polymers by Combination of Anionic Polymerization and Hydrosilation Chemistry" Macromolecular Symposia 2013, 323, 51-57. 5. Yol, A. M.; Janoski, J.; Quirk, R. P.; Wesdemiotis, C. "Sequence Analysis of Styrenic Copolymers by Tandem Mass Spectrometry" Anal. Chem. (Submitted)