Date of Graduation

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor

Charles L. Wilkins

Committee Member

David Paul

Second Committee Member

Ingrid Fritsch

Third Committee Member

Bill Durham

Keywords

Pure sciences; Analysis of synthetic polymers; Macromolecules; Mass spectrometry; Sample preparation

Abstract

New method for the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and Fourier transform mass spectrometry (MALDI-FTMS) analysis of low molecular weight polyvinyl acetate (PVAc) was developed and then applied to the characterization of commercially available chewing gum. The optimization of MALDI analysis of PVAc was achieved by investigating the influence of sample preparation variables such as the choice of solvent and choice of matrix-analyte ratio. It was demonstrated that the use of ethyl acetate as a solvent and 2,5-Dihydroxybenzoic acid as a matrix yielded the highest signal intensity for the pure polymer sample. The application of TOF technique did not produce accurate molecular structure of PVAc, and so FTMS method was employed as well and allowed to accurately establish the identity of the end groups of the polymer.

A sample preparation protocol for the successful MALDI analysis of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was developed by investigating the influence of the matrix, solvent, deposition method and matrix-to-analyte ratio. It was found that the application of dithranol as a matrix, lowest molar matrix:analyte ratio of 250:1, toluene as a solvent for both matrix and analyte and aerospray sample deposition technique for MALDI analysis produced spectra with the highest intensity of PCBM signal, the smallest amount of fragments, the fewest products of gas phase reactions and the best reproducibility. Gas-phase reactions of PCBM in the high vacuum conditions of the FTMS and TOF mass spectrometry experiments were also investigated and a possible mechanism for these reactions was proposed. It was suggested that during or after desorption/ionization step of MALDI process, several kinds of oxidized and reduced PCBM derivatives are formed.

The influence of the sample preparation parameters (the choice of the matrix, matrix:analyte ratio, salt:analyte ratio) was investigated and optimal conditions were established for the MALDI time-of-flight mass spectrometry analysis of the poly(styrene-co-pentafluorostyrene) copolymers. These were synthesized by atom transfer radical polymerization. Use of 2,5-Dihydroxybenzoic acid as matrix resulted in spectra with consistently high ion yields for all matrix:analyte:salt ratios tested. The optimized MALDI procedure was successfully applied to the characterization of three copolymers obtained by varying the conditions of polymerization reaction. It was possible to establish the nature of the end groups, calculate molecular weight distributions, and determine the individual length distributions for styrene and pentafluorostyrene monomers, contained in the resulting copolymers. Based on the data obtained, it was concluded that individual styrene chain length distributions are more sensitive to the change in the composition of the catalyst (the addition of small amount of CuBr2) than is the pentafluorostyrene component distribution

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