Electrospray ionization (ESI) and matrix assisted laser desorption-ionization (MALDI) mass spectrometry were used to determine the composition (monomer ratios) and structure (end group analysis), relative to 1H NMR spectroscopy and theoretical predictions, for three different copolymers: poly(butyl acrylate/vinyl acetate) (PBA/PVAc), poly(methyl methacrylate/vinyl acetate) (PMMA/PVAc) and poly(butyl acrylate/methyl methacrylate) (PBA/PMMA). The ESI results were found to be in excellent agreement with 1H NMR spectroscopy for PBA/PVAc and PBA/PMMA copolymers whereas there was more divergence in the case of PMMA/PVAc. In the case of PBA/PMMA copolymers similar distributions of products were observed by ESI-MS and MALDI-MS; two major product classes were observed differing by their end-groups. One class has hydrogen and dodecylthio end groups while in the other the dodecylthio has been replaced by alpha-cyanoisopropyl from the initiator. The relative abundance of these distributions as a function of copolymer conversion for a series of reaction conditions was investigated by both ESI and MALDI.
The collision-induced dissociation (CID) mass spectra for a variety of chain lengths of four ionized polymer samples have been quantified according to their observed total relative fragment ion abundances. The CID mass spectra of oligomers of ionized PMMA with three different types of end groups and polystyrene, PS, were obtained at fixed centre-of-mass collision energies and collision numbers. For the PMMA polymers, the total fragment ion abundance increases with increasing chain length, consistent with an increase in internal energy deposition with size of the ion. A discontinuity in the increase in total fragment ion abundance appears to correspond to a change in conformation of the polymer ions from linear (at short chain lengths) to cyclic (at long chain lengths). Ionized PS does not exhibit this change in conformation as all chain lengths show compact structures and accordingly the total fragment ion abundance does not change with increasing chain length.
Protonation of polymers in the gas-phase was achieved by the dissociation of proton-bound complexes of the oligomers with small peptides and amino acids. Protonated PMMA and PBA oligomers were shown to fragment in unique pathways that involved losses of neutral molecules from their side chains, until all that is left is a hydrocarbon backbone. For PMMA the neutrals were primarily CO and methanol, while for PBA butyl ether is lost. We also explored the threshold fragmentation of the proton-bound complexes as a function of the amino acid used (and its proton affinity) which allowed a kinetic bracketing of the oligomer PA as a function of chain length. The results were consistent with a change from bidentate to tridentate binding of the proton with increasing length of the PMMA oligomers.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/29558 |
| Date | January 2008 |
| Creators | Alhazmi, Abdulrahman M |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 131 p. |
Page generated in 0.002 seconds