17th International Mass Spectrometry Conference :: Prague, 2006
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|Presentation date:||Thu, Aug 31, 2006|
|Presentation time:||14:30 – 16:00|
Abdulrahman M. Alhazmi1, Marie-Soleil Giguere, Paul M. Mayer11 University of Ottawa, Ottawa, Canada
Correspondence address: Abdulrahman M. Alhazmi, University of Ottawa, Chemistry Department, 10 Marie Curie, Ottawa, K1N 6N5 Canada.
Keywords: Electrospray Ionization (ESI); MALDI; Oligomers; Polymer.
Novel aspect: Explore the copolymer information in molecular level by mass spectrometry.
The composition and chemical structure of copolymers influence the physical and chemical properties of the materials from which they are made. It is also important to understand the kinetics of copolymer formation since it will affect the nature and distribution of the final products. In free radical polymerization, knowledge of the reactivity ratio of two monomers permits the prediction of the outcome of the polymerization, i.e, will each monomer prefer to react with itself or with each other? Methods used to estimate the copolymer reactivity ratio involve a variety of statistical approaches but all rely on one important piece of information, the measured ratio of each monomer present in the copolymer. Techniques like infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies are commonly used to identify the chemical groups present in the repeat units of a polymer. However, these techniques give a bulk picture of a copolymer sample whereas mass spectrometry (MS) has the potential to provide molecular level information. In this study we have examined the performance of Electrospray ionization (ESI-MS) and matrix assisted laser desorption-ionization (MALDI-MS) for determining the composition (monomer rations) and structure (end group analysis) relative to 1H NMR and theoretical predictions for three different families of copolymers: poly(butyl acrylate/vinyl acetate) (PBA/PVAc), poly(methyl methacrylate/vinyl acetate) (PMMA/PVAc) and poly(butyl acrylate/methyl methacrylate) (PBA/PMMA). In each case the peaks in the ESI mass spectrum could be assigned to oligomers containing a distinct number of each co-monomer. The overall monomer ratios were calculated by summing the number of each monomer in each oligomer, weighed by the relative intensity of that oligomer. The monomer ratio results were compared to 1H NMR and theoretical predictions. We found that the ESI results were in excellent agreement with NMR for PBA/PVAc and PBA/PMMA copolymers whereas there was more divergence in the case of PMMA/PVAc. In addition we found two major distributions of PBA/PMMA oligomers, differing by their end-groups. Distribution A has a hydrogen atom and the chain-transfer agent (CTA, dodecanethiol) as end-groups while in distribution B the CTA has been replaced by isobutyronitrile from the initiator (AIBN). We were able to investigate the relative abundance of these distributions as a function of copolymer conversion for a series of reaction conditions by both ESI and MALDI. We found an increasing abundance of the isobutyronitrile-containing co-polymers with increasing reaction time, consistent with theoretical predictions of CTA consumption over the course of the reaction. This is an example of the type of analysis that was not possible with 1H NMR due to the lack of distinguishable protons between the two types of co-polymers.