Ionization of polymers in mass spectrometry is usually achieved by forming metal ion adducts. The metal ion has been shown by Wesdemiotis to often play a spectator role in the collision-induced dissociation (CID) chemistry of these species, wherein they fragment according to a free-radical mechanism similar to that found in their pyrolysis. The result is a predominance of low-mass ions in the CID mass spectrum. We have changed this behavior by generating protonated oligomers in the gas phase by first forming proton-bound complexes of the oligomers with amino acids or peptides by electrospray ionization. These complexes dissociate first by loss of the amino acid/peptide to form protonated oligomers, which then undergo a unique fragmentation chemistry. In this article we discuss the results for poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) (PBA). Initially, protonated PMMA and PBA lose methanol and butanol, respectively, from the side chains of the respective monomers. The resulting PMMA-derived ion then undergoes a series of neutral losses corresponding to 32 and 28 Da, methanol and carbon monoxide. This continues as collision energy increases until a final, carbon-rich backbone ion is formed, which then undergoes a classic hydrocarbon fragmentation pattern. The PBA-derived ions are proposed to fragment by the loss of butylether molecules to form anhydride rings along the oligomer chain. The number of ether molecules lost corresponded to half the number of available side chains in the oligomer. The resulting poly-anhydride ion dissociates by small molecule loss. A though the predominant mode of ionization for peptides and proteins in mass spectrometry is protonation in solution, the same cannot be said for synthetic polymers. Typically, synthetic polymers such as poly(methyl methacrylate) (PMMA) are not basic enough in solution to acquire a proton from an added acid. To overcome this limitation, salts incorporating metal ions are usually added to the polymer/ solvent solution before electrospray ionization (ESI) (or to the polymer/matrix solution before ionization by matrix-assisted laser desorption/ionization). This generates gas-phase polymer oligomers ionized by the metal ion. This has consequences for the analysis of these oligomers by collision-induced dissociation (CID) mass spectrometry. For example, Jackson and Scrivens studied poly(alkyl methacrylates) (PAMAs), i.e., PMMA and poly(n-butyl methacrylate) (PBMA) by different mass spectrometry techniques [1][2][3][4][5][6][7]. In each case the CID mass spectrum was dominated by low mass-to-charge ratio (m/z) fragment ions. In the case of PMMA the fragments were proposed to be generated mainly by homolytic cleavage and 1,5 hydrogen rearrangement reactions along the polymer backbone [2,7]. Low-intensity peaks at high m/z were assumed to be formed by neutral losses and fragmentation along the polymer backbone [5]. The end result was a variety of fragment ion progressions each differing by one monomer unit. Bowers et al. proposed a mechanism that rat...

Electrospray ionization (ESI-MS) and matrix assisted laser desorption-ionization (MALDI-MS) 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). We found that the ESI results were 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 observe by ESI-MS and MALDI-MS with the two major products classes 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. MALDI results consistently underestimated (relative to ESI) the butylacrylate monomer ratio in PBA/PMMA and the abundance of co-polymer oligomers terminated by a dodecylthio group from the chain transfer agent.

The collision-induced dissociation (CID) of a series of oligomer chain lengths of four polymer samples have been quantifi ed according to their observed total relative fragment ion abundances. The CID mass spectra of oligomers of ionized poly(methyl methacrylate) (PMMA), with three different types of end groups and polystyrene (PS), were obtained at fi xed center-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 the size of the ion. A discontinuity in the increase in total fragment ion abundance appears to correspond with 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.

Bromoaromatics are ubiquitous in chemistry, and their manufacture is often wasteful. Halogen exchange under hydrothermal conditions constitutes a viable alternative for their synthesis in some cases. The preparation of 1,2-dibromobenzene and 1-bromo-2-chlorobenzene from 1,2-dichlorobenzene, by treatment with hydrobromic acid in hydrothermal media at temperatures ranging from 240˚C to 320˚C was investigated as a viable alternative to de novo synthesis. The effects of temperature, exchange duration and the presence of Fe 3+ salts on product yields are discussed. Yields for both targeted haloarenes of up to 37% and 48%, respectively, were achieved, with very limited formation of 1,3-and 1,4-dihalobenzene isomers. A mechanism for halogen exchange was proposed.

On Q. Lou and D. A. Shipp examine atom transfer radical polymerization (ATRP) in terms of recent developments in activators regenerated by electron transfer ATRP and electrochemically mediated ATRP. Thus polymers with predictable and well‐defined properties can be synthesized.