Molar Mass Characterization and Solution Behaviour of Poly(ether amide) Dendrimers

APCI/APPI for synthetic polymer analysis

Modern mass spectrometry of synthetic polymers involves soft ionization techniques. Whereas matrix-assisted laser desorption/ionization (MALDI) and electrospray (ESI) are employed routinely, atmospheric pressure chemical ionization (APCI) and more recently atmospheric pressure photoionization (APPI) are used to a lesser extent. However, these latter ionization methods coupled to liquid-phase separation techniques create new opportunities for the characterization of polymers, especially for low molecular weight compounds or for the polymers that are poorly ionizable by the usual methods. After a part devoted to the description of classical MS methods employed for polymer analysis (MALDI, ESI, and their use with chromatography), APCI and APPI techniques will be described, discussed, and selected examples will present the interest of these ionization sources (or interfaces for LC/MS) in the field of polymer analysis.

Determination of Charge and Molecular Weight of Rigid-Rod Polyelectrolytes

Rod-like polyelectrolytes are an interesting model system because their persistence length is independent of the ionic strength and pH of the surrounding medium and they permit the investigation of polyelectrolytes in the absence of conformational degrees of freedom. In this work, rigid-rod poly(aramide) polyelectrolytes were synthesized by the Higashi method. Electrophoresis NMR spectroscopy in conjunction with diffusion NMR spectroscopy has been applied to determine the effective charge of the polymer. The charge was determined from the balance between the force in the electric field and the hydrodynamic friction in the steady-state electrophoretic motion. Because only organic counterions were present, and were identified in the proton NMR spectra, the counterions were investigated as well, and the fraction of condensed counterions was determined directly. From the effective charge per molecule and the knowledge of the fraction of condensed counterions, the total charge per molecule was determined. Finally, from the total charge, the number of repeat units and thus the molecular weight were inferred.