Characterization of oligo(acrylic acid)s and their block co-oligomers

Abstract

Oligo(acrylic acid), oligoAA are important species currently used industrially in the stabilization of paints and also for the production of self-assembled polymer structures which have been shown to have useful applications in analytical separation methods and potentially in drug delivery systems. To properly tailor the synthesis of oligoAA, and its block co-oligomers synthesized by Reversible-Addition Fragmentation chain Transfer (RAFT) polymerization to applications, detailed knowledge about the chemical structure is needed. Commonly used techniques such as Size Exclusion Chromatography (SEC) and Electrospray Ionization-Mass Spectrometry (ESI-MS) suffer from poor resolution and non-quantitative distributions, respectively. In this work free solution Capillary Electrophoresis (CE) has been thoroughly investigated as an alternative, allowing for the separation of oligoAA by molar mass and the RAFT agent end group. The method was then extended to block co-oligomers of acrylic acid and styrene. Peak capacities up to 426 were observed for these 1D CE separations, 10 times greater than what has been achieved for Liquid Chromatography (LC) of oligostyrenes. To provide a comprehensive insight into the chemical structure of these materials H andC Nuclear Magnetic Resonance (NMR) spectroscopy was used to provide an accurate average chain length and reveal the presence of branching. The chain length at which branching is detected was investigated with the results showing a degree of branching of 1% of the monomer units in oligoAA with an average chain length of 9 monomer units, which was the shortest chain length at which branching could be detected. This branching is suspected to be a result of both intermolecular and intramolecular transfer reactions. The combination of free solution CE and NMR spectroscopy is shown to provide a near complete elucidation of the chemical structure of oligoAA including the average chain length and branching as well as the chain length and RAFT agent end group distribution. Furthermore, the purity in terms of the dead chains and unreacted RAFT agent was quantified. The use of free solution CE and H NMR spectroscopy demonstrated in this work can be routinely applied to oligoelectrolytes and their block co-oligomers to provide an accurate characterization which allows for better design of the materials produced from these oligomers.

Facile-controlling of the coating amount of poly(acrylic acid)-b-polystyrene coated on silica nanoparticles for polymer electrolyte membrane

“…11) This core-shell type NPs were fabricated from inexpensive, commercially available and easy to handle materials, and therefore it can be expected to use as a good candidate for the alternative of Nafion®. [12][13][14] In this system, the interface between the silanol group (-SiOH) from the surface of silica NPs and the carboxylic group (-COOH) of coated PAA form the proton conductive channels which are significantly critical for proton conductivity of this PEM system. 6,11,15) The coated PS provides several functions to this PEM, one is suppressing the swelling of the PAA under the PEFC operation with high humidity, indicating that coated PS contributes to long-term stable PFECs operation with maintaining PFEC performance under high humidity operation.…”

Self-Assembled Nanostructure Library from Monodisperse Sequence-Defined Oligo(phosphodiester)s

“…This method was recently applied by Sutton et al for the separation of oligo(acrylic acid)s through free solution capillary electrophoresis. 36 We observed that oligomers containing NAP could be visualized after running polyacrylamide gel electrophoresis (PAGE) and staining with GelRed®, a molecule used to stain DNA (Figure 2b). The cationic and aromatic GelRed® molecules most likely interact electrostatically with the anionic oligo(phosphodiester)s, and with NAP units via π-π stacking.…”

Degree of branching in poly(acrylic acid) prepared by controlled and conventional radical polymerization

“…The instrumental parameters for one-dimensional 15 and twodimensional 63 NMR were described in accompanying publications. One-dimensional NMR conditions like the concentration, number of scans, repetition delay, solvent were described in earlier work 15 but also summarized with the information for additional samples in the Supporting Information (Table S2).…”