EPR Studies on Telechelic Polymers:  Characterization of Ion Multiplets

Abstract

Endfunctionalized polyisoprenes (PI) and polystyrenes (PS) with either one sulfonate or ammonium end group and α,ω-macrozwitterionic PI and PS have been synthesized and investigated by CW-EPR using the spin probe technique. From the extrema separation of the temperature dependent spectra a characteristic temperature, T‘50G, is introduced which can be employed as a measure for the temperature dependence of the chain end association in these telechelic ionomers. In this way it is shown that the mobility of an ionic 2,2,6,6-tetramethylpiperidine-N-oxyl derivative is dramatically restricted when compared to the corresponding nonionic probe. For PI the reduction in probe mobility corresponds to temperature shifts as high as 140 K relative to the dynamics of the polymer, indicating the presence of highly immobilized ion multiplets. As shown by the temperature dependent data, the method is sensitive to additional immobilization of the ionic domains induced by bulky substituents adjacent to the ionic chain ends. Comparison of the EPR results with structural data from SAXS measurements reveals that the main factors governing the dynamics of multiplets are the chemical type of ionic end group and the nature of the polymer backbone. Analysis of the EPR data for telechelic PS shows that in high-T g polymers the dynamics of the ionic aggregates occurs at comparable time scales as the dynamics of the polymer backbone.

Dead-Time Free Measurement of Dipole–Dipole Interactions between Electron Spins

“…The determined distances are in good agreement with previous work or model calculations, and the Pake-type spectra of the dipolar coupling patterns could be obtained. The advantage of the new sequence of being able to measure broad dipolar spectra is demonstrated for a polymer system, a modified poly(isoprene) (PI) with an ionic endgroup for each chain (ionomer) (22,23). The chains form ionic clusters as the ammonium end groups aggregate, and an ionic spin probe can be attached to them.…”

Probing How Counterion Structure and Dynamics Determine Polyelectrolyte Solutions Using EPR Spectroscopy

“…Magnetic resonance methods, such as electron paramagnetic resonance (EPR) spectroscopy [15] on spin-carrying counterions, being local, sufficiently sensitive and highly selective, have the potential to provide complementary information on microscopic structure and dynamics of polyelectrolyte materials [16,17]. Ionic spin probes, which substitute for low-molecular-weight counterions, have been previously used to gain detailed information on structure and dynamics of polymer systems containing charges [16][17][18][19][20][21][22][23][24][25][26].…”

Electron spin relaxation due to small-angle motion: Theory for the canonical orientations and application to hierarchic cage dynamics in ionomers

“…7,8 As a model system to study cage motion over a wide range of time scales we employ ionic spin probes that are immobilized on the surface of ionic clusters in ionomers due to electrostatic attachment. 37,38 Such attachment was found to prevent wide-angle reorientation of the probes up to temperatures that are 100 K higher than the glass transition temperature. 38 Yet, small angle motion at temperatures above the glass transition temperature is expected to depend on rearrangement of the cage surrounding the probe, which is formed by the polymer chains that enter the ionic cluster.…”

“…37,38 Such attachment was found to prevent wide-angle reorientation of the probes up to temperatures that are 100 K higher than the glass transition temperature. 38 Yet, small angle motion at temperatures above the glass transition temperature is expected to depend on rearrangement of the cage surrounding the probe, which is formed by the polymer chains that enter the ionic cluster. This model system thus allows one to study slow cage dynamics in a polymer.…”