Molecular dynamics in polystyrene from electron spin resonance (ESR) measurements: comparison between spinprobes and ‐labels attached to the chain ends

Abstract

AbstractThe commercially available 15N‐TemponeN‐Tempone: 4‐oxo‐2,2,6,6‐tetramethylpiperidine‐15N‐oxyl; Tempol: 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine ‐15N‐oxyl. nitroxide radical has been used for the endfunctionalization of anionically polymerized polystyrene. The temperature dependence of molecular motions of the nitroxide radicals in this chain end labeled polystyrene (PS) and a PS/Tempol mixture has been studied using cw‐ESR. Furthermore, these two samples were compared with a mixture of PS with a biradical which has a large molecular volume and is used in its unoxidized form as a polymer additive in commercial products. The temperature dependent spectra were evaluated to give T50G. This allows the volume for reorientation of the radicals and that of a polymer unit to be compared. The temperature dependent spectra were simulated in order to yield the rotational correlation time τR. In contrast to the Tempol probe radical which is highly mobile even at temperatures well below the glass transition temperature (Tg) the spin‐label strongly couples to the α‐process of polystyrene. The biradical exhibits an intermediate mobility and seems to be weakly coupled to the glass transition dynamics. Line shape analysis shows that the motional behavior of the PS/Tempol mixture can adequately be described by the model of isotropic rotational diffusion, whereas for the chain end label significant deviations from this model are observed indicating anisotropic motion due to restrictions imposed by the polymer chain.