Utilization of Polymer-Tethered Probes for the Assessment of Segmental Polymer Dynamics near the Glass Transition

The approach of utilizing polymer-tethered fluorescent molecules in probing segmental dynamics of polymers near the glass transition was validated by the examination of the rotational dynamics of the probes that were randomly dispersed in the same polymer hosts as the tethered polymers. Poly(alkyl methacrylate)-and polystyrene-tethered fluorescent probes, located either at the end or in the middle of a polymer chain, were tethered either with flexible dodecyl or hexyl alkyl chains by atom transfer radical polymerization and post-polymerization modification, respectively. Different polymeric systems with different glass transition temperature and fragility differing by & AP;100 K and & AP;80, respectively, were studied. Although the polymer-tethered probes report increased average rotational relaxation times compared to segmental dynamics of polymers, the temperature dependence of the polymer dynamics reported by the probe was not altered as confirmed by the goodness-of-fit test of the Vogel-Fulcher-Tammann (VFT) equation. Through the comparison of fi reported by a bigger untethered probe in the same system, the origin of the vertical shift of VFT was interpreted as the result of an increased restriction of probes upon tethering, which was not associated with an increase in the probing length scale. To summarize, the rotational dynamics of the tethered probe accurately captures the degree of non-Arrhenius temperature dependence and nonexponential relaxation of the host polymers regardless of Tg and fragility of the system or the tethering condition.