Role of Chemical Tethering in Polymer Glass Formation

This study investigates the role of chemical tethering in polymer dynamics within the framework of Adam–Gibbs (AG) theory, employing star polystyrene (PS) as a model system, with each arm capped with an adamantane (Ad) group and varying the number of arms ( f ) and core rigidities. Results indicated that the glass transition temperature ( T g ) and dynamic fragility ( m ) of the Ad-capped star PS increased with an increasing f value and core rigidity. These increases were associated with an increase in the potential energy barrier per monomer segment (Δμ), as described by the AG theory, but with an unaltered length for cooperatively rearranging regions at T g, establishing a linear relationship between Δμ and T g and m. This relationship indicated that chemical tethering impedes polymer cooperative dynamics by constraining the internal rotation of C–C bonds in the tethered polymer backbone and increasing the Δμ value during cooperative motion. The findings of the study offer new insight into the polymer glass transition, which varies according to the molecular topology and tethering architecture of the polymer.