The Role of Chain-End Association Lifetime in Segmental and Chain Dynamics of Telechelic Polymers

Broadband dielectric spectroscopy, differential scanning calorimetry, and rheology were employed to study the impact of hydrogen (H)-bonding end-groups on segmental and chain dynamics of telechelic polypropylene glycol (PPG) and poly­(dimethylsiloxane) (PDMS). Polymer chains with three types of H-bonding end-groups possessing different interaction strengths and a non-H-bonding end-group as reference were compared. The glass transition temperature (T_g) of H-bonding PPG systems with low molecular weight increases compared to the reference, and the T_g difference varies with chain-end interaction strength. In contrast, their shear viscosities (for T_g-scaled temperature, i.e., when the shift in T_g is accounted for) are similar to that one of the reference. This is in strong contrast to the behavior of telechelic PDMS with the same set of end-groups, where the T_g increase of all H-bonding systems is independent of H-bond strengths, while shear viscosity increases significantly only for the strongest H-bonding end-groups. These observations are explained by the difference in lifetime of the end-group associations relative to segmental and chain relaxation times.