Broadband Dielectric Spectroscopy Study of Dynamics of Telechelic Polypropylene Glycol Melts

Excellent polymer electrolytes require a combination of high ionic conductivity and mechanical strengths. An in-depth understanding of the relationship between polymers'microscopic structure and dynamics and macroscopic conductive and mechanical properties is essential for the molecular design of high-performance polymer electrolytes. In the present paper,we selected low temperature of glass transition(T-g)and non-crystalline telechelic polypropylene glycol melts as a model system to investigate the molecular dynamics of associating polymers. Allyl-terminated polypropylene glycols having molecular weights of 1000, 2000 and 4000 were synthesized by chemically modifying the end groups,and the influence of chain-end interaction strength and molecular weight on their multi-scale dynamics was investigated using broadband dielectric spectroscopy. The polypropylene glycols with two different end groups exhibit both the alpha-relaxation associated with the segmental motion and the normal mode relaxation associated with the global motion of the chain. End group interactions influence both two relaxations; stronger interactions lead to longer relaxation time at the same temperature. This effect becomes more pronounced for thelower-molecular-weight samples,because the motion has been suppressed for the denser end groups therein. The generalized entropy theory was utilized to study the glass formation of telechelic polymer melts having variable sticky interaction strength and molecular mass,and theoretical predictions were shown to be in qualitative agreement with experimental results. These dynamic details can be used in guiding the molecular design of polymer electrolytes.