title: Segmental Dynamics and Dielectric Constant of Polysiloxane Polar Copolymers as Plasticizers for Polymer Electrolytes.
abstract: Dielectric relaxation spectroscopy was used to investigate the segmental dynamics of a series of siloxane-based polar copolymers combining pendant cyclic carbonates and short poly(ethylene oxide) (PEO) chains. The homopolymer with cyclic carbonate as the only side chain exhibits higher glass transition temperature T(g) and dielectric constant ε(s) than the one with only PEO side chains. For their copolymers the observed T(g) (agreeing well with the predicted values from the Fox equation) and ε(s) decrease with increasing PEO side chain content. These polar polymers exhibit a glassy β relaxation with Arrhenius character, attributed to local chain motions of side groups attached to the main chain, and a segmental α relaxation, associated with the glass transition with a Vogel temperature dependence. As PEO side chain content increases, narrowing of the local glassy β relaxation was observed in the copolymers. The segmental α dynamics were observed to be faster, with an increase in breadth and decrease in strength with increasing PEO side chain content. Owing to the trade-off between T(g) and ε(s), copolymers of intermediate composition result in the highest ionic conductivity when these copolymers are used to plasticize Li single-ion conducting ionomers.
authors.affiliation: Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.|Functional Composites Department, Korea Institute of Materials Science , Changwon 642-831, Korea.
authors.forename: U Hyeok
authors.initials: UH
authors.lastname: Choi
authors.affiliation: Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.|Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Siwei
authors.initials: S
authors.lastname: Liang
authors.affiliation: Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.|State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun 130022, People's Republic of China.
authors.forename: Quan
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: James
authors.initials: J
authors.lastname: Runt
authors.affiliation: Materials Science and Engineering, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Ralph H
authors.initials: RH
authors.lastname: Colby
keywords: dielectric constant; glass transition temperature; lithium ion battery; plasticizer; polymer electrolyte; siloxane-based polar copolymer