Tuning Polymer Glass Formation Behavior and Mechanical Properties with Oligomeric Diluents of Varying Stiffness.

Small-molecule diluents are important tools in the control of polymers' glass formation, transport, and mechanical properties. While recent work has indicated that these diluents can impose a more diverse range of effects than previously appreciated, use of these additives to rationally control polymer properties requires a predictive understanding of their effects. Here we employ molecular dynamics simulations to show that diluent-induced changes in a polymer's glass transition temperature can be predicted based on the diluent's Debye-Waller factor ⟨⟩, a measure of picosecond time scale rattle-space, via a functional form previously found to predict nanoconfinement-induced shifts in polymer . Moreover, we show that diluent-induced alterations in polymer segmental relaxation time are related to changes in modulus and ⟨⟩ via the Generalized Localization Model of relaxation. These results provide new design principles for the use of oligomeric diluents in achieving independent, targeted control of structural relaxation and glassy moduli.