Influences of "Bonded" and "Unbonded" Monomers on Glass Transition Temperatures in Amorphous Polymer/POSS Composites

We report that a fraction of “bonded” or “unbonded” monomers to particle interfaces dictates the composition dependence of the glass transition temperatures (Tg) of polyhedral oligomeric silsesquioxane (POSS)-containing nanocomposites. Although Tg is one of the most critical physical parameters of nanocomposites, confounding interfacial effects make Tg prediction challenging. To this end, we design a model nanocomposite to systematically study Tg of nanocomposites by leveraging the “all interfacial” nature of ultrasmall POSS fillers. An amine-functionalized POSS is loaded into random copolymers of styrene and 2-vinyl pyridine. The POSS forms hydrogen bonds only with 2-vinyl pyridine, which behaves as a “bonded” monomer. The influence of copolymer composition and POSS loading on the Tg of this model composite is successfully explained by modifying the Fox equation. In this presentation, further implications about the different POSS composites will be discussed.