Perfluoroalkylated POSS Fillers with Molecular Weight Distributions for Low Refractive Index Fluorinated Polymer Composite Materials

Abstract The development of fillers that enable reduction of the refractive index (RI) of materials through facile mixing is a significant approach for not only simplifying material fabrication but also tuning their physical properties. In this study, we designed and synthesized a series of perfluoroalkylated fillers comprising a polyhedral oligomeric silsesquioxane (POSS) core and perfluoroalkyl side chains with molecular weight distributions. We found that the synthesized fillers can efficiently decrease the RI of a fluorinated polymer, particularly at low filler loadings, compared to the fillers bearing perfluoroalkyl groups of the identical length at all eight vertices. From analysis through packing coefficients, it was suggested that the random introduction of side chains with varying lengths should suppress filler agglomeration. Consequently, we successfully obtained a low-RI and transparent composite film while maintaining the toughness of the polymer material. We demonstrate not only the broad designability of POSS molecules with eight vertices but also the general applicability of this method for quantitatively evaluating the agglomeration state of fillers within the matrix using packing coefficients.