Imparting low dielectric constant and high toughness to polyimide via physical blending with trifluoropropyl polyhedral oligomeric silsesquioxane

Polyhedral oligomeric silsesquioxane (POSS) is commonly used to lower the dielectric constant of polyimide (PI), but the toughness generally deteriorates. In this paper, trifluoropropyl POSS (FPOSS) is surprisingly found to impart superior dielectric constant and toughness to PI, even though the phase separation and aggregation of FPOSS are observed due to the thermodynamical immiscibility between FPOSS and PI. The dielectric constant of FPOSS/PI with 2.0 wt% FPOSS is reduced to 2.47 from 3.17. Furthermore, the tensile energy to break of FPOSS/PI is unexpectedly increased to 10.2 MJ/m(3) from 3.3 MJ/m(3), indicating the great improvement in toughness. The toughening mechanism is ascribed to the debonding of FPOSS aggregates from PI matrix with a void growth during tensile test. Meanwhile, lateral coalescence of the voids is avoided due to the adequate inter-aggregate distance when the width of the ligaments between the aggregates decreases with elongation of matrix.