Fluorinated polyimide with polyhedral oligomeric silsesquioxane aggregates: Toward low dielectric constant and high toughness

An amphiphilic alternating copolymer with hydrophobic polyhedral oligomeric silsesquioxane (POSS) segments and hydrophilic anhydride segments, which is able to self-assemble into nanoscale POSS aggregates, is introduced into fluorinated polyimide (FPI) films to polish up their toughness while lowering their dielectric constant. The dielectric constant of POSS/FPI composite films with 2.8 wt% amphiphilic alternating copolymer significantly decreases to 2.09 from 3.14 for pure FPI. Furthermore, a sharp brittle-ductile transition is observed in the tensile energy to break versus interparticle distance curve. When the interparticle distance is reduced to 215 nm, the elongation at break and tensile energy to break of POSS/FPI composite films increase to 27.5% and 23.5 MJ/m3 from 8.3% to 6.8 MJ/m3 respectively. The tensile-fractured surfaces of POSS/FPI composite films reveal that the toughening mechanism is mainly attributed to the prevention of crack propagation and the debonding of POSS aggregates with a plastic void growth.