Preparation and characterization of low-κ polyhedral oligomeric silsesquioxane/polyimide hybrid films

A series of Polyimide (PI)/Phenyl-POSS (POSS) hybrid films with low dielectric constants and excellent comprehensive properties have been successfully prepared via physical blend methods by incorporating different proportions of POSS into the polyimide precursors (Pyromellitic dianhydride- 4, 4′-Diaminodiphenyl ether). An appropriate amount of POSS doping can effectively improve the optical and dielectric properties of hybrid films due to the contribution of POSS with hollow, cage-like molecular structure to weakening intermolecular charge transfer complexation and increasing nanopore volume fraction in hybrid films. Instead, excessive amount of POSS doping can reduce dielectric properties due to the interface polarization effect induced by POSS agglomeration. When the doping amount is 15%, the highest light transmission reaches to 84.5%. When the doping amount is 25%, the dielectric properties have been are best improved. The dielectric constant and loss at 104 Hz are reduced to 2.37 and 0.0018 respectively. However, the mechanical properties decrease in response to the increase of POSS content, because POSS molecular dispersing in the folded molecular chains hinders the interaction of molecular chains PI matrix. The correlation between the dielectric properties of PI/POSS films and their nonopore volume fraction has been explained with the help of positron lifetime spectra.