Nanoporous, Ultralow-Dielectric-Constant Fluoropolymer Films from Agglomerated and Crosslinked Hollow Nanospheres of Poly(pentafluorostyrene)-block-Poly(divinylbenzene)

摘要

A simple approach to fabricating crosslinked and nanostructured fluoropolymer films with ultralow-k has been described. The surface-initiated ATRP process has allowed the preparation of well-defined SiO_2-g-PFS-b-PDVB core-shell structures. PFS-b-PDVB hollow nanospheres with different PFS shell thicknesses can be readily prepared by controlling the PFS chain lengths during the surface-initiated ATRP process. Obviously, the dimension of the hollow cores can also be controlled by changing the size of initiator-immobilized silica nanoparticles. The thin outer layer of crosslinked PDVB with residual double bonds helped ⅰ) initially to maintain a well-defined core-shell structure of the SiO_2-g-PFS-b-PDVB hybrids, ⅱ) to promote crosslinking between the agglomerated nanospheres during UV exposure, ⅲ) to preserve the core void of each hollow nanosphere after SiO_2 removal, and ⅳ) to enhance the mechanical properties of the nanopo-rous fluoropolymer film. The nanoporous fluoropolymer films, with porosity contributions from the interstitial spaces between the nanospheres and the core voids of the hollow spheres, exhibited a k as low as 1.7.