Nanoporous thin films based on polylactide-grafted norbornene copolymers

Abstract

Thermally stable vinyl polymerized polynorbornene (PNB) is one of the challenging materials in porous low dielectric films for packaging applications. Nanoporous PNB thin films were obtained with poly(D,L-lactide) (PLA)-grafted norbornene copolymers. Thermally labile PLA chains act as pore generators in PNB films. Thermally stable PNB main chains were synthesized by Pd-catalyzed vinyl polymerization and PLA side chains were grafted onto the PNB main chains by ring opening polymerization. The brittle and poor processible properties of PNB could easily be controlled by the copolymerization with norbornene derivatives. In thin films, the PLA chains were found to thermally decompose at about 250°C while the PNB matrix was stable during this pore generating process. The porosity of the porous PNB thin films could be controlled up to 18% with pore sizes below 5 nm range by varying the chain length of grafted PLA. Introduction of cross-linking epoxy groups onto the PNB main chains resulted in the formation of well-defined nanopores without any extensive pore collapse during the vitrification of the PNB matrix. Additionally, it is demonstrated that the photopatterning of the thin films could be achieved using photoinitiator. © 2008 American Chemical Society.