Grafted Epoxide Functionalized Polypropylene Carbonate Porogen for Low Dielectric Constant Epoxy Films

Abstract

A nanoporous epoxy film was formulated by using chemically modified epoxide-terminated polypropylene carbonate (ePPC) as the porogen in an epoxy resin formulation. The ePPC was grafted onto styrene maleic anhydride (SMA) copolymer and further used to chemically crosslink with poly(bisphenol A diglycidyl ether) (pBPADGE). The SMA-pBPADGE crosslinking was initiated with a tertiary amine catalyst. After curing of the pBPADGE resin film, the ePPC was thermally decomposed and created volatile, small molecules that diffused through the film leaving a nanoporous epoxy film. The pore size distribution within the epoxy film with ePPC loadings of 5 to 20 wt% after thermal degradation of the porogen was mostly between 6 to 18 nm as measured by nitrogen absorption experiments. The dielectric constant of the resulting 20% porous epoxy film was 2.77 and dielectric loss of 0.015. Mechanical properties and glass transition temperature of the cured film decreased slightly compared to the same film without pores. The reduced modulus of the epoxy film with 20% pore volume was 8 GPa and the glass transition temperature of 142°C.