A method and composition for producing a low k dielectric film via plasma enhanced chemical vapor deposition comprise the steps of: providing a substrate within a reaction chamber; introducing into the reaction chamber gaseous reagents including at least one structure-forming precursors comprising a silacycloalkane compound, an oxygen source, and optionally a porogen; applying energy to the gaseous reagents in the reaction chamber to induce reaction of the gaseous reagents to deposit a low k dielectric film having dielectric constant of 3.2 or less. In certain embodiments, the structure-forming precursor further comprises a hardening additive.