Poly(p-xylylene) (also known as parylene N) has previously been used to pore seal ultralow k (≤ 2.2) (ULK) dielectrics. The parylene polymers may facilitate the integration of ULK dielectrics by: substantially improving their fracture toughness, hermetically sealing the pores, being able to use standard wet chemical cleans, and minimally impacting the observed dielectric constant, while minimally disrupting current process flow integrations. This paper introduces a new cross-linkable polymer that is deposited using thermal chemical vapor deposition (CVD) on the same tool that is used for parylene N deposition. The polymer, poly(ethynyl-p-xylylene) (parylene X), was deposited at room temperature. A series of 30 min post-deposition anneals in helium shows that the deposited material cross-linked between 200°C and 300°C with full conversion at 380°C for a ~300 A film. After the low molecular weight species out-gassed during anneals at 200°C, there was less than a percent weight loss to 450°C with no change in the optical constants and no optical loss. Previous work with poly(ethyl-p-xylylene) suggests that the dielectric constant of parylene X will be significantly lower than parylene N.