A method of forming an air gap within a semiconductor structure by the steps of: (a) using a sacrificial polymer to occupy a space in a semiconductor structure; and (b) heating the semiconductor structure to decompose the sacrificial polymer leaving an air gap within the semiconductor structure, wherein the sacrificial polymer of step (a) is: (a) a copolymer of 5-ethylidene-2-norbornene and vinylbenzocyclobutene (or a vinylbenzocyclobutene derivative); or (b) a copolymer of 5-ethylidene-2-norbornene and 5-(3benzocyclobutylidene)-2-norbornene; or (c) a polymer of 5-(3benzocyclobutylidene)-2-norbornene. In addition, a semiconductor structure, having a sacrificial polymer positioned between conductor lines, wherein the sacrificial polymer is: (a) a copolymer of 5-ethylidene-2-norbornene and vinylbenzocyclobutene (or a vinylbenzocyclobutene derivative); or (b) a copolymer of 5-ethylidene-2-norbornene and 5-(3benzocyclobutylidene)-2-norbornene; or (c) a polymer of 5-(3benzocyclobutylidene)-2-norbornene.