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 copolymer of bis[3-(4-benzocyclobutenyl)]1,n (n=2-12) alkyldiol diacrylate (such as bis[3-(4-benzocyclobutenyl)]1,6 hexanediol diacrylate) and 1,3 bis 2[4-benzocyclobutenyl(ethenyl)]benzene. In addition, a semiconductor structure, having a sacrificial polymer positioned between conductor lines, wherein the sacrificial polymer is a copolymer of bis[3-(4-benzocyclobutenyl)]1,n (n=2-12)alkyldiol diacrylate and 1,3 bis 2[4-benzocyclobutenyl(ethenyl)]benzene.