A method for forming thin polymer layers having low dielectric constants or semiconductor substrates. In one embodiment, the method includes the vaporization of stable di-p-xylylene, the pyrolytic conversion of such gaseous dimer material into reactive monomers, and blending of the resulting gaseous p-xylylene monomers with one or more comonomers having silicon-oxygen bonds and at least two pendent carbon--carbon double bonds. The copolymer films have low dielectric constants, improved thermal stability, and excellent adhesion to silicon oxide layers in comparison to parylene-N homopolymers.