Crosslinking between polymer chains having olefin groups occurs by heating the polymer chains in the presence of a catalyst. Mixtures of polymer and catalyst can be dried and cast into films at ambient temperatures and remain non-crosslinked and soluble for extended periods. However, upon heating of the polymer to temperatures of about 300.degree. C. or greater in the presence of a catalyst, the polymer chains of the film are cured to produce an insoluble crosslinked matrix. The sudden and relatively complete nature of the crosslinking between the polymers under specific conditions is particularly useful to allow chromophores poled in a noncrosslinked polymer mixture to retain their uniform orientation after crosslinking has occurred.