A versatile polymeric support system for the synthesis of oligonucleotides is provided featuring a universal primer which allows chain elongation, in either the 3' or 5' direction, with any currently available DNA or RNA synthesis method, by a process which utilizes oxidatively cleaved primers to facilitate chain elongation and release. The support system is capable of withstanding mildly basic and acidic reaction conditions, while still permitting a convenient and quantitative release, either before or after removal of protecting groups from reactive groups, of synthesized oligonucleotides from a single polymeric support. Removal of the protecting groups before cleavage of the oligomer from the support permits the use of the immobilized oligomer as an affinity hybridization support for both isolating and detecting complementary polynucleic acids.