The present invention concerns a method for producing polymers suitable as carrier-free delivery system of bioactive molecules, in particular bioactive peptides. The method comprises the polycondensation of one or more different monomers, including monomers comprising the peptides, monomers comprising a cross-linker and, optionally, monomers comprising an adjuvant. The invention also relates to the polymers obtained by the method, which are suitable as medicaments, such as vaccines. In a particular embodiment, the bioactive peptide is a neoantigen and the polymer is used as a cancer vaccine.