This invention provides a novel method for purifying synthetic oligomers comprising capping, polymerizing and separating any failure sequences produced during oligomer synthesis. Either the failure sequence or the full-length oligomer may be polymerized. Optionally, small molecule impurities may also be incorporated into the polymerized material. The invention provides novel capping agents having a polymerizable functional group. The invention also provides kits comprising at least one composition of the present invention.