a method and apparatus for sequentially degrading at least a portion of a polymer of backbone repeating units , the polymer having a terminal repeating unit comprised of a nucleophile and a backbone carbonyl carbon distant from the nucleophile , comprising the steps of first initiating attack of said nucleophile upon said backbone carbonyl carbon by raising the energy level to activate said nucleophile for said attack . secondly , forming a ring comprising the terminal repeating unit , thereby simultaneously releasing the ring and generating a shortened polymer having a terminal repeating unit capable of nucleophile attack upon the backbone carbonyl carbon and , lastly , maintaining the reaction conditions necessary for repeating steps a and b until the portion of the polymer desired is degraded . in a related embodiment , polyamide nucleic acid sequences can be determined by generating a nested set of polymer fragments , each fragment having n - x repeating units where n is the total number of repeating units in the parent polymer and x is the number of degradation cycles the fragment has been subjected to , and then analyzing the nested set of polymer fragments to determine polymer sequence . an apparatus embodying the method of sequential degradation is also described . analysis may be by mald - tof .