oligomer

 A molecule composed of a small number of linked monomer units; a short polymer; -- compounds called oligomers have less than one hundred monomer units and usually less than thirty. Oligomers of increasing length are called dimer, trimer, tetramer, pentamer, hexamer, heptamer, octamer, nonamer, decamer, etc. In colloquial laboratory jargon, they may also be referred to as nine-mer, ten-mer, eleven-mer, twelve-mer, etc., especially for oligomers of greater than eight units.  [PJC]