AbstractThe formation of ring and chain molecules during an irreversible step‐growth polymerization has been modelled on a three‐dimensional twenty six choice cubic lattice, and examined by the Monte‐Carlo method. Movements were not allowed in the system in this preliminary study. The limiting value of the extent of reaction was found to bep= 0,9837 (±0,0003), and the number fraction of molecules found to be rings was 0,300 (±0,045), but the weight fraction was much smaller, 0,056 (