Whereas monodisperse polymers are ubiquitous in Nature, they remain elusive to synthetic chemists. Absolute control over polymer length and structure is essential to imparting chemical functionality, reproducible properties, and specific solid-state behavior. Precise polymer length has proven to be extremely difficult to control. The most successful examples are generally similar to solid-phase oligo nucleotide or peptide synthesis, wherein the polymer is built up one unit at a time with each sequential monomer addition requiring purification and deprotection (or other functional group activation) step. We have discovered a stepwise homogeneous catalyst-transfer polymerization to prepare monodisperse oligo(3-hexylthiophene) using temperature to limit additions to one unit per chain per cycle. This is the first reported example of a one-pot synthesis of monodisperse oligomers that requires no additional purification or intermediate steps. It is our hope that the strategy of temperature cycling to "freeze" intermediates will be generalizable to other living polymerization techniques, such as other catalyst-transfer polymerization systems, and those where a resting state involves an association between the catalyst and growing chain.