Hexa-n-alkylcyclotrisiloxanes with side chains ranging from butyl up to decyl were polymerized anionically with cryptated lithium as the counterion. The polymerizations usually yielded polymers with low polydispersity, demonstrating the presence of a single growing species and the successful breaking up of aggregates. Formation of bimodal molecular weight distributions in the polymerization of the cyclic trimers containing heptyl up to decyl side chains can be explained by the presence of traces of siloxanediol, leading to some chains growing at both ends.