The synthesis and characterization of two novel cyclic siloxanes, diacetoxydi-ethyltetramethylcyclotetrasiloxane and diacetoxytriethylpentamethylcyclopentasiloxane, and cyclolinear polymers synthesized from these monomers are presented. The cyclic siloxanes were synthesized from tetramethylcyclotetrasiloxane and pentamethylcyclopentasiloxane, respectively, by acetylation followed by ethylation. The cyclic monomers were characterized with H-1 NMR spectroscopy. Subsequently, the cyclic siloxanes were self-condensed into cyclolinear polysiloxanes and cocondensed (extended) with silanol-terminated polydimethylsiloxane into high-molecular-weight polymers containing cyclic units with linear polydimethylsiloxane spacers (extended cyclolinear polysiloxanes). The molecular weights of both the cyclolinear polysiloxanes and extended cyclolinear polysiloxanes were determined. (c) 2006 Wiley Periodicals, Inc.