A main-chain elastomer was synthesized for the first time by a cross-linking hydrosilylation of a cyclosiloxane with a new main-chain liquid crystalline semiflexible polyether. Imposing a uniaxial mechanical field to the unstretched nematic polydomain sample results in a macroscopic alignment of the director. For this process the sample has to be stretched by a factor of about 5, which considerably exceeds the effect observed for nematic side-chain elastomers.