studies on thermostable materials, heptacyclicladdersiloxanes and ladderpolysilsesquioxane were synthesized. The first heptacyclicladdersiloxanes were obtained by chlorination of pentacyclic laddersiloxanes prepared using our stereocontrolled synthesis procedure; thereafter, the heptacyclicladdersiloxanes were made to react with disiloxanediol. Ladderpolysilsesquioxane was obtained from cis–trans–c