The synthesis of new poly(siloxysilanes) by polyhydrosilation of AB(2), AB(4), and AB(6) monomers using a solid-supported catalyst is described. Analysis of the polymers by gel permeation chromatography shows weight-average molecular weight values near 5-10 000 amu with polydispersities of similar to 2. Addition of fresh monomer to the polymerized material only leads to a slight increase in molecular weight. In all cases, polymerization is accompanied by significant intramolecular cyclization side reaction. These results can be explained by considering factors such as the unequal reactivity of the different oligomeric species and their tendency to form cyclic species, but no clear evidence for a growth-limiting effect arising from steric crowding could be seen. End capping of the terminal silicon hydride groups by hydrosilation with a variety of reagents has been demonstrated, affording a diversity of functionalized poly(siloxysilane) materials.