Metal-free hydrosilylation using tris(pentafluorophenyl)borane (B(C6F5)(3)) as a catalyst enables the rapid polymerization of alpha-diketone and bis(silane) monomers under ambient conditions to give high molecular weight poly(silyl ether)s (PSEs). A wide selection of commercially available monomers bearing different backbone and side-chain functional groups are shown to be compatible with these metal-free conditions. Significantly, the thermal properties of these poly(silyl ether)s are highly tunable, with novel semicrystalline materials being obtained in a variety of cases. These poly(silyl ether) materials serve as a versatile platform for materials with designed degradation profiles and crystallinity.