The influence of vinyl bonds on the phase separation and decomposition of polydimethylsiloxane (PDMS) was investigated for a saturated PDMS (s-PDMS) and an unsaturated poly(dimethylsiloxane-co-vinyl-methylsiloxane) (v-PDMS) with the same molecular weight, and the resulting pore sizes were investigated for two base polymer systems, one with an excess of hydrogen bonds (PHMS, polyhydromethylsoloxane) and one with stoichiometric hydrogen to vinyl bonds (PSO, polysiloxane). For PHMS, the samples with s-PDMS have lower ceramic yield and higher total porosity, while the samples with v-PDMS contain nearly no porosity after pyrolysis to 1300 degrees C due to extensive hydrosilylation between the hydrogen and vinyl groups. For the PSO, both s-PDMS and v-PDMS produce micron-sized pores, but the v-PDMS produces smaller pores with a narrower size distribution than the s-PDMS. The fundamental differences in the polymer phase separation and decomposition arising from the addition of vinyl bonds to the PDMS chains and the effect of the base polymer hydrogen content are discussed. (C) 2018 Elsevier B.V. All rights reserved.