Using high-resolution magic angle spinning (MAS) solid-state NMR spectroscopy and density-functional theory (DFT) calculations, we determine the microstructure of the silicon-based functional polymer poly(1,4Si6) arising from the dehydrocoupling polymerization of cyclosilane 1,4Si6. 1H–29Si refocused-INEPT solid-state NMR experiments allow the unambiguous determination of the number of attached protons to a silicon atom for each 29Si NMR signal in 1,4Si6 and poly(1,4Si6). One-dimensional 1H → 29Si cross-polarization MAS (CPMAS) NMR spectra of poly(1,4Si6) show the development of SiH resonances upon polymerization, and peak integration indicates an average degree of polymerization of 20. The 1H → 29Si CPMAS spectrum of poly(1,4Si6) also shows two sets of isotropic signals, suggesting the presence of at least two distinct species. Two-dimensional 29Si dipolar double-quantum–single-quantum and single-quantum–single-quantum homonuclear correlation NMR spectra reveal similar connectivity in the two species, po...