Hybrid materials based on poly(n-butyl methacrylate-co-(3-(methacryloxypropyl)) trimethoxysilane) were synthesized via a sol-gel process. From a phase behavior study of these hybrid materials using a differential scanning calorimeter (DSC) and solid-state nuclear magnetic resonance (NMR) spectroscopy, it was found that the hybrid system was miscible for organic and inorganic phases with low silane content, but exhibited heterogeneously when silane content was increased to 40 mol% or more. Furthermore, the hybrid system became more complicated when 50 mol% or more silane introduced. It was also found that an inorganic Si-O-Si network developed, which resulted in side chain segments into two different molecular environments and with different relaxation behaviors. The development of an inorganic matrix of a Si-O-Si structure and the corresponding polymer chain environment were also discussed in detail.