Adhesion measurements performed on a polyethylene (PE)-grafted-glass interface showed that the structure of the PE free chains (matrix) was an important parameter. The fracture energy was higher for interfaces prepared from a linear matrix, such as high-density polyethylene (HDPE), than for those from a branched PE [low-density polyethylene (LDPE)]. Therefore, the microstructure of the grafted PE/PE matrix interface or interphase was investigated as a function of the molar masses of the connectors and the structure (linear or branched) of the free PE matrix chains. As the grafted chains were linear, a cocrystalline structure with free chains of the HDPE matrix was generated. PE connecting chains led to a low capacity for cocrystallization with LDPE. Cocrystallization. was studied with blends based on functionalized PE chains and PE matrices. These blends were assumed to be miscible, as substantiated by a single differential scanning calorimetry (DSC) peak. The DSC analyses were confirmed by wideangle X-ray scattering, which revealed a crystalline orientation of the chains in the interphase, that is, in the vicinity of the glass surface.