The adhesion between glass and polyethylene (high-density polyethylene (HDPE) or low-density polyethylene (LDPE)) was improved by means of polyethylene chains grafted on the glass surface. Chlorosilane-terminated polyethylene (PE) with different molar masses were synthesized in order to obtain (i) semicrystalline polymers able or not to crystallize with the free chains of the polyethylenes matrices and (ii) polymer chains which could react with the silanol groups from the glass surface. The grafting of alkylchlorosilanes (alkyl chain length varying from C4H9 to C30H61) was considered in comparison to the polymer chains. The adhesion developed at the polyethylene/glass interface was studied as a function of the molar mass of functionalized-polyethylene grafted on the glass surface. For that purpose, the asymmetric double cantilever beam test was used to determine the fracture energy, Gi, of the interface. On both high-density and low-density polyethylene/glass joints, the fracture energy of the interface, Gi, was found to increase with the length of the interfacial connecting chains. The locus of the failure was studied by means of wettability measurements and atomic force microscopy analysis of the surfaces after separation. The higher values of the fracture energy of the interface with HDPE can be explained by a better compatibility of the tethered-PE chains with the free chains of the PE matrix which are more linear than LDPE. It was demonstrated that for the shortest chains (alkylchlorosilanes), the connectors were extracted from the bulk PE (LDPE or HDPE) whereas for the polymeric chains, a cohesive failure occurred for the glass/HDPE interfaces. Such a study can be used to design the connecting polymeric chains for improving the adhesion between glass and a semicrystalline polymer.