The C-H functionalization of polymers enables the direct incorporation of new functional groups into polymer backbones, presenting significant opportunities for the upcycling of commodity polymers. However, developing reactions that achieve selective functionalization while preserving the intrinsic features of polymers and avoiding undesirable structure deformation remains a considerable challenge. In this study, we present a transition metal-free post-functionalization approach for polyethers via a photoinduced α-C-H amidation reaction. This strategy provides a route to previously unattainable α-amino polyethers, which exhibit distinct physical properties from those of the parent polymer. By leveraging a polar-radical relay mechanism, we effectively incorporate C-N bonds into the polyether backbone while suppressing degradation and cross-linking. Conducted under mild and convenient conditions, this approach demonstrates significant site selectivity at the ethereal α-position, even in the presence of other types of C-H bonds, achieving tailed post-functionalization of macromolecules. Furthermore, the present strategy holds promise for broader applications, including the amidative degradation of commodity polymers and transformation of polyethylene glycol (PEG) network.