A new and highly efficient polymer, post polymerization, modification platform based on an inverse electron demand Diels-Alder reaction is reported. Well-defined polymers were synthesized from allyl glycidyl ether and glycidol by anionic ring-opening polymerization with postpolymerization modifications conducted with a number of tetrazine derivatives that carried functional groups spanning from carboxylates and esters to primary amines. Analysis of polymerization kinetics by real-time H-1 NMR, and GPC revealed a rapid and high degree of side-chain conversion (>95%), with the generation of well-defined functional polymers, in both organic and aqueous solvents, without the need for additives or catalysts.