ABA block-type copolymers with poly(2-methacryloyloxyethyl phosphorylcholine(MPC)) as the middle B segment and poly(glycidyl methacrylate(GMA)) as the A segments (PMbG) were synthesized by an activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The PMbGs were reactive copolymers, as the epoxide group available in the poly(GMA) segment could be chemically modified by nucleophilic addition reactions, which allowed the functionalization of PMbG with a wide range of functional groups for various purposes. The PMbGs had narrow molecular weight distributions with predetermined chain lengths, while the length of the middle poly(MPC) segment could be designed and synthesized with a fixed degree of polymerization of both poly(GMA) segments in a single polymer chain. The functionalization of PMbGs by 3-aminophenylboronic acid allowed the preparation of a phenylboronic acid moiety connecting ABA block-type copolymers (PMbBs). The PMbGs were also reacted with diethanolamine (DEA) to introduce hydroxyl groups. The DEA-functionalized copolymers (PMbDs) could interact with PMbBs in aqueous media, forming hydrogels spontaneously. As the reactive groups were separated by the poly(MPC) segment, the network structure depended on the polymerization degree of the poly(MPC) segment. The diffusivity of various proteins in the PMbB/PMbD hydrogels depended on the molecular weight of these proteins and was regulated by adjusting the chain length of poly(MPC) between cross-linking positions of the hydrogel network, that is, the polymerization degree of the poly(MPC) segment. (C) 2017 Elsevier Ltd. All rights reserved.