Poly(butylene 2,6-naphthalate) (PBN)/poly(ethylene glycol) (PEG) copolymers were synthesized by the two-step melt copolymerization process of dimethyl-2,6-naphthalenedicarboxylate (2,6-NDC) with 1,4-butanediol (BD) and PEG. The copolymers produced had different PEG molecular weights and contents. The structures, thermal properties, and hydrophilicities of these copolymers were studied by H-1 NMR, DSC, TGA, and by contact angle and moisture content measurements. In particular, the intrinsic viscosities of PBN/PEG copolymers increased with increasing PEG molecular weights, but the melting temperatures (T-m), the cold crystallization temperatures (T-cc), and the heat of fusion (Delta H-f) values of PBN/PEG copolymers decreased on increasing PEG contents or molecular weights. The thermal stabilities of the copolymers were unaffected by PEG content or molecular weight. Hydrophilicities as determined by contact angle and moisture content measurements were found to be significantly increased on increasing PEG contents and molecular weights. (c) 2006 Wiley Periodicals, Inc.