Poly(ethylene glycol) derivatives containing periodic side-chain carboxyl groups: synthesis and characterization

The aim was the synthesis of chain-extended poly(ethylene glycol) (PEG) derivatives containing periodic side-chain carboxyl groups. The chain extension of PEG diols with pyromellitic dianhydride was performed in toluene or dimethylformamide solution and in bulk. The degree of chain extension (DoCE) was between 6 and 21, the highest value being recorded when the reaction was performed using low-molecular-weight PEG. The recorded limited increase of molecular weight could be at least partially attributed to the rather low reactivity of the aromatic dianhydride. To overcome this issue, a more reactive aliphatic dianhydride, ethylenediaminetetraacetic dianhydride (EA), was tested. However, the reaction of PEG with EA only afforded a DoCE of 2.5. Appreciably higher DoCE values were obtained when EA was reacted with bisamino-terminated PEG. Independent of prepolymer and dianhydride structure, all chain-extended products displayed less of a tendency to crystallization than the starting prepolymer, very likely due to interference by anhydride residues. The low in vitro cytotoxicity of the chain-extended polymers and the presence of carboxyl groups point to their possible use in biomedical applications, particularly in controlled drug release and tissue engineering.