Chemical Modification of Surface Active Poly(ethylene oxide)−Poly(propylene oxide) Triblock Copolymers

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Abstract
A general route has been developed to chemically modify a series of poly(ethylene oxide)−poly(propylene oxide) triblock copolymers with molecular weights from 6500 to 14 600. It is initiated by the introduction of p-nitrophenyl groups; such nitrophenyl conjugated copolymers are stable in an organic milieu and in a dry state but are seen to react easily with amino-containing molecules including small peptides. Among them, introduction of 2-pyridyl disulfide groups after coupling with 2-(2-pyridyldithio)ethylamine enables the selective attachment of thiol-containing molecules. The released thiopyridone in such thiol−disulfide reactions can be used to quantify the content of 2-pyridyl disulfide groups. In addition, a new type of modified copolymers was developed for the radioisotope (125I) labeling purpose that consists of a reaction of nitrophenyl conjugated copolymers with hydrazine and a subsequent coupling with N-succinimidyl 3-(4-hydroxyphenyl)propionate (Bolton−Hunter reagent). Adsorption studies of 125I-labeled and 2-pyridyl disulfide conjugated copolymers on polystyrene particles are consistent with previous determinations of surface coverage using other technologies, in turn indicating that this new chemical modification does not alter their surfactant properties on hydrophobic solid phase. The coating of common hydrophobic surfaces with 2-pyridyl disulfide conjugated copolymers has been demonstrated as a general and robust immobilization method to generate a high-sensitivity bioactive surface with low nonspecific binding. The optimal space between immobilized ligands can also be controlled by incubating the solid phase with solutions containing mixtures with different ratios of unmodified and modified copolymers.