AbstractThe radiation‐induced grafting of methacrylic acid onto polyurethane has been carried out in the presence of solvents. The swelling of polyurethane was highest when the solubility parameter of the monomer solution was 11.0. The molecular weight of polyurethane did not change with the irradiation dose up to 30 Mrad in the absence of solvent. The irradiation in the presence of solvent, on the other hand, decreased the molecular weight. The grafting yield in CCl4, benzene, andn‐hexane decreased monotonously with the decrease in monomer concentration. The large decrease of the grafting yield in CCl4was proved to be due to the high possibility of chain transfer to CCl4. When such solvents as water, methanol, and DMF were used, on the other hand, a maximum grafting yield was obtained when the monomer concentration was ca. 75. The hydrogen bonding among polyurethane, methacrylic acid, and solvent was found to affect both the swelling and the grafting yi
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