| Summary: | The copolymerization of acrylonitrile (AN) with a hydrophilic monomer is an effective way to prepare hydrophilic polyacrylonitrile (PAN)-based functional materials. In this study, γ-ray radiation-induced copolymerization of AN and 4-vinylpyridine (4-VP) in dimethylsulfoxide (DMSO) was carried out. The chemical structure, molecular weight, thermal properties, and hydrophilicity of the synthesized copolymers were characterized. The γ-ray radiation could initiate the copolymerization of AN and 4-VP in DMSO at room temperature (0~35 ℃). The monomer conversion reached above 90% at the absorbed dose of 25 kGy, but the molecular weight of the copolymer depended on the dose rate. When the absorbed dose was 30 kGy, a P(AN-co-4-VP) random copolymer solution with a viscosity of 250 Pa⸱s was obtained directly after the monomer solution was irradiated by γ-rays at a lower dose rate of 11 Gy/min. The P(AN-co-4-VP) copolymer had a weight-average molecular weight of 1.34×105, and the relative content of AN and 4-VP units in the copolymer chains was identical to the feed ratio of AN and the 4-VP comonomer. When the dose rate exceeded 20 Gy/min, molecular weight of the synthesized copolymer decreased remarkably. Thermal properties of the P(AN-co-4-VP) random copolymer with the relative molar ratio of 4-VP to AN of 2% were generally the same as those of the PAN homopolymer. The 4-VP units in the polymer chains did not participate in the ring formation or crosslinking reaction of the side ‒C≡N groups. However, the water contact angle of the P(AN-co-4-VP) random copolymer decreased gradually with increase in 4-VP content, indicating that the introduction of 4-VP units can improve the hydrophilicity of the copolymers. This study provides a new idea for the hydrophilic modification of PAN as well as proves that DMSO solutions with a high mass fraction (>20%) of the homo- or copolymer of AN can be obtained directly via radiation-induced solution polymerization, thus expanding the potential applications of the high-energy radiation technique in the field of solution polymerization of AN.
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