Preparation of Thermo-sensitive oxidizable N-vinylcaprolactam-based terpolymers and their self-assembling property

Poly(N-vinylcaprolactam-co-hydroxyethyl acrylate-co-phenyl vinyl sulfide) (poly(VC-co-HEA-co-PVS)) and poly(N-vinylcaprolactam-co-N-vinylpyrrolidone-co-phenyl vinyl sulfide) (poly(VC-co-VP-co-PVS)) were synthesized as thermos-sensitive oxidizable terpolymers. The copolymerization was confirmed by the ¹H-NMR and FT-IR spectroscopy. VC homopolymer exhibited its lower critical solution temperature (LCST) around 32 ℃. The copolymerization of HEA with VC and of VP with VC decreased and increased the LCST of VC homopolymer, respectively. The inclusion of PVS (an oxidizable monomer) in the copolymers decreased the LCST. The PVS of the copolymers could be oxidized by H₂O₂, solution (0.1%), evidenced by ¹H-NMR spectroscopy. Upon the oxidation, the LCST of poly(VC-co-PVS) and poly(VC-co-HEA-co-PVS) increased markedly possibly due to an increase in the hydrophilicity of PVS. However, the LCST of poly(VC-co-VP-co-PVS) was not markedly affected by the oxidation. The interface activity of poly(VC-co-PVS) and poly(VC-co-HEA-co-PVS) slightly decreased but that of poly(VC-co-VP-co-PVS) markedly increased by the oxidation. The critical micelle concentration of the copolymers was determined by a fluorescence method, and it was 0.087 to 0.105 mg/mL. The micelles of the copolymers were found as circular objects on a transmission electron microscope. The mean hydrodynamic diameters of micelles were 107.4 to 471.6 nm, depending on the polymer composition. The PVS-containing copolymers formed larger micelles than VC homopolymer, possibly because the monomer could enhance an intermolecular hydrophobic interaction due to its phenyl group.