Thermoresponsive Pyrrolidone Block Copolymer Organogels from 3D Micellar Networks

A new series of amphiphilic pyrrolidone diblock copolymers poly[N-(2-methacrylaoyxyethyl)pyrrolidone]-block-poly(methyl methacrylate) (PNMP -b-PMMA ; where m is fixed at 37 and n is varied from 45 to 378) is developed. Spontaneously situ-gelling behaviors are observed in isopropanol when n varies from 117 to 230, whereas only dissolution or precipitation appears when n is beyond this region. Further analysis reveals that uniform thermoinduced reversible gel-sol transitions are observed in those organogels, which is attributed to the disassembly from micellar networks to micelles as confirmed by electron microscopy and other techniques. The gel-sol transition temperature is highly dependent on n and increases as n increases. Conformational interactions analyzed using ¹H NMR and 2D Noesy NMR suggest that the thermoinduced stretch of solvophilic PNMP segments within micelles and the sequencing variation in the isopropanol molecules are the major cause of the gel-sol transitions.