Thermo-Responsive Behaviors And Molecular Structure Dependence Of Pyrrolidone Based Water-Soluble Polymers

This thesis describes the molecular structure dependent thermo-responsive behaviors of pyrrolidone based water-soluble polymers. A series of well-defined poly[N-(2-methacryloyloxyethyl)pyrrolidone] (PNMEP), poly[N-(3-acryloyl- oxypropyl)pyrrolidone] (PNAPP) and poly[N-(3-methacryloyloxypropyl) pyrrolidone] (PNMPP) were synthesized via visible light activating RAFT polymerization at 25 oC. Kinetic studies indicate a rapid and well-controlled behavior of this polymerization. Gel permeation chromatography (GPC) and 1H NMR analysis confirm their intact molecular structure, well-defined molecular weight and narrow distribution. Light scattering and temperature-variable 1H NMR analyses demonstrate that the cloud point of PNMEP is 1.5 oC lower than that of PNAPP at a degree of polymerization (DP) of 104. Additional backbone methyl groups in PNMPP leads to a dramatic cloud point lowering, e.g. cloud point of PNMPP at DP=100 is 37 oC lower than that of PNAPP at DP=104. This is contrary to what observed in poly(N-isopropylacrylamide) (PNIPA) and its polymethacrylamide analogues. These pyrrolidone based polymers shows a dramatic solvent isotopic effect different from that of PNIPA, e.g. the cloud point of PNMEP (DP=237) is 8.5 oC lower in D2O than in H2O. Increasing chain length or hydrophobicity of monomer units may suppress this solvent isotopic effect. This phase transition is also correlated to Hofmeister series but more sensitive than PNIPA. Small Na₂CO₃ leads to a dramatic cloud point lowering; while NaI significantly improves the cloud point, up to full dissolution in H2O at 95 oC. The solvent isotopic effect in NaCl or Na₂CO₃ solution is the same as in solution absence of salt. Upon heating D2O solution of PNMEP absence of salt, the polymer firstly forms the fully hydrated irregular colloidal aggregates close to cloud point on heating, the phase transition occurs at the fully hydrated state at cloud point, further heating leads to the dehydration and separation of this polymer from D2O. However, in NaCl solution, dehydration occurs subsequently from apolar backbones, spacers, and finally from pyrrolidone groups.