Effect of Molecular Structure on Thermoresponsive Behaviors of Pyrrolidone-Based Water-Soluble Polymers

Abstract

This paper describes the molecular structure dependent thermoresponsive behaviors of pyrrolidone-based water-soluble polymers. A series of well-defined poly[N-(2-methacryloyloxyethyl)pyrrolidone] (PNMEP), poly[N-(3-acryloyloxypropyl)pyrrolidone] (PNAPP), and poly[N-(3-methacryloyloxypropyl)pyrrolidone] (PNMPP) were synthesized via visible light activating RAFT polymerization at 25 °C. 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. Laser light scattering and temperature-variable 1H NMR analyses demonstrate that the cloud point of a PNMEP sample at a degree of polymerization (DP) of 96 is 1.5 °C lower than that of PNAPP at a DP = 104. Additional backbone methyl groups in PNMPP lead to a dramatic cloud point lowering, e.g., cloud point of PNMPP at a DP = 100 is 37 °C lower than that of PNAPP at a DP = 104. This is contrary to what was observed in poly(N-isopropylacrylamide) (PNIPA) and its polymethacrylamide analogues. These pyrrolidone-based polymers show a dramatic solvent isotopic effect that is different from that of PNIPA; e.g., the cloud point of PNMEP at a DP = 237 is 8.5 °C lower in D2O than in H2O. Increasing polymer chain length or hydrophobicity may suppress this solvent isotopic effect. This phase transition is correlated to Hofmeister series but more sensitive than PNIPA. Na2CO3 dramatically lowers cloud point, while NaI significantly improves cloud point, up to full dissolution in H2O at 95 °C. The solvent isotopic effect in NaCl or Na2CO3 solution is the same as what observed in solution absent of salt. Upon heating D2O solution of PNMEP, the polymer first forms the hydrated irregular colloidal aggregates near the cloud point, the phase transition occurs at the fully hydrated state at cloud point, and further heating leads to the dehydration and separation from D2O. However, in NaCl solution, the dehydration of PNMEP occurs subsequently from apolar backbones, spacers, and finally pyrrolidone groups.

Thermoresponsive Synergistic Hydrogen Bonding Switched by Several Guest Units in a Water‐Soluble Polymer

“…DLS results demonstrated that the CP values in D 2 O were lower than in H 2 O (Figure S3, Supporting Information), which was similar to what observed in the pyrrolidone‐based homopolymers,12 suggesting that phase transition was induced mainly by hydrophobic association. More importantly, this CP‐lowering tendency strongly depended on the comonomer distribution, following the order of PNMEP 32 ‐ b ‐P(NMEP 34 ‐ stat ‐FPHPMA 5 ) (Δ T = 0.2) < P(NMEP 65 ‐ stat ‐FPHPMA 5 ) (Δ T = 2.9) < PNMEP 57 ‐ b ‐P(NMEP 7 ‐ stat ‐FPHPMA 6 ) (Δ T = 3.9) < PNMEP 63 ‐ b ‐PFPHPMA 7 (Δ T = 5.3).…”

Poly( N -2-(methacryloyloxy)ethyl pyrrolidone)-poly(benzyl methacrylate) diblock copolymer nano-objects via RAFT alcoholic dispersion polymerisation in ethanol

“…solution polymerisation [45][46][47][48]. For example, Deng et al prepared three PNMEP-based diblock copolymers by chain-extending a PNMEP macro-CTA with either glycidyl methacrylate, oligo(ethylene glycol) monomethacrylate or 2-(dimethylamino)ethyl methacrylate in methanol at 30 °C using visible light-mediated RAFT polymerisation.…”

“…Compared to related pyrrolidone-functional monomers such as N-vinyl pyrrolidone, [49][50][51][52][53][54] there are rather few literature reports describing the RAFT polymerisation of NMEP [45][46][47][48]. Thus, a detailed study of the kinetics of the RAFT solution homopolymerisation of PNMEP in ethanol at 70 °C was conducted.…”

Steric hindrance effect on thermo-responsive behaviors of well-defined water-soluble semi-rigid polymers

“…28,[46][47][48] To elucidate the influence of the steric hindrance on molecular weight dependence, the cloud points of P(2-HPPVTA) (0. Figure 4.…”