Amphoteric diblock copolymers (SA ) composed of poly(2-acrylamido-2-methylpropanesulfonic acid sodium salt) (PAMPS) with poly(3-(acrylamido)propyl trimethylammonium chloride) (PAPTAC) blocks were synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Three SA were prepared with a fixed degree of polymerization (DP) for the PAMPS block (= 82) and different DP values for the PAPTAC blocks ( n = 37, 83, and 183). The solubility of SA was studied at different sodium chloride (NaCl) concentrations. SA precipitated in pure water due to attractive electrostatic interactions with interpolymer chains. Conversely, SA and SA dissolved in pure water. In pure water SA dissolved as a unimer state due to electrostatic repulsion of excess anionic charges in the polymer chain. The long anionic PAMPS block segment in SA covered the short cationic PAPTAC block segment within a single polymer chain. In pure water SA dispersed as polyion complex micelles due to electrostatic repulsion of the cationic PAPTAC shells. The oppositely charged PAMPS and PAPTAC blocks in SA formed a core, while the excess PAPTAC block formed shells. SA showed lower critical solution temperature (LCST)-type thermo-responsive behavior at certain NaCl concentrations, and the LCST increased with the NaCl concentration. The mechanism of LCST behavior involves hydrogen bonding interactions between the pendant amide groups and water molecules.

Thermosensitive poly(N-vinylamide) derivatives bearing an oligo ethylene glycol (OEG) chain at the N-position were designed for development of a kinetic hydrate inhibitor (KHI). Novel N-vinylamide monomers bearing an OEG chain at the N-position were synthesized and copolymerized with N-vinylformamide (NVF) or methyl Nvinylacetamide (MNVA) by free radical polymerization. Then, thermosensitive behaviors, such as lower critical solution temperature (LCST), of the synthesized poly(Nvinylamide) derivatives were investigated by light transmittance and DSC measurement. The LCST values were observed over a wide temperature range from 45 to 90 °C due to the ethoxy OEG chain at the N-position. Their phase transition properties were investigated under dilute condition by light scattering measurement. Furthermore, KHI values of the synthesized polymers were evaluated by the THF hydrate crystal growth method. On the basis of these results, it is expected that the polymers of synthesized poly(N-vinylamide) derivatives will gain a prominent position in the oil industry.

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Biocompatible amphiphilic statistical copolymers P(MEA/MPCm) composed of 2-methoxyethyl acrylate (MEA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) were prepared with three different mol% of the hydrophilic unit MPC (m = 6, 12 and 46 mol%). The monomer reactivity ratios of MEA (rMEA) and MPC (rMPC) were 0.53 and 2.21, respectively. The rMEA × rMPC value of 1.17 demonstrated that statistical copolymerization was successful. P(MEA/MPC12) and P(MEA/MPC46) copolymers did not undergo aggregation in water, whereas the P(MEA/MPC6) copolymer formed micelles in water with a hydrodynamic radius (Rh) of 96.9 nm and a critical aggregation concentration, which was determined using pyrene fluorescence, at 0.0082 g/L. The restricted motion of the protons in the hydrophobic MEA units in the micelles’ cores provided additional evidence of self-association in P(MEA/MPC6).

Poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPSNa) was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. An ionic liquid polymer (PAMPSP4448) was then prepared by exchanging the pendant counter cation from sodium (Na+) to tributyl-n-octylphosphonium (P4448+). We studied the ultrasound- and thermo-responsive behaviors of PAMPSP4448 in water. When the aqueous PAMPSP4448 solution was heated from 5 to 50 °C, the solution was always transparent with 100% transmittance. Unimers and interpolymer aggregates coexisted in water in the temperature range 5–50 °C. Generally, hydrogen bonding interactions are broken as the temperature increases due to increased molecular motion. Above 25 °C, the size of the interpolymer aggregates decreased, because hydrophobic interactions inside them were strengthened by dehydration accompanying cleavage of hydrogen bonds between water molecules and the pendant amide or sulfonate groups in PAMPSP4448. Above 25 °C, sonication of the aqueous solution induced an increase in the collision frequency of the aggregates. This promoted hydrophobic interactions between the aggregates to form larger aggregates, and the aqueous solution became turbid. When the temperature was decreased below 8 °C, hydrogen bonds reformed between water molecules and the pendant amide or sulfonate groups, allowing PAMPSP4448 to redissolve in water to form a transparent solution. The solution could be repeatedly controlled between turbidity and transparency by sonication and cooling, respectively.