Thermo-responsive diblock copolymer, poly(N-isopropylacrylamide)-block-poly(N-vinylisobutyramide) was synthesized via switchable reversible addition–fragmentation chain transfer (RAFT) polymerization and its thermal transition behavior was studied. Poly(N-vinylisobutyramide) (PNVIBA), a structural isomer of poly(N-isopropylacrylamide) (PNIPAM) shows a thermo-response character but with a higher lower critical solution temperature (LCST) than PNIPAM. The chain extension of the PNVIBA block from the PNIPAM block proceeded in a controlled manner with a switchable chain transfer reagent, methyl 2-[methyl(4-pyridinyl)carbamothioylthio]propionate. In an aqueous solution, the diblock copolymer shows a thermo-responsive behavior but with a single LCST close to the LCST of PNVIBA, indicating that the interaction between the PNIPAM segment and the PNVIBA segment leads to cooperative aggregation during the self-assembly induced phase separation of the diblock copolymer in solution. Above the LCST of the PNIPAM block, the polymer chains begin to collapse, forming small aggregates, but further aggregation stumbled due to the PNVIBA segment of the diblock copolymer. However, as the temperature approached the LCST of the PNVIBA block, larger aggregates composed of clusters of small aggregates formed, resulting in an opaque solution.

A series of well-defined poly(arylene ether sulfone)s (PESs) as a rod-type block was synthesized by chain-growth condensation polymerization from a diphenyl sulfone-type initiator containing a fluorine leaving group and an allyl moiety. Interestingly, these oligomeric PESs exhibited lower critical solution temperature (LCST)-type phase transition behavior in organic solvents, i.e., 1,2-dimethoxyethane (DME) and chloroform. The clouding point temperature was affected by the molecular weight and concentration of the polymers. The cloud temperature decreased as the molecular weight polymers and the concentration of polymer solution increased. And also two series of rod-coil type poly(arylene ether sulfone)-b-polylactides were synthesized by controlled ring-opening esterification polymerization of dl-lactide with a PES-derived macroinitiator in which the allyl group was transformed into an aliphatic hydroxyl group by a thiol-ene click reaction. These diblock copolymers also exhibited LCST behavior in DME, and the nanoscale size of the aggregates increased upon heating.

Herein, a study on a new lower critical solution temperature (LCST) polymer in an organic solvent by an electrochemical technique has been reported. The phase-transition behavior of poly(arylene ether sulfone) (PAES) was examined on 1,2-dimethoxyethane (DME). At a temperature above the LCST point, polymer molecules aggregated to create polymer droplets. These droplets subsequently collided with an ultramicroelectrode (UME), resulting in a new form of staircase current decrease. The experimental collision frequency and collision signal were analyzed in relation to the concentration of the polymer. In addition, the degree of polymer aggregation associated with temperature change was also observed.