New Perspectives for the Design of Molecular Actuators: Thermally Induced Collapse of Single Macromolecules from Cylindrical Brushes to Spheres

Abstract

Polymethacrylates with densely grafted poly‐N‐isopropylacrylamide side chains change their shape at the lower critical solution temperature from cylindrical brushes (left) to spherical structures (right). This is an interesting example of a temperature‐induced cylinder‐to‐sphere transition observed for single macromolecules.

Solution Behavior of Temperature‐Responsive Molecular Brushes Prepared by ATRP

“…[26] These observations indicate that the unique nature and compact structure of molecular brushes facilitate intramolecular collapse above the LCST when the average distance between molecules is much larger than their hydrodynamic dimensions. Therefore, the brushes undergo a transition from extended cylinders to more compact morphologies with increasing temperature.…”

“…[4] A temperature-induced coil collapse of single molecular brush macromolecules with poly(N-isopropylacrylamide) side chains was also reported. [5] Within the context of the current study, we were primarily interested in how water-soluble molecular brushes respond to changes in solution temperature. Polymers that undergo a transition from hydrophilic to hydrophobic upon heating demonstrate lower critical solution temperature (LCST) behavior.…”

“…Polymer conformation can be influenced by external factors, such as solvent, [3] light, [4] and temperature. [5] Conformational changes of single molecules were observed, and the mechanism and driving forces for the conformational variation can be unique for a specific brush molecule. [6][7][8] Recently, we reported the synthesis of copolymer brushes containing azobenzene…”

Photochemically Initiated Single Polymer Immobilization

“…Studies with physisorbed single polymers are therefore mostly conducted under ambient conditions. By varying the environment parameters such as temperature, [19] humidity, [20] and solvent vapour, [21] the corresponding changes in polymer chain conformation, swelling, segment movement can be directly visualized. The work by Kumaki and co-workers is a fine example where the lateral chain diffusion force, the interfacial interactions, and the AFM tip effect were fine-tuned to capture the molecular movement of single polymer molecules.…”

Well-Defined Thermoresponsive Copolymers with Tunable LCST and UCST in Water

“…For thermoresponsive polymers, approaches take advantage of thermally induced, reversible phase transitions. [9][10][11] Polymers that exhibit lower critical solution temperature (LCST) behavior become less hydrophilic above their LCST because the elongated polymer chains shrink into an insoluble bead. On the contrary, polymers that exhibit upper critical solution temperature (UCST) behavior become more hydrophilic in water with increasing temperature.…”