Comb-Branched Poly( <i>N</i> -isopropylacrylamide) with a Polysaccharide (Amylose) Backbone: Architecture-Controlled Formation of Thermoresponsive Nanoparticles in Aqueous Solutions

Comb-branched poly(<i>N</i>-isopropylacrylamide) (PNIPAm) grafted from polysaccharide (amylose) main chains (Am-<i>g</i>-PN) with molar ratios <i>n</i>_NIPAm/<i>n</i>_AGU ranging from 5 to 21 were successfully prepared from enzymatically synthesized linear amylose with a molar mass of 50 kg mol^-1. All four Am-<i>g</i>-PN samples were completely soluble in water at low temperatures. The dimensional and hydrodynamic properties, as determined by small-angle X-ray scattering (SAXS), static light scattering (SLS), and dynamic light scattering (DLS), were consistent with a comblike branched architecture. The aqueous solutions became turbid with increasing temperature, similar to the behavior observed in linear PNIPAm, while the phase separation temperature increased with a higher molar ratio of glucose units due to the hydrophilic nature of the amylose main chain. Notably, almost no thermal hysteresis was observed during the heating and cooling processes. Following both constant-rate and rapid heating processes at 50 (or 60) °C, SAXS measurements revealed the formation of relatively narrowly dispersed nanoparticles with a mean radius of 50-200 nm, whereas such narrowly dispersed particles were not observed for linear PNIPAm. These findings emphasize the critical role of the comb-branched architecture in regulating thermoresponsive phase behavior and nanoparticle formation while offering new insights into the colloid and interface science of stimuli-responsive polymers.