Thermoresponsive self-assemblies of cyclic and branched oligosaccharide-block-poly(N-isopropylacrylamide) diblock copolymers into nanoparticles

This paper discusses the thermoresponsive nanoparticles obtained by self-assemblies of nonlinear oligosaccharide-based diblock copolymer systems. These diblock copolymers were synthesized by Cu(I)-catalyzed 1,3-dipolar azide/alkyne cycloaddition ("click" reaction) of propargyl-functionalized β-cyclodextrin (βCyD) and xyloglucooligosaccharide (XGO) with poly(N-isopropylacrylamide) (PNIPAM) having a terminal azido group prepared by atom transfer radical polymerization (ATRP). Elastic and quasi-elastic light scattering analysis of the dibock copolymers in H(2)O indicated that thermodynamic phase transitions of the PNIPAM blocks at their cloud points (T(cp)s ≈ 34 °C), around lower critical solution temperatures (LCSTs), triggered their self-assemblies into the nanoparticles. These nanoparticles had narrow size distributions and small interphases (i.e., sharp boundaries). The mean hydrodynamic radii (R(h)s) of the βCyD and XGO-based nanoparticles were determined to be around 150 and 250 nm upon slow heating (i.e., step-by-step heating), and 364 and 91.5 nm upon fast heating, respectively, depending on a predominance of the interchain association or the intrachain contraction. Transmission electron microscope (TEM) and field emission gun-scanning electron microscopy (FEG-SEM) images of the nanoparticles clearly showed compact spherical nanoparticles whose cores are mainly made with the PNIPAM blocks, whereas the rough shells consist in the oligosaccharidic blocks.