New thermoresponsive graft copolymers were synthesized by the cationic ring-opening polymerization of 2-methyl-2-oxazoline (MeOxa) or 2-ethyl-2-oxazoline (EtOxa), initiated by the random copolymers of chloromethylstyrene (CMS) and N-isopropylacrylamide (NIPAAm) using the “grafting from” method with a yield of 66−94%. The polymers were characterized by NMR, GPC, and DSC, and the conformational transition (lower critical solution temperature, LCST) of macroinitiators and graft copolymers was determined by the turbidity and DSC measurements. The transition temperature of the graft copolymers could be fine-tuned through the composition of the macroinitiator and the graft copolymer. An increasing quantity of the hydrophobic comonomer chloromethylstyrene in the macroinitiator lowered its LCST, while in the graft copolymer an increasing content of the hydrophilic segment of poly(2-methyl-2-oxazoline) or poly(2-ethyl-2-oxazoline) raised the transition temperature. For graft copolymers with a high content of long poly(2-alkyl-2-oxazoline) grafts, stabilized aggregates with a thermoresponsive core can be formed at the LCST instead of precipitation of the material.

New non‐ionic hydrogels were synthesized by radical homopolymerization of vinyl end‐functionalized poly(2‐methyl‐2‐oxazoline) bis(macromonomers), or by radical copolymerization of these bis(macromonomers) with N‐vinyl‐2‐pyrrolidone (NVP). The poly(2‐methyl‐2‐oxazoline) bis(macromonomers) were synthesized through “living” cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline (MeOXA), using, simultaneously, the known “initiating” and “end‐capping” method for synthesis of macromonomers. Chloromethyl styrene was used as initiator and N‐(4‐vinylbenzyl)‐piperazine was used as the terminating agent. Well defined poly(2‐methyl‐2‐oxazoline) bis(macromonomers) were obtained with Pn = 4, 11, and 17. The hydrogel structures were characterized by high‐resolution magic angle spinning NMR technique and their solvent absorption capacity was tested by swelling experiments in different solvents. The bis(macromonomers) were characterized by NMR spectroscopy and gel permeation chromatography.Schematic of polymerizationmagnified imageSchematic of polymerization

Amphiphilic graft copolymers with a thermosensitive PNiPAAm backbone and pH-sensitive hydrophilic poly(2-carboxyethyl-2-oxazoline) graft chains are synthesized. In aqueous solution, stable micelle-like aggregates are formed by increasing the temperature in the pH range 4.5-5.5. The micelles are crosslinked by electron-beam irradiation, yielding stable core-shell nanogels of about 100 nm diameter with reversible thermoand pH-dependent swelling behavior. The temperature sensitivity is provided by a conformational change in the PNiPAAm core, whereas the thickness of the poly(2-carboxyethyl-2-oxazoline) corona depends on pH. The reversible bisensitivity of core-crosslinked nanogels is verifi ed by DLS, while AFM measurements demonstrate the predicted core-shell structures of the aggregates. other sensitivities, that is, pH, light, magnetic fi eld, solvent quality, etc., and their effects on the reversible self-assembly in aqueous solutions or on hydrogel organization.Poly( N -isopropylacrylamide) (PNiPAAm) is the most frequently studied thermosensitive polymer and shows a phase transition in aqueous solutions at a physiological interesting temperature range. [ 2 ] The formation of PNiPAAm-based block copolymers with pH-responsive poly(acrylic acid) (PAA) [ 3 ] or poly( N -acryloylpyrrolidine) [ 1 , 4 ] offered new self-assembly possibilities. In dependence on the applied temperature and pH value, the PNiPAAmblock -PAA copolymers change their hydrophobic and hydrophilic balance and form different types of micelles. [ 3 ] Also random PNiPAAm-co -PAA and PAA-graft -PNiPAAm structures were realized by Chen and Hoffman, [ 5 ] and the temperature-induced phase transition over a wide range of pH values could be demonstrated. Topp et al. [ 6 ] reported on the synthesis of block copolymers of types A-B and A-B-A composed of poly(ethylene glycol) (PEG) and PNiPAAm as well as their micellization behavior. The design of these copolymers is based on the hydrophobic character of PNiPAAm above its lower critical solution temperature 4 5 6 7 8 9 1 0 30 35 40 45 50 55 60 R h (nm) pH 59 nm 44 nm 47 nm 34 nm Δ Δ Δ ΔT 25 °C 50 °C 12 % 100 % Degree of dissociation Δ Δ Δ ΔT

Graft copolymers with thermo‐sensitive PNIPAAm backbone and hydrophilic PEtOxa graft chains demonstrated typical amphiphilic behavior. For specific compositions stable micelle‐like aggregates were formed depending on the temperature. Applying long polyoxazoline side chains ($\overline {DP} $ > 120), stable reversible micelle‐like aggregates with hydrodynamic radii of 30–40 nm could be obtained between 33 and 55 °C. These graft copolymers have been successfully crosslinked by electron‐beam irradiation in the micellar state yielding core/shell type nanogels with thermo‐reversible swelling behavior. The temperature dependent volume change of the new thermo‐responsive nanogels due to the phase transition of the PNIPAAm core has been verified by DLS.magnified image