Copolymer microgels from mono- and disubstituted acrylamides: Phase behavior and hydrogen bonds

The influence of microgel morphology and monomer Substitution pattern of different copolymers on their phase transition is demonstrated by temperature-dependent light scattering, Fourier transform infrared spectroscopy, and small-angle neutron scattering. The data clearly illustrate that the ability of the neighbored side chains to form intramolecular hydrogen bonds and the flexibility of the backbone influence the phase transition temperature significantly. Copolymer microgels consisting of N-isopropylacrylamide (NIPAM) and N,N-diethylacrylamide (DEAAM) or N-isopropylmethacrylamide and DEAAM show a nonlinear dependence of the phase transition temperature on composition due to favored hydrogen bonds between DEAAM and the monosubstituted acrylamide. In the case of DEAAM-NIPAM copolymers this leads to a depression of the transition temperature below that of the homopolymers. Different microgel architectures, namely core-shell systems and random copolymer microgels, demonstrate the relevance of the local distribution of the monomer units inside the particle on the location of the phase transition.