Exploring the Volume Phase Transition Behavior of POEGA- and PNIPAM-Based Core-Shell Nanogels from Infrared-Spectral Insights

The volume phase transition behavior of well-defined thermally responsive poly(2-methoxyethyl acrylate-copoly(ethylene glycol) methyl ether acrylate)/poly(N,N'-dimethylacrylamide) (P(MEA-co-PEGA)/PDMA) and poly(N-isopropylacrylamide)/poly(N,N'-dimethylacrylamide) (PNIPAM/PDMA) core-shell nanogels, synthesized via reversible addition fragmentation chain transfer (RAFT) mediated aqueous dispersion polymerization, is studied and compared by applying FTIR measurements in combination with two-dimensional correlation spectroscopy (2Dcos). Analysis through spectral insights clearly illustrates that the continuous dehydration of the C=O groups in the P(MEA-co-PEGA)/PDMA nanogel core predominates the linear volume phase transition while the hydrogen bonding transformation in the PNIPAM/PDMA nanogel core leads to the abrupt decrease in nanogel size on heating. Additionally, considering the core and the shell separately, the data shows that, for both nanogels, the inner core contributes much more to the volume phase transition and the outer shell only undergoes slight dehydration following the core on heating.