Intra-molecular interactions dominating the dehydration of a poly(2-isopropyl-2-oxazoline)-based densely grafted
Yuanyuan Zhou1, Hui Tang1, Peiyi Wu1
1The State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science and Laboratory for Advanced Materials, Fudan University, Shanghai 200433, China. huitang@fudan.edu.cn peiyiwu@fudan.edu.cn.
Abstract:
Temperature-induced phase transition together with the liquid-liquid phase separation (LLPS) phenomenon of poly(oligo(2-isopropyl-2-oxazoline)methacrylate) with the comb-shaped architecture (comb-PiPOx) in aqueous solution has been discussed at the molecular level. Differing from linear poly(2-isopropyl-2-oxazoline) (linear-PiPOx), polymer-rich liquid droplets appear at higher temperature compared with the phase transition determined by differential scanning calorimetry (DSC) in comb-PiPOx solution. As investigated using variable-temperature Fourier transform infrared (FTIR) spectra analysis, the densely grafted architecture gives rise to an intra-molecular interaction (hydrophobic interaction of alkyl groups and H-bond of carbonyl groups) dominating the dehydration process of comb-PiPOx. With temperature increment, most of the water within hydrated polymers is expelled to the outer water phase through intra-molecular association, corresponding to the transition temperature. Afterwards, the dehydration of methyl groups on side chain ends reflects the massive aggregation of polymer chains through inter-molecular association, accompanied by hysteretic LLPS.
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