Abstract
The self-assembling process during the polymerization of N-Isopropylacrylamide (NIPA) was investigated with time-resolved small angle X-ray scattering (SAXS). During the polymerization process at 35.0 °C which is above the cloud point curve of poly-N-Isopropylacrylamide (PNIPA)/water solution, the phase separation via spinodal decomposition occurs simultaneously. The SAXS profile can be well expressed by the sum of Porod law and Ornstein-Zernike form. The time changes in the parameters yielded by fitting can be divided into four regions: (i) Region I, t<130s: In this region, The polymerization and the macrophase separation via spinodal decomposition progresses simultaneously. The molecular weight of PNIPA increases with time and the concentration difference between two phases increases with time. The domain formation from the concentration fluctuations is dominant. (ii) Region II, 130s<t<350s: Similar to Region I, The polymerization and the spinodal decomposition progresses simultaneously and the molecular weight of PNIPA increases with time and the concentration difference between two phases increases with time. However, the coarsening of the phase-separated structure becomes dominant rather than the domain formation. (iii) Region III, 350s<t<1500s: The polymerization has finished and the polymer rich and poor regions reach each equilibrium value. The coarsening still progresses in the time change in the structures in PNIPA/water systems. (iv) Region IV: 1500s<t: The coarsening of the phase-separated structure is pinned down by the crosslink due to sequential hydrogen bond formation between polymer chains and water molecules.
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Takenaka, M., Iwase, N., Nishitsuji, S. et al. Self-Assembling in Polymerization Processes of N-Isopropylacrylamide. Polym J 39, 1112–1116 (2007). https://doi.org/10.1295/polymj.PJ2007082
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DOI: https://doi.org/10.1295/polymj.PJ2007082