Temperature-Dependent Phase Behavior of the Thermoresponsive Polymer Poly(N-isopropylmethacrylamide) in an Aqueous Solution
Temperature-Dependent Phase Behavior of the Thermoresponsive Polymer Poly(N-isopropylmethacrylamide) in an Aqueous Solution
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DOI：
10.1021/acs.macromol.0c01256
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发表时间：
2020-08-25
期刊：
影响因子：
5.5
通讯作者：
Papadakis, Christine M.
中科院分区：
文献类型：
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作者：
Ko, Chia-Hsin;Claude, Kora-Lee;Papadakis, Christine M.
聚N-异丙基甲基丙烯酰胺(PNIPMAM)是一种热敏性聚合物，在水溶液中表现出较低的临界溶液温度(LCST)行为。我们用浊度法、差示扫描量热法(DSC)、小角和极小角中子散射(SANS和VSANS)和拉曼光谱研究了PNIPMAM溶液在D2O中随温度变化的相行为，并将PNIPMAM的结果与其类似物聚N-异丙基丙烯酰胺(PNIPAM)的结果进行了比较。我们发现，PNIPMAM链仅在宏观浊点温度T-CP以上2-3℃脱水。即使在单相态，PNIPMAM的链状构象也比PNIPAM致密，存在着松散堆积、大尺度不均匀和物理交联性。这归因于疏水部分之间具有吸引力的分子间相互作用。PNIPMAM的相变范围比PNIPAM宽。当加热到两相状态时，PNIPMAM链断裂并形成中红球。它们比PNIPAM的更大，更有水分。这归因于额外的甲基引起的空间位阻，从而削弱了两相状态下聚合物内部的相互作用。因此，PNIPMAM链主链上的甲基对水合作用和相变附近的结构行为有重要影响。
Poly(N-isopropylmethacrylamide) (PNIPMAM) is a thermoresponsive polymer, exhibiting lower critical solution temperature (LCST) behavior in an aqueous solution. We investigate the temperature-dependent phase behavior of PNIPMAM solutions in D2O using turbidimetry, differential scanning calorimetry (DSC), small-angle and very small angle neutron scattering (SANS and VSANS), and Raman spectroscopy, covering a large concentration range, and compare the results from PNIPMAM with the findings from its analogue poly(N-isopropylacrylamide) (PNIPAM). We find that the PNIPMAM chains only dehydrate 2-3 degrees C above the macroscopic cloud point temperature, T-CP. Even in the one-phase state, loosely packed, large-scale inhomogeneities and physical cross-links are observed, and the chain conformation of PNIPMAM is more compact than the one of PNIPAM. This is attributed to the attractive intermolecular interactions between the hydrophobic moieties. The phase transition of PNIPMAM is broader than the one of PNIPAM. Upon heating to the two-phase state, the PNIPMAM chains collapse and form mesoglobules. These are larger and more hydrated than those for PNIPAM. This is attributed to the steric hindrance caused by the additional methyl groups, which weaken the intrapolymer interactions in the two-phase state. Thus, the methyl groups in the backbone of the PNIPMAM chains have a significant impact on the hydration and the structural behavior around the phase transition.