A simple FTIR spectroscopic method for the determination of the lower critical solution temperature of N‐isopropylacrylamide copolymers and related hydrogels
A simple FTIR spectroscopic method for the determination of the lower critical solution temperature of N‐isopropylacrylamide copolymers and related hydrogels
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DOI：
10.1002/(sici)1099-0488(20000401)38:7
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发表时间：
2000-04
期刊：
影响因子：
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通讯作者：
A. Percot;X. X. Zhu-X.;M. Lafleur
中科院分区：
文献类型：
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作者：
A. Percot;X. X. Zhu-X.;M. Lafleur
基于N-异丙基丙烯酰胺（NIPAAm）的线性和交联聚合物具有不寻常的热性能。聚（N-异丙基丙烯酰胺）（PNIPAAm）的水溶液在加热到高于下临界溶解温度（LCST）时相分离，而相关的水凝胶在LCST下经历溶胀-收缩转变。制备了NIPAAm/丙烯酰氧基琥珀酰亚胺（98/2 mol/mol）线性共聚物和两种不同结晶度的水凝胶。采用傅里叶变换红外（FTIR）光谱来确定转变温度，并通过探测作为温度函数的特征谱带来深入了解转变的分子细节。本文所述的FTIR光谱法允许测定线性和交联聚合物的转变温度。PNIPAAm和由与聚赖氨酸或N，N′-亚甲基双丙烯酰胺（MBA）交联产生的凝胶的转变温度在相同的范围内，30-35 °C。对于凝胶，转变温度随着聚合物基质的亲水性而增加。在LCST处观察到的光谱变化对于游离链和水凝胶是相似的，这意味着在过渡期间类似的分子重组。CH伸缩区表明，N-异丙基基团和主链都经历了构象变化，并变得更加有序加热后高于LCST。酰胺I带的分析表明，线性聚合物的酰胺基团主要参与与低于LCST的水分子的氢键合，该链在水溶液中是柔性的和无序的。在转变过程中，聚合物和水之间约20%的分子间氢键被破坏并被分子内氢键取代。在与MBA交联的凝胶的LCST处也观察到类似的变化。© 2000 John Wiley & Sons，Inc.聚合物科学杂志B：聚合物物理38：907-915，2000年
Linear and crosslinked polymers based on N-isopropylacrylamide (NIPAAm) exhibit unusual thermal properties. Aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAm) phase-separate upon heating above a lower critical solution temperature (LCST), whereas related hydrogels undergo a swelling–shrinking transition at an LCST. A linear copolymer made of NIPAAm/acryloxysuccinimide (98/2 mol/mol) and two hydrogels with different hydrophilicities were prepared. Fourier transform infrared (FTIR) spectroscopy was employed to determine the transition temperature and provide insights into the molecular details of the transition via probing of characteristic bands as a function of temperature. The FTIR spectroscopy method described here allowed the determination of the transition temperature for both the linear and crosslinked polymers. The transition temperatures for PNIPAAm and the gel resulting from the crosslinking with polylysine or N,N′-methylenebisacrylamide (MBA) were in the same range, 30–35 °C. For the gels, the transition temperature increased with the hydrophilicity of the polymer matrix. The spectral changes observed at the LCST were similar for the free chains and the hydrogels, implying a similar molecular reorganization during the transition. The CH stretching region suggests that the N-isopropyl groups and the backbone both underwent conformational changes and became more ordered upon heating above the LCST. An analysis of the amide I band suggests that the amide groups of the linear polymer were mainly involved in hydrogen bonding with water molecules below the LCST, the chain being flexible and disordered in a water solution. During the transition, around 20% of these intermolecular hydrogen bonds between the polymer and water were broken and replaced by intramolecular hydrogen bonds. Similar changes were also observed at the LCST of a gel crosslinked with MBA. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 907–915, 2000