Conformation transition and molecular mobility of isolated poly(ethylene oxide) chains confined in urea nanochannels
Conformation transition and molecular mobility of isolated poly(ethylene oxide) chains confined in urea nanochannels
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DOI：
10.1016/j.polymer.2007.10.033
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发表时间：
2007-11
期刊：
影响因子：
4.6
通讯作者：
Haimu Ye;Min Peng;Jun Xu;Baohua Guo;Qun Chen;Tianliang Yun;Hui Ma
中科院分区：
文献类型：
--
作者：
Haimu Ye;Min Peng;Jun Xu;Baohua Guo;Qun Chen;Tianliang Yun;Hui Ma
由主体小分子和客体聚合物形成的包合物为研究限制在纳米通道中的孤立高分子链的行为提供了一个新的平台。用不同的分析方法研究了聚氧乙烯(PEO)-尿素包合物(IC)及其转变过程中的PEO链构象。根据FTIR和拉曼光谱的结果，初步确定亚稳态四方IC中的PEO链为TGG‘构象。用原位FTIR和非原位WAXD观察了亚稳的四方IC向稳定的三角晶型转变。这种转变是一个动力学的固-固过程，甚至可以在室温下发生。活化能约为222kJ/mol，表明该转变是通过几个氢键的协同断裂而发生的。实验室框架自旋-晶格弛豫时间T1(13C)的测量表明，纳米受限PEO链的分子运动比纯晶型PEO强，但弱于整形非晶态PEO。二次谐波显微镜显示，三方IC比四方IC表现出更强的非线性光学活性。分子间氢键的形成归因于介稳的四方晶胞向稳定的三角晶胞转变的驱动力。
Inclusion compounds formed from host small molecules and guest polymers have provided a novel platform to study the behavior of isolated polymer chains confined in nanochannels. In this article, the PEO chain conformation in the metastable poly(ethylene oxide) (PEO)–urea inclusion compound (IC) and its transition was characterized via a combination of different analytical methods. Based on the FTIR and Raman spectroscopy results, PEO chains in the metastable tetragonal IC are tentatively assigned to the tgg′ conformation. The structural changes of the metastable tetragonal IC to the stable trigonal form were observed via in situ FTIR and ex situ WAXD. The transformation is a kinetic solid–solid process and can even occur at room temperature. The activation energy of about 222kJ/mol indicates that the transition occurred via cooperative disruption of several hydrogen bonds. Measurement of the laboratory frame spin-lattice relaxation time T1(13C) shows that molecular motions of the nanoconfined PEO chains are more intensive than the neat crystalline PEO but weaker than those of the neat amorphous PEO. Second harmonic generation microscopy demonstrates that the trigonal IC exhibits stronger nonlinear optical activity than the tetragonal IC. The intermolecular hydrogen bonding is attributed to the driving force for the transformation of the metastable tetragonal IC into the stable trigonal form.