Department of Chemistry and Biotechnology , Yokohama National University , 79-5 Tokiwadai , Hodogaya-ku, Yokohama 240-8501 , Japan.
Graduate School of Science and Engineering , Yamaguchi University , 1-16-2 Tokiwadai , Ube , Yamaguchi 755-8611 , Japan.
J Phys Chem B. 2018 Oct 11;122(40):9419-9424. doi: 10.1021/acs.jpcb.8b08111. Epub 2018 Sep 27.
We report the time-resolved small-angle neutron scattering (SANS) study of tetra-arm poly(ethylene glycol) (TetraPEG) polymer network formation in a typical ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([Cmim][TFSA]). To observe time-dependent SANS profiles, the reaction rate for the AB-type cross-end coupling reaction of TetraPEG macromers was controlled by adding an analogous protic IL, 1-ethylimidazolium TFSA ([CimH][TFSA]). At polymer concentrations higher than the overlap concentration ( c*), the SANS profile remained unchanged during the gelation reaction, indicating that the network structure was independent of macromer connectivity in a semidiluted solution. On the other hand, at low polymer concentrations, an increase in the SANS profile intensity was clearly observed. The correlation length (ξ), estimated by a fitting analysis based on the Ornstein-Zernike function, increased as the reaction proceeded. This result indicated that the sparsely dispersed macromers formed clusters during the cross-linking process and polymer size growth followed thereafter. We found that the network formation process and homogeneity of the network structure were strongly dependent on the polymer concentration in IL solutions.
我们报告了在典型的离子液体 1-乙基-3-甲基咪唑双（三氟甲磺酰基）酰胺 ([Cmim][TFSA]) 中，四臂聚乙二醇（TetraPEG）聚合物网络形成的时间分辨小角中子散射（SANS）研究。为了观察时间依赖性 SANS 曲线，通过添加类似的质子离子液体 1-乙基咪唑双（三氟甲磺酰基）酰胺 ([CimH][TFSA]) 来控制 TetraPEG 大分子的 AB 型交叉端偶联反应的反应速率。在高于重叠浓度 (c*) 的聚合物浓度下，凝胶化反应过程中 SANS 曲线保持不变，表明在半稀释溶液中，网络结构与大分子连接性无关。另一方面，在低聚合物浓度下，SANS 曲线强度的增加明显。通过基于奥恩斯坦-泽尔尼克函数的拟合分析估计的相关长度 (ξ) 随着反应的进行而增加。这一结果表明，在交联过程中稀疏分散的大分子形成了簇，随后聚合物尺寸增长。我们发现，网络形成过程和网络结构的均一性强烈依赖于离子液体溶液中的聚合物浓度。
