Gelation Originated from Growth of Wormlike "Living Polymer" of Symmetrically Dendronized Large-Ring Crown Ether in Dilute Solutions
作者：tang rp, et al
關鍵字：Crown Ether
論文來源：期刊
具體來源：Macromolecules
發表時間：2009年
The hierarchical pathway from homogeneous solution to gel of a large-ring crown ether
symmetrically substituted with four first-generation Percec-type dendrons (1) in n-dodecane has been followed by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and fluorescence anisotropy methods. The 1/n-dodecane mixture requires a rather low gelation concentration of ～0.1% (w/v) at room temperature. Mainly on the basis of in situ thermal SAXS measurements, we have found that upon
cooling from the homogeneous solutions of 1/n-dodecane the 1 molecule first undergoes a solution selfassembly to form wormlike micelle with the core of crown ether and the shell of alkyl tails, which is “living polymers” containing only one disklike molecule of 1 per cross-sectional repeating unit. The driving force of the assembly can be mainly attributed to the reduction of free energy during microphase separation among the different regions of molecules with distinct chemical properties and the lipophilic-lipophobic interaction in the solvent that is selective for the alkyl tails. Growth of the “living polymer” proceeds continuously with lowering temperature and eventually brings the wormlike chains to entangle and to enter the miscibility gap of 1/n-dodecane. We propose that phase separation of the “living polymer” solution is the main mechanism ofthe gelation, which gives a three-dimensional network of the slow-component of the “living polymer”. The 1/n-dodecane gel is “wet” with the solvent molecules participating in the “polymer”-rich phase. The lyotropic orderings of rectangular and nematic-like packing of the wormlike micelles can be obtained using slow and fast cooling protocol, respectively, which are very different from the hexagonal columnar phase found in the bulk and xerogel samples.Wehave also tested whether the channel formed by dibenzo-30-crown-10 moiety at the cylindrical micelle center of 1 can accommodate guest molecules. Using rhodamine B as an example, we
have demonstrated that 1 can solubilize the cationic dye in n-dodecane at high temperature. After themicellization and gelation, the rhodamine B molecules are successfully introduced into the crown ether cavities.