Effects of Dendron Generation and Salt Concentration on Phase Structures of Dendritic–Linear Block Copolymers with a Semirigid Dendron Containing PEG Tails

• Published in: Macromolecules Vol. 45; no. 15; pp. 6176 - 6184
• Main Authors: Cai, Huanhuan, Jiang, Guoliang, Shen, Zhihao, Fan, Xinghe
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.08.2012
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts; Terpolymer; 1,3-Dipolar cycloaddition; Triazole derivative copolymer; End group; Temperature effect; Polymer solid electrolyte; Composition effect; Ether copolymer; Ethylene oxide polymer; Domain structure; Supramolecular structure; Nitroxyl; Electrical properties; Thermal transition; Ionic conductivity; Ethylene oxide copolymer; Experimental study; Monodispersed polymer; Chemical modification; Free radical polymerization; Morphology; Preparation; Concentration effect; Lithium compound; Block copolymer; Styrene copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma300654j

We prepared a series of dendritic–linear block copolymers (DLBCPs) bearing a semirigid Percec-type dendron with ionophilic poly(ethylene glycol) (PEG) tails and a polystyrene (PS) linear polymer by nitroxide-mediated living radical polymerization (NMRP). As the DLBCPs are connected by an ester linkage, through hydrolysis the molecular weights of the DLBCPs were precisely characterized by gel permeation chromatography and MALDI-TOF MS. Differential scanning calorimetry, small-angle X-ray scattering, and transmission electron microscopy were used to investigate the phase behaviors of the DLBCPs. Results show that the PEG tails of the semirigid dendron display a cold crystallization peak and a melting peak during the second heating process, while for the neat DLBCPs, the crystallization of the PEG tails is completely inhibited, and only the glass transition temperature (T g) of the PS block is observed. However, T g of the dendron block can be observed by complexing the DLBCPs with LiCF3SO3, suggesting that microphase separation occurs in the doped DLBCPs. Comparing the phase behaviors of the DLBCPs having the same dendron weight fraction (w D = 0.14) with varying dendron generation and salt concentration, we found that the G1 or G2 DLBCP undergoes a phase transition from a hexagonally packed cylinder structure to a lamellar structure with increasing content of LiCF3SO3. However, the G3 DLBCP only displays a lamellar phase, and the lamellar thickness increases with increasing salt concentration. The difference can be attributed to the different degree of chain branching, which leads to different interface curvature.