Physically-networked block copolymer systems

Physically Networked Block Copolymer Systems as Dielectric Elastomers... 700... 

Yanul, R A., Kirsh, Y. E., Verbrugghe, S., Goethals, E. J. and Du Prez, F. E. (2001) Thermoresponsive properties of poly(N-vinylcaprolactam)-poly(ethylene oxide) aqueous systems Solutions and block copolymer networks , Macromolecular Chemistry and Physics, 202,1700-1709. 

Figure 5.27 Experimental phase diagram of AB/ABA block copolymer blends dissolved in a B-selective solvent according to sol-gel and cloud-point measurements. A phase-separated regime is found to exist at low AB and total (AB + ABA) polymer concentrations. At higher AB or total polymer concentrations, the system forms a physical gel network. A further increase in AB content ultimately disrupts the ABA network and induces liquid-like behaviour. (Reprinted with permission from Vega, D. A., Sebastian, J. M., Loo, Y.-L. and Register, R. A. J. Polym. Sci. B Polym. Phys. 39, 2183, 2001. Copyright (2001) Wiley-Interscience.)...

In the presence of a selective solvent, ordered block copolymers form micelles that, at sufficiently high copolymer concentrations, serve to stabilize a diree-dimensional network and promote physical gelation. This study examines the steady and dynamic rheological properties of micellar solutions composed of AB diblock, ABA triblock and bidisperse mfactures of AB and ABA copolymer molecules. Of particular interest is the unexpected improvement in network development upon addition of an AB copolymer to an ABA copolymer at constant solution composition. This behavior is observed for ABA/solvent systems above and below the critical gelation concentration, and is interpreted in terms of the volume exclusion that occurs in bidisperse mixture of grafted chains. 

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