(819f) Dynamics of Rod-Coil Block Copolymer Melts

Authors: 
Wang, M., Massachusetts Institute of Technology
Olsen, B. D., Massachusetts Institute of Technology
Timachova, K., Massachusetts Institute of Technology



Rod-coil block copolymers have attracted extensive interest as functional materials for organic electronics and biomaterials. While equilibrium nanostructures and thermodynamics continues to be widely investigated, technological applications necessitate a knowledge of the underlying molecular mechanisms of motion. A fundamental theory for the dynamics of rod-coil block copolymers is important for understanding diffusion, mechanics, and self-assembly kinetics. Recently our group has proposed a reptation theory for the dynamics of entangled rod-coil block copolymers. Our previous simulations and experiments have shown that the tracer diffusion of rod-coil block copolymers is slower than rod or coil homopolymers. This effect arises because of the mismatch between the curvature of the entanglement tubes of the rod and coil blocks. 

In this study we extend our mechanisms for tracer diffusion to the disordered isotropic melt state. Experimental diffusion measurements are performed on a model weakly segregated rod-coil block copolymer. The model rod blocks are composed of poly(alkoxyphenylene vinylene) synthesized by a Siegrist polycondensation, and the coil blocks are composed of polyisoprene synthesized by living anionic polymerization. The disordered isotropic state is verified by small angle X-ray scattering and birefringence measurements. Diffusion is measured by forced Rayleigh scattering, using a newly developed photochromic dithienylethene dye that is sensitive to red laser wavelengths outside the visible absorption window of the poly(alkoxyphenylene vinylene) blocks. An additional vinyl functionality was added to the dye for convenient incorporation during anionic polymerization, resulting in highly monodisperse samples. The diffusion results in the isotropic melt are compared to the previously developed reptation theories and experimental results for tracer diffusion.