Xiong, X., Eckelt, J., Zhang, L., Wolf, B.A.
"Thermodynamics of block copolymer solutions as compared with the corresponding homopolymer solutions Experiment and theory"
Macromolecules in print.
Abstract: The interaction of butadiene-styrene block copolymers of different molecular architecture with tetrahydrofurane (THF) was studied by vapor pressure and light scattering experiments in the temperature range from 25 to 55 °C. The thus obtained Flory-Huggins interaction parameters, c, as a function of j, the volume fraction of the polymers, were compared with that of the corresponding homopolymers in the same solvent. The results are very similar for all block copolymers (diblock, triblock and star-shaped, butadiene in the center) and for all temperatures. In contrast to the c(j) curves of the homopolymers, which are always located above their tangents, the dependencies for the block copolymers exhibit a maximum in the range of moderate polymer concentrations, where the heats of dilution are close to athermal in the range of low j values but become pronouncedly endothermal for high j values. These findings can be well modeled by an approach considering the phenomena of chain connectivity and conformational relaxation of polymers, if one accounts for the unfavorable interactions between the monomeric units of the different blocks.
preprint number: 301