Static and dynamic light scattering measurements of polyphenylacetylene [PPA] in different organic solvents.

Abstract: The molecular conformation and the behaviour of stereoregular polyphenylacetylene (PPA), prepared by catalytic polymerization in the presence of a Rh(I) complex and dissolved in three different organic solvents (tetrahydrofuran (TI-EF), toluene and chloroform), have been studied by means of static and dynamic light scattering measurements. The results have been compared with those obtained from UV-VIS measurements carried out on the same systems. A very complex phenomenology appears. In THF, the polymer molecular weight, M-w, increases with rime, remains approximately constant in toluene and decreases in chloroform. On the contrary, the hydrodynamic radius, R-H, maintains constant at a value of about 270 nm in THF, while in toluene and chloroform a steady-state condition is reached after 500-1000 min, with a value of the hydrodynamic radius of the order of 150-200 nm. These results suggest that each solvent: produces a different effect on the pristine structure of PPA. THF induces the entanglement of the polymer chain and an apparent higher molecular weight, toluene promotes a structural modification, probably a narrow helicoidal red form and chloroform leads to both isomerization and degradation. (C) 2000 Elsevier Science S.A. All rights reserved.