Static and dynamic light scattering measurements of polyphenylacetylene (PPA) in different organic solvents (tetrahydrofuran, toluene and chloroform)

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.