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 polyphenylace tylene (PPA), prepared by catalytic polymerization in the presence of a Rh( I) complex and dissolved in three different organic solvents (tetrahydrofur an (TI-EF), toluene and chloroform), have been studied by means of static a nd dynamic light scattering measurements. The results have been compared wi th 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 de creases in chloroform. On the contrary, the hydrodynamic radius, R-H, maint ains constant at a value of about 270 nm in THF, while in toluene and chlor oform 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 sugges t that each solvent: produces a different effect on the pristine structure of PPA. THF induces the entanglement of the polymer chain and an apparent h igher molecular weight, toluene promotes a structural modification, probabl y a narrow helicoidal red form and chloroform leads to both isomerization a nd degradation. (C) 2000 Elsevier Science S.A. All rights reserved.