Zur Taktizität von Poly(α-methylstyrol), 5. Die Abhängigkeit der Taktizität von der Reaktionstemperatur und der Anfangsmonomerkonzentration

The tacticity of poly(α-methylstyrene) was measured by ¹H NMR spectroscopy. The polymerisation initiated in tetrahydrofuran by butyllithium gives a dependence on the initial monomer concentration and a S-shaped plot of log(m/r) vs. 1/T, which is not influenced by a stronger reaction medium like 1,2-dimethoxyethane or hexamethylphosphoric triamid or by addition of LiB(C₆H₅)₄. The activation parameters of the two straight lines A and B limiting the experimental curve are according to the equation The temperature dependence of the propagation rate constant k_w measured dilatometricly between ?11°C and ?75°C gives a linear Arrhenius plot. The rate constant of depolymerisation k_d was calculated using the equilibrium monomer concentration. The activation parameters are The influence of ionic dissociation on the tacticity is discussed. The results lead to the conclusion, that the contact ion pair, the solvent separated ion pair, and the free anion generate tacticities, which are undistinguishable by the applied experimental methods.