Synthesis, kinetic study and characterization of living anionic polymerized polystyrene in cyclohexane

In this study, living anionic polymerization of styrene with varying molecular weights and narrow polydispersity index was successfully carried out at 45 °C in cyclohexane as a solvent and sec-butyllithium as an initiator. The kinetic study of the living anionic polymerization of styrene was investigated, as well as, the effect of its monomer concentration. For kinetic study, multi-stage dosing of initiator was proposed for calculation of the propagation rate constant and amounts of impurities. The results obtained by gel permeation chromatography (GPC) confirmed that polydispersity index of the synthesized polystyrene was close to the measured value. It has also revealed that the multi-stage dosing of initiator has been an appropriate and accurate method to determine the propagation rate constant. The results also demonstrated that the optimum initial concentration of the monomer in this system was 0.15 mol.L⁻¹. Tacticity and microstructure of the synthesized samples were studied by ¹³C NMR technique. The probability of meso addition was calculated and the corresponding value was 0.395. ¹H NMR spectroscopy was used to obtain the number-average molecular weights of the samples, which were in accordance with the values estimated by GPC method. FTIR spectra showed that by detecting the changes in the areas ratio of two comparable bands at 1940 cm⁻¹ and 1370 cm⁻¹, the molecular weights of the synthesized samples could be estimated. Thermal analysis indicated that very low molecular weight PS liquid resin has negative T_g and broad thermal decomposition range.

Graphical abstract