Stereoregularity of polystyrene and mechanism of polymerization

The Stereoregularity of polystyrenes prepared with radical, anionic, and cationic initiators was determined by means of 13 C‐NMR spectroscopy. Aromatic C 1 carbon spectra measured on o ‐dichlorobenzene solutions consisted of about six peaks and the peak at the highest magnetic field (at 146,3 ppm) was assigned to an rrrr pentad. The proportion of racemic dyads P r , was directly calculated from the proportion of the rrrr pentad peak assuming that the Bernoullian statistics holds for the polymerization of styrene. The P r values of polystyrenes prepared with radical initiators at temperatures from 80° to 0°C were 0,72–0,73, while the cationic polymerizations gave P r values ranging from 0,54 to 0,68. The P r values of the same polystyrenes were also calculated by use of a p ‐xylene/chloroform mixture as solvent for the 13 C‐NMR measurements. For anionically obtained polystyrenes, considerably different P r values were found using both solvent systems. From this, it was considered that the anionic polymerization of styrene with butyllithium as catalyst does not obey the Bernoullian statistics.