Investigation of poly(α-methyl styrene) tacticity synthesized by photo-polymerization

Abstract

In this work, poly(α-methyl styrene) (PAS) was synthesized by free radical photo-polymerization. The tacticity and microstructure of PAS were studied by 13C nuclear magnetic resonance spectroscopy (13C NMR). Assignments of all stereo sequences were carried out at pentad and hexad levels of quaternary aliphatic, quaternary aromatic, and methylene carbons using 13C NMR in deuterated chloroform at 20 °C and 50 °C, respectively. It was found that by increasing the NMR acquisition temperature, higher resolution and higher splitting of the peaks were achieved for all mentioned carbons. Bernoullian and first-order Markov statistics were used for all carbons and the results were compared with experimental data by statistical method. It was shown that Bernoullian statics model fit slightly better than first-order Markov statics model for the assigned sequences. The results indicated that corresponding values of probability (Pm) was equal to 0.234, suggesting that the racemic addition was almost higher than the meso-one. The effect of the deuterated solvent on the peak resolution and the splitting of syndiotactic and isotactic sequences was investigated by replacing deuterated tetrahydrofuran with deuterated chloroform. It was observed that the peak resolution and the splitting in deuterated chloroform are much more than deuterated tetrahydrofuran.