Molecular Characterization of Poly (2-methyl-1,3-pentadiene) and Its Hydrogenated Derivative, Atactic Polypropylene

The anionic polymerization of (E)-2-methyl-1,3-pentadiene leads to near-monodisperse poly(1,3-dimethyl-1-butenylene) (PDMB). The hydrogenation of PDMB yields atactic polypropylene (PP). We report the complete characterization of the microstructure and thermal properties of these two polymers. The carbon-13 NMR spectral analysis reveals that PP is a head-to-tail, ideal-Bernoullian (P_m= 0.502) material. The characteristic ratios for the two polymers were determined under θ conditions, and, for the case of PP, good agreement is found with the value calculated by Suter and Flory using the five-state rotational isomeric state (RIS) model. The glass transition temperature for the ideal-Bernoullian PP was found to be -2.5 °C, which is about 10 °C higher than values previously reported for non-Bernoullian atactic PP. The conversion of PDMB to atactic PP results in an increase in flexible bonds from three to four along the backbone and in a 28% increase (0.100-0.128 cal g^-1°C^-1) in the change of heat capacity at T_gbetween the glassy and liquid states of the respective polymers. Comparisons with previous studies on the thermal properties of PP are discussed.