Preparation and characterization of syndiotactic polypropylene

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Abstract
The preparation and characterization of syndiotactic polypropylene are reported. The influence of polymerization variables on the syndiotactic regulating capacity of the VCl4–AlEt2Cl catalyst were investigated. Vanadates could be substituted for VCl4, and Al(C6H5)2Cl or AlEt2Br for AlEt2Cl under suitable conditions. Hydrogen functioned as a chain transfer agent for the AlEt2Cl–VCl4 catalyst, and polymerizations which were terminated with tritiated alcohols yielded polymers containing bound tritium. The syndio‐regulating capacity of the AlEt2Cl–VCl4 catalyst was increased under specific conditions when cyclohexene, oxygen, or tert‐butyl perbenzoate was incorporated. A polymerization mechanism is proposed. According to this mechanism, preference for a monomer complexing mode which minimizes steric repulsions between methyl groups of the new and last added monomer unit is responsible for syndiotactic propagation. Characterization included determination of infrared syndiotactic indices, melting points (65–131°C.), glass transition temperature, densities (0.859 to 0.885 g./cc.), nuclear magnetic resonance spectra, birefringence, differential thermal analysis spectrograms, solubility, and heat of fusion (∼450 cal./mole).