Influence of Chemical Structure and Solubility of Bisamide Additives on the Nucleation of Isotactic Polypropylene and the Improvement of Its Charge Storage Properties

A comparative study on the influence of chemical structure and solubility of a series of low-molecular-weight 1,4-phenylene−bisamides in isotactic polypropylene (i-PP) was conducted to explore their performance as nucleating agents and electret additives. The series consists of three isomers of dicyclohexyl-substituted 1,4-phenylene−bisamide and three asymmetrically substituted cyclohexyl/n-alkyl-1,4-phenylene−bisamides with different chain lengths. The symmetry of the molecules, the type of substitution and the length of the alkyl chain influence the solubility in the i-PP melt, the nucleation efficiency, the ratio of the α- to β-crystal modification and the charge storage properties. The best β-nucleating efficiency was observed for the symmetrically substituted compounds, whereas the nucleation efficiency was substantially reduced in the presence of n-alkyl-substituents. The charge storage behavior of i-PP was improved only for the three dicyclohexyl-substituted 1,4-phenylene bisamides at concentrations of 100 ppm and even below. For example, a film comprising 10 ppm additive displayed charge retention of 90% after an accelerated aging (annealing for 24 h at 90 °C).