Macromolecules, Vol.31, No.22, 7651-7658, 1998
Two-component gelators and nucleating agents for polypropylene based upon supramolecular assembly
The supramolecular assembly of octyl-, hexadecyl-, and benzyl substituted complementary tectonics based upon barbiturates (BA) and 2,4, 6-triaminopyrimidines (TP) were studied in bulk, in cyclohexane, and in a polypropylene matrix. As evidenced by means of wide-angle X-ray scattering, FTIR spectroscopy; and atomic force microscopy (AFM), BA/TP assembly led to the formation of nanofibrillated superstructures, whereas the individual BA and TP components exhibited layered superstructures. Nanostructure formation resulting from BA/TP assembly in polypropylene melt accounted for nucleation of polypropylene crystallization, especially when using benzyl-substituted BA and TP derivatives instead of the corresponding n-alkyl-substituted derivatives. As a function of the benzyl ring substitution pattern it was possible to vary interlayer spacing and to influence nucleation with optimum nucleation efficiency observed for 1.61 nm spacing in the case of MeBz-BA/Bz-TP. Injection molding in the presence of MeBz-BA/Bz-TP and of Bz-BA/MeBz-TP assemblies revealed increased stiffness, as determined by Young＇s modulus, without sacrificing impact strength when the content of nucleating assembly was increased from 0 to 2 wt %. Transcrystallization of polypropylene onto BA/TP nanostructures was imaged by means of crossed-polarized light microscopy.