We report the discovery of a family of organic compounds, substituted 1,3,5-benzenetrisamides, thatsdepending on subtle details of their chemical structuresare capable of selectively and extremely efficiently nucleating the growth of the common R-crystal modification of the major industrial polymer isotactic polypropylene (i-PP), rendering this normally turbid material highly transparent ("clarified") at exceedingly low concentrations (as low as a weight fraction of 0.0002), inducing the mechanically distinct, tough i-PP β-polymorph, or promoting growth of hybrids of both crystallographic modifications with heretofore unknown combinations of the above desirable optical-mechanical properties. In addition, these trisamide-based compounds exhibit excellent thermal stability and do not feature absorption of visible light, adding to a most favorable set of characteristics that provides marked benefits over the presently employed nucleating/clarifying agents.

This paper presents the synthesis and properties of 1,3,5‐benzenetrisamides with a particular focus on structure‐efficiency relationships of nucleation and optical property enhancement of isotactic poly(propylene) (i‐PP). A family of twenty 1,3,5‐benzenetrisamide derivatives was synthesized, in which the direction of the amide linkage between the core and the peripheral substituents, as well as their length (C‐3 to C‐6) and flexibility were systematically varied. Dissolution‐ and recrystallization temperatures of the additives in the polymer melt, the crystallization temperature of i‐PP, and the optical properties clarity and haze were determined in the additive concentration range from 200 to 2 500 ppm. Within the reported series of compounds, few exhibited very good nucleating and clarification abilities, only one with outstanding characteristics, whereas other, very closely related derivatives were found to be incapable to nucleate or clarify i‐PP, although, intriguingly, most are structural isomers. We conclude that it is the particular chemical structure of the additive that determines its crystallization/self‐assembly process, and, therewith, the structure of the heterogeneous nuclei, and at a higher hierarchical level the morphology of the poly(propylene) solid state and its final properties; and, hence, that a predictive understanding is still elusive.magnified image

The crystal structure of 1,3,5-tris(2-fluoro-2-methylpropionylamino)benzene was solved by combining powder X-ray diffraction, solid-state NMR spectroscopy and quantum chemical calculations.