The new paradigm for materials discovery envisioned for this project is based on the synergistic application of (i) molecular level simulation, (ii) experimental validation, (iii) materials design and optimization, and (iv) industrial application, to identify essential relationships between molecular structure, morphology and performance. In the program, this paradigm is realized through the discovery and design of additives (nucleating agents, clarifiers, nanofillers, etc.) that alter the semicrystalline morphology of polyolefins, and thereby their properties as well. Molecular simulations are used to conduct broad screenings of additive classes and then validated experimentally in select cases using a new technique to measure heterogeneous nucleation kinetics. Evolutionary strategies and related methods are used to design and optimize candidates within and across additive classes, for subsequent synthesis, development and characterization within the laboratories of the industrial collaborator. This project advances scientific and technical knowledge regarding how the properties and performance of polyolefins can be transformed through rational design of additives that can manipulate crystallization kinetics and semicrystalline morphology. It results in new theoretical and computational methods that not only predict nucleation kinetics, but also provide insight into nucleation mechanisms.