For the first time, bulk material containing high fraction of nascent phase has been processed and analyzed. The obtained materials Lire "auto-composites" composed of nascent and recrystallized polymer. Obtaining such materials has been made possible thanks to high velocity compaction (HVC). Contrary to conventional processes, HVC allows obtaining a chosen fraction of nascent polymer in bulk materials. Polyoxymethylene (POM) and ultra high molecular weight polyethylene (UHMWPE) nascent powders have been processed by HVC. In this study, the semicrystalline nanostructure and the molecular topology (tie molecules and entangled loops) of the materials Lire discussed. A specific attention is paid to the nascent nanostructure of POM and UHMWPE. The modifications occurring within nascent phase during HVC have been addressed and the differences between nascent POM and nascent UHMPWE are emphasized. Finally, the mechanical properties of HVC materials are discussed in relation with material micro and nanostructures.