The market of synthetic polymers has grown almost exponentially during the last few decades due to their unique properties and versatile applications. This book reviews research on key parameters that affect polymer particle morphology formation during polymerization, specific crystallization during polymerization in constrained condition, the role of the entanglements tie molecules in re-arrangement of the nascent morphology into high performance article and fibers, as well as the structural reminiscence in the products derived from polyethylene reactor powders and the search for a novel routes to high performance fibers.