In the physics of polymer/clay nanocomposites, the first part of the book is related to the crystallization kinetics and structure of Poly (trimethylene terephthalate)/monolayer nanomica system while the second part is rendered to the structure-property relationships of Poly (trimethylene 2, 6-naphthalate)/layered clay nanocomposites under uniaxial drawing and cold crystallization conditions. This book includes, i) The segregation phenomena of nanomica owing to the crystallization behavior of PTT ii) The analysis of Avrami equation and secondary nucleation theory for PTT/MNM nanocomposite system iii) The formation of the house of cards type structure of layered clay in the PTN matrix iv) The alteration of glass transition behavior before and after drawing v) The analysis of CRR theory for the PTN/layered clay nanocomposite system. vi) The analysis of Time Temperature superposition and WLF equation for PTN/layered clay nanocomposites