SYNTHESIS, CHARACTERIZATION AND APPLICATION OF A2+B3 AROMATIC-ALIPHATIC HYPERBRANCHED POLYESTER. 1-ABSTRACT: 1-1- INTRODUCTION: Poly(ethylene terephthalate) (PET), as a high-strength and high-modulus thermoplastic polyester, is widely employed in many applications such as synthetic fibers films and beverage, food, other liquid containers and parts in automotives and electronics due to its superior thermal and mechanical properties, low permeability, and chemical resistance.[1, 2] On the other hand hyperbranched polymers (HBPs) have become the focus of interdisciplinary research, and received considerable attention due to their unique highly branched dendritic structure have peculiar and often unique chemical and physical properties such as three-dimensional morphology, a large number of reactive end-groups, very high solubility, low intrinsic, and solution viscosity due to the lack of chain entanglement resulting from their compact molecular structure [3, 4]. The crystallization behavior is an important factor in the processing of semicrystalline thermoplastics, and the speed at which crystallization takes place under particular conditions can determine the quality of the finished product. From these points we think that study on non-isothermal crystallization kinetics of recycled PET is very important. 1-2- KEY WORDS: Synthesis; Hyperbranched Polyester; Non-isothermal crystallization; Nucleating agent; Recycled PET. 1-3- OBJECTIVE: The objective of the research reported in this paper is synthesis and investigation the effect of HBPET on the recycled PET as nucleation agent. 1-4- RESULTS AND DISCUSSIONS: A new types of carboxyl-terminated hyperbranched polyesters (HBPET) with aromatic-aliphatic structure were synthesized by single step-melt polycondensation of adipic acid (as A2 monomer) and phloroglucinol (as B3 monomer) as a core via A2+ B3 approach, at three different monomer mole ratios (A2/B3 =1:1, 1.5:1, 2:1 respectively). FTIR spectroscopy indicated that