Fibers and Polymers 2003, Vol.4, No.3, 107-113 107 Chemical Modification of Isotactic Polypropylene by Melt Blending Jun Young Kim, Eun Su Seo, Dae Soon Park 1 , Kwang Min Park 2 , Seong Wook Kang 3 , Chang Hyung Lee 4 , and Seong Hun Kim * Department of Fiber & Polymer Engineering, Center for Advanced Functional Polymers, Hanyang University, Seoul 133-791, Korea 1 Performance Material Division, 3M Korea Ltd., 374-5 Pyongjom-Ri, Taean-Eup, Hwasung-Si, Kyonggi-Do 445-974, Korea 2 PVC R&D Center, LG Chem. Ltd. Research Park, P.O. Box 61,Yu Seong, Science Town Daejeon 305-380, Korea 3 Polymer Processing Technology Team, LG Chem. Ltd. Tech Center, 84 Jangdong, Yusung-gu, Daejeon 305-380, Korea 4 Department of Medical Devices & Radiation Health, Korea Food & Drug Administration, 5 Nokbeon-dong, Eunpyung-gu, Seoul 122-704, Korea (Received August 2, 2003; Revised September 2, 2003; Accepted September 9, 2003) Abstract: The branched polypropylene (b-PP) was prepared by melt blending process with initiator, antioxidant, and func- tional monomers to improve the melt strength through the melt grafting. The melt flow index (MFI) of the b-PP was increased with increasing the initiator content. On the introduction of the alkylamine as the branching agents the MFI of the b-PP was increased, while that of the b-PP with the pentaerythritol triacrylate (PT) was decreased. It may be caused by the chain scission of the i-PP backbone due to the reduced thermal stability of the i-PP on the melt blending. The MFI of the b-PP without the antioxidant was increased due to the chain scission occurred during the melt processing, while on the introduction of the antioxidant, the MFI of the b-PP was decreased. The crystallization temperature of the b-PP was higher than that of PP, which was attributed to the branched chain structure. It was found that the PT was the most effective functional monomers for enhancing the melt properties of the b-PP. Keywords: Branching, Gel content, Isotactic polypropylene, Melt strength Introduction At present, polyolefin-based polymers have been the most widely utilized in various industrial fields since the Zigler- Natta discovery in 1955 [1-3]. Among them, the isotactic polypropylene (i -PP) is a semicrystalline polymer with desirable properties such as high mechanical properties, good chemical resistance and abrasion resistance, low dielectric constant, and excellent elasticity, and is one of the most widely used thermoplastic polymers because of its various applications and low cost. However, the i-PP has several drawbacks such as low melt strength and impact strength, poor interfacial adhesion and thermal stability, non-polarity, inherent poor compatibility, and linear chain structure, which have been limited in its application requiring high melt strength such as blow molding and thermoforming [4-6]. The branching can enhance the melt properties of a polymer, and various methods to produce the branched PP (b-PP) have been reported [7-10]. Therefore, the drawbacks of the i-PP may be overcome by the chemical modification through the grafting technique with functional monomers [11-15]. Recently, the modification of the i-PP through the reactive extrusion process has been widely used due to its efficiency and cost effectiveness, and the grafted or branched PP was produced by adding an organic peroxide [16-18]. In this research, the b-PP was prepared by melt blending process with adding the initiator, antioxidant, and functional monomers to improve the melt properties through the chemical modification. The effects of the branching agent and antioxidant on the properties of the b-PP were investigated. Experimental Materials and Preparation The i-PP used for in this research was supplied by Sam Sung General Chemicals Co., and it has a melt flow index (MFI) of 7 g/10 min. The initiator masterbatch (I-MB) of commercial grade Perkadox 14S which contains 10 wt% of bis(t-butyl-peroxy-i-propylbenzene) was used as the initiator. Dodecylamine (DA), hexadecylamine (HA), octadecylamine (OA), trimethylolpropane triacylate (TT), pentaerythritol triacrylate (PT), and thiourea (TU) used as the branching agents in this research were purchased from Aldrich Co. Tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate] methane (TM) and tris(2,4-di-tert-butyl-phenyl)phosphate (TP) used as the antioxidants, were supplied by Sam Sung General Chemicals Co. The i-PP was dried by 60 o C for 2 hr before being used, and the branching agents and antioxidants were used as received without further purification. The i-PP was melt blended with I-MB and the branching agents in a Haake Rheomix 600 internal mixer at 200 o C with the fixed rotor speed of 60 rpm. The melt blending time and the I-MB *Corresponding author: kimsh@hanyang.ac.kr