Kinetic Study on Stereospecific Polymerization of 1,3-Butadiene Using a Nickel Based Catalyst System in Environmentally Friendly Solvent Archana Singh, † Ankur Chavda, ‡ Subrahmanyam Nandula, † Raksh Vir Jasra, and Madhuchhanda Maiti* Reliance Technology Group, Vadodara Manufacturing Division, Reliance Industries Ltd., Vadodara-391346, Gujarat, India * S Supporting Information ABSTRACT: The present work describes the stereospecific polymerization of 1,3-butadiene catalyzed by a nickel naphthenate/ triethylaluminum/boron trifluoride etherate catalytic system in a noncarcinogenic solvent mixture. The detailed study on the effect of various parameters on the polymerization and product characteristics is reported. The catalyst concentration and reaction temperature did not have any significant effect on microstructure. Moreover, the conversion was observed to be the maximum at a 1.07 boron trifluoride/alkylaluminum molar ratio. The effect of catalyst concentration showed that at lower concentrations, a lower number of active sites leads to higher molecular weight (M w ) while the polydispersity index (PDI) exhibited a reverse trend. The polymerization was first order with respect to monomer as well as catalyst concentration. The overall rate constant was found to be 0.032 s -1 mol -1 for this catalyst system. The activation energy of the polymerization was found to be 14.1 kcal mol -1 . 1. INTRODUCTION Polybutadiene rubber (BR) is the second most important synthetic general-purpose rubber produced worldwide. 1 The global consumption of BR is approximately around 2.8 million metric tons per year, and it is forecasted to have an average growth of around 4.0% per year from 2010 to 2015. 2 Polybutadiene rubber is a homopolymer produced by polymer- ization of 1,3-butadiene (BD). The butadiene molecule may enter the polymer chain either by 1,4-addition or 1,2-addition. In 1,4-addition, the unsaturated bond may be either of cis or trans configuration. According to the content of cis-BR, it is commercially available in two main forms: low cis-BR and high cis-BR. The major use of high cis-BR is in tires, with over 70% of the polymer produced going into tire sidewalls and treads. Polymerization of BD to high cis-BR is commercially done by solution polymerization using Ziegler-Natta catalysts. Tita- nium (Ti), 3 cobalt (Co), 4 nickel (Ni), 5 and neodymium (Nd) 6 are the most commonly used metals in the Ziegler-Natta catalyst system for the commercial production of high cis-BR. 7 Among the above-mentioned systems, the cobalt-based catalyst system got the earliest recognition at the commercial level, but the major studies have been done with aromatic solvents like benzene, which is not eco-friendly. The nickel based system overcomes this drawback and offers the advantage of an eco- friendly solvent. Besides, it gives higher conversion than the cobalt-based catalyst system. 7 There are a few reports on the polymerization of 1,3- butadiene using nickel-based catalyst systems. 8-22 Jang et al. investigated the activation of a metal alkyl-free Ni-based catalyst with tris(pentafluorophenyl)borane in the polymerization of 1,3-butadiene. 12 In an excellent review paper of Ricci et al., the authors discussed that the catalyst structure strongly affects the polymerization and stereoselectivity. 13 Endo et al. studied the polymerization of BD with transition metals and methylalumi- noxane (MAO) catalysts and observed the highest catalytic activities with nickel(II) acetylacetonate in combination with MAO. 14 Throckmorton studied the effect of cocatalyst on the preparation of a high cis-BR using a nickel based novel ternary catalyst system. 16 Schroder et al. studied the molar mass distribution of polybutadiene, synthesized with nickel octanoate based Ziegler-Natta catalysts. 17,18 Kwag et al. also studied the catalyst activation process of nickel naphthenate, 1,3-butadiene, boron trifluoride etherate, and triethyl aluminum by using X-ray absorption and crystal field spectroscopy and proposed an optimum model of the nickel active site with density functional theory. 19 However, very little work has been reported about the kinetics of such nickel based Ziegler -Natta catalysts. Yoshimoto et al. studied the kinetics of the nickel based system but in the carcinogenic solvent benzene. 20 Lee and Hsu investigated the kinetics of the nickel stearate-diethyl aluminum chloride-water system; but such systems yield less than 96% cis- content. 21,22 The commercially used nickel based catalyst system consists of nickel naphthenate, boron trifluoride etherate, and triethyl aluminum. However, the detailed kinetics of such a system in noncarcinogenic solvent is not available in the literature. Furthermore, the effect of some polymerization reaction parameters on the polymer properties needs to be reported. Hence, in the present work, we have tried to address these concerns using nickel naphthenate as a catalyst in a noncarcinogenic solvent n-heptane/toluene (50:50) mixture. Additionally, we have studied the effect of the catalyst concentration, boron trifluoride/alkylaluminum ratio, catalyst aging temperature, as well as reaction temperature on the polymerization and product characteristics. Received: January 3, 2012 Revised: May 16, 2012 Accepted: August 9, 2012 Published: August 9, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 11066 dx.doi.org/10.1021/ie300010y | Ind. Eng. Chem. Res. 2012, 51, 11066-11071