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Published: Kem. Ind. 52 (10) (2003) 473–481
Paper reference number: KUI-19/2003
Paper type: Conference paper
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Optimization of Alkyl Methacrylate Terpolymerization Proces and Polymer Properties in Solution

A. Jukić, M. Rogošić, K. Sarić and Z. Janović


The optimization procedure of the long chain methacrylic acid esters terpolymerization reactions and proceses by the free radical initiation under homogeneous conditions, as well as the properties of the obtained terpolymers as lubricating oil rheology modifiers, has been described. The examined monomers were: methyl methacrylate (MMA), dodecyl methacrylate (DDMA) and octadecyl methacrylate (ODMA). The relationship between monomer mixture and terpolymer composition was displayed by a graphic method, and lines of unique and binary azeotropic compositions were established (Figs. 1 and 2). Also, the azeotropic ternary point was observed at a molar ratio for MMA/DDMA/ODMA of 0.385/0.590/0.025. However, regarding the similarity in values of copolymerization reactivity ratio of binary monomer pairs, the wide pseudo-azeotropic region having homogeneous terpolymer composition, could be estimated. The polymerization reactions were performed in 2 mol dm-3 base mineral oil solutions, in a 1 dm3 reactor, under controlled temperature of the adiabatic and isothermal procedure, at 95-125 °C and at 100 °C, respectively. By changing the concentrations of Trigonox-S70 (initiator), as well as of n-dodecyl mercaptan (chain transfer agent), the set of terpolymers of different molar mases was obtained. By changing the feed monomer mixture ratio, the terpolymer composition was varied, too. The properties of the additives, such as kinematic viscosity, viscosity index, and shear stability in mineral oil solutions were determined and correlated to their molecular mas (Table 1). A kinetic model of Salaün and coworkers20 was developed to account for the continuous, uniform addition of initiator solution during the polymerization proces. The model was succesfully tested against the experimental data (Fig. 3). Considering the optimization procedure, correlations of the polynomial form (eq. 18) between the structural properties, i.e., number average molar mas, polydispersity index and terpolymer (monomer feed) composition and the application properties of the additives, i.e., shear stability index and viscosity index, was found. The correlations are shown in Figs. 4 and 5, with parameters given in Table 3. We reformulated the so-called polymeric additive performance index of Salaün and coworkers20 to take the form of eq. 21. In an attempt to find the optimum reaction conditions (as given by the minimum of eq. 21, we fixed the feed monomer composition and searched for the best values of number average molar mas and polydispersity index. The minimum was found for the monodisperse terpolymer (Fig. 6). Since the adiabatic copolymerization proces produced, in general, broader molar mas distributions in comparison to the isothermal one, the latter proces was found to be in preference over the former, giving lower values of performance index (better rheological properties of products) under similar experimental conditions.

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alkyl methacrylates, rheology additives, terpolymerization, process optimization, process modelling