engleski

Optimization of alkyl methacrylate terpolymerization process in solution

The optimization procedure of the long chain methacrylic acid esters terpolymerization processes 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. Also, the azeotropic ternary point was observed at a molar ratio for MMA/DDMA/ODMA of 0.385/0.590/0.025. 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 base mineral oil solutions, under controlled temperature of the adiabatic and isothermal procedure, at 95-125 oC and at 100 oC, respectively. By changing the concentrations of peroxide initiator, as well as of chain transfer agent and monomer mixture ratio, the set of terpolymers of different molecular weigths was obtained. 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 mass. A kinetic model of Salaün was developed to account for the continuous, uniform addition of initiator solution during the polymerization process. The model was successfully tested against the experimental data. Considering the optimization procedure, correlations of the polynomial form between the structural properties, i.e., number average molecular weight, polydispersity index and terpolymer (monomer feed) composition and the application properties of the additives, i.e., shear stability index and viscosity index, was found. In an attempt to find the optimum reaction conditions we fixed the feed monomer composition and searched for the best values of number average molecular weight and polydispersity index. The minimum was found for the monodisperse terpolymer. Since the adiabatic copolymerization process produced, in general, broader molecular weight distributions in comparison to the isothermal one, the latter process was found to be in preference over the former, giving lover values of performance index (better rheological properties of products) under similar experimental conditions.

alkyl methacrylate; terpolymerization; process; optimization

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