Regression Model of a-Methylstyrene Anionic Solution Polymerization with n-Butyllithium Based Initiator

Regression Model of a-Methylstyrene Anionic Solution Polymerization with n-Butyllithium Based Initiator

Abstract:
By replacing polystyrene hard blocks with poly-á-methylstyrene ones, the service temperature of thermoplastic elastomers can be considerably enhanced, because the glass transition temperature of the latter is about 170°C. The thermodynamics of polymerization of á-methylstyrene is well-known (ÄH and ÄS are -35.1 kJ.mol-1 and -104 J.mol-1 K-1, respectively) so that the “ceiling” (equilibrium) concentration of AMS at various temperatures may be calculated. The living polymer molecules can attain a state of dynamic chemical equilibrium with the monomer molecules. If the temperature is subsequently raised above the ceiling temperature, the Gibbs free energy again favors the monomer. The higher the á-methylstyrene concentration and the lower the polymerization temperature, the higher is the achievable monomer conversion, but never hundred percent. Using n-butyllithium initiator alone, at low reaction temperature, when the maximum achievable theoretical conversion is the highest, the polymerization of á-methylstyrene occurs very slowly in hydrocarbon reaction media. Sasol Germany GmbH developed a high performance living anionic polymerization active center modifier, the purity of which is in agreement with those imposed by the highly sever conditions imposed by these reactions: 2-(2-ethoxyethoxy)-2-methylpropane. The purpose of this paper is to establish a regression model in order to determine the optimal conditions (temperature, reaction time, active center modifier concentration) of á-methylstyrene anionic polymerization in toluene (melting point - 93°C), initiated by n-butyllithium - 2-(2-ethoxyethoxy)-2-methylpropane system, using the factorial design of experiments. Keywords: polystyrene, poly-á-methylstyrene, n-butyllithium

Issue: 2005 Volume 42, Issue 3

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