Piloting of anionic polymerization of styrene in tetrahydrofurant

Abstract

Anionic polymerization of styrene in THF with n-butyllithium/alpha-methylstyrene initiator is described as a first step in preparation of a styrenic block copoly-mer. In order to suppress rapid decay of living alpha-methylstyrene unimers, which occurred at room temperature, the initiation reaction was carried out at −20(+5)°C. The kinetic parameters of this decay reaction were determined and used for process optimization. By combining experiments with modelling of styrene propagation reaction all key process parameters were defined for l-L, 38-L, and 189-L reactors. A good match was demonstrated between the model and experimental propagation exotherm for semibatch reaction conditions. Overall, it was demonstrated that technical grade THF and styrene could be used at pilot plant scale to prepare well-defined polymers up to Mn 22 000 via the “living” polymerization mechanism. The resulting polymers had narrow molecular weight distributions (1.06 < Mw/Mn < 1.30). La polymerisation anionique du styrene dans du THF avec l'initiateur n-butyllithium/alpha-methyl-styrene est decrite comme une premiere etape dans la preparation d'un copolymere styrenique bloc. Afin d'enrayer la degradation rapide des unimeres d'alpha-methylstyrene vivants, qui survient a la temperature ambiante, la reaction d'initiation a ete realisee a −20(+5)°C. Les parametres cinetiques de cette reaction de degradation ont ete determines puis utilises a des fins d'optimisation du procede. En combinant des experiences avec la modelisation de la reaction de propagation du styrene, tous les parametres ont ete definis pour des reacteurs de 1 L, de 38 L et de 189 L. On a trouve un bon accord entre le modele et l'exotherme de propagation experimental pour des conditions de reaction semi-continues. De facon generale, il a ete demontre que le THF et un styrene de grade technique pourraient ctre utilises a l'echelle d'usine pilote pour preparer des polymeres bien definis jusqu'a un Mn de 22 000 par l'intermediaire du mecanisme de polymerisation “vivante”. Les polymeres obtenus ont des distributions de poids moleulaire etroites (1.06 < Mw/Mn < 1.30).