Patent ID: 7883671

Claim:
Process for the (co)polymerization of styrene, carried out by employing a liquid polymerization reaction mixture that includes styrene, in a mechanically stirred reactor in the form of a vessel comprising a side wall having the shape of a cylinder of revolution with a vertical axis (A), a bottom head and a top head that are joined to the side wall, the vessel being provided with a mechanical stirring device comprising (i) a central shaft of vertical axis coincident with the axis (A), connected to a drive system comprising a motor for rotating the central shaft, (ii) at least one stirring member attached to the central shaft and (iii) at least one baffle attached to the vessel, wherein the baffle is away from the side wall of the vessel and takes the form of a cylinder of vertical axis and of cross section chosen from one of the three following shapes: a first shape comprising a rhombus possessing a long diagonal and a short diagonal, which have respective lengths (D) and (d) such that the ratio (D/d) is chosen within a range from 0.1/1 to 0.9/1, the short diagonal being directed along a radial direction with respect to the axis (A) or along a direction making an angle (α) of greater than 0 and less than or equal to 45° to the said radial direction; a second shape comprising a rhombus identical to that of the first shape, except that each of the two acute angles located at the ends of the long diagonal is replaced with an identical or different circular arc, having a centre located on the long diagonal, a radius of length (r) such that the ratio (2r/d) is chosen within a range from 0.1/1 to 0.8/1, and two ends contiguous with the two respective sides of the acute angle; and a third shape comprising a rhombus identical to that of the second shape, except that only the acute angle located at the end of the long diagonal and facing in the opposite direction to the rotation of the central shaft is replaced with the circular arc.