VISCOMETRIC INVESTIGATION OF THE AGGREGATION AND TRANSFER-REACTIONS OF POLYSTYRYLLITHIUM IN ETHYLBENZENE AT ELEVATED-TEMPERATURES

A high-vacuum falling-ball viscometric method has been used to measure the equilibrium constant for the aggregation of free polystyrylanions in ethylbenzene, The rate of the transfer reaction between polystyryl lithium and ethylbenzene has also been measured. All measurements have been made in the absence of monomer under conditions relevant to larg e-scale polymerization processes, i.e. with solutions containing a hig h weight fraction of polyanions (approximately 15-70% w/w) and at temp eratures in the region of 70 degrees C. The equilibrium constant (K-d) for the aggregation of polystyrylanions was found to be in the range 2 x 10(-3) mol1(-1) to 3 x 10(-2) for polystyrylanions of Mn 30 to 161 kgmol(-1) at 70 degrees C. The chain-transfer constant (k(tr)) determ ined at 70 degrees C over a range of polymer molecular weights and con centrations is (2.21 +/- 0.05) x 10(-5) 1mol(-1) s(-1). A number of as sumptions have been made in order to arrive at the constants which are reported, including, (i) some concerning the viscosity behaviour of c oncentrated polymer solutions, (ii) that the polymers studied are esse ntially monodisperse, (iii) that polystyrylanions are two-fold associa ted in ethylbenzene, and (iv) that only the free polystyrylanions enga ge in the transfer reaction. (C) 1997 Elsevier Science Ltd.