TERMINATION KINETICS OF FREE-RADICAL POLYMERIZATION OF STYRENE OVER AN EXTENDED TEMPERATURE AND PRESSURE RANGE

The termination rate coefficient k(t) of the free radical bulk polymer ization of styrene is determined between 30 and 90 degrees C up to a m aximum pressure of 2 800 bar. The majority of polymerization experimen ts has been carried out at monomer conversions up to 20 per cent. In t his range a single value of k(t) is sufficient to describe termination rate at constant pressure and temperature. Toward higher conversion, significant changes in k(t) are observed. The data are measured by a p ulsed laser polymerization technique and partly by conventional chemic ally initiated experiments, both with 2,2'-azoisobutyronitrile (AIBN) as the initiator. Online spectroscopy is applied toward measurement of styrene conversion. The experimental termination rate coefficients up to 20 per cent monomer conversion are adequately represented by the e xpression: ln[k(t)(p, T)/(L . mol(-1) . s(-1))] = 20.785 - 1.050 . 10( -3) p/bar + 5.2 . 10(-8) p(2)/bar(2) - 753/T/K + 0.1060/TK . p/bar Act ivation volume and activation energy of k(t) are very close to the cor responding activation parameters that characterize the pressure and te mperature dependence of the inverse of styrene monomer viscosity. Vary ing laser pulse repetition rate has been used to investigate a potenti al chain-length dependence of k(t) at low conversion. It turns out tha t effects of this kind are not sufficiently pronounced to be safely es tablished in view of the experimental precision of +/-25 per cent that is reached in the k(t) determinations.