Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PL-1SUSPENSION POLYMERIZATION REACTIONS AND REACTORSJoris Wieme, Marie-Françoise Reyniers and Guy B. MarinLaboratory for Chemical Technology, Ghent University,Krijgslaan 281 (S5) – B9000 Ghent, Belgium,Tel: +32 (0)9 264 4516, Fax: +32 (0)9 264 4999The suspension polymerization process is a well established method to manufacture anumber of important commodity plastics, including poly(vinyl chloride) (PVC). PVC isworldwide, by volume, the third largest thermoplastic with annual demands close to 30 Mton.Producers of polymers in general and of poly(vinyl chloride) in particular strive for certaincustomer specified properties such as e.g. thermal stability, tensile strength, processability andglass transition temperature. These properties are controlled by fundamental polymerproperties such as the molar mass distribution (MMD) and the content of structural defects(branches and unsaturations). The latter influences to a large extent the thermal stability of thepolymer product as thermal degradation reactions start at thermally labile structural segmentsin the polymer chains. Considering the great industrial importance of the vinyl chloridesuspension polymerization process, it is critical to develop models linking polymer propertiesto the applied polymerization conditions such as polymerization temperature, amount andtype of initiator, batch time, etc.In the present contribution a fundamental kinetic model describing the free radicalpolymerization of vinyl chloride at the elementary reaction level while systematicallyaccounting for diffusion limitations, is presented. In the presented kinetic model all occurringelementary reactions are grouped into four reaction families consisting of forward and reversereaction steps: bond dissociation/radical recombination, radical addition/β-scission, hydrogenabstraction and chlorine shift reactions. By applying this set of elementary reaction families toall species in the reaction mixture, the reaction network is generated. All radical structuresformed during the polymerization process are classified into seven groups according to thestructure of their radical center. The formation of different structural defects in the polymerproduct can be directly linked to the presence of these distinct radical types and by derivingmass balances for these distinct radical species the structural defects content can bedetermined. The method of moments is applied to calculate the moments of the MMD.As one of the reactive phases becomes highly viscous throughout the polymerizationprocess, diffusion limitations play an important role. This is accounted for by calculatingapparent rate coefficients for all elementary reactions. These apparent rate coefficients are6