CHARACTERIZATION TECHNIQUES FOR THE STUDY OF SILICA FRAGMENTATION IN THE EARLY STAGES OF ETHYLENE POLYMERIZATION

Cryomicrotomy of embedded particles, sequential removal of polymeric components via carefully controlled plasma ashing, and a combination of these preparative techniques allowed the microscopic characterization of the internal morphology and chemical composition of inorganic supports, supported catalysts, growing and fully grown polymer particles, and extruded films at submicrometer resolution. Videotaped polymerizations under a microscope at commercially used pressures provided additional insights into the particle growth process. The basic morphological units of polymer growth in olefin polymerization-grade silicas such as Davison 952 appear to be the intermediate, microspheroidal aggregates of 0.05-0.1-mu-m diameter. Polymerization initially causes replication of these nodules. The support lattice cracks within the first filling of the pore structure, but the dispersal of the resultant fragments into the submicrometer residues observed in the fully grown polymer particle (15-fold growth) is a more gradual process which is not yet completed after a 5-fold growth of the particle.