Structure and Morphology of Nascent Polyethylenes Obtained by TiCl3 Heterogeneous Ziegler-Natta Catalyst

Abstract

Structural and morphological studies of the as-polymerized polyolefins have received considerable attention in the voluminous literature on Ziegler-Natta polymerization, due to scientific and technological reasons (1–3). The first studies concerned the growth of the polymer on the catalyst surface in an attempt to get more information about the very complex polymerization mechanism, by which the olefin is converted into the polymer (4–6). On the other hand, by controlling the crystallization process of the polymer during its formation (simultaneous polymerization and crystallization) the possibility of obtaining extended chain crystals of polyolefins could be considered (7,8). Finally, the studies carried out in the industry are motivated to control the overall morphology of the forming polymer particles inside the reactor, due to the fact that its size, shape and porosity affect the stirrability of the polymer mass, the rate of polymerization and consequently the polymer production (9). In reference to this, the coming third generation of Ziegler-Natta catalysts will be those that, by controlling the overall nascent morphology (average size and distribution, shape, bulk, density, etc.) of the polymer particles, the pelletizing step of the process could be unnecessary using high active catalytic systems (10).