Homogeneous Ziegler‐Natta systems for the ethylene polymerization, deriving from R2R2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ‐alkyl and the π‐cyclo‐pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ‐alkyl derivatives of IVB transition metals, such as Zr(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity. Active species containing ZrOAl bonds have been postulated.

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A theoretical model is developed for the time evolution of volume particle size distributions ( PSDs) of polymer colloids during the nucleation stage. Analytic expressions for the PSD and related cumulants are presented, Negatively skewed distributions are observed only when the formation rate of mature latex particles is a monotonically decreasing function of time. When this model is tested against experimental PSD data of styrene polymerization at 5O"C, agreement between theory and experiment is found only assuming a monotonically decreasing nucleation rate. The fitting is completely missed when the production rate of mature latex particles is predicted according to the coagulative nucleation scheme. Theory and experiment can combine introducing an extended coagulative nucleation model, According to this approach, the nucleation time is much shorter than predicted by earlier theories. As a consequence, most of the mechanistic information convoluted with early-time PSDs is lost.

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Crosslinking mechanisms of acrylic rubber containing both carboxylic and epoxy curing active sites were studied on low molecular weight polymers using different recipes. High cure rates were obtained with quaternary ammonium salts and/or triaryl nucleophiles of Group Va elements. A reaction mechanism based on carboxylate onium salt activity was suggested. Very high reaction rates were obtained with catalysts having low basicity and high steric hindrance, whereas polyamines like o-tolylbiguanidine were less effective. A very simple method for scorch time regulation was devised.