The “comonomer effect” is an intriguing kinetic phenomenon in olefin copolymerization that still remains without a detailed explanation. It typically relates to the rate of enhancement undergone in ethylene and propene catalytic polymerization just by adding small fractions of an alpha-olefin. The difficulty lies in the fact that changes caused by the presence of the comonomer in reaction parameters are so conspicuous that it is really difficult to pin down which of them is the primary cause and which ones are side factors with marginal contribution to the phenomenon. Recent investigations point to the modification of the catalyst active sites as the main driving factor. In this work, the comonomer effect in the metallocene copolymerization of propene and 1-nonene is analysed and correlated to the comonomer role in the termination of the chain-growing process. The associated termination mechanisms involved furnish most of chain-free active sites, in which the selective interaction of the comonomer was proposed to trigger the insertion of monomers. A thorough characterisation of chain-end groups by means of the 1H NMR technique allows for detailing of specific transfer processes, ascribed to comonomer insertions, as well as evidencing the influence of the growing chain’s microstructure over the different termination processes available.

No abstract

The equilibrium solubility data of L-phenylalanine (C 9 H 11 NO 2 ) dissolved in hydrogen peroxide solutions with different concentrations were obtained at 273.15 and 283.15 K by the use of a static method under ambient pressure (p = 101.2 kPa), and the ternary phase diagrams of the C 9 H 11 NO 2 − H 2 O 2 −H 2 O system were constructed according to the determined solubility. At 273.15 and 283.15 K, two neat solid phases were generated in the ternary C 9 H 11 NO 2 −H 2 O 2 −H 2 O system, which corresponded to C 9 H 11 NO 2 and Lphenylalanine perhydrate C 9 H 11 NO 2 •H 2 O 2 •0.5H 2 O. The adduct C 9 H 11 NO 2 • H 2 O 2 •0.5H 2 O was identified by the traditional method of Schreinemaker's wet residue. The solubilities of C 9 H 11 NO 2 and C 9 H 11 NO 2 •H 2 O 2 •0.5H 2 O in water slightly increased with a rise in temperature. The crystalline region of the adduct of C 9 H 11 NO 2 •H 2 O 2 •0.5H 2 O shrunk as the experimentation temperature increased, indicating a little effect of temperature on the yield of C 9 H 11 NO 2Finally, the effect of ethanol and sodium chloride on the phase equilibrium was studied. Adding a certain amount of ethanol and sodium chloride can reduce the solubility of L-phenylalanine.