Métodos para a hidrogenação de ligações olefínicas em polímeros

Castor oil hydrogenation by a catalytic hydrogen transfer system using limonene as hydrogen donor

“…1). It is well documented in palladium chemistry that the carbon-carbon double bond can migrate along the carbon chain (24), and it appears that this happened in our experiments, with the double bond migrating toward the hydroxy group at C12, where dehydrogenation was more likely to proceed (Fig. 1).…”

“…These results suggest that when limonene was added to the catalyst before the castor oil, the active sites of the catalyst became unavailable because they were blocked by the limonene disproportionation reactions, and the double bonds of the castor oil could not reach the sites because of steric hindrance and/or diffusion effects. This was unexpected because recent studies on the hydrogenation of polymeric systems (24,25) have shown that in such systems, CTH proceeds in the same way as classic hydrogenation. Our results suggest the formation of palladium hydride (Pd-H) by hydrogen transfer from the hydrogen donor to the palladium, with the hydride donating hydrogen to the double bond of the castor oil and generating a semihydrogenated intermediate that is converted into the saturated product by transfer of another hydrogen from the hydride.…”

Synthesis of Renewable Poly(limonene): A Kinetic Modeling Study to Improve the Polymerization

“…In radical polymerization it is common to observe a period of inactivityor low activitybetween the moment the reagents are introduced and the moment when the polymerization actually starts. This time is known as the induction period and may be a possible reason for the low conversions obtained for that set of initial conditions [10]. The induction period can be controlled by parameters such as initiator concentration, presence of impurities and catalyst concentration [11].…”