Modeling of Isoprene Solution Coordinative Chain Transfer Polymerization

Abstract

The present manuscript investigates the solution coordinative chain transfer polymerization (CCTP) of isoprene initiated by the ternary Ziegler‐Natta catalyst system composed by neodymium versatate (NdV3), diisobutylaluminum (DIBAH), and dimethyldichlorosilane. A kinetic mechanism is proposed and the kinetic parameters are estimated to allow the appropriate description of dynamic trajectories of average molecular weights and isoprene conversions obtained in solution CCTP polymerizations for the first time. A data reconciliation strategy is applied to evaluate the amount of DIBAH used as a chain transfer agent, as this very active compound can be consumed by undesired side reactions. Additionally, the impacts of key operation variables on the control of the average molecular weights and monomer conversion are evaluated to elucidate the living nature of the polymerization. As observed experimentally, the temperature effect on the course of the polymerization is not so pronounced as the effect of NdV3, isoprene, and DIBAH initial concentrations. The kinetic mechanism is described better and kinetic constants are estimated more precisely when the dynamic trajectories of average molecular weights are fitted during the whole batch. In this case, the proposed model is able to predict well the experimental trajectories of average molecular weights of the produced polymer and monomer conversion.

Terpene Coordinative Chain Transfer Polymerization: Understanding the Process through Kinetic Modeling

“…4 and 5 are 2.8 × 10 −3 and 3.5 × 10 −3 mol L −1 , respectively. The percent of the [AlR x ] 0 regarding the initial concentration of DIBAH are 5.08, 16.09 and 11.95%, which are in the same interval reported by Cavalcante de Sá et al (from 10 to 40%) for the isoprene CCTP experiments using another initial reagent concentrations ([RHCl 2 ] 0 /[Nd] 0 = 0.5) and temperatures [16]. As mentioned previously, the termination steps, the operating conditions and the reagent ratios considered in this work do not allow a strict comparison with that work, but we could highlight the low effective concentration of DIBAH involved in the CCTP for both systems.…”

“…It is well known that the DIBAH has a dual function during the polymerization, acting as a chain transfer agent for the control of the average molecular weights and narrow distributions, and also acting as a scavenger of impurity moiety, e.g., the moisture and carboxylic acids [36]. That means that the effective concentration of DIBAH involved in the formation of dormant chains (P n Al II , in Figure 1) is somewhat uncertain and it can depend on the unavoidable presence of impurities in the reaction medium and on the particularly employed reaction conditions [16].…”

“…To estimate the effective concentration of DIBAH which takes place in the chain transfer step, Cavalcante de Sá et al [16] used a reconciled amount of DIBAH; we understand by a reconciled amount, an equivalent proportion related with Np. This procedure was feasible because no deactivation reaction was considered in the reaction mechanism.…”

“…where R = 8.314 J mol −1 K −1 and absolute temperature (T) is given in Kelvin (K). Cavalcante de Sá et al [16] estimated the kinetic rate constants for the solution CCTP of isoprene, initiated by Ziegler-Natta catalyst (using Nd compound, DIBAH and R H Cl 2 ) for isothermal polymerization at 60 and 70 • C in a ratio [Mon] 0 /[Nd] 0 = 20 and [R H Cl 2 ] 0 /[Nd] 0 = 0.5. A model for a single-site system was developed and the value of the pre-exponential factor and the activation energy were A 0 (k p ) = 4.54 × 10 2 L mol −1 s −1 and E a (k p ) = 2.14 × 10 4 J mol −1 for the k p , and A 0 (k trc ) = 7.65 × 10 6 L mol −1 s −1 and E a (k trc ) = 4.84 × 10 4 J mol −1 for the k trc .…”

“…Deterministic approaches have also been developed to study the CCTP processes. Most of the deterministic models developed to describe this process are based on the Method of Moments [15][16][17], since it is a great and versatile tool widely used by the polymerization reaction engineering community to develop an improved fundamental understanding of complex mechanistic schemes and new polymerizations. The isoprene polymerization under CCTP conditions with the ternary Ziegler-Natta catalyst system composed of neodymium versatate (NdV 3 ), diisobutylaluminum hydrade (DIBAH) and dimethyldichlorosilane (Me 2 SiCl 2 ) was simulated, the kinetic rate parameters were estimated, and the evolution and the conversion and average molecular weights fitted in good way to the experimental data [16].…”