Polymerization of 1-Octene by a Pyridylamidohafnium Catalyst: A SEC, ¹H NMR and Small Angle Neutron Scattering Study

Abstract

We assayed the polymerization of 1-octene in toluene-d 8 polymerized by a pyridylamidohafnium catalyst precursor activated by the cocatalyst tris(pentafluorophenyl)boron. In situ small angle neutron scattering and 1 H NMR spectroscopy were used together with time-resolved SEC to investigate the polymerization process. The catalyst system contains several polymerization active species. About 98% of the active catalyst is of uniform activity. The resulting polymers show relatively narrow molecular weight distributions. The residual catalyst exhibits an increased activity, leading to the formation of notably higher molecular weights than is generated by the majority of available active centers. With the help of NMR and SEC results the small angle neutron scattering data could be interpreted quantitatively. Good agreement was found between the expected scattering profile for nonaggregated chains and their measured counterparts. At no stage during the polymerization process could more than single polymer chains be detected.

Theoretical Elucidation of the Effect of Counteranions on the Olefin Polymerization Activity of (Pyridylamido)Hf(IV) Catalyst by QM and REMD Studies: MeB(C6F5)3– versus B(C6F5)4–

“…This catalyst has recently been utilized in a new polymerization technology, chain shuttling polymerization (CSP), − where ethylene/1-octene multiblock copolymers can be obtained by introducing a chain transfer agent into a solution mixture of two catalyst species with different 1-octene incorporation abilities. Hence, a lot of mechanistic studies − and ligand modifications − of (pyridylamido)­Hf­(IV) catalyst have been conducted so far.…”

Atomistic chemical computation of Olefin polymerization reaction catalyzed by (pyridylamido)hafnium(IV) complex: Application of Red Moon simulation

“…For these reasons, to further develop some new polymerization methodologies, it is fundamentally important to precisely understand their microscopic mechanisms themselves. In fact, polymerization reactions are investigated by using various methods such as nuclear magnetic resonance (NMR) spectroscopy, stopped‐flow technique, dilatometry, and so on . Nevertheless, from the microscopic point of view, it is still limited to clarify the dynamic aspect of catalytic polymerization (CP) reaction, that is, to observe instantaneous and microscopic structure of the polymer assembly at each moment of the polymerization process.…”

Harnessing autocatalytic reactions in polymerization and depolymerization

“…[27] Moving forward, experiments such as small-angle neutron scattering (SANS) and neutron spin echo coupled with new molecular theories could provide for a more complete picture of autoacceleration so that it might be used to improve industrial polymerization processes and material properties. For example, [28,29] SANS (in combination with 1 H-NMR) has been used to study the kinetics of polymerization and detect aggregation in solution. As the scattering from the polymers depends on their concentration in solution, the scattering intensity (I) at a particular wave vector (q) and time (t) during polymerization can be fitted by I (q, t) ∼ φ(t)n agg (t)V w (t)P agg (q, t) , where φ(t) is the time-dependent polymer concentration, n agg (t) is number of aggregates, V w (t) is molecular volume of a growing chain, and P agg (q, t) is the form factor of the aggregate.…”

“…In the absence of detailed molecular models, ad hoc expressions of the form factor have been used to gain insights into the aggregation state during the initiation and propagation stages of polymerization. In this regard, work by Niu et al [28,29] is noteworthy focusing on the polymerization of butadiene and 1-octene. Studies using SANS and neutron spin echo can provide insights into the role of aggregation and resulting heterogeneous dynamics of polymer chains for different percentages of conversion.…”