Realistic Representation of Kinetics and Microstructure Development During Chain Shuttling Polymerization of Olefin Block Copolymers

Abstract

Olefin block copolymers (OBCs) are new class of thermoplastic elastomers having low glass transition temperature soft blocks and highly crystalline hard blocks synthesized by reversible chain shuttling between two catalysts with considerably different comonomer responses through a chain transfer agent. Theoretical representation of kinetics and microstructure evolution in chain shuttling polymerization (CSP) is of vital importance especially since the existing characterization tools have severe limitations in retrieving the blocky nature of OBCs. In this work, we correspondingly develop an effective model to represent CSP in practical conditions and compare our predictions to the existing experimental data. We illuminate kinetics and microstructure development in both OBC chains and individual blocks. We specifically clarify the effect of varying the reversibility of transfer reactions through tuning chain shuttling agent and hydrogen concentrations on OBC chains and blocks in terms of their corresponding molecular weight and chemical composition distribution and draw guidelines for achieving OBCs with desired properties.

A Perspective on Modeling and Characterization of Transformations in the Blocky Nature of Olefin Block Copolymers

“…The bimodal distribution vanishes at higher CSA levels and turns into a narrow peak at higher CSA levels. Similar behavior could be obtained in tracing MWD development as a function of CSA level, 23 however the difference is more profound in CCD. The studied simulation runs highlighted the importance of selecting suitable CSA level for production of pure OBC chains and avoiding undesired formation of polymer blends or random 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 13 copolymers, which is a prerequisite for studying the effects of reaction parameters on microstructure and properties of the produced blocky copolymers.…”

Structural analysis of linear/branched ethylene block copolymers

“…The extent of crystallization in the absence of CSA is therefore expected to scale with Cat A fraction. Nonetheless, in CSP, despite the fact that the total fraction of linear and branched segments depend on catalyst composition, the length of crystallizable linear sequences is determined by the frequency of reversible chain transfer . The length of linear segments depends just modestly on catalyst composition, due to homo‐shuttling back to the predominant catalyst .…”

“…CSP has provided a unique route to incorporate two different comonomer distribution sequences in a single polymer chain in a one‐step reaction pathway. Such OBCs are composed of units of predominantly ethylene, as hard crystallizable blocks, and high‐comonomer ethylene/1‐octene sequences, as soft amorphous segments, made by cross‐shuttling of growing chains between two catalysts with different comonomer selectivity in ethylene/1‐octene copolymerization reaction . Besides copolymerization, CSP concept has been also applied for production of linear/branched multi‐block polyethylene employing α‐diimine Ni(II) catalyst for making branched segment through chain walking and ansa ‐ethylenebis(1‐ η 5 ‐Indenyl)zirconium dichloride metallocene catalyst for linear enchainment, in ethylene homopolymerization .…”

Characteristics of linear/branched polyethylene reactor blends synthesized by metallocene/late transitional metal hybrid catalysts

“…The introduction of long-chain branches in the main backbone using dual catalytic system with one catalyst producing the so-called macromer due to high rate of b-hydride elimination and the other being open to incorporate the bulky macromere in the growing chain belongs to this category as well [8,9]. Also, the recent discovery by Dow chemicals on production of olefinic multi-block copolymers (OBC) using a chain shuttling agent, transferring the growing chain between two catalysts with distinguishable difference in comonomer incorporation ability [10][11][12][13][14][15], can also be accounted. However, many of the dual catalytic systems simply benefit from catalysts that produce chains possessing different microstructures independently.…”