Molecular Kinetic Study of “Chain Shuttling” Olefin Copolymerization

Abstract

Statistical olefin block copolymers (OBCs) with "hard" and "soft" linear low-density polyethylene (LLDPE) blocks can be synthesized by tandem catalysis under "coordinative chain transfer polymerization" (CCTP) conditions. This process, disclosed in 2006 and commonly referred to as "chain shuttling copolymerization" (CSCP), is now exploited commercially by Dow Chemical, to produce thermoplastic elastomers with the Infuse trade name. Whereas the general kinetic principles of CSCP as well as the fundamental physical properties of the products are rather well-understood, the details are still poorly defined, to the point that even average block numbers and lengths of commercial Infuse grades are not available in the public domain. In this paper, we report the results of a molecular kinetic investigation in which high throughput experimentation tools and methods were employed to unravel the microstructure and architecture of these materials. The problem was factored in two parts. First, each of the two catalysts in the original Dow Chemical formulation was studied individually in ethene/1-hexene CCTP. Next, the two catalysts together were used in CSCP experiments under otherwise identical reaction conditions. The robust database thus obtained enabled us to disambiguate the interpretation of the results, and sort out system behavior as a function of the relevant variables. Plausibly, the process turned out to be governed by the relative probabilities of "self-shuttling" versus "cross-shuttling" (that is, of exchanging blocks of the same or different type). In particular, the synthesis of OBCs with long hard blocks and an excess of soft blocks, which are those featuring the most desirable application properties, requires a moderate chain shuttling rate and an excess of the catalyst with the higher comonomer incorporation ability; as a result, at practical average molecular weight values, these products are characterized by a pronounced interchain disuniformity, with an abundant fraction of chains undergoing exclusively "self-shuttling" at the aforementioned catalyst, and therefore consisting of just one soft block.

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

“…Therefore, it is possible to grow PO chains with a varying ethylene/αolefin composition either, by the sequential variation of ethylene/α-olefin feed ratio or by employing a dual catalytic system with distinctly different monomer reactivities. Thus, we can successfully produce diblock and multiblock copolymers composed of hard crystalline, and soft rubbery PO blocks [22][23][24][25][26].…”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…In CCTP performed with I, PO chains are generated as a form of (polyolefinyl) 2 Zn with a rather narrow molecular-weight distribution (M w /M n ≈ 1.7) and with negligible formation of PO chains not attached to Zn sites, owing to a feature of I ensuring the rapid alkyl exchange process and the absence of the β-elimination process [16,18]. Due to these characteristics, it is possible to grow PO chains with variation of ethylene/α-olefin composition, either by sequential variation of the ethylene/α-olefin feed ratio or by means of a dual catalytic system with distinctly different monomer reactivity, enabling commercial production of olefin block copolymers composed of hard crystalline and soft rubbery PO blocks [19][20][21][22][23]. A method has also been developed to grow polystyrene (PS) chains further from the CCTP product (polyolefinyl) 2 Zn, thereby allowing for the synthesis of commercially relevant PO-block-PS and PS-block-PO-block-PS via one-pot synthesis [14,[24][25][26][27].…”

Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO2‐Based Block Copolymers from Monomer Mixtures

“…[2] Specifically,s witchable catalysts that display different polymerization activities in response to stimuli provide au nique opportunity to regulate polymer sequence and architecture from mixtures of monomers for fine-tuning of the material properties at the molecular scale. [3] Ty pically,t he polymerization activity of ak nown catalyst is modulated by the incorporation of stimulus-responsive functional group into the ligand as well as by direct alternation of the oxidation state of the metal center. [4] Fore xample, Diaconescu and co-workers pioneered ar edox switch that allowed the one-pot synthesis of polylactide-b-polycaprolactone.…”