Chain shuttling catalyst systems

High Throughput Method for the Discovery of Chain Shuttling Catalyst Systems. 74... 

While properties of conventional RCPs are controlled by a few simple parameters (e.g., crystallinity and molecular weight), OBCs from CCTP and chain shuttling catalyst systems have opened up new dimensions for polymer designers to control the properties of the neat polymer and formulated products. The balance of properties can now be controlled independently by tailoring the ratio of individual crystallinity of each block and the ratio of hard and soft blocks (which controls the overall composition and crystallinity), the overall molecular weight, and the molecular weight of... 

The molecular weight distribution of a polymer produced with a chain shuttling catalyst/CSA system is highly dependent on reaction conditions. The extent of reversibility with the catalyst/CSA pairs was therefore further explored through a series of polymerizations over a range of monomer conversions (i.e., yield). A representative example from this secondary screening process is described below for precatalyst 17. Several members from this well-studied bis(phenoxyimine)-based catalyst family [39] were identified as poor incorporators in the primary screen. A series of ethylene/octene copolymerizations using 17 was performed across a... 

Experiments were conducted with a dual catalyst chain shuttling system in a continuous solution polymerization reactor. A series of ethylene-octene copolymers of similar melt index were produced with a composition of ca. 30% (by weight) hard and 70% soft blocks. The level of DEZ was systematically varied to study the effects of CSA ratio on polymer microstructure. 

In contrast, a continuous reactor process is controlled at steady state, thereby ensuring a homogeneous copolymer composition. Therefore, a diblock prepared in a series of CSTRs has precise block junctions and homogeneous compositions of each block. In this case, effective CCTP gives a polymer with precisely two blocks per chain, instead of the statistical multiblock architecture afforded by dual catalyst chain shuttling systems. 

The catalytic system used to make OBCs uses a chain-shuttling agent (CSA) to shuttle or transfer growing chains between two distinct catalysts with different comonomer (alpha-olefm) selectivity." This is shown in Figure 9. Synthesis of olefin block polymer via chain shuttling requires the chain transfer to be reversible. OBCs are produced in a continuous solution polymerization process more economically favorable than the batch processes employed to make styrenic block copolymers. 

The demonstration of the viability of chain shuttling between different active species in mixed catalyst systems may offer alternative and possibly easier routes into well-controlled stereobloek polypropylenes and block (co)polymers in general. The fundamentals of this process still need to be better understood, but the fact that existing catalysts with a known behavior ean be employed makes the search for effective chain shuttling agents and conditions potentially of very broad scope and perspective. 

The GPC trace is dramatically different when a CSA is added in the mixed catalyst system in that a simple composite GPC is not obtained (Figure 12). Inclusion of either triethylaluminum (TEA) or DEZ in the mn produces a single peak in the GPC, reflecting low Mn and narrow M /Mn (see Table 2). The octene incorporation data for mns with 8pmol of CSA indicate an intermediate incorporation level between those foimd for polymers made by 2 and 4 individually. These data indicate that both catalysts are aaive and undergoing rapid chain shuttling to produce statistical multiblock OBCs. 

Operating an efficient chain shuttling system in a continuous process also affects the molecular weight distribution of the resulting copolymer. Extremely narrow molecular weight distributions can be achieved with fast chain shuttling between two different catalysts in a batch process. However, the same chemistry in a continuous process ideally results in a Schulz-... 

As stated above, reversible chain transfer between two different catalysts, also known as chain shuttling, is a useful strategy for the catalytic synthesis of BCPs. BCPs can be envisioned from dual-catalyst chain shuttling processes through both homopolymerization and copolymerization systems. In either case, catalysts must be selected that give polymers with chemically... 

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