A Comprehensive Review on Controlled Synthesis of Long-Chain-Branched Polyolefins: Part 2, Multiple Catalyst Systems and Prepolymer Modification

Abstract

Long-chain branching plays an important role in the performance of polyolefi ns (POs). The existence of a very small amount of long-chain branches (LCBs), i.e., <1 per 10 000 carbons, can signifi cantly improve processability of the polyolefi n materials, which is highly desired for those intractable polyolefi ns with narrow molecular weight distribution and high degree of crystallinity. Numerous literatures have been published on the controlled synthesis of long-chain-branched POs. In the previous paper, the major literatures of single catalyst systems have been summarized. This paper provides a comprehensive review for the binary and multiple catalyst systems and a brief summary of some other methods for the controlled synthesis of long-chainbranched POs. The controllability of long-chain-branched structures in the various preparation procedures with single or two reactor systems, and in one or two-step processes, is analyzed and compared in-depth. world polymer market. In the recent years, shortage in the fossil fuel resources has powerfully stimulated the technological innovation and improvement of the PO industry, as the monomers such as ethylene and propylene are originally based on nonrenewable crude oil refi ning. A Comprehensive Review on ControlledPOs are widely used in various application areas due to their good physical and mechanical properties, superior processability, good chemical and environmental resistance, good recyclability, and low costs. The good performance of PO materials intrinsically depends on its chain microstructure, [ 1,2 ] which includes three major aspects: molecular weight (MW) and molecular weight distribution (MWD), short-chain branching, and long-chain branching. Therefore, the tailor design of PO materials requires at least good control of these three basic structure elements.(1) Control of MWs and MWDs : POs with a narrow MWD have less solvent-extractable components, i.e., those

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

“…In the previous two papers of this review series, we have summarized the synthesis of longchain branched POs. [6,7] In this paper, we will give a comprehensive review on the characterization of long-chain branched polymers.…”

“…The structural properties of branches include: branch length, branch topology, degree of branching, and M b (average molecular mass between adjacent branching points), with all giving significant effect on the final physical properties of POs. In the previous two papers of this review series, we have summarized the synthesis of long‐chain branched POs . In this paper, we will give a comprehensive review on the characterization of long‐chain branched polymers.…”

Resolving long-chain branch formation in tandem catalytic coordinative chain transfer polymerization of ethylene via thermal analysis

“…Long-chain branches have been traditionally introduced in polyolefins either by utilizing specialized metallocene catalysts, which are capable of forming macromers and incorporating them, or by combining two catalysts, whereupon one generates macromers from ethylene and the other incorporates them along with the monomer [15,16]. The latter approach can be employed in one reactor, as a tandem catalytic system, or in two sequential reactors, as a cascade polymerization, by which macromers are formed in the first reactor through excessive chain transfer to monomer or β-hydride elimination reactions, and are subsequently incorporated along with monomers in the second reactor by a highly comonomer-selective catalyst.…”

“…The latter approach can be employed in one reactor, as a tandem catalytic system, or in two sequential reactors, as a cascade polymerization, by which macromers are formed in the first reactor through excessive chain transfer to monomer or β-hydride elimination reactions, and are subsequently incorporated along with monomers in the second reactor by a highly comonomer-selective catalyst. The low degree of control on the extent and length of long-chain branches in the single catalyst systems hampers the application of the former, while the separation and purification of unreacted macromers and, consequently, the high production cost of the two-catalyst systems suppress the industrial development of the latter [16]. In that sense, the new developments based on the CCTP reaction become more promising [17,18].…”

100th Anniversary of Macromolecular Science Viewpoint: Polymers from Lignocellulosic Biomass. Current Challenges and Future Opportunities

“…LevA and GVL are functionally simpler than the compound classes described earlier and, as a result, are precursors to monomers that are typically derived from petroleum. ,− LevA is generated through the continued acid-catalyzed transformation of furans, especially HMF, − ,− and formation of GVL from LevA requires an additional reductive catalytic step typically accomplished with a supported ruthenium catalyst. ,− Several schemes have been developed that use LevA or GVL as starting materials for the synthesis of drop-in replacements to petrochemical monomers. For example, Bond et al demonstrated that butenes can be generated from GVL in high yields (>90% of theoretical molar yield) through catalytic decarboxylation. , Butenes have drop-in potential in polyolefin process streams. − This GVL-to-butenes decarboxylation route also can be modified to produce adipic acid ,, and ε-caprolactam, ,,, both of which are commercially relevant in the production of polyamides (e.g., nylon-6 and nylon-6,6, respectively). Finally, new materials derived from the LevA/GVL platform have been reported, including high- T g (>200 °C) α-methylene-γ-valerolactone (MGVL)-based polymers and related polyurethanes. , …”