Tacticity is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical properties of the polymer. The regularity of the macromolecular structure influences the degree to which it has rigid, crystalline long range order or flexible, amorphous long range disorder. Precise knowledge of tacticity of a polymer also helps understanding at what temperature a polymer melts, how soluble it is in a solvent and its mechanical properties.
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:
Polyethylene or polythene is the most common plastic in use today. It is a polymer, primarily used for packaging. As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene.
In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar. Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups.
A post-metallocene catalyst is a kind of catalyst for the polymerization of olefins, i.e., the industrial production of some of the most common plastics. "Post-metallocene" refers to a class of homogeneous catalysts that are not metallocenes. This area has attracted much attention because the market for polyethylene, polypropylene, and related copolymers is large. There is a corresponding intense market for new processes as indicated by the fact that, in the US alone, 50,000 patents were issued between 1991-2007 on polyethylene and polypropylene.
Amorphous poly alpha olefin is a commodity chemical used in multiple applications.
Free-radical polymerization (FRP) is a method of polymerization, by which a polymer forms by the successive addition of free-radical building blocks. Free radicals can be formed by a number of different mechanisms, usually involving separate initiator molecules. Following its generation, the initiating free radical adds (nonradical) monomer units, thereby growing the polymer chain.
Coordination polymerisation is a form of polymerization that is catalyzed by transition metal salts and complexes.
A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is a alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More specialized polyolefins include polyisobutylene and polymethylpentene. They are all colorless or white oils or solids. Many copolymers are known, such as polybutene, which derives from a mixture of different butene isomers. The name of each polyolefin indicates the olefin from which it is prepared; for example, polyethylene is derived from ethylene, and polymethylpentene is derived from 4-methyl-1-pentene. Polyolefins are not olefins themselves because the double bond of each olefin monomer is opened in order to form the polymer. Monomers having more than one double bond such as butadiene and isoprene yield polymers that are contain double bonds (polybutadiene and polyisoprene) and are usually not considered polyolefins. Polyolefins are the foundations of many chemical industries.
In polymer chemistry, branching is the regular or irregular attachment of side chains to a polymer's backbone chain. It occurs by the replacement of a substituent on a monomer subunit by another covalently-bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type. Branched polymers have more compact and symmetrical molecular conformations, and exhibit intra-heterogeneous dynamical behavior with respect to the unbranched polymers. In crosslinking rubber by vulcanization, short sulfur branches link polyisoprene chains into a multiple-branched thermosetting elastomer. Rubber can also be so completely vulcanized that it becomes a rigid solid, so hard it can be used as the bit in a smoking pipe. Polycarbonate chains can be crosslinked to form the hardest, most impact-resistant thermosetting plastic, used in safety glasses.
Olefin fiber is a synthetic fiber made from a polyolefin, such as polypropylene or polyethylene. It is used in wallpaper, carpeting, ropes, and vehicle interiors.
Polymethylpentene (PMP), also known as poly(4-methyl-1-pentene), is a thermoplastic polyolefin. It is used for gas-permeable packaging, autoclavable medical and laboratory equipment, microwave components, and cookware. It is commonly called TPX, which is a trademark of Mitsui Chemicals.
John E. Bercaw is an American chemist and Centennial Professor of Chemistry, Emeritus at the California Institute of Technology.
The Cossee–Arlman mechanism in polymer chemistry is the main pathway for the formation of C–C bonds in the polymerization of alkenes. The mechanism features an intermediate coordination complex that contains both the growing polymer chain and the monomer (alkene). These ligands combine within the coordination sphere of the metal to form a polymer chain that is elongated by two carbons.
James Carl Stevens, a chemist, was the first Distinguished Fellow, at the Dow Chemical Company, retiring in January 2015. His area of expertise is organometallic chemistry and his primary field of research is in the area of polyolefin catalysis, particularly in the area of polyethylene, polypropylene, ethylene/styrene copolymers, and the combinatorial discovery of organometallic single-site catalysts. Stevens major contributions have come in the discovery and commercial implementation of single-site polyolefin catalysts. He invented and led the commercialization of constrained geometry catalyst for the polymerization of olefins. These have been commercialized by Dow as a number of polymers, elastomers and plostomers.
Living free radical polymerization is a type of living polymerization where the active polymer chain end is a free radical. Several methods exist. IUPAC recommends to use the term "reversible-deactivation radical polymerization" instead of "living free radical polymerization", though the two terms are not synonymous.
In polymer chemistry, chain walking (CW) or chain running or chain migration is a mechanism that operates during some alkene polymerization reactions. CW can be also considered as a specific case of intermolecular chain transfer. This reaction gives rise to branched and hyperbranched/dendritic hydrocarbon polymers. This process is also characterized by accurate control of polymer architecture and topology. The extent of CW, displayed in the number of branches formed and positions of branches on the polymers are controlled by the choice of a catalyst. The potential applications of polymers formed by this reaction are diverse, from drug delivery to phase transfer agents, nanomaterials, and catalysis.
Reversible deactivation radical polymerizations are members of the class of reversible deactivation polymerizations which exhibit much of the character of living polymerizations, but cannot be categorized as such as they are not without chain transfer or chain termination reactions. Several different names have been used in literature, which are:
Functionalized polyolefins are olefin polymers with polar and nonpolar functionalities attached onto the polymer backbone. There has been an increased interest in functionalizing polyolefins due to their increased usage in everyday life. Polyolefins are virtually ubiquitous in everyday life, from consumer food packaging to biomedical applications; therefore, efforts must be made to study catalytic pathways towards the attachment of various functional groups onto polyolefins in order to affect the material's physical properties.
