Polyolefin

Last updated

A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an 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 contain double bonds (polybutadiene and polyisoprene) and are usually not considered polyolefins. Polyolefins are the foundations of many chemical industries. [1]

Contents

Industrial polyolefins

Most polyolefin are made by treating the monomer with metal-containing catalysts. The reaction is highly exothermic.

Traditionally, Ziegler-Natta catalysts are used. Named after the Nobelists Karl Ziegler and Giulio Natta, these catalysts are prepared by treating titanium chlorides with organoaluminium compounds, such as triethylaluminium. In some cases, the catalyst is insoluble and is used as a slurry. In the case of polyethylene, chromium-containing Phillips catalysts are used often. Kaminsky catalysts are yet another family of catalysts that are amenable to systematic changes to modify the tacticity of the polymer, especially applicable to polypropylene.

Thermoplastic polyolefins
low-density polyethylene (LDPE),
linear low-density polyethylene (LLDPE),
very-low-density polyethylene (VLDPE),
ultra-low-density polyethylene (ULDPE),
medium-density polyethylene (MDPE),
polypropylene (PP),
polymethylpentene (PMP),
polybutene-1 (PB-1);
ethylene-octene copolymers,
stereo-block PP,
olefin block copolymers,
propylene–butane copolymers;
Polyolefin elastomers (POE)
polyisobutylene (PIB),
poly(a-olefin)s,
ethylene propylene rubber (EPR),
ethylene propylene diene monomer (M-class) rubber (EPDM rubber).

Properties

Polyolefin properties range from liquidlike to rigid solids, and are primarily determined by their molecular weight and degree of crystallinity. Polyolefin degrees of crystallinity range from 0% (liquidlike) to 60% or higher (rigid plastics). Crystallinity is primarily governed by the lengths of polymer's crystallizable sequences established during polymerization. [2] Examples include adding a small percentage of comonomer like 1-hexene or 1-octene during the polymerization of ethylene, [3] or occasional irregular insertions ("stereo" or "regio" defects) during the polymerization of isotactic propylene. [4] The polymer's ability to crystallize to high degrees decreases with increasing content of defects.

Low degrees of crystallinity (0–20%) are associated with liquidlike-to-elastomeric properties. Intermediate degrees of crystallinity (20–50%) are associated with ductile thermoplastics, and degrees of crystallity over 50% are associated with rigid and sometimes brittle plastics. [5]

Polyolefin surfaces are not effectively joined together by solvent welding because they have excellent chemical resistance and are unaffected by common solvents. They inherently have very low surface energies and don't wet-out well (the process of being covered and filled with resin). They can be adhesively bonded after surface treatment, and by some superglues (cyanoacrylates) and reactive (meth)acrylate glues. [6] They are extremely inert chemically but exhibit decreased strength at lower and higher temperatures. [7] As a result of this, thermal welding is a common bonding technique.

Practically all polyolefins that are of any practical or commercial importance are poly-alpha-olefin (or poly-α-olefin or polyalphaolefin, sometimes abbreviated as PAO), a polymer made by polymerizing an alpha-olefin. An alpha-olefin (or α-olefin) is an alkene where the carbon-carbon double bond starts at the α-carbon atom, i.e. the double bond is between the #1 and #2 carbons in the molecule. Alpha-olefins such as 1-hexene may be used as co-monomers to give an alkyl branched polymer (see chemical structure below), although 1-decene is most commonly used for lubricant base stocks. [8]

1-hexene, an example of an alpha-olefin 1-Hexene.svg
1-hexene, an example of an alpha-olefin

Many poly-alpha-olefins have flexible alkyl branching groups on every other carbon of their polymer backbone chain. These alkyl groups, which can shape themselves in numerous conformations, make it very difficult for the polymer molecules to align themselves up side-by-side in an orderly way. This results in lower contact surface area between the molecules and decreases the intermolecular interactions between molecules. [9] Therefore, many poly-alpha-olefins do not crystallize or solidify easily and are able to remain oily, viscous liquids even at lower temperatures. [10] Low molecular weight poly-alpha-olefins are useful as synthetic lubricants such as synthetic motor oils for vehicles and can be used over a wide temperature range. [8] [10]

Even polyethylenes copolymerized with a small amount of alpha-olefins (such as 1-hexene, 1-octene, or longer) are more flexible than simple straight-chain high-density polyethylene, which has no branching. [7] The methyl branch groups on a polypropylene polymer are not long enough to make typical commercial polypropylene more flexible than polyethylene.

Uses

Polyolefins are used for blow moulded or rotationally moulded components, e.g. toys, [13] for heat-shrink tubing used to mechanically and electrically protect connections in electronics, [13] and for rash guards or undergarments for wetsuits.[ citation needed ]

Polyolefin sheets or foams are used in a wide variety of packaging applications, sometimes in direct contact with food. [14]

Polyolefin elastomer POE is used as a main ingredient in the molded flexible foam technology such as in the fabrication of self skinned footwear (for example, Crocs shoes), seat cushions, arm rests, spa pillows, etc. Hydrogenated polyalphaolefin (PAO) is used as a radar coolant. Head makes polyolefin tennis racket strings. Polyolefin is also used in pharmaceutical and medical industry for HEPA filter certification—a PAO aerosol is passed through the filters and the air that exits is measured with an aerosol detector. [15]

Elastolefin is a fiber used in fabrics. [16] IKEA's Better Shelter uses structural panels made out of polyolefin foam, stating, "They are tough and durable.". [17] Piping systems for the conveyance of water, chemicals or gases are commonly produced in Polypropylene, and to a much greater extent Polyethylene. Piping systems in high-density Polyethylene (HDPE, PE100, PE80) are fast becoming the most commonly used drinking water, waste water and natural gas distribution piping systems in the world.

Polyalphaolefin, commonly referred to as a synthetic hydrocarbon, is used in various types of air compressors and turbines including reciprocating, centrifugal, and rotary screw compressors where high pressures and temperatures can be an issue. These base fluids are the most widely used variety of synthetic oil blends mainly for their ability to maintain performance in spite of temperature extremes and their similarity to—but improved performance over—mineral oil base fluids. [18]

Polypropylene is commonly used in car bumpers, interior trims, and other components [19] where TiO₂ is added to improve the UV stability of the plastic, ensuring that parts do not degrade or lose color when exposed to sunlight over time. [20] Polyethylene films are widely used in agriculture for greenhouses, mulching, and silage wraps. [21]

Recycling

Despite hype rosier than practice, real recycling of polyolefins has been insufficient in the decades since they became ubiquitous, often not due to technical limitations but because of economic realities. [22] Polyolefin waste can potentially be converted into many different products, including pure polymers, naphtha, clean fuels, or monomers, [23] but only to the extent that money-losing processes are not required, in the reality of the business world. In the 2020s, improved catalysts have been developed that may bring commercial recycling of polyolefins closer to a circular economy of recovery of the monomers, more comparable to the existing situation with PET polyester bottles. [22]

Related Research Articles

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:

<span class="mw-page-title-main">Petrochemical</span> Chemical product derived from petroleum

Petrochemicals are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as maize, palm fruit or sugar cane.

<span class="mw-page-title-main">Polyethylene</span> Most common thermoplastic polymer

Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, cups, jars, etc.). As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.

<span class="mw-page-title-main">Polypropylene</span> Thermoplastic polymer

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.

<span class="mw-page-title-main">Synthetic oil</span> Lubricant consisting of artificially made chemical compounds

Synthetic oil is a lubricant consisting of chemical compounds that are artificially modified or synthesised. Synthetic lubricants can be manufactured using chemically modified petroleum components rather than whole crude oil, but can also be synthesized from other raw materials. The base material, however, is still overwhelmingly crude oil that is distilled and then modified physically and chemically. The actual synthesis process and composition of additives is generally a commercial trade secret and will vary among producers.

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.

<span class="mw-page-title-main">Linear low-density polyethylene</span> Polymer

Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.

In polymer chemistry, vinyl polymers are a group of polymers derived from substituted vinyl monomers. Their backbone is an extended alkane chain [−CH2−CHR−]. In popular usage, "vinyl" refers only to polyvinyl chloride (PVC).

Coordination polymerisation is a form of polymerization that is catalyzed by transition metal salts and complexes.

<span class="mw-page-title-main">Straight-chain terminal alkene</span>

Straight-chain terminal alkenes, also called linear alpha olefins (LAO) or normal alpha olefins (NAO), are alkenes (olefins) having a chemical formula CnH2n, distinguished from other alkenes with a similar molecular formula by being terminal alkenes, in which the double bond occurs at the alpha position, and by having a linear (unbranched) hydrocarbon chain.

<span class="mw-page-title-main">Hot-melt adhesive</span> Glue applied by heating

Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.

Thermoplastic olefin, thermoplastic polyolefin (TPO), or olefinic thermoplastic elastomers refer to polymer/filler blends usually consisting of some fraction of a thermoplastic, an elastomer or rubber, and usually a filler.

<span class="mw-page-title-main">John E. Bercaw</span> American chemist (born 1944)

John E. Bercaw is an American chemist and Centennial Professor of Chemistry, Emeritus at the California Institute of Technology.

Polybutylene (polybutene-1, poly(1-butene), PB-1) is a polyolefin or saturated polymer with the chemical formula (CH2CH(Et))n. Not be confused with polybutene, PB-1 is mainly used in piping.

In polymer chemistry, a comonomer refers to a polymerizable precursor to a copolymer aside from the principal monomer. In some cases, only small amounts of a comonomer are employed, in other cases substantial amounts of comonomers are used. Furthermore, in some cases, the comonomers are statistically incorporated within the polymer chain, whereas in other cases, they aggregate. The distribution of comonomers is referred to as the "blockiness" of a copolymer.

<span class="mw-page-title-main">James C. Stevens</span> American organometallic chemist

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.

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.

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.

References

  1. 1 2 Whiteley, Kenneth S.; Heggs, T. Geoffrey; Koch, Hartmut; Mawer, Ralph L.; Immel, Wolfgang (2000). "Polyolefins". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a21_487. ISBN   978-3-527-30673-2.
  2. ↑ Tashiro, Stein, Hsu, Macromolecules 25 (1992) 1801-1810
  3. ↑ Alizadeh et al., Macromolecules 32 (1999) 6221-6235
  4. ↑ Bond, Eric Bryan; Spruiell, Joseph E.; Lin, J. S. (1 November 1999). "A WAXD/SAXS/DSC study on the melting behavior of Ziegler-Natta and metallocene catalyzed isotactic polypropylene". Journal of Polymer Science Part B: Polymer Physics. 37 (21): 3050–3064. Bibcode:1999JPoSB..37.3050B. doi:10.1002/(SICI)1099-0488(19991101)37:21<3050::AID-POLB14>3.0.CO;2-L.
  5. ↑ A. J. Kinloch, R. J. Young, The Fracture Behaviour of Polymers, Chapman & Hall, 1995. pp. 338-369. ISBN   0 412 54070 3
  6. ↑ "Properties and Applications of Polyolefin Bonding" " Master Bond Inc." Retrieved on June 24, 2013
  7. 1 2 James Lindsay White, David D. Choi (2005). Polyolefins: Processing, Structure Development, And Properties. Munich: Hanser Verlag. ISBN   1569903697.[ page needed ]
  8. 1 2 R. M. Mortier, M. F. Fox and S. T. Orszulik, ed. (2010). Chemistry and Technology of Lubricants (3rd ed.). Netherlands: Springer. ISBN   978-1402086618.[ page needed ]
  9. ↑ "Properties of Alkanes Archived 2013-01-07 at the Wayback Machine ." Retrieved on June 24, 2013
  10. 1 2 L. R. Rudnick and R. L. Shubkin, ed. (1999). Synthetic Lubricants and High-performance Functional Fluids (2nd ed.). New York: Marcel Dekker. ISBN   0-8247-0194-1.[ page needed ]
  11. ↑ "Comparison of PE and PP".
  12. ↑ "Polyalphaolefin (PAO) Lubricants Explained". www.machinerylubrication.com. Retrieved 2022-06-26.
  13. 1 2 Kucklick, Theodore R. (2012). The Medical Device R&D Handbook, Second Edition. CRC Press. p. 19. ISBN   9781439811894.
  14. ↑ Kit L. Yam, ed. (2010). The Wiley Encyclopedia of Packaging Technology. John Wiley & Sons. ISBN   9780470541388 . Retrieved 2016-11-20.
  15. ↑ "HEPA/ULPA Cleanroom Filter Testing". Clean Air Solutions. Retrieved 15 October 2012.
  16. ↑ "Mellior International". Melliand International Worldwide Textile Journal (11th–12th ed.). IBP Business Press Publishers: 4. 2006. ISSN   0947-9163.
  17. ↑ "Product: Better Shelter". BetterShelter.org. Retrieved 29 March 2015.
  18. ↑ "Synthetic PAO Compressor Oils". Petroleum Service Company.
  19. ↑ Chirayil, Cintil; Joy, Jithin (2015). "Polyolefins in Automotive Industry". In AlMa, Al-Ali (ed.). Polyolefin Compounds and Materials. Springer, Chem. doi:10.1007/978-3-319-25982-6_11. ISBN   978-3-319-25980-2.
  20. ↑ Trento, Chin (Dec 27, 2023). "Application of Titanium Dioxide in the Plastic Industry". Stanford Advanced Materials. Retrieved Sep 23, 2024.
  21. ↑ Wang, Yu-Zhong; Yang, Ke-Ke (2004). "Agricultural Application and Environmental Degradation of Photo-Biodegradable Polyethylene Mulching Films". Journal of Polymers and the Environment. 12: 7–10. doi:10.1023/B:JOOE.0000003122.71316.8e.
  22. 1 2 Sanders, Robert (2024-08-29), "New process vaporizes plastic bags and bottles, yielding gases to make new, recycled plastics", UC Berkeley News
  23. ↑ "Millions of tons of plastic waste could be turned into clean fuels, other products: Chemical conversion process could transform polyolefin waste". ScienceDaily. Retrieved 2019-04-18.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.