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Polymers: Macromolecules Chapter 21. Larry Emme Chemeketa Community College. The terms polymer and monomer are part of our everyday speech. Poly = many Mono = one
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Polymers: Macromolecules Chapter 21 Larry Emme Chemeketa Community College
The terms polymer and monomer are part of our everyday speech. • Poly = many Mono = one • “Mer” is derived from the Greek meros, meaning “part.” So, a monomer is a “one part” and a polymer is a “many part.” What is a “mer”?
There exist in nature some very large molecules (macromolecules) that contain tens of thousands of atoms. • Starch, glycogen, cellulose, proteins, silk, and DNA • Synthetic macromolecules touch every phase of our lives.
Polyethylene • Polyethylene is an example of a synthetic polymer. • Ethylene, derived from petroleum, is made to react with itself to form polyethylene.
Polymerization • The process of forming very large, high-molar-mass molecules from smaller units is called polymerization. • The large molecule, or unit, is called the polymer. • The small unit is called the monomer. • Ethylene is a monomer; polyethylene is a polymer • Because of their large size, polymers are often called macromolecules or plastics.
Classification of Synthetic Polymers • Rubberlike materials or elastomers • Flexible films • Synthetic textiles and fibers • Resins (or plastics) for casting, molding, and extruding • Coating resins for dip-, spray-, or solvent-dispersed applications • Miscellaneous (e.g. hydraulic fluids, foamed insulation, ion-exchange resins)
Polymer Types • Addition Polymer • Produced by successive addition reactions • Polyethylene is an example of an addition polymer. • Condensation Polymer • Formed when monomers combine and split out water or some other simple substance. • Essentially a substitution reaction • Nylon is a condensation polymer.
Polymer Types • Thermoplastic Polymers • Soften on reheating • Thermosetting Polymer • Set to an infusible solid and do not soften on reheating
Addition Polymerization • Addition polymerization starts with monomers that contain C=C bonds. • When these bonds react, each alkene carbon bonds to another monomer.
Free radicals catalyze or initiate many addition polymerizations. • Organic peroxides (ROOR) are frequently used for this purpose. • The reaction proceeds in three steps: • Free-radical formation • Propagation of polymeric chain • Termination
Recycling • Unfortunately, the C-C bonds of common addition polymers, like polyethylene, are different from those of most natural polymers and cannot be metabolized by many microorganisms. • Recycling seems to be the best solution to the problem of disposing of these long-lived addition polymers.
Recycling 23
Choose as a plastic container those with recycle numbers 1, 2, 4, and/or 5These plastics are considered safest for the storage of food and drink, as they appear not to leach chemicals into contained food and drink at room temperatures.
Avoid using plastic containers in the microwaveAny material has a greater chance of leaching chemicals when heated. The better bets for containers in the microwave are those made of glass and ceramic. • Avoid plastic cling wraps in the microwaveThese plastic wraps have been shown to leach chemicals when heated.
Avoid water bottled in plastic containersNot only is the water sitting in the bottle for possibly a long time, increasing the chance of the leaching of chemicals from the container, but the water in the bottled water industry is much more poorly monitored than a municipal water system. Also, don't re-use the containers for food or drink storage.
Avoid using polyvinyl chloride (PVC) plastics (plastic recycle number 3)"The nonprofits Center for Health, Environment & Justice (CHEJ) and Environmental Health Strategy Center have asked companies to phase out the use of polyvinyl chloride (PVC), a type of plastic widely used in construction and consumer goods, because it poses serious health threats at every stage of its life cycle." PVC is made with phthalates, which can leach into the food or liquid contained, and is shown to have adverse health affects.
Avoid polystyrene as a food or drink container (plastic recycle number 6)These are the foam trays, egg cartons, opaque plastic cutlery, etc. The chemical styrene can leach into food and drink and cause adverse health effects.
Avoid as a food or drink container polycarbonates and other plastic recycle number 7 plasticsThe plastic recycle number 7 includes many different plastics, but is often polycarbonate (a common material from which sports drinking bottles are made), which can leach Bisphenol-A (BPA) into the contained food or drink. Bisphenol-A (BPA) is an endocrine disruptor, and there is considerable evidence of adverse health effects at low doses.
Butadiene Polymers • Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene).
Copolymers • A copolymer contains two different kinds of monomer units.
Vulcanized Rubber • Vulcanization extends the useful temperature range of rubber products and imparts greater abrasion resistance to them. • The vulcanization process is usually accomplished by heating raw rubber with sulfur and any other auxiliary agents.
Geometric Isomerism in Polymers • The recurring double bonds in isoprene and butadiene polymers make it possible to have polymers with specific spatial orientation as a result of cis-trans isomerism.
Geometric Isomerism in Polymers • Natural rubber is cis-polyisoprene with all-cis configuration about the carbon-carbon double bonds. • Gutta-perch, also obtained from plants, is a trans-polyisoprene with an all-trans configuration.
