Presentation on theme: "1. 2 What is a “mer”? –The terms polymer and monomer are part of our everyday speech. –Poly = manyMono = one –“Mer” is derived from the Greek meros, meaning."— Presentation transcript:
2 What is a “mer”? –The terms polymer and monomer are part of our everyday speech. –Poly = manyMono = one –“Mer” is derived from the Greek meros, meaning “part.” So, a monomer is a “one part” and a polymer is a “many part.”
4 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.
5 Polyethylene Polyethylene is an example of a synthetic polymer. Ethylene, derived from petroleum, is made to react with itself to form polyethylene.
6 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.
11 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.
12 Polymer Types Thermoplastic Polymers –Soften on reheating Thermosetting Polymer –Set to an infusible solid and do not soften on reheating
17 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
18 Step 1: Free-radical Formation The peroxide splits into free radicals: RO:OR 2 RO.
19 Step 2: Propagation of polymeric chain The initial free radical adds to ethylene to form a new free radical. The chain continues to elongate (polymerize) as long as free radicals continue to add to ethylene: RO. + CH 2 =CH 2 ROCH 2 CH 2. ROCH 2 CH 2. + CH 2 =CH 2 ROCH 2 CH 2 CH 2 CH 2. ROCH 2 CH 2 CH 2 CH 2. + CH 2 =CH 2 RO(CH 2 CH 2 ) n.
20 Step 3: Termination Polymerization stops when the free radicals are used up. This occurs when free radicals combine to form a stable compound: RO. + RO(CH 2 CH 2 ) n. RO(CH 2 CH 2 ) n OR RO(CH 2 CH 2 ) n. + RO(CH 2 CH 2 ) n. RO(CH 2 CH 2 ) n (CH 2 CH 2 ) n OR
21 Addition Polymers: Use and Reuse (Recycling)
22 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.
24 Choose as a plastic container those with recycle numbers 1, 2, 4, and/or 5 These 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.
25 Avoid using plastic containers in the microwave Any 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 microwave These plastic wraps have been shown to leach chemicals when heated.
26 Avoid water bottled in plastic containers Not 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.
27 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.
28 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.
29 Avoid as a food or drink container polycarbonates and other plastic recycle number 7 plastics The 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.
31 Butadiene Polymers Natural rubber is a polymer of isoprene (2- methyl-1,3-butadiene).
32 Copolymers A copolymer contains two different kinds of monomer units.
33 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.
35 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.
36 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.