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Chapter 10 Polymers John Singer, Jackson Community College Chemistry for Changing Times, Thirteenth Edition Lecture Outlines 2013 Pearson Education, Inc. Slide 2 2 Chapter 10 2013 Pearson Education, Inc. Polymerization Polymers are macromolecules. Many of them have formula weights in the thousands. The word polymer is derived from Greek. Poly means many. Mer comes from meros meaning parts. Polymers consist of many smaller molecules called monomers that are connected to form the larger macromolecule. Slide 3 3 Chapter 10 2013 Pearson Education, Inc. Natural Polymers Many natural substances exist as polymers including Starch Cotton (cellulose) Wood (cellulose) Proteins Slide 4 4 Chapter 10 2013 Pearson Education, Inc. Celluloid Celluloid, produced by treating natural cellulose with nitric acid, was one of the earliest synthetic polymers. Cellulose nitrate was used for billiard balls, mens fashion collars, and movie film. Celluloid still has uses today. The first completely synthetic polymers were phenol-formaldehyde resins. Slide 5 5 Chapter 10 2013 Pearson Education, Inc. Polyethylene Perhaps the most common synthetic polymer is the plastic, polyethylene. Slide 6 6 Chapter 10 2013 Pearson Education, Inc. Polyethylene Slide 7 7 Chapter 10 2013 Pearson Education, Inc. Polyethylene High density polyethylene (HDPE) exists as mostly linear molecules that pack closely together. It is used for milk jugs, bottle caps, toys, etc. Low density polyethylene (LDPE) is a more highly branched form of polyethylene. It is used to make plastic bags, plastic films, electric wire insulation, etc. Slide 8 8 Chapter 10 2013 Pearson Education, Inc. Polyethylene These two bottles, both made of polyethylene, were heated in the same oven for the same length of time. Which is made of HDPE and which is made of LDPE? Slide 9 9 Chapter 10 2013 Pearson Education, Inc. Thermoplastic and Thermosetting Polymers Thermoplastic polymers will soften upon heating. Polyethylene is one such polymer. Thermosetting polymers were heated to harden when they were formed. They will not soften upon heating, but will discolor and decompose. Slide 10 10 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Addition polymerization occurs when monomers add to one another in such a way that the resulting molecule contains all atoms that are present in the monomers. Addition polymers are all derivates of polyethylene. Slide 11 11 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Polystyrene Slide 12 12 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Polystyrene Slide 13 13 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Polyvinyl Chloride Slide 14 14 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Polyvinyl Chloride Slide 15 15 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Polytetrafluoroethylene (PTFE) Slide 16 16 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Slide 17 17 Chapter 10 2013 Pearson Education, Inc. Addition Polymers Conducting Polymers: Polyacetylene contains conjugated double bonds and can conduct electricity. Slide 18 18 Chapter 10 2013 Pearson Education, Inc. Molding Plastics Plastic materials can be made to flow under heat and pressure. Compression molding: Heat and pressure are applied directly to the polymer powder in the mold cavity. Injection molding: The plastic is melted and forced by a plunger into cold molds to set. Slide 19 19 Chapter 10 2013 Pearson Education, Inc. Molding Plastics Extrusion molding: Process during which a molten polymer is extruded through a die in continuous form to be cut into lengths or coiled. Blow molding: Process during which a bubble of molten polymer is blown up like a balloon inside a hollow mold. This is how bottles are formed. Slide 20 20 Chapter 10 2013 Pearson Education, Inc. Rubber and Other Elastomers Elastomers are polymers that will elongate when subjected to a tensile force. They will return to the original shape when the force is removed. Rubber is an elastomer. Natural rubber is composed of isoprene units. Isoprene is polymerized into polyisoprene (rubber). Slide 21 21 Chapter 10 2013 Pearson Education, Inc. Rubber and Other Elastomers Natural rubber is soft and tacky when hot. Reacting it with sulfur cross-links the polyisoprene and makes the rubber harder. This process is known as vulcanization and was discovered by Charles Goodyear. Slide 22 22 Chapter 10 2013 Pearson Education, Inc. Synthetic Rubber Synthetic rubber is similar to polyisoprene. One example is polybutadiene. Slide 23 23 Chapter 10 2013 Pearson Education, Inc. Synthetic Rubber Neoprene is very similar to polybutadiene, but contains chlorine in place of the methyl group. It is more resistant to solvents like oil and gasoline. Slide 24 24 Chapter 10 2013 Pearson Education, Inc. Synthetic Rubber Another synthetic rubber is styrene-butadiene rubber (SBR). SBR is a copolymer of styrene (25%) and butadiene (75%). It is tougher and more resistant to oxidation than natural rubber, but its mechanical properties are less satisfactory. Slide 25 25 Chapter 10 2013 Pearson Education, Inc. Polymers in Paints Elastomers are often used as binders in paints. Paints made with elastomeric binders are more resistant to cracking. Latex paints are such a product. These paints use water as a solvent and are more environmentally friendly than oil-based paints. Slide 26 26 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers In condensation polymerization, small molecules such as water, alcohols, ammonia, or HCl are released as by-products. Slide 27 27 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Nylon is a polyamide. Most nylon is manufactured as fibers. Slide 28 28 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Polyesters are condensation polymers made from molecules containing alcohol and carboxylic acid functional groups. The linkage is an ester. Slide 29 29 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Phenol-formaldehyde resin was the first synthetic polymer. It was known as Bakelite in honor of its discoverer, Leo Baekeland. Leo Baekeland received a patent in 1909 for this polymer. Slide 30 30 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Formaldehyde can be condensed with urea to make urea- formaldehyde resins and with melamine to form melamine- formaldehyde resins. Slide 31 31 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Polycarbonates are tough, clear polymers used in protective helmets, safety glasses, and dental crowns. Slide 32 32 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Polyurethanes are similar to nylon. They may be elastomers or tough and rigid, depending on the monomers used. Polyurethanes are used in foam rubber, skate wheels, and tough furniture finishes. Slide 33 33 Chapter 10 2013 Pearson Education, Inc. Condensation Polymers Epoxy resins are often sold as two-part liquids. They make durable, clear coatings and are an excellent adhesive. They are very strong when cross-linked. Slide 34 34 Chapter 10 2013 Pearson Education, Inc. Composite Materials Composite materials are composed of high-strength fibers (i.e., fiberglass, graphite, or ceramic fibers) held in a polymeric matrix. Examples of composite materials include boat hulls, tennis rackets, automobile panels, fishing rods, etc. Slide 35 35 Chapter 10 2013 Pearson Education, Inc. Silicones Silicones are polymers that contain silicon rather than carbon. An example is polysiloxane. Slide 36 36 Chapter 10 2013 Pearson Education, Inc. Silicones Silicone polymers take many forms depending on their structure and degree of cross-linking. They can be in the form of liquid oils, gels, synthetic rubber elastomers, etc. Slide 37 37 Chapter 10 2013 Pearson Education, Inc. Properties of Polymers Polymers have very high molecular weights. Since the strength of intermolecular forces increases with molecular weight, polymeric materials exhibit very strong intermolecular forces. For these reasons, polymeric materials exist as strong fibers and polymers form viscous solutions. Slide 38 38 Chapter 10 2013 Pearson Education, Inc. Properties of Polymers The molecules of crystalline polymers line up in neat rows forming fibers of great strength. Crystalline polymers tend to be very rigid. Amorphous polymers, on the other hand, have molecules that are randomly tangled. Amorphous polymers tend to be soft and rubbery. Slide 39 39 Chapter 10 2013 Pearson Education, Inc. Properties of Polymers The glass transition temperature (T g ) is the temperature above which the polymer is tough and rubbery, and below which it is like glasshard, brittle, and stiff. Slide 40 40 Chapter 10 2013 Pearson Education, Inc. Some synthetic polymers can be converted to fibers. Many can exhibit properties that are superior to natural fibers. The majority of fibers and fabrics used in the United States are synthetic. Properties of Polymers Slide 41 41 Chapter 10 2013 Pearson Education, Inc. Plastics and the Environment Most plastics do not decompose readily in the natural environment. Unwanted plastic waste can be dealt with by disposal in landfills, incineration, biodegradation, and recycling. Slide 42 42 Chapter 10 2013 Pearson Education, Inc. Disposal of Plastics Landfills Plastics make up 11% by mass of solid waste and 20% by volume. More than half of all solid waste ends up in landfills. Landfill space is becoming increasingly difficult to obtain. Slide 43 43 Chapter 10 2013 Pearson Education, Inc. Disposal of Plastics Incineration Many plastic materials have significant fuel value and incineration of solid waste, along with using the heat energy to generate electricity, is attractive. However, the combustion of plastics and rubbers is not without problems. Many of these materials release toxic gases when combusted. PVC plastic, for instance, releases HCl gas when burned. Slide 44 44 Chapter 10 2013 Pearson Education, Inc. Disposal of Plastics Degradable Plastics About half of our waste plastic comes from packaging. Expect to see more biodegradable and photodegradable plastics used for packaging in the near future. Slide 45 45 Chapter 10 2013 Pearson Education, Inc. Recycling Over the long term, recycling may be the best way of dealing with waste plastics. Recycled plastics can be separated into the various types, chopped into flakes, melted, and remolded or spun into fibers. Disposal of Plastics Slide 46 46 Chapter 10 2013 Pearson Education, Inc. Plastics and Fire Hazards Many people are injured each year due to accidental ignition of plastics. Federal regulations require that childrens sleepwear be made of flame retardant materials. Because some plastics release toxic gases during combustion, firefighters must protect themselves from these toxic fumes. Slide 47 47 Chapter 10 2013 Pearson Education, Inc. Plasticizers and Pollution Certain plastics, such as vinyl polymers, are stiff and brittle; plasticizers are used to make the materials more flexible. Many of these plasticizers have low volatility. Eventually these materials can become stiff and brittle as the plasticizers vaporize. Slide 48 48 Chapter 10 2013 Pearson Education, Inc. Plasticizers and Pollution Early plasticizers were polychlorinated biphenyls (PCB). Slide 49 49 Chapter 10 2013 Pearson Education, Inc. Plasticizers and Pollution More recent plasticizers are less toxic phthalate esters. Slide 50 50 Chapter 10 2013 Pearson Education, Inc. Plastics and the Future It is difficult to imagine the world without synthetic polymers and plastics. Many are made from petroleum or natural gas. Much research is being conducted on developing synthetic polymers from renewable resources. These materials represent both a challenge and hope for our future.