Chemistry for Changing Times 12 th Edition Hill and Kolb Chapter 10 Polymers: Giants among Molecules John Singer Jackson Community College, Jackson, MI © 2010 Pearson Prentice Hall, Inc.

10/2 Polymerization Polymers are composed of macromolecules. Many of them have formula weights in the thousands. The word polymer comes from the 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.

© 2010 Pearson Prentice Hall, Inc. 10/3 Natural Polymers Many natural substances exist as polymers including: Starch Cotton (cellulose) Wood (cellulose) Proteins

© 2010 Pearson Prentice Hall, Inc. 10/4 Celluloid Celluloid is one of the earliest synthetic substances that is a polymer. It is produced when natural cellulose is treated with nitric acid. Cellulose nitrate was used for billiard balls, men’s fashion collars, and movie film. The first truly synthetic polymers were phenol- formaldehyde resins.

© 2010 Pearson Prentice Hall, Inc. 10/5 Polyethylene Perhaps the most common synthetic polymer is the plastic, polyethylene.

© 2010 Pearson Prentice Hall, Inc. 10/6 Polyethylene

© 2010 Pearson Prentice Hall, Inc. 10/7 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.

© 2010 Pearson Prentice Hall, Inc. 10/8 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?

© 2010 Pearson Prentice Hall, Inc. 10/9 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.

© 2010 Pearson Prentice Hall, Inc. 10/10 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.

© 2010 Pearson Prentice Hall, Inc. 10/11 Addition Polymers Polystyrene

© 2010 Pearson Prentice Hall, Inc. 10/12 Addition Polymers Vinyl Polymers

© 2010 Pearson Prentice Hall, Inc. 10/13 Addition Polymers Polytetrafluoroethylene (PTFE)

© 2010 Pearson Prentice Hall, Inc. 10/14 Addition Polymers

© 2010 Pearson Prentice Hall, Inc. 10/15 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.

© 2010 Pearson Prentice Hall, Inc. 10/16 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.

© 2010 Pearson Prentice Hall, Inc. 10/17 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).

© 2010 Pearson Prentice Hall, Inc. 10/18 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.

© 2010 Pearson Prentice Hall, Inc. 10/19 Synthetic Rubber Synthetic rubber is similar to polyisoprene. One example is polybutadiene.

© 2010 Pearson Prentice Hall, Inc. 10/20 Synthetic Rubber Neoprene is very similar to polybutadiene, but contains chlorine in the place of the methyl group. It is more resistant to solvents like oil and gasoline.

© 2010 Pearson Prentice Hall, Inc. 10/21 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.

© 2010 Pearson Prentice Hall, Inc. 10/22 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.

© 2010 Pearson Prentice Hall, Inc. 10/23 Condensation Polymers In condensation polymerization, small molecules such as water, alcohols, ammonia, or HCl are released as by-products.

© 2010 Pearson Prentice Hall, Inc. 10/24 Condensation Polymers Nylon is a polyamide. Most nylon is manufactured as fibers.

© 2010 Pearson Prentice Hall, Inc. 10/25 Condensation Polymers Polyesters are condensation polymers made from molecules containing alcohol and carboxylic acid functional groups. The linkage is an ester.

© 2010 Pearson Prentice Hall, Inc. 10/26 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.

© 2010 Pearson Prentice Hall, Inc. 10/27 Condensation Polymers Polycarbonates are tough, clear polymers used in protective helmets, safety glasses, and dental crowns. Lexan is one such polycarbonate.

© 2010 Pearson Prentice Hall, Inc. 10/28 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.

© 2010 Pearson Prentice Hall, Inc. 10/29 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.

© 2010 Pearson Prentice Hall, Inc. 10/30 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.

© 2010 Pearson Prentice Hall, Inc. 10/31 Silicones Silicones are polymers that contain silicon rather than carbon. An example is polysiloxane. 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.

© 2010 Pearson Prentice Hall, Inc. 10/32 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.

© 2010 Pearson Prentice Hall, Inc. 10/33 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.

© 2010 Pearson Prentice Hall, Inc. 10/34 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 glass―hard, brittle, and stiff.

© 2010 Pearson Prentice Hall, Inc. 10/35 Properties of Polymers 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.

© 2010 Pearson Prentice Hall, Inc. 10/36 Disposal of Plastics 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.

© 2010 Pearson Prentice Hall, Inc. 10/37 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.

© 2010 Pearson Prentice Hall, Inc. 10/38 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 exhibit toxic gases when combusted. PVC plastic, for instance, releases HCl gas when burned.

© 2010 Pearson Prentice Hall, Inc. 10/39 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.

© 2010 Pearson Prentice Hall, Inc. 10/40 Disposal of Plastics 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.

© 2010 Pearson Prentice Hall, Inc. 10/41 Plastics and Fire Hazards Many people are injured each year due to accidental ignition of plastics. Federal regulations require that children’s sleepwear be made of flame retardant materials. Some plastics release toxic gases during combustion. Firefighters must protect themselves from toxic gases.

© 2010 Pearson Prentice Hall, Inc. 10/42 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.

© 2010 Pearson Prentice Hall, Inc. 10/43 Plasticizers and Pollution Early plasticizers were polychlorinated biphenyls (PCB).

© 2010 Pearson Prentice Hall, Inc. 10/44 Plasticizers and Pollution More recent plasticizers are less toxic phthalate esters.

© 2010 Pearson Prentice Hall, Inc. 10/45 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 hope and challenge for our future.