1 Hein * Best * Pattison * Arena Jerry Poteat Science Department Georgia Perimeter College © John Wiley and Sons, Inc. Version 1.0 Chapter 21 Polymers: Macromolecules

2 Chapter Outline 21.1 Macromolecules 21.2 Synthetic Polymers 21.3 Polymer Types 21.4 Addition Polymerization 21.5 Addition Polymers: Use and Reuse (Recycling) 21.6 Butadiene Polymers 21.7 Geometric Isomerism in Polymers

Macromolecules

4 What is a macromolecule? A macromolecule is a very large molecule consisting of repeating units called monomers. A collection of macromolecules is called a polymer.

5 Cotton is made of celluose macromolecules Microchips are made of synthetic macromolecules

6 Other natural macromolecules (i.e. polymers) include starch, silk, glycogen, and proteins Synthetic macromolecules are based on petroleum (i.e. crude oil).

7 Polymerization of Ethylene to form Polyethylene

8 Polymers are prepared by polymerizing a monomer. The reaction is called polymerization.

Synthetic Polymers

10 Six Categories of Synthetic Polymers 1.Elastomers ( rubberlike materials, ) 2.Films 3.Textile fibers ( e.g. nylon, Dacron ) 4.Plastics ( used for casting, molding, and extruding) 5.Coatings ( resins for dip-, spray-, or solvent-dispersed applications 6.Miscellaneous (e.g. hydraulic fluids, foamed insulation, ion-exchange resins)

Polymer Types

12 Polymers are classified by how they are prepared and by how they are used.

13 Major Types of Polymer by Preparation Addition Polymer –Monomers add successively to a growing polymer chain –Polyethylene and polystyrene are addition polymers. Condensation Polymer –Polymer chain grows when monomers combine and split out water or other small molecule. –Nylon and polyurethane are condensation polymers.

14 Major Types of Polymer by Use Thermoplastic Polymers –Soften on reheating –Polyethylene and polystyrene are examples Thermosetting Polymer –An infusible solid and does not soften on reheating –Phenolics is an example

15 This is a structural comparison of thermoplastic and thermosetting polymers.

Addition Polymerization

17 Addition Polymerization In this type of polymerization C=C bonds of monomers react to form larger monomers until the unit is a larger polymer chain as seen here. Table 21.1 on the next slide shows ethylene monomer based polymers

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19 Many addition polymers are prepared by a free radical process. Free radicals are generated from a free radical source such as organic peroxides (general formula = ROOR) Preparation of Addition Polymers

20 Free radical polymerization consist of three steps: Free-radical formation Propagation of the chain Termination

21 Step 1: Free-radical Formation The peroxide splits into free radicals: RO:OR  2 RO.

22 Step 2: Propagation of polymeric chain A free radical adds to ethylene to form a new free radical. This free radical continues the growth of the polymer chain as shown below. 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.

23 Step 3: Termination The chain stops growing when free radicals react with each other to form a stable molecule. 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

Addition Polymers: Use and Reuse (Recycling)

25 Recycling Addition polymers are not biodegradeable so they must be recycled. Polymers are separated by a recycling code as shown below.

Butadiene Polymers

27 Some addition polymers are prepared from 1,3-butadiene or 1,3-butadiene derivatives

28 Comparison of natural rubber and butadiene polymers Note: Natural rubber is a polymer of isoprene and isoprene is a derivative of butadiene.

29 Copolymers A copolymer is a polymer that has two types of monomer units in its chain.

30 Vulcanized Rubber The physical properties of rubber can be altered by vulcanization. Vulcanization is the cross-linking of polymer chains with sulfur atoms by applying heat. Vulcanization increases the abrasion resistance and the useful temperature range of rubber.

31 A Segment of Vulcanized Rubber

Geometric Isomerism in Polymers

33 Geometric Isomerism in Polymers The double bonds in isoprene and butadiene polymers allow for cis-trans isomers. Cis-trans isomers are molecules that differ only in the spatial orientation of their atoms.

34 Geometric Isomerism in Polymers Gutta-perch is trans-polyisoprene Natural rubber is cis-polyisoprene.

35 Geometric Isomerism in Polymers

36 Chapter 21 Summary  Polymers are collections of macromolecules that are either natural (e.g. cotton) or synthetic ( e.g plastic ).  Macromolecules are very large molecules made from monomers.  Monomers are the smallest repeating units of macromolecules  Synthetic polymers are classified by how they are prepared ( i.e. addition (ionic or free-radical) and condensation) and by how they are used in applications ( i.e. thermoplastic or thermosetting).  Synthetic polymers are prepared by a reaction called polymerization  Copolymers are polymers that contain two different monomer units