Polymers Larry Scheffler Version 1.0
Definitions • Polymer: a long chain molecule made up of many small identical units. • Monomer: the smallest repeating unit of a polymer (propene in polypropylene). .
IUPAC Definition • A polymer is a substance composed of molecules characterized by the multiple repetition of one or more species of atoms or groups of atoms (constitutional repeating units) linked to each other in amounts sufficient to provide a set of properties that do not vary markedly with the addition of one or a few of the constitutional repeating units.”
Common Polymers • Polymers are common in nature. Wood, rubber, cotton, silk, proteins, enzymes, and cellulose are all examples of polymers • A wide variety of synthetic polymers have been produced, largely from petroleum based raw materials. These include polyurethane, teflon, polyethylene, polystyrene, and nylon.
Polymer Recycling Codes Common household polymers
Polymers • The number code indicates the polymer type
Polymers • Types of synthetic and natural polymers.
Addition Polymers • Addition polymerization: a reaction in which unsaturated monomers combine with each other to form a polymer • Example: Tetrafluoroethene can be polymerized to form polytetrafluoroethene, commonly known as Teflon
Addition Polymers • Some common addition polymers • Many plastics are addition polymers made from hydrocarbon sources. • The hydrocarbon must be unsaturated in order to polymerize
Addition Polymers • Polyvinyl chloride • Polyvinyl chloride or PVC is wide used for pipes and other structural materials • Vinyl chloride is also known as chloroethene
Condensation Polymers • Condensation polymers form from condensation reactions. • In a condensation polymer a smaller molecule such as water is eliminated • In order to form a condensation polymer the monomer must have two functional groups
Example of a Condensation Polymer • Nylon 6-6 is a condensation polymer • It is also a copolymer since it is made from two different monomers
Example of a Condensation Polymer 2 • Dacron is also a condensation polymer Ethylene Glycol (1,2ethanediol) para Terephthalic acid Dacron is an example of a polyester • It is also a copolymer since it is made from two different monomers
Co-polymers • Co polymers are made from than one monomer • Many natural polymers are copolymers. For example, proteins are condensation polymers formed by joining as many as 20 different amino acids
Polymer Structure • Molecular Mass: • Polymers are high molecular mass structures • Extremely large molecular weights are to be found in polymers with very long chains. • Molecular Shape: • Polymer chain molecules are usually straight chains • These chains may bend, coil and kink, leading to extensive intertwining and entanglement of neighboring chain molecules. • These random coils and molecular entanglements are responsible for many of the important characteristics of polymers.
The Polymer Structure Determines its Characteristics The physical properties of a polymer, such as its strength and flexibility depend on: • Chain length - In general, the longer the chains the stronger the polymer; • Side groups - Polar side groups give stronger attraction between polymer chains, making the polymer stronger; • Branching - Straight, unbranched chains can pack together more closely than highly branched chains. These polymers are more crystalline and therefore stronger; • Cross-linking - If polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.
Structure: Linear Polymers • Linear Polymers have monomer units that are joined together end to end in single flexible chain. • Linear polymers have extensive van der Waals attractions between the chains. • Examples: polyethylene, polyvinyl chloride, polystyrene, and nylon
Structure: Branched Polymers • Branched Polymers have side or branch chains are connected to the main ones. • The branches, considered to be the part of the main-chain molecules, result from side reactions that occur during the synthesis of the polymer. • The packing efficiency is reduced with the formation of side branches, which results in a lowering of the polymer density
Structure: Cross-Linked Polymers • Adjacent linear chains are joined one to another at various positions by covalent bonds. • The process of cross linking is achieved either during synthesis or by a nonreversible chemical reaction that is usually carried out at an elevated temperature. • This cross linking is accomplished by additive atoms or molecules that are covalently bonded to the chains. • Many of the rubber elastic materials are cross linked. In case of rubbers, it is called vulcanization
Structure: Network Polymers • Network Polymers have trifunctional monomer units, • Having three active covalent bonds allow these polymers to form three-dimensional networks instead of the linear chain framework • Network polymers have distinctive mechanical and thermal properties. • Examples include epoxies and other adhesives.
Polymer Microstructure Polyolefins with side chains have stereocenters on every other carbon With so many stereocenters, the stereochemistry can be complex. There are three main stereochemical classifications for polymers.
Microstructure and Properties • Tacticity affects the physical properties • Atactic polymers will generally be amorphous, soft, flexible materials • Isotactic and syndiotactic polymers will be more crystalline, thus harder and less flexible. • Polypropylene (PP) is a good example • Atactic polypropylene is a low melting, gooey material • Isoatactic polypropylene is is high melting (176º), crystalline, tough material that is industrially useful • Syndiotactic polypropylene is has similar properties, but is very clear. It is harder to synthesize