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Modern Materials: Polymers and Biomaterials Chapter 12 Supplementary Reading on Polymers h // http://courses.chem.psu.edu/chem112/materials/polymers.html h d /h / i l / l h l MJ Bojan CHEM 112 Polymers and BioMaterials 1 Polymers: High molecular weight materials formed from many small molecules called monomers Examples of polymers: plastics DNA proteins rubber Examples of polymers: plastics, DNA, proteins, rubber How can we understand this important group of molecules? p g p Structure affects function MJ Bojan CHEM 112 Polymers and BioMaterials 2 Most polymers are formed via one of these types of reaction of reaction. Polymer Synthesis 1. Addition polymers Monomer containing a double bond polymerizes via addition reaction Polyethylene, Polystyrene Rubber cross‐linking 2. Ring opening Cyclic monomer opens to form a linear chain (e.g. polymerization of sulfur) 3. Condensation polymers d l polymers form via condensation reaction, a small molecule (H2O, HCl, CO2) is eliminated in the reaction Silicone polymers, Polyurethanes, Nylon, Proteins MJ Bojan CHEM 112 Polymers and BioMaterials 3 Synthesis of ADDITION POLYMERS: Synthesis of ADDITION POLYMERS: Double bond opens up, two electrons are used to form two new C‐C single bonds connecting monomers. ethylene monomers H H C H C H H C H H H C H C H C H H H H H H H H C C C C C C H H H H H H polyethylene * MJ Bojan CHEM 112 Polymers and BioMaterials * 4 Synthesis of ADDITION POLYMERS: By modifying the monomer a variety of polymers can be made. H H C CH2 C H CH2 n H ethylene polyethylene(gladwrap) F H F C CF2 C F tetrafluoroethylene H C CF2 n F C stryrene t MJ Bojan polystyrene(Styrofoam) H CH3 CH3 C n H Cl polyvinyl chloride(PVC) vinyl chloride C CH CH2 C CH n Cl H CH2 CH2 C H Teflon,TFal H C H C O C CH3 O methyl methacrylate MMA CHEM 112 Polymers and BioMaterials C n CH3 O O polyMMA l MMA (Pl (Plexiglass) i l ) 5 Rubber is an example of a naturally occurring addition polymer addition polymer. Problem MJ Bojan CHEM 112 Polymers and BioMaterials 6 Ring Opening Polymerization: a cyclic monomer opens to form a linear chain form a linear chain Condensation Polymerization: Two molecules join to form a larger molecule by elimination of a small molecule such l l l b l f ll l l h as water MJ Bojan CHEM 112 Polymers and BioMaterials 7 Ethers, Esters, and Amides are formed via condensation reactions: d i i alcohol R−O−H + alcohol → ether + H−O−R’ → R−O−R’ carboxylic acid + alcohol → O C R + H−O−R’ → R OH carboxylic acid + amine O R C MJ Bojan + OH ester O → H N H R C + water + H2O + water + H2O OR' amide O → R C + water + H2O NHR' CHEM 112 Polymers and BioMaterials 8 Polyesters and polyamides are formed via condensation reactions. condensation reactions. Each monomer has two functional groups two functional groups. O O C C (CH2)4 H N (CH2)6 N H Nylon 6,6 (polyamide) MJ Bojan CHEM 112 Polymers and BioMaterials 9 There are several classifications or types of Polymers. Plastic: materials that can be formed into shapes. p Thermoplastic: materials that can be shaped more than once. Thermosetting plastic: material that can only be shaped once. Elastomer: material that is elastic in some way. If a moderate amount of deforming force is added, the elastomer will return to its original shape. Useful for fibers. h U f l f fib MJ Bojan CHEM 112 Polymers and BioMaterials 10 Properties of Polymers depend on their structure an bonding bonding. Properties depend on: 1) Structure, Structure orientation of chains 2) Identity of side groups 3) Chain length 4) Degree of cross‐linking MJ Bojan CHEM 112 Polymers and BioMaterials 11 Degree of crystallinity is the amount of ordering in a polymer Polymer chains tend to be flexible and easily entangled or folded; tend to be disordered Crystallinity affects − hard to crystallize; often amorphous hard to crystallize; often amorphous physical properties: crystalline polymers are stiffer, harder, more stiffer, harder, more dense Crystallinity affects optical properties: 1) Amorphous polymers are transparent (glasslike) 2)) Partly crystalline and partly glassy polymers are y y p yg yp y translucent Side chains MJ Bojan CHEM 112 Polymers and BioMaterials 12 There are ways to Increase order or crystallinity in a polymer Interactions between chains of a polymer lend elements of order to the structure of polymers. Stretching (or extruding) the polymer chains as they form can increase the amount of order, leading to a greater degree of crystallinity y y in the polymer. p y MJ Bojan CHEM 112 Polymers and BioMaterials Average molecular mass affects degree of crystallinity. crystallinity low and high density polyethylene LDPE: average molecular mass of 104 amu Sodium polyacrylate: O- HDPE: average molecular mass of 106 amu -O O CH2 C C CH CH CH2 O CH2 better known as… MJ Bojan CHEM 112 Polymers and BioMaterials 14 Polymer properties can be modified by crosslinking polymer chains together crosslinking polymer chains together. • Crosslinking: covalent bonds between chains: increases stiffness, strength Examples: rubber, Silicone • Metal Metal ions can serve as cross ions can serve as cross‐linking linking agents agents Example: Sodium alginate • Intermolecular Intermolecular forces can hold polymer chains together: forces can hold polymer chains together: a) LDF’s hold chains in nonpolar polymers together: Polyethylene, polypropylene b) Dipole dipole forces: PVC b) Dipole‐dipole forces: PVC c) H‐bonding PVA plays an important role in biological polymers DNA Proteins, DNA, Proteins MJ Bojan CHEM 112 Polymers and BioMaterials 15 Cross linking with covalent bonds formed between chains make the polymer stiffer; more crystalline Example: Vulcanization of Rubber • • Natural rubber is too soft and chemically reactive to make a useful material. B By vulcanizing l i i the rubber (crosslinking th bb ( li ki the chains with sulfur) useful th h i ith lf ) f l materials are made. S8 heat Isoprene (monomer) MJ Bojan Natural rubber (gummy) CHEM 112 Polymers and BioMaterials Cross‐linked rubber (tough elastomer) 16 Silicones represent a different kind of polymer: based on silicon rather than carbon based on silicon rather than carbon. Silicones are chains of alternating silicon and oxygen atoms with organic substituents on the silicon. organic substituents on the silicon Monomer: R2SiCl2 silicon compound with organic groups (R) attached. Formed via Condensation reaction E Example: l dichlorodimethylsilane [(CH3)2SiCl2] with water (H2O). The silicone formed is dimethylsiloxane The silicone formed is dimethylsiloxane. MJ Bojan CHEM 112 Polymers and BioMaterials 17 By changing the R group, the properties of the polymer are changed. changed Properties depend on: Properties of Silicones 1) 2) 3) Nontoxic, stable (unreactive) Nontoxic, stable (unreactive) flame resistant hydrocarbon substituents act to repel water. repel water. Silicones are either rubbers or oils depending on the chain length and degree of cross‐linking. g g R group R‐group Chain length Degree of cross‐linking – No crosslinks: liquid silicone oils No crosslinks: liquid silicone oils high T lubricants, hot oil baths – Few cross links; silicone rubber Few cross links; silicone rubber caulking material – More cross links: silicone resins More cross links: silicone resins coatings and adhesives – All All cross links: SiO li k SiO2 = quartz t MJ Bojan Uses: Lubricants Car polish Gaskets, sealants Waterproofing (organic groups form barrier) CHEM 112 Polymers and BioMaterials 18 Metal ions can serve as cross‐linking agents Gummy worms: polymer of Sodium alginate Alginate is a polysaccharide found in seaweed: (It’s edible!) Used to thicken food (like milkshakes) To make gummy worms: add crosslinker: CaCl2 add crosslinker: CaCl Ca+2 ions hold chains together. MJ Bojan CHEM 112 Polymers and BioMaterials 19 Intermolecular forces can hold polymer chains together: Polyvinylalcohol (PVA) is an Addition Polymer catalyst CH2 CH2 CH heat vinyl alcohol vinyl alcohol OH CH OH x linear chain polymer x = 103 ‐ 104 poly(vinyl alcohol) Add a cross‐linker: borax B4O72−(forms H‐bonding crosslink) + B 4O72− MJ Bojan CHEM 112 Polymers and BioMaterials viscoelastic20 Biological Polymers: Proteins are polyamides. The monomers are amino acids: Th i id React via condensation polymerization H H N C H O + C OH R * H H N C R H H N C H O R H N C C H R O H N C H OH O C + C H H H N C R O C OH O C * R Protein MJ Bojan amide linkage or peptide bond 21 The sequence of amino acids is the primary structure of the protein. Secondary structure of proteins: Alpha helices and beta sheets Tertiary structure (protein folding) is even more complex. This structure is p p y important in protein activity. MJ Bojan CHEM 112 Polymers and BioMaterials 22 Biological Polymers DNA and RNA are polyesters ((of H3PO4)). The monomers are nucleotides React via condensation polymerization p y Monomer; nucleotide Polymer; polynucleotide MJ Bojan CHEM 112 Polymers and BioMaterials 23 The DNA and RNA strands are held together by H‐ bonds. Bases are paired MJ Bojan CHEM 112 Polymers and BioMaterials 24 Biomaterials: are any materials that have biomedical applications. For example, the materials that are used to fill teeth are biomaterials. Characteristics of Biomaterials The biomaterials must be biocompatible: The body’s immune system must not attack th bi the biomaterial. t i l Physical requirements: Biomaterials must be created for a specific environment. Artificial heart valves must open and close 70 to 80 times per minute Artificial heart valves must open and close 70 to 80 times per minute. Chemical requirements: g Biomaterials must be of medical grade. Polymers are very important biomaterials: beware of fillers, stabilizers, etc. MJ Bojan CHEM 112 Polymers and BioMaterials 25 The different types of The different types of Polymers have bio applications. Polymers have bio applications. Plastic: materials that can be formed into shapes. Thermoplastic: materials that can be shaped more than once. (Used as replacements for blood vessels.) Thermosetting: materials that can only be shaped once (Used in dental devices, and orthopedics such as hip replacements.) Elastomer: material that is elastic in some way. If a moderate amount of deforming force is added, the elastomer will return to its original shape. Used as catheters, and for covering leads on implanted electronics, like pacemaker. , p MJ Bojan CHEM 112 Polymers and BioMaterials 26 Polymers are be used in many biological applications. Examples of Biomaterial Applications Heart Replacement and Repairs: Polyethylene terephthalate, called Dacron™, Polyethylene terephthalate called Dacron™ is often used in the manufacture of artificial heart valves. Dacron™ is used because tissue will grow through a polyester mesh. Vascular grafts: g A vascular graft is the replacement for A vascular graft is the replacement for a piece of blood vessel. Dacron™ is used for large arteries. * MJ Bojan F F C C F F * Polytetrafluoroethylene, is used for smaller vascular grafts. CHEM 112 Polymers and BioMaterials 27 Polymers are be used in many biological applications. Artificial Tissue: • • • • Artificial skin, which is grown in the laboratory, is used to treat patients with extensive skin loss. The challenge with growing artificial skin is The challenge with growing artificial skin is getting the cells to align properly. Therefore a scaffold must be used for the cells. The most successful scaffold is lactic acid‐ glycolic acid copolymer. Hip Replacements: • About 200 000 total hip replacements are performed each year About 200,000 total hip replacements are performed each year. • A metal ball, a cobalt chromium alloy, is often used in a hip replacement. • This alloy is attached to a titanium alloy and cemented using a tough thermoset polymer. • The acetabulum, which accommodates the femur, is lined with a polyethylene layer MJ Bojan CHEM 112 Polymers and BioMaterials 28