ENGR-45_Lec-29_PolyMer_Structures.ppt 1 Bruce Mayer, PE Engineering-45: Materials of Engineering Bruce Mayer, PE Licensed Electrical & Mechanical Engineer Engineering 45 Polymer Structures

ENGR-45_Lec-29_PolyMer_Structures.ppt 2 Bruce Mayer, PE Engineering-45: Materials of Engineering Learning Goals – Polymer Structure  Learn The Basic Electronic Structure of Very Long Organic Molecules  Understand Basic MicroStructural Features of Polymers  Calculate Molecular Weights for Long- Chain Polymers  Learn the Difference between ThermoSETTING and ThermoPLASTIC Polymers

ENGR-45_Lec-29_PolyMer_Structures.ppt 3 Bruce Mayer, PE Engineering-45: Materials of Engineering Ancient Polymer History  Originally natural polymers were used Wood, Cotton, Leather, Rubber, Wool, Silk  Early Human-History Uses for the Natural PolyMers Rubber balls used by Incas Noah used pitch (a natural polymer) for Sealing the Ark

ENGR-45_Lec-29_PolyMer_Structures.ppt 4 Bruce Mayer, PE Engineering-45: Materials of Engineering Organic Chemistry  Recall PolyMer  Many Mers  Mer  a Single Chemical Unit  Almost All Solid Polymer Materials are “Organic” in Nature  Organic → Based on CARBON  Almost All Organic Chemicals are a combination of Carbon And HYDROGEN

ENGR-45_Lec-29_PolyMer_Structures.ppt 5 Bruce Mayer, PE Engineering-45: Materials of Engineering C-H Bond  ReCall from Periodic Table the Valences for C & H C → Grp IVa → 4 Valence e − H → Grp 1A → 1 Valence e −  Thus in a C-H molecule Both can Attain the Noble-Gas Configuration if 4 H’s Give their e − ’s to 1 Accepting C  Four-H’s and 1-C Yield the METHANE molecule

ENGR-45_Lec-29_PolyMer_Structures.ppt 6 Bruce Mayer, PE Engineering-45: Materials of Engineering Single, Double, Triple Bonding  First Note That the Methane Molecule is NOT Planer in 3D As Might be Expected the H’s Take Equal Separation to Form a Tetrahedral Structure  In Methane, Each H Atom Shares ONE e − This Configuration is Shown Schematically as Each C-H is connected by a SINGLE Bond as depicted the Single-Line Connection

ENGR-45_Lec-29_PolyMer_Structures.ppt 7 Bruce Mayer, PE Engineering-45: Materials of Engineering 1X, 2X, 3X Bonding cont.1  Another Electronic Configuration, Ethylene, Has the two adjacent Carbons sharing TWO e − to achieve the Neon Configuration  In this case the C=C connection is termed a DOUBLE Bond  Similarly, in Acetylene two Carbons Share 3 e − to form a TRIPLE Bond

ENGR-45_Lec-29_PolyMer_Structures.ppt 8 Bruce Mayer, PE Engineering-45: Materials of Engineering The C-H Chain Basic-Mer  Consider the Base Methane Molecule with the end-H’s Removed  The CH 2 Fragment, or Mer, can Repeat Almost endlessly, creating very large PolyMer Chain Molecules  There can be Many basic Mers consisting of 2X or 3X bonded C’s Other Atoms, or Ions (Molecule Fragments) may Substitute for H  The Central Carbon Can Connect to Similar Fragments with a 1X Bond to form a CHAIN

ENGR-45_Lec-29_PolyMer_Structures.ppt 9 Bruce Mayer, PE Engineering-45: Materials of Engineering PolyMer MicroStructure  Some Typical Repeating-Mer (PolyMer) Structures  C-C Forms a Very Strong intRAmolecular Bond The CoValent IntERmolecular Bond Strength Varies with the Form of the Chain-to-Chain Electronic interaction Direction of increasing strength

ENGR-45_Lec-29_PolyMer_Structures.ppt 10 Bruce Mayer, PE Engineering-45: Materials of Engineering Mer Forms in 3D PE: polyethylene Phenol-formaldehyde (Bakelite) PVC: polyvinyl chloride PET: polyethylene terephthalate (a polyester)

ENGR-45_Lec-29_PolyMer_Structures.ppt 11 Bruce Mayer, PE Engineering-45: Materials of Engineering Example → PolyEthylene  Poly (many) Mer (parts): A large molecule made up of one or more repeating units (mers) linked together by covalent chemical bonds.  The PolyEthylene Chemical Reaction n = number of monomers reacting >> 1

ENGR-45_Lec-29_PolyMer_Structures.ppt 12 Bruce Mayer, PE Engineering-45: Materials of Engineering Effect of Molecular Weight on the Properties of PolyEthylene

ENGR-45_Lec-29_PolyMer_Structures.ppt 13 Bruce Mayer, PE Engineering-45: Materials of Engineering PolyMer Chemistry  Polymer MACROmolecules Produce NONcrystalline Solids by the interMolecular Bonding  The Chain-Creating “PolyMerization” Chemical Reaction usually Proceeds with the aid of a catalyst, R monomers + catalyst (initiator) = polymer chain Poly Ethylene polyethylene (C 2 H 4 Mer) C H

ENGR-45_Lec-29_PolyMer_Structures.ppt 14 Bruce Mayer, PE Engineering-45: Materials of Engineering Molecular Geometry  As indicated in the Previous Slide Any Three Carbons in the “BackBone” form Something near the Classic Tetrahedral Angle ( °)  However the Molecules are NOT constrained to TWO Dimensions  The BackBones can Rotate, Kink, or Coil to Generate Randomly Complex Shapes

ENGR-45_Lec-29_PolyMer_Structures.ppt 15 Bruce Mayer, PE Engineering-45: Materials of Engineering Isomerism  IsoMerism  two compounds with same chemical formula can have quite different structures Example: C 8 H 18 –n Octane –2-methyl-4-ethyl pentane (IsoOctane)

ENGR-45_Lec-29_PolyMer_Structures.ppt 16 Bruce Mayer, PE Engineering-45: Materials of Engineering Cross-linking  Generally, amorphous polymers are weak.  Cross-linking adds strength: vulcanized rubber is polyisoprene with sulphur-based cross-links:

ENGR-45_Lec-29_PolyMer_Structures.ppt 17 Bruce Mayer, PE Engineering-45: Materials of Engineering PolyMer Size Characterization  MOLECULAR WEIGHT, M w  Mass of a mol of chain-molecules  Average CHAIN SIZE, n  Number of Mers per Chain Also Called the “Degree of PolyMerization”  Some Consequences: M w ↑  T melt ↑ short chains (~100 g/mol): liquid or gas long chains (1000 g/mol): waxy solid, soft resin “high polymer” (>10,000 g/mol): solid  Also M w ↑  TS↑ Longer chains are entangled (anchored) better

ENGR-45_Lec-29_PolyMer_Structures.ppt 18 Bruce Mayer, PE Engineering-45: Materials of Engineering MOLECULAR WEIGHT M w is more sensitive to higher molecular weights Molecular weight, M i : Mass of a mole of chains. Lower M higher M

ENGR-45_Lec-29_PolyMer_Structures.ppt 19 Bruce Mayer, PE Engineering-45: Materials of Engineering Molecular Weight Calculation  Example: average mass of a class Σ=10Σ=1860

ENGR-45_Lec-29_PolyMer_Structures.ppt 20 Bruce Mayer, PE Engineering-45: Materials of Engineering Tacticity  isotactic – all R groups on same side of chain  syndiotactic – R groups alternate sides  atactic – R groups random

ENGR-45_Lec-29_PolyMer_Structures.ppt 21 Bruce Mayer, PE Engineering-45: Materials of Engineering Cis/Trans IsoMerism cis Form cis-isoprene (natural rubber)  Bulky groups on same side of chain trans Form trans-isoprene (gutta percha)  bulky groups on opposite sides of chain

ENGR-45_Lec-29_PolyMer_Structures.ppt 22 Bruce Mayer, PE Engineering-45: Materials of Engineering CoPolyMers  Two or More MonoMers PolyMerized ToGether random block graft Adapted from Fig. 14.9, Callister 7e. alternating A B random – A and B randomly vary in chain alternating – A and B alternate in polymer chain block – large blocks of A alternate with large blocks of B graft – chains of B grafted on to A backbone

ENGR-45_Lec-29_PolyMer_Structures.ppt 23 Bruce Mayer, PE Engineering-45: Materials of Engineering PolyMer Crystallinity  % Crystalinity  % of Material that is crystalline  TS and E often increase with % crystallinity  Annealing causes crystalline regions to grow. % crystallinity increases Simulated conformation of a polymer chain consisting of 100 main chain repeat units and 50 side chains, each consisting of 20 repeat units.

ENGR-45_Lec-29_PolyMer_Structures.ppt 24 Bruce Mayer, PE Engineering-45: Materials of Engineering PolyMer Xtals - Spherulites  Polymer Single Xtals Often Form Plate-like, or Lamellar, Structures by Folding Back on themselves  In Bulk Material, Amorphous regions of Twisted & Kinked “Tie Molecules:”connect the Lamellae Lamellae Tie Molecules  Upon Heating the Layered Structures Become Spherical with an “Onion- Layer”, or Spherulitic, Structure

ENGR-45_Lec-29_PolyMer_Structures.ppt 25 Bruce Mayer, PE Engineering-45: Materials of Engineering Polymer-ChainStructure v. Heating ThermoPlastic ThermoSetting

ENGR-45_Lec-29_PolyMer_Structures.ppt 26 Bruce Mayer, PE Engineering-45: Materials of Engineering ThermoPlastic Polymers  Polymers which melt and solidify withOUT chemical change are called thermoplastics.  They support hot-forming methods such as injection-molding

ENGR-45_Lec-29_PolyMer_Structures.ppt 27 Bruce Mayer, PE Engineering-45: Materials of Engineering ThermoSet Polymers  Polymers which irreversibly change when heated are called thermosets.  Most often, the change involves cross-linking which strengthens the polymer (setting).  Thermosets will not melt, and have good heat resistance.  They are often made from multi-part compounds and formed before setting (e.g. epoxy resin)  Setting accelerates with heat or, for some polymers, with UV light.

ENGR-45_Lec-29_PolyMer_Structures.ppt 28 Bruce Mayer, PE Engineering-45: Materials of Engineering ThermoSets vs ThermoPlastics  ThermoPlastics little cross linking ductile Soften, then Melt with heating Examples –polyethylene (PE) –Polypropylene (PP) –Polycarbonate (Lexan) –polystyrene (StyroFoam)  ThermoSets large cross linking –10 to 50% of mers hard and brittle do NOT soften with heating –Decompose Instead Examples: vulcanized rubber, epoxies, polyester resin, phenolic resin 1 st Synthetic Polymer

ENGR-45_Lec-29_PolyMer_Structures.ppt 29 Bruce Mayer, PE Engineering-45: Materials of Engineering WhiteBoard Work  Prob 14.9 For the Kinked & Twisted Polymer at right Find –Total Length, L –End-to-End distance, r Given –Eqns & –M n for Linear PolyPro = 300 kg/mol Simulated conformation of a polymer chain consisting of 100 main chain repeat units and 50 side chains, each consisting of 20 repeat units.

ENGR-45_Lec-29_PolyMer_Structures.ppt 30 Bruce Mayer, PE Engineering-45: Materials of Engineering Appendix - BakeLite  The First Synthetic Polymer  Invented by Leo Beakeland ( ) in 1907 in Yonkers, NY  Chemical Name → phenol formaldehyde (Phenolic)  Historic Products A Bakelite record invented by Edison. (USA) Bakelite billiard balls invented by Hyat Burroughs. (UK) The telephone receiver made of Bakelite by Western Electric. (USA) Photo camera from Kodak by Eastman gets a Bakelite case. (USA) Philips radio company starts with its own Bakelite production, called Philite. (Netherlands) First Bakelite chair First Philite radio speaker made by Philips. (Netherlands) –See also 