POLYMERS

1. POLYMERS Group Members Seda KOCA Bengi AYDİLEK Didem Büşra KABAKÇI Gözde ERGİN 11.11.2009 Hacettepe University

2. The Outline • Reactions of polymers Addition Polymerization Step Growth Polymerization • Kinetic Of Polymerization • Polymerization Processes Bulk Polymerization Solvent Polymerization Suspention Polymerization Emulsion Polymerization Special Processes

3. The Outline • Chemical and Physical Structures of Polymers • Polymer’s molecular structures Confriguration and conformation of polymers Chain structures of polymers • Physical Structures of Polymers Polymer crystallinity Crystallinity and amorphousness of polymers

4. Outline Types of Polymers and Polymer Processing Members of Polymers Definition of Thermosets & Thermoplastics Common products and their properties Forming Techniques of Polymers Extrusion of polymers Injection Molding Blow Molding Thermoforming Compression Molding Casting

5. The Outline • Recycling of Polymers Definiton of Recycling Why is recycling important? Benefits Recycling of polymers

6. Reactions of Polymers Addition Polymerization (Chain Growth) Step Growth Polymerization (Condensation)

8. Differences between step-growth polymerization and chain-growth polymerization

9. Step of Radical Chain Polymerization • Initiation • Propagation • Termination

10. INITIATION

11. PROPAGATION

12. TERMINATION Dead Polymer i.) Coupling or Combination; ii.) Disproportionation

13. CHAIN TRANSFER REACTIONS Transfer to monomer reaction Transfer to initiator reaction Transfer to solvent reaction

14. IONIC CHAIN POLYMERIZATION • Using catalyst, not initiator • Highest reaction rate • Termination step is just disproportionation • Environment must be pure • Reaction occurs in the cold

15. Anionic Polymerization=Living Polymerization If the starting reagents are pure and the polimerization reactor is purged of all oxygen and traces of water, polimerization can proceed until all monomer is consumed.

16. CONDENSATION POLYMERIZATION • Using catalyst • Minumum two functional groups required • Usually linear • Molecular weight increases slowly at low conversion • High extents of reaction are required to obtain high chain length

17. KINETICS OF POLYMERIZATION • Reaction rate of ionic polimerization more than radicalic polimerization • So kinetics of ionic polimerization are not calculated • But kinetics of radicalic polimerization can be analysed

18. Kinetic of Radicalic Polymerization Initiation; Propagation; Termination;

19. Kinetic of Radicalic Polymerization • Ro = overall rate of polimerization • Rp = rate of chain propagation • Ri = rate of initiation step • Rt = rate of termination step

20. Kinetic of Condensation Polymerization • Equivalent reactivity of functional groups. • It may be first, second or third order by depending upon.

21. Kinetic of Condensation Polymerization • Assumption = a stoichiometry balance of monomer concentration

22. POLYMERIZATION PROCESSES • Bulk Polymerization • Solvent Polymerization • Suspention Polymerization • Emulsion Polymerization • Special Processes • Electrochemical Polymerization • Radiation Polymerization • Grow-discharge (Plasma)

23. Bulk Polymerization • The simplest technique • It gives the highest-purity polymer • Ingredients : monomer, monomer-soluble initiator, perhaps a chain transfer agent

24. Solution Polymerization • Ingredients : monomer initiator solvent • Heat can be removed by conducting the polymerization in an organic solvent or water • Initiator or monomer must be soluble in solvent • Solvents have acceptable chain-transfer characteristics • Solvents have suitable melting or boiling points for the conditions of polymerization

25. Suspention Polymerization • Coalescense of sticky droplets is prevented by PVA • Near the end of polymerization, the particles harder and they can be removed by filtration, then washing • Ingredients : water-insoluble monomer, water-insoluble initiator, sometimes chain transfer agent suspention medium (water-usually)

26. Emulsion Polymerization • Particles are formed monosize with emulsion polymerization • Polymerization is initiated when the water-soluble radical enters a monomer-containing micelles. • Ingredients : water-insoluble monomer, water-soluble initiator, chain transfer agent, dispersing medium (water), fatty acid, surfactant such as sodium salt of a long chain

27. Molecular structure of polymers Typical structures are : • linear (end-to-end, flexible, like PVC, nylon)  • branched • cross-linked (due to radiation, vulcanization) • network (similar to highly cross-linked structures,termosetting polymers) Figure1. Schematic representation of (a) linear, (b and c) branched, and (d and e) cross-linked polymers. The branch points and junction points are indicated by heavy dots (Plastic Technology Handbook-Manas Chanda Salil K. Roy)

28. Molecular configuration of polymers Side groups atoms or molecules with free bonds, called free-radicals, like H, O, methyl affects polymer properties. Stereoregularity describes the configuration of polymer chains : Isotactic is an arrangement where all substituents are on the same side of the polymer chain. Syndiotactic polymer chain is composed of alternating groups Atactic the radical groups are positioned at random Figure 2: Isotactic Syndiotactic and Atactic combinations of a stereoisomers of polymer chain (http://www.microscopy-uk.org.uk/mag/imgsep07/atactic.png) Chemical Structure of Polymers

29. Molecular configuration of polymers FIGURE.3. Diagrams of (a) isotactic, (b) syndiotactic, and (c) atactic configuration in a vinyl polymer. The corresponding Fischer projections are shown on the right. (Plastic Technolgoy Handbook)

30. Table 1. Properties of Polypropylene Stereoisomers(Plastic Technology Handbook)

31. Molecular configuration of polymers Geometrical isomerism: • The two types of polymer configurations are cis and trans. These structures can not be changed by physical means (e.g. rotation). • The cis configuration  substituent groups are on the same side of a carbon-carbon double bond. • Trans the substituents on opposite sides of the double bond. Figure4.cis trans configurations of polyisoprene ( http://openlearn.open.ac.uk/file.php/2937/T838_1_019i.jpg )

32. Conformations of a Polymer Molecule • Conformation The two atoms have other atoms or groups attached to them configurations which vary in torsional angle are known as conformations (torsional angle:The rotation about a single bond which joins two atoms ) • Polymer molecule can take on many conformations. • Different conformation different potential energies of the moleculeSome conformations: Anti (Trans), Eclipsed (Cis), and Gauche (+ or -)

33. Other Chain Structures • Copolymerspolymers that incorporate more than one kind of monomer into their chain (nylon) • Three important types of copolymers: • Random copolymer contains a random arrangement of the multiple monomers. • Block copolymer contains blocks of monomers of the same type • Graft copolymer contains a main chain polymer consisting of one type of monomer with branches made up of other monomers. • Figure 5 :Block CopolymerGraft CopolymerRandom Copolymer http://plc.cwru.edu/tutorial/enhanced/FILES/Polymers/struct/struct.htm

34. Physical Characteristics of Polymers • The melting or softening temperature ↑ molecular weight↑ • The molecular shape of the polymer has influence on the elastic properties. ↑ coils the ↑ elasticity of the polymer • The structure of the molecular chains has an effect on the strength and thermal stability. ↑ crosslink and network structure within the molecule ↑ the strengthandthermal stability.

35. Polymer Crystallinity • Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous content • X-ray scattering and electron microscopy have shown that the crystallites are made up of lamellae which,in turn, are built-up of folded polymer chains • Figure.6 Schematic representation of (a) fold plane showing regular chain folding, (b) ideal stacking oflamellar crystals, (c) interlamellar amorphous model, and (d) fringed micelle model of randomly distributed crystallites • (Plastic Technology Handbook)

36. Polymer crystallinity • Crystallinity occurs when linear polymer chains are structurally oriented in a uniform three dimensional matrix. Three factors that influence the degree of crystallinity are: • i) Chain length ii) Chain branching iii) Interchain bonding Figure 7: Crystalline chain http://plc.cwru.edu/tutorial/enhanced/FILES/Polymers/orient/Orient.htm

37. Polymer cristallinity Crystallinity influences: Hardness,modulus tensile, stiffness, crease, melting point of polymers. • Most crystalline polymers are not entirely crystalline. The chains, or parts of chains, that aren't in the crystals have no order to the arrangement of their chains • Crystallinity makes a polymers strong, but also lowers their impact resistance • Crystalline polymers are denser than amorphous polymers, so the degree of crystallinity can be obtained from the measurement of density  Wc=Φcρc/ ρ ρ density of entire sample ρc  density of the crystalline fraction. Φc volume fraction Wc mass fraction

38. Determinants of Polymer Crystallinity • The degree of crystallinity of a polymer depends on the rate of cooling during solidification as well as on the chain configuration. • In most polymers, the combination of crystalline and amorphous structures forms a material with advantageous properties of strength and stiffness. Figure 8: Mixed amorphous crystalline macromolecular polymer structure (http://web.utk.edu/~mse/Textiles/Polymer%20Crystallinity.htm)

39. Polymer cristallinity • Polymer molecules are very large so it might seem that they could not pack together regularly and form a crystal. Regular polymers may form lamellar crystals with parallel chains that are perpendicular to the face of the crystals. • A crystalline polymer consists of the crystalline portion and the amorphous portion. The crystalline portion is in the lamellae, and the amorphous portion is outside the lamellae . Figure 9. Arrangement of crystalline and amorphous portions http://pslc.ws/mactest/crystal.htm#structure

40. Cristillanity and amorphousness • An amorphous solid is formed when the chains have little orientation throughout the bulk polymer. The glass transition temperature is the point at which the polymer hardens into an amorphous solid. • In between the crystalline lamellae,regions with no order to the arrangement of the polymer chains  amorphous regions • Polyethylene can be crystalline or amorphous. Linear polyethylene is nearly 100% crystalline. But the branched polyethylene is highly amorphous. Figure 10.Linear and Branched Polyethylene (http://pslc.ws/macrog/kidsmac/images/pe03.gif )

41. Examples... • Highly crystalline polymers: Polypropylene, Nylon, Syndiotactic polystyrene.. • Highly amorphous polymers: Polycarbonate, polyisoprene, polybutadiene • Polymer structure and intermolecular forces has a major role of a polymer’s crystallinity.

42. Classification of Polymers …with regard to their thermal processing behavior ; • Thermoplastic Polymers (Thermoplastics) soften when heated and harden when cooled • Thermosetting Polymers (Thermosets) once having formed won’t soften upon heating

43. Thermoplastics • have linear or branched structure chains are flexible and can slide past each other

44. have strong covalent bonds and weak intermolecular van der Waals bonds • elastic and flexible above glass transition temperature • can be heat softened, remolded into different forms • reversible physical changes without a change in the chemical structure

45. Thermosets • chains chemically linked by covalent bonds • hardening involves a chemical reaction which connects the linear molecules together to form a single macromolecule.

46. Thermosets • once polymerization is complete, cannot be softened, melted or molded non-destructively. • have higher thermal, chemical and creep resistance than thermoplastics • Thermosets suitable materials for Composites Coatings Adhesive applications

47. Common thermoplastics Commodity Polymers POLYETHYLENES POLYPROPYLENE POLYSTYRENE POLYVINYLCHLORIDE-PVC POLYMETHYLMETHACRYLATE-PMMA Engineering Polymers(have a thermal resistance 100-150°C) POLYCARBONATE NYLON(POLYAMIDE) POLYETHYLEN TEREPHATALATE-PET High Performance Polymers (have a thermal resistance >150°C) POLYTETRAFLUOROETHYLENE-teflon POLYARYLETHERKETONES-PEEK

48. POLYETHYLENE • prepared directly from the polymerization of ethylene (C2H4). • two main types are; low-density (LDPE) and high-density polyethylene (HDPE) • Advantages cheap good chemical resistance high impact strength

49. Limitations low heat resistance (upper temperature limit is 60°) degrade under UV irradiation.  high gas permeability, particularly CO2 • Applications extensively for piping and packaging chemically resistant fittings, garbage bags containers, cable covering

50. POLYPROPLYLENE • improved mechanical properties compared to polyethylene; has a low density (900–915 kg/m3), harder, and has a higher strength Good chemical and fatigue resistance • Disadvantages Oxidative degradation, high thermal expansion, high creep poor UV resistance • Applications medical components, films for packaging (e.g. cigarette packets)reusable containers, laboratory equipment