Lecture # 01, 02, 03 Polymer Science and Engineering (TM-2052)

1. Lecture # 01, 02, 03Polymer Science and Engineering (TM-2052) By: Muhammad Haseeb Iqbal National Textile University

2. Recommended Books • “Polymer Science and Technology” by Joel R. Fried • “Polymer Science” by V.R Gowarikar, N.V. Vishwanathan, JayadevSreedhar • “Principles of Polymer Science” by P. Bahadur, N.V. Sastry • “Principles of polymerization” by George Odian • “Essentials of Polymer Science and Engineering” by Paul C. Painter, Michael M. Coleman

3. Concepts to be covered • Introduction - What are polymers? • Basic Polymer Engineering Terminologies • Recent scenario of polymer industry • Brief History of Polymers • Polymer waste disposal • Types Of Linking In Polymers • Representation of polymer architectures • Functionality of Polymers • Recycling Codes for plastics • Polymer Structure • Copolymers • Tacticity / Stereochemistry • Geometric isomerism

4. Introduction A polymer is a large molecule (macromolecule) -composed of repeating structural unit connected by covalentchemical bonds. - The word is derived from the Greek words (poly), meaning "many"; and (meros), meaning "part" Example:- Polystyrene, poly-vinyl-chloride etc. - They are complex and giant molecules and are different from low molecular weight compounds. -`Macro-molecules’ are made up of much smaller molecules.

6. Basic Polymer Science & Engineering Terminologies Monomer Compound or compounds used in the preparation of polymer. (may or may not be equivalent to the repeat unit) Constitutional repeat units Repeating units constituting the polymer molecule Oligomer: A molecule consisting of reaction of several repeat units of monomer, but not large enough to be considered as a polymer (dimer, trimer, tetramer…) Degree of Polymerization (DP) Number of repeating units in a polymer Molecular weight of a polymer Molecular weight of repeating unit × DP Primary bonds - the covalent bonds that connect the atoms of the main chain Secondary bonds - non-covalent bonds that hold one polymer chain to another, including hydrogen bonding and other dipole-dipole attractions

7. Industrial Scenario Polymers replacing metals in every application Fig: Us production (109 Kg/year) from 1970 to 2000 of various polymers

8. 1846 Christian Schönbein invented nitrocellulose (gun cotton). Cellulose nitrate is a hard elastic material which is soluble and easy to be shaped. 1862 Alexander Parkes made articles from plasticized cellulose nitrate 1870 John and Isaiah Hyatt patented celluloid 1892 Charles Cross, Edward Bevan, and Clayton Beadle patented regenerated cellulose, i.e., viscose rayon fibers and cellophane films History of Macromolecules and Polymers

9. History of Macromolecules and Polymers

10. 1977 Alan Heeger, Alan MacDiarmid, and Hideki Shirakawa discovered and developed conducting polymers History of Macromolecules and Polymers

11. Polymer Waste Disposal and Remedies • Problems associated with polymers • Resources • Polymer waste disposal • Possible solutions • Recycling of used polymers • Making them biodegradable • Use of recycled glass, rubber, polyethylene, polypropylene, polystyrene and polyester into manufacturing of valuable products. • Challenge regarding recycling of polymers • Thermoset plastics and rubbers are difficult to recycle • More research needs to be done in order to commercialize biodegradable polymers

12. Types Of Linking In Polymers Linear Polymers: A polymer in which the molecules form long chains without branches or cross-linked structures. examples: nylon, polyester, PVC etc.

13. Branched Polymer: A polymer chain having branch points that connect three or more chain segments. Examples: polythene, glycogen, starch etc

14. Cross linked Polymer: Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. Examples: malamine formaldehyde resin etc

15. Bakelite Linear & Branched Polymers are know as thermoplastic materials. Cross linked Polymer are know as thermosetting materials.

16. (a) star polymer (b) comb polymer (c)ladder polymer Representation of polymer architectures (d) semi- ladder (or stepladder) polymer

17. (f) polycatenane (e) polyrotaxane (g) dendrimer Representation of polymer architectures A rotaxane is a mechanically-interlocked molecular architecture consisting of a "dumbbell shaped molecule" which is threaded through a "macrocycle" A catenane is a mechanically-interlocked molecular architecture consisting of two or more interlocked macrocycles.

18. Functionality of Polymers • The functionality of a monomeric structural unit is defined as the number of covalent bonds which it forms with other reactants. • A structural unit in a linear polymer chain segment forms two bonds and is • Consider the example of polyethylene terephthalate (PET or "polyester"). The monomers which could be used to create this polymer are ethylene glycol and terephthalic acid: • HO-CH2-CH2-OH and HOOC-C6H4-COOH • therefore bifunctional, as for the PET structural units • In the polymer, there are two structural units, which are -O-CH2-CH2-O- and -CO-C6H4-CO- • The repeat unit is • -CH2-CH2-O-CO-C6H4-CO-O-

19. Contd. • In branched polymers, there aretrifunctional units at each branch point. • For example in the synthesis of PET, a small fraction of the ethylene glycol can be replaced by glycerol which has three alcohol groups. This trifunctional molecule inserts itself in the polymeric chain and bonds to three carboxylic acid groups forming a branch point. • Finally, the formation of cross-linkedpolymers involvestetrafunctional structural units. • Other values of functionality exist. Unless the macromolecule is cyclic, it will have monovalent structural units at each end of the polymer chain.

20. Plastic Recycling Codes

21. Polymer structure The properties of polymers are strongly influenced by details of chain structure. These include: • Copolymers • Tacticity / Stereochemistry • Geometric isomerism

22. Homo-polymer vs Copolymer A homo-polymer is a polymer which is formed from only one type of monomer. e.g PE,PP,PVC etc A hetero-polymer, also called a copolymer, is a polymer formed when two (or more) different types of monomer are linked in the same polymer chain, as opposed to a homo-polymer where only one monomer is used. e.g ABS plastic, SBR, Nitrile rubber, styrene-acrylonitrile, styrene-isoprene-styrene (SIS) and ethylene-vinyl acetate.

23. HETERO POLYMERS

24. Graft copolymer Random copolymer

25. Tacticity Tacticity – stereoregularity or spatial arrangement of R units along chain Isotactic – all R groups on same side of chain Syndiotactic– R groups alternate sides

26. Tacticity (cont.) Atactic atactic – R groups randomly positioned

27. Geometric isomerism Isomerism Compounds having same molecular formula but different structural formula and differ from each other in physical and chemical properties are known as “Isomers” and this phenomenon is called “Isomerism”. Isomerism is due to the difference in the arrangement of atoms in molecules. • In organic chemistry, is a form of stereoisomerism  describing the orientation of functional groups within a molecule. e.g Cis and Trans

28. Cis/trans Isomerism The terms cis and trans are from Latin, in which cis means "on the same side" and trans means "on the other side" or "across“. For example 1,4-cis-polyisoprene CH2groupon same side of chain 1,4-trans-polyisoprene H atom and CH3 group on opposite sides of chain

29. How to Determine Microstructure? NMR is a very powerful way to determine the microstructure of a polymer. NMR spectrum of CH3 region of atactic polypropylene

30. Why is this important? • 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 PP is a low melting, gooey material • Isoatactic PP is high melting (176º), crystalline, tough material that is industrially useful • Syndiotactic PP has similar properties, but is very clear. It is harder to synthesize