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

Recommended Books “Polymer Science and Technology” by Joel R. Fried “Polymer Science” by V.R Gowarikar, N.V. Vishwanathan, Jayadev Sreedhar “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

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

Introduction A polymer is a large molecule (macromolecule) -composed of repeating structural unit connected by covalent chemical 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.

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

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

History of Macromolecules and Polymers 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 Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, and flash string) is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it was originally known as guncotton. Celluloids are a class of compounds created from nitrocellulose and camphor, with added dyes and other agents. Generally considered the first thermoplastic The main use was in movie and photography film industries, which used only celluloid films prior to acetate films that were introduced in the 1950s. Celluloid is highly flammable, difficult and expensive to produce and no longer widely used, although its most common uses today are in table tennis balls, musical instruments and guitar picks. In 1862 the first man-made plastic, nitrocellulose, (branded Parkesine) was created by Alexander Parkes from cellulose treated with nitric acid and a solvent. In 1868, American inventor John Wesley Hyatt developed a plastic material he named Celluloid, improving on Parkes' invention by plasticizing the nitrocellulose with camphor so that it could be processed into finished form and used as a photographic film

History of Macromolecules and Polymers

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

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

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.

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

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

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

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

Representation of polymer architectures (f) polycatenane (e) polyrotaxane (g) dendrimer 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.

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-

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-linked polymers involves tetrafunctional 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.

Plastic Recycling Codes

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

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.

HETERO POLYMERS

Graft copolymer Random copolymer

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

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

Isomerism Geometric 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. Geometric isomerism In organic chemistry, is a form of stereoisomerism  describing the orientation of functional groups within a molecule. e.g Cis and Trans

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 CH2 group on same side of chain 1,4-trans-polyisoprene H atom and CH3 group on opposite sides of chain

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

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