Organic Chemistry Lecture 5: Polymers (KSIU, 2024) PDF

CHE 111: Organic Chemistry For level 1 : Biotechnology and Petroleum Programs (Faculty of Basic Sciences) Lecture 5: Polymers A/Prof. Omayma Fawzy Abdel Gawad Date : 4 / 11 / 2024 1 Polymer defin...

CHE 111: Organic Chemistry For level 1 : Biotechnology and Petroleum Programs (Faculty of Basic Sciences) Lecture 5: Polymers A/Prof. Omayma Fawzy Abdel Gawad Date : 4 / 11 / 2024 1 Polymer definition A large molecule composed of repeating structural units, known as monomers, is connected by covalent chemical bonds. Polymer science is a relatively new branch of science. It deals with the chemical, physical, and mechanical properties and applications of macromolecules. The terms polymer and monomer were derived from the Greek roots poly (many), mono (one), and mer (part). General properties of polymers 1. High Molecular Weight: Polymers consist of long chains of repeating units, resulting in high molecular weights. 2. Macromolecular substances do not have sharp melting points, but on heating, they soften through a range of temperatures but not a specific temperature. This is because any polymeric sample is composed of polymeric chains of various lengths, so each molecule will melt at its melting point, resulting in a melting range for the whole sample. 3. Macromolecules do not dissolve readily in the appropriate solvent, but rather absorb slowly large amounts of the solvents and largely increase their volume leading to what is known as a swelling which is then followed by complete dissolution.  Classification of Macromolecules 1. According to the origin: Natural polymers – Synthetic polymers – Semi-synthetic polymers 1. Natural Polymers: Natural polymers are derived from natural sources and are typically found in living organisms. They are often biodegradable and renewable. Examples of natural polymers include: Proteins – Polysaccharides - Nucleic Acids - Natural Rubber 2. Synthetic Polymers: Synthetic polymers are human-made polymers created through chemical reactions. They are derived from non-natural sources, such as petrochemicals. Examples of synthetic polymers include: Synthetic Rubber - Polystyrene: 3. Semi-synthetic Polymers: Semi-synthetic polymers are derived from natural polymers through chemical modifications or processing. These polymers retain some of the properties of natural polymers while incorporating synthetic modifications. Examples of semi-synthetic polymers include: Cellulose Derivatives  2. Classification of polymers according to the nature of the preparation reaction: Addition polymers – Condensation polymers 1. Addition Polymers: Addition polymers are formed through an addition or chain-growth polymerization process. In this process, monomers with unsaturated double bonds (such as ethylene or vinyl monomers) undergo repeated addition reactions to form a polymer chain. Addition polymers typically do not involve the elimination of any byproducts during polymerization. Examples of additional polymers include polyethylene, polypropylene, and polyvinyl chloride (PVC). 2. Condensation Polymers: Condensation polymers are formed through a condensation or step-growth polymerization process. In this process, two different monomers react, typically with the elimination of a small molecule like water or alcohol. The monomers join together to form a polymer chain, and the polymerization continues as more monomers are added. Examples of condensation polymers include nylon, polyester, and polyurethane. 3. Chemical Classification It is based on the chemical constitution of the polymeric chains. Carbon-chain polymers – Hetero-Chain polymers – Organo-Metallic-Chain polymers 1. Carbon-chain polymers In this case, the backbone chains are composed only of carbon atoms e.g. Polyethylene, Polystyrene 2. Hetero-chain polymers In this case, the backbone chains contain in addition to carbon atoms, atoms of other elements such as Oxygen, Nitrogen, Sulfur, Phosphorous e.g. Polyamides, Polyesters 3. Organo-metallic-chain polymers In which the backbone chains contain atoms of Si or Ti e.g. Glass, Hemoglobin 4. Classification according to the shape of the polymeric chains: Linear polymers - Branched polymers – Cross-linked polymers (3D) 1. Linear Polymers: Linear polymers have a straight chain structure. The polymer chains are composed of monomer units that are linked end-to-end, without significant cross-linking or branching. Examples include polyethylene, and polypropylene. 2. Branched Polymers: Branched polymers have a main chain with side branches or smaller chains branching off from it. The branching can occur randomly or at regular intervals. Branched polymers often exhibit different physical properties compared to linear polymers, such as lower density and improved melt flow. Examples include low-density polyethylene (LDPE) and polyethylene with long- chain branching (LCB). 3. Crosslinked or Network Polymers: Crosslinked or network polymers have a three-dimensional network structure due to the presence of covalent bonds between polymer chains. This crosslinking provides increased strength, rigidity, and dimensional stability. Crosslinked polymers are often insoluble and infusible. Examples include vulcanized rubber, epoxy resins, and crosslinked polyethylene (PEX).  5. Classification according to the effect of heat: Thermoplastic polymers – Thermosetting polymers 1. Thermoplastics: Thermoplastics are polymers that soften and become more malleable when heated, and they can be melted and re-molded multiple times without undergoing significant chemical change. When cooled, they solidify and retain their new shape. This behavior is reversible, allowing for recycling and reshaping. Examples of thermoplastics include polyethylene, polypropylene, polystyrene, and polyvinyl chloride (PVC). 2. Thermosetting Polymers: Thermosetting polymers, also known as thermosets, undergo a chemical reaction when heated, resulting in a crosslinked three-dimensional network structure. Once set, thermosets cannot be re-melted or re-molded. They retain their shape and properties even at high temperatures and are generally more rigid and heat-resistant than thermoplastics. Common examples of thermosetting polymers include epoxy resins, phenolic resins, and polyurethane.  6. Classification according to Physico-Mechanical properties: Elastomers – Plastomers – Fibers 1. Elastomers: Elastomers are polymers that exhibit a high degree of elasticity, which allows them to undergo significant deformation under stress and return to their original shape when the stress is released. Elastomers typically have a flexible, amorphous structure and can be stretched to several times their original length without permanent deformation. 2. Plastomers: Plastomers are a class of polymers that exhibit properties intermediate between elastomers and plastics. They have relatively low crystallinity and are more flexible and less rigid compared to typical plastics. Plastomers have a combination of elastomeric and plastic properties, such as good elasticity, processability, and heat sealability. 3. Fibers These polymers are characterized by high elastic modulus and a small range of elastic deformation. The effect of temperature on the mechanical properties is very limited. This is due to strong cohesive forces between neighboring chains. Applications: 1. Construction Piping: Widely used for plumbing and drainage systems due to its resistance to corrosion and chemical damage. 2. Electrical Insulation: PVC is used as an insulating material for electrical wires and cables. 3. Consumer Goods Toys: Many children's toys are made from PVC due to its safe, durable nature. Footwear: Used in the production of various types of shoes, especially waterproof options. Synthesis of Nylon 66 1. Textiles Apparel: Used in clothing such as activewear, hosiery, and swimwear due to its elasticity and moisture-wicking properties. Home Furnishings: Found in carpets and curtains for its durability and stain resistance. 2. Consumer Goods Footwear: Used in shoe laces, reinforcement, and synthetic leather products. Sports Equipment: Found in items like fishing lines, tennis strings, and athletic gear. 3. Packaging Films and Bags: Employed in flexible packaging for food and other products for its strength and barrier properties. 1. Which one of the following is a conjugate acid-base pair? a. NaF and F- b. HNO3 and HNO2 c. HI and I– d. NH4+ and NH2- e. H2O and H2O2 Answer: c. HI and I– 2. A student proposed the following Lewis structure shown for acetaldehyde. Why is this structure not feasible? Draw an acceptable Lewis structure for acetaldehyde. Show the formal charges of all nonhydrogen atoms in both the correct and incorrect structures. The formal charges on the correct and incorrect structures are as follows: 3. Draw Lewis electron structures for the following. 1.Br2 2.CH3Br 3.SO42− 4.O2 5.S22− 6.BF3 1. 2. 3. 4. 5. 6. 4. Is H–O–N=O a reasonable structure for the compound HNO2? Justify your answer using Lewis electron dot structures. Yes. This is a reasonable Lewis structure, because the formal charge on all atoms is zero, and each atom (except H) has an octet of electrons. 5. Which of the following is NOT correct for sp2 hybridization? Answer: 3. The bond angels are approximately 109.5˚ 6. When is the intramolecular hydrogen bond formed? Answer: 3. When a hydrogen atom is in between the two highly electronegative atoms 7. Answer: 2. With no electron 8. Macromolecules do not have …………… melting point a. sharp b. mixed c. range d. limit Answer: a. sharp 9. Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is (a) Neutral (b) Strongly alkaline (c) Strongly acidic (d) Weakly acidic (e) Weakly alkaline Arrange the pH in increasing order of hydrogen ion concentration. Answer: (a) D (b) C (c) B (d) A (e) E Increasing order of hydrogen ion concentration 11 < 9 < 7 < 4 < 1 i. e., C < E < D < A < B 36