Polymers Sheet 5 PDF

Sheet 5 Polymers Question 1: Compare between addition and condensation polymerization? Aspect Addition Polymerization Condensation Polymerization Byproducts No byproducts formed Small byproducts (e.g., water) formed Monomers...

Sheet 5 Polymers Question 1: Compare between addition and condensation polymerization? Aspect Addition Polymerization Condensation Polymerization Byproducts No byproducts formed Small byproducts (e.g., water) formed Monomers Contains double/triple bonds Contains functional groups (e.g., -OH, - COOH) Chain Homochain polymer (ONE type Hetero chain polymer of atoms) (more than one type of atoms) Process Type Chain-growth mechanism Step-growth mechanism Example Polyethylene, Polypropylene Nylon Polymers PVC Question 2: What are the basic differences between thermoplastics and thermosetting plastics? Give examples. Aspect Thermoplastics Thermosetting Plastics Behavior on Can be melted and reshaped multiple times Cannot be remelted or reshaped heating without undergoing any chemical changes. Recyclability Can be recycled. Cannot be recycled Structure Linear or slightly branched Cross-linked or networked Heat Lower Higher resistance Examples: o Polyethylene (PE) o Bakelite o Polyvinyl chloride (PVC) o Epoxy resins o Polystyrene (PS) o Melamine Question 3: Describe the process of vulcanization of rubber. Definition:  Vulcanization is a chemical process that involves heating natural rubber with sulfur to improve its strength, elasticity, and durability. Process: 1. Mixing: Natural rubber is mixed with sulfur and other additives (like accelerators and activators). 2. Heating: The mixture is heated to a temperature of about 140–160°C (284–320°F).  3. Cross-linking: Sulfur atoms form cross-links between the long rubber polymer chains. o These cross-links prevent the rubber chains from sliding past each other, making the material stronger and more elastic. Result:  The vulcanized rubber becomes: o More durable and resistant to wear. o Elastic over a wide range of temperatures. o Less sticky and more resistant to solvents and heat. Example:  Car tires are made from vulcanized rubber, providing the strength and flexibility needed for rough surfaces. Question 4: Explain the mechanism of the following polymerization process: Y Y n H2C CH CH2 CH n This represents Addition Polymerization (specifically, free radical polymerization). Mechanism Steps: 1. Initiation:  Formation of free radicals: A free radical initiator (like benzoyl peroxide) decomposes into free radicals upon heating. Example: R-R→2R∙  The free radical attacks the double bond of the monomer (H₂C=CH-Y), breaking the π-bond and forming a new radical: 2. Propagation:  The newly formed radical reacts with another monomer, continuing the chain reaction: This process repeats, forming a long polymer chain. 3. Termination:  Two growing chains (radicals) combine to form a stable polymer, ending the reaction:  Overall Reaction: Example: If Y = Cl, the monomer is vinyl chloride (CH₂=CHCl), and the polymer formed is polyvinyl chloride (PVC). Question 5: Show the chemical equation for the production of nylon 6,6. Nylon 6,6 Production Process: Nylon 6,6 is produced by the condensation polymerization of adipic acid (a dicarboxylic acid) and hexamethylenediamine (a diamine): 1. Monomers: o Adipic acid: HOOC(CH2)4COOH o Hexamethylenediamine: H2N-(CH2)6-NH2 2. Polymerization Reaction: 3. Explanation: o The carboxyl group (-COOH) of adipic acid reacts with the amino group (- NH₂) of hexamethylenediamine. o This releases a molecule of water (H₂O) for each amide bond formed. o Type of Polymerization: Condensation polymerization. o Byproduct: Water (H₂O). Question 6: Classify the polymers according to: origin source, structure, intermolecular forces, and mode of polymerization. 1. Classification by Origin Source:  Natural Polymers: Occur naturally in nature. o Examples:  Cellulose (from plants)  Rubber (from rubber trees)  Proteins (like silk, wool)  Nucleic acids: RNA and DNA  Synthetic Polymers: Made through chemical processes by humans. o Examples:  Polyethylene (PE)  Polyvinyl chloride (PVC)  Nylon  Semisynthetic Polymers: Derived from natural sources but modified chemically. o Examples:  Cellulose acetate (from cellulose, used in photographic film)  Vulcanized rubber 2. Classification by Structure:  Linear Polymers: Monomers are linked in straight chains. o Example: Polyethylene (PE)  Branched Polymers: Linear chains with side branches. o Example: Low-density polyethylene (LDPE)  Crosslinked Polymers: Monomers form a network of interconnected chains. o Example: Bakelite (used in electrical insulations) 3. Classification by Intermolecular Forces: Summary Table: Property Fibers Plastics Elastomers Intermolecular Forces Strong (hydrogen bonds) Moderate Weak Strength High Moderate to high Low to moderate Elasticity Low Varies (some rigid, High some flexible) Crystallinity High Varies (amorphous Low or crystalline) Processing Drawn into strands or Molded, shaped, or Molded, then threads extruded vulcanized Applications Textiles, ropes, Packaging, furniture, Tires, seals, elastic composites electronics bands 4. Classification by Mode of Polymerization:  Addition Polymerization (Chain-growth Polymerization): o Monomer Type: Contains double bonds or other reactive groups. o Example: Polyethylene (from ethylene)  Condensation Polymerization (Step-growth Polymerization): o Monomer Type: Contains functional groups (e.g., -OH, -COOH). o Example: Nylon 6,6 (from hexamethylenediamine and adipic acid) Question 7: List the factors that affect the crystallinity of polymers. Factors Affecting Crystallinity of Polymers: Crystallinity in polymers refers to the degree of structural order within the material, 1. Intermolecular Forces: o Strong Intermolecular Forces (e.g., Hydrogen Bonding): Promote crystalline structures by holding chains together tightly. o Example: Nylon 6,6 forms strong hydrogen bonds. 2. Molecular Structure: o Linear Polymers: Tend to have higher crystallinity because their chains can pack closely together. o Branched Polymers: Tend to have lower crystallinity because the branches prevent the chains from aligning neatly. o Cross-linked Polymers: Do not crystallize because their network structure prevents packing.  3. Tacticity: o Isotactic Polymers: Have all side groups on the same side of the polymer chain, promoting crystallinity. o Syndiotactic Polymers: Alternating side groups can also crystallize. o Atactic Polymers: Random side group arrangement prevents crystallization, making them amorphous. o Example: Atactic polystyrene is amorphous. Factor Effect on Crystallinity Example Molecular structure Linear chains increase crystallinity Polyethylene (PE) Intermolecular forces Strong forces promote crystallization Nylon 6,6 Tacticity Isotactic and syndiotactic structures crystallize Isotactic polystyrene Processing conditions Mechanical stretching and annealing increase Cold-drawn fibers it Question 8: Explain how the crystallinity affects the different properties of polymers. Effect of Crystallinity on Polymer Properties: Summary Table: Property Effect of High Crystallinity Effect of Low Crystallinity (Amorphous state) Mechanical Strength High strength, rigidity Softness, flexibility Density Increased density Lower density  Crystalline regions packs the  chains are less closely packed molecules more tightly. Transparency Opaque Transparent Melting Point Higher melting point Lower melting point  The ordered structure of crystalline  The disordered regions have less regions requires more energy to break intermolecular attraction. the intermolecular forces. Solubility Lower solubility, higher chemical resistance Higher solubility  The tightly packed crystalline regions  The amorphous regions are make it more difficult for solvents to more easily attacked by penetrate. solvents). Elasticity Low elasticity High elasticity Permeability Low permeability High permeability Question 9: Multiple Choice Questions 1) What is a polymer? a) A small molecule with a single repeating unit b) A large molecule made up of repeating structural units c) A type of metal d) A small molecule with multiple functional groups Answer: b) A large molecule made up of repeating structural units 2) Which of the following is an example of a natural polymer? a) Polyethylene b) PVC c) Cellulose d) Nylon Answer: c) Cellulose 3) What type of polymerization involves the joining of monomers with the loss of a small molecule such as water? a) Addition polymerization b) Condensation polymerization c) Free-radical polymerization d) Ionic polymerization Answer: b) Condensation polymerization 4) Which of the following is a characteristic of thermoplastic polymers? a) They cannot be melted and re-shaped b) They are resistant to heat and do not soften c) They can be melted and re-shaped multiple times d) They undergo chemical changes when heated Answer: c) They can be melted and re-shaped multiple times 5) What type of intermolecular forces holds chains of nylon 6:6 together? a) Ionic bonding b) Metallic bonding c) H-bonding d) Covalent bonding Answer: c) H-bonding 6) As the crystallinity increases, the density of the polymer: a) Increases b) Decreases c) Remains constant d) No relation between them Answer: a) Increases 7) The process involving heating of rubber with sulfur is called: a) Vulcanization b) Galvanization c) Cathodic protection d) Passivation Answer: a) Vulcanization 8) PVC polymer is: a) Synthetic b) Natural c) Semisynthetic d) None of them Answer: a) Synthetic 9) Polymers composed of only one repeating unit in the polymer chains are known as: a) Homopolymers b) Copolymers c) Macromolecules d) Monomers Answer: a) Homopolymers 10) Polymers are classified as fibers, plastics, or elastomers on the basis of: a) Intermolecular forces b) Origin source c) Mode of polymerization d) Tacticity Answer: a) Intermolecular forces 11) What is the main difference between addition and condensation polymerization? a) Addition polymerization involves the loss of small molecules, while condensation polymerization does not b) Condensation polymerization involves the loss of small molecules, while addition polymerization does not c) Addition polymerization requires heat, while condensation polymerization does not d) Condensation polymerization requires heat, while addition polymerization does not Answer: b) Condensation polymerization involves the loss of small molecules, while addition polymerization does not 12) What type of polymer is formed from the polymerization of ethylene? a) Polypropylene b) Polystyrene c) Polyvinyl chloride d) Polyethylene Answer: d) Polyethylene 13) What is the repeating unit in the polymer polystyrene? a) Styrene monomer b) Ethylene glycol c) Propylene monomer d) Vinyl chloride monomer Answer: a) Styrene monomer 14) Which type of polymer is known for its ability to return to its original shape after being stretched or compressed? a) Thermoplastic b) Thermoset c) Elastomer d) Copolymer Answer: c) Elastomer 15) What is the degree of polymerization? a) The molecular weight of a polymer b) The number of repeating units in a polymer chain c) The density of a polymer d) The melting point of a polymer Answer: b) The number of repeating units in a polymer chain 16) How is the degree of polymerization (DP) calculated? a) DP = (Total molecular weight of polymer) / (Molecular weight of repeating unit) b) DP = (Molecular weight of repeating unit) / (Total molecular weight) c) DP = (Density of polymer) / (Volume of polymer) d) DP = (Molecular weight of monomer) / (Number of repeating units) Answer: a) DP = (Total molecular weight of polymer) / (Molecular weight of repeating unit) 17) What is the significance of the degree of polymerization in determining the properties of a polymer? a) It determines the color of the polymer b) It affects the thermal and mechanical properties of the polymer c) It has no impact on the properties of the polymer d) It determines the solubility of the polymer Answer: b) It affects the thermal and mechanical properties of the polymer 18) Which of the following is true about polymers with a high degree of polymerization? a) They have low molecular weight b) They have short chain lengths c) They exhibit higher mechanical properties d) They have lower viscosity Answer: c) They exhibit higher mechanical properties 19) How does the degree of polymerization affect the viscosity of polymer solutions? a) Higher DP decreases viscosity b) Higher DP increases viscosity c) DP has no effect on viscosity d) DP only affects the viscosity of solid polymers Answer: b) Higher DP increases viscosity 20) How does the degree of polymerization affect the melting point of a polymer? a) Higher DP decreases the melting point b) Higher DP increases the melting point c) DP has no effect on the melting point d) DP only affects the melting point of crystalline polymers Answer: b) Higher DP increases the melting point 21) What is the primary characteristic of addition polymerization? a) Loss of small molecules such as water or methanol b) Formation of a single product from multiple monomers c) Involves step-growth mechanism d) Requires a catalyst for initiation Answer: b) Formation of a single product from multiple monomers 22) Which of the following is a key feature of condensation polymerization? a) Involves free radical initiators b) No byproducts are formed c) Loss of small molecules like water or ammonia during polymer formation d) Only occurs with unsaturated monomers Answer: c) Loss of small molecules like water or ammonia during polymer formation 23) Which polymer is typically formed through addition polymerization? a) Nylon b) Polyester c) Polyethylene d) Bakelite Answer: c) Polyethylene 24) During addition polymerization, what happens to the double bonds in the monomers? a) They remain unchanged b) They are converted into triple bonds c) They open up to form single bonds, creating a polymer chain d) They form ionic bonds Answer: c) They open up to form single bonds, creating a polymer chain 25) What type of polymerization involves monomers with functional groups such as hydroxyl or carboxyl groups? a) Addition polymerization b) Condensation polymerization c) Free radical polymerization d) Emulsion polymerization Answer: b) Condensation polymerization 26) Which of the following is not a byproduct of condensation polymerization? a) Water b) Methanol c) Ammonia d) Ethylene Answer: d) Ethylene 27) Which polymerization process is used to produce nylon 6,6? a) Addition polymerization b) Condensation polymerization c) Free radical polymerization d) Emulsion polymerization Answer: b) Condensation polymerization 28) Polymers can be classified based on their origin into which categories? a) Natural and synthetic b) Organic and inorganic c) Thermoplastic and thermosetting d) Addition and condensation Answer: a) Natural and synthetic 29) Which of the following is an example of a natural polymer? a) Polyethylene b) Nylon c) Silk d) Polystyrene Answer: c) Silk 30) How are elastomers typically processed to improve their properties? a) Melting and molding b) Electroplating c) Vulcanization d) Polymerization Answer: c) Vulcanization 31) Thermoplastic polymers are characterized by which of the following properties? a) They cannot be remelted once hardened b) They can be remelted and reshaped multiple times c) They are biodegradable d) They are always crystalline Answer: b) They can be remelted and reshaped multiple times 32) What is a key characteristic of thermosetting polymers? a) They can be softened and remolded repeatedly b) They form cross-linking bonds c) They are soluble in water d) They are elastic and flexible Answer: b) They form cross-linking bonds 33) Polymers can be classified based on their structure into which categories? a) Crystalline and amorphous b) Linear, branched, and cross-linked c) Thermoplastic and thermosetting d) Natural and synthetic Answer: b) Linear, branched, and cross-linked 34) How are copolymers different from homopolymers? a) Copolymers contain only one type of monomer b) Copolymers contain two or more different types of monomers c) Homopolymers are always synthetic d) Homopolymers contain multiple types of monomers Answer: b) Copolymers contain two or more different types of monomers 35) What type of polymerization process is typically used to produce polyethylene? a) Condensation polymerization b) Addition polymerization c) Ring-opening polymerization d) Step-growth polymerization Answer: b) Addition polymerization 36) Based on molecular structure, what type of polymer is characterized by a highly ordered, repeating arrangement of monomers? a) Amorphous polymer b) Crystalline polymer c) Elastomer d) Thermoplastic polymer Answer: b) Crystalline polymer 37) Which polymer is a common example of a thermoplastic? a) Epoxy resin b) Polyethylene (PE) c) Bakelite d) Urea-formaldehyde Answer: b) Polyethylene (PE) 38) What is a key difference between thermoplastic and thermosetting polymers? a) Thermoplastics are more resistant to heat than thermosets b) Thermosetting polymers can be reshaped by heating, while thermoplastics cannot c) Thermoplastics can be remelted and reshaped, while thermosetting polymers form permanent bonds d) Thermosetting polymers are always biodegradable, while thermoplastics are not Answer: c) Thermoplastics can be remelted and reshaped, while thermosetting polymers form permanent bonds 39) Which property is typically higher in thermosetting polymers compared to thermoplastics? a) Color b) Flexibility c) Solubility in water d) Thermal stability Answer: d) Thermal stability 40) Which of the following is a disadvantage of thermoplastic polymers? a) They cannot be recycled b) They are less resistant to high temperatures than thermosetting polymers c) They cannot be used in flexible applications d) They are always brittle Answer: b) They are less resistant to high temperatures than thermosetting polymers 41) What does the term "crystallinity" in polymers refer to? a) The color of the polymer b) The degree of order of the polymer chains c) The density of the polymer d) The chemical composition of the polymer Answer: b) The degree of order of the polymer chains 42) How does crystallinity affect the hardness of polymers? a) Increases flexibility and decreases strength b) Decreases both flexibility and strength c) Increases strength and decreases flexibility d) Increases both flexibility and strength Answer: c) Increases strength and decreases flexibility 43) What effect does high crystallinity have on the solubility of a polymer? a) Decreases the solubility b) Increases the solubility c) Has no effect on the solubility d) Polymers are insoluble in all solvents Answer: a) Decreases the solubility 44) How does the presence of crystalline regions impact the transparency of a polymer? a) Increases transparency b) Decreases transparency c) Has no effect on transparency d) Makes the polymer opaque Answer: b) Decreases transparency 45) Which factor typically influences the degree of crystallinity in polymers? a) Dragging of polymer chains b) Chemical structure of the polymer c) Strength of intermolecular forces d) Color of the polymer Answer: b) Chemical structure of the polymer 46) What is the primary advantage of using amorphous polymers over crystalline polymers? a) Higher strength and rigidity b) Greater optical clarity and transparency c) Higher melting points d) Increased thermal stability Answer: b) Greater optical clarity and transparency 47) How does the crystallinity of a polymer affect its density? a) Crystalline polymers have lower density b) Crystalline polymers have higher density c) Crystallinity does not affect density d) Crystalline polymers have the same density as amorphous polymers Answer: b) Crystalline polymers have higher density 48) What does the term "tacticity" refer to in polymers? a) The molecular weight of the polymer b) The arrangement of pendant groups along the polymer chain c) The color of the polymer d) The degree of polymerization Answer: b) The arrangement of pendant groups along the polymer chain 49) Which type of tacticity describes a polymer with pendant groups arranged in a random fashion? a) Isotactic b) Syndiotactic c) Atactic d) None of them Answer: c) Atactic 50) What is the characteristic of an isotactic polymer? a) Pendant groups are arranged randomly b) Pendant groups alternate in position along the chain c) Pendant groups are all on the same side of the polymer chain d) The polymer chain has no pendant groups Answer: c) Pendant groups are all on the same side of the polymer chain 51) Which tacticity of polymers results in the highest degree of crystallinity? a) Isotactic b) Syndiotactic c) Atactic d) Heterotactic Answer: a) Isotactic 52) What is the effect of tacticity on the melting point of polymers? a) Tacticity has no effect on the melting point b) Isotactic polymers generally have higher melting points c) Atactic polymers generally have higher melting points d) Syndiotactic polymers have the lowest melting points Answer: b) Isotactic polymers generally have higher melting points 53) How does tacticity affect the physical properties of a polymer? a) It only affects the color b) It has no impact on physical properties c) It influences crystallinity, melting point, and mechanical strength d) Both a and c Answer: c) It influences crystallinity, melting point, and mechanical strength