Question 1

Compared with nylon fibres, Dacron (Terylene) polyester fibres generally exhibit which combined property trends in routine textile service and chemical exposure?

Accepted Answer

Introduction / Context: Polyester (Dacron/Terylene) and nylon are the two most common synthetic fibres. Their comparative behavior under heat, chemicals, and dyeing affects fabric engineering, apparel finishing, and industrial textile selection. Recognizing the overall trends helps with appropriate material choice. Given Data / Assumptions: Polyester is PET; nylon refers to aliphatic polyamides (e.g., nylon-6, nylon-66). We compare heat resistance, acid/alkali resistance, and dyeability. General textile conditions (not extreme lab conditions) are assumed. Concept / Approach: Polyester typically has better heat resistance and dimensional stability than nylon under ironing or hot-washing conditions. Chemically, polyester is more resistant to many acids but is susceptible to alkaline hydrolysis. Dyeability of PET is more challenging due to its hydrophobic, highly crystalline nature and lower amide hydrogen bonding sites compared to nylon; it often requires carriers or higher temperatures (disperse dyes) to achieve deep shades. Step-by-Step Solution: Assess heat resistance → PET usually superior to nylon.Assess acid/alkali → PET better against acids; nylon better against base → PET poorer in alkali.Assess dyeability → nylon dyes readily; PET is harder to dye → poorer dyeability for Dacron. Verification / Alternative check: Textile finishing guides corroborate that PET shows good hot pressing tolerance and acid resistance but requires disperse dyes and elevated temperatures, while strong alkalis can hydrolyze ester linkages. Why Other Options Are Wrong: Each single statement is true; collectively they form the most complete answer, hence “All of the above”. Common Pitfalls: Assuming one property (e.g., toughness) predicts chemical resistance; ignoring different dye classes used for nylon vs. polyester. Final Answer: All of the above

Question 2

In elastomer nomenclature, the commercial name “Neoprene” corresponds to which specific polymer type?

Accepted Answer

Introduction / Context: Trade names often obscure the underlying polymer chemistry. For design and materials selection, it is critical to link commercial names to their real polymer identity and performance envelope. Neoprene is a classic case frequently encountered in seals, hoses, and protective apparel. Given Data / Assumptions: Neoprene is a long-established elastomer brand name. Typical applications include wetsuits, belts, hoses, and vibration mounts. Need to map the brand to the polymer backbone and repeating unit. Concept / Approach: Neoprene is polychloroprene, obtained by polymerization of chloroprene (2-chloro-1,3-butadiene). The chlorinated backbone imparts oil and weathering resistance superior to many non-polar rubbers, with useful flame resistance and good mechanical strength, distinguishing it from SBR, polyurethane elastomers, or thermoset phenolics. Step-by-Step Solution: Identify monomer → chloroprene.Polymerize to obtain → polychloroprene = Neoprene.Exclude unrelated polymers (SBR, PU, phenolics) based on chemistry and application domains. Verification / Alternative check: Materials databases and rubber handbooks consistently equate Neoprene to polychloroprene (CR), confirming the identity. Why Other Options Are Wrong: Polyurethane: Different chemistry and uses. Phenol–formaldehyde: A thermoset resin, not an elastomer. SBR: Copolymer of styrene and butadiene; lacks chlorine and different performance profile. Common Pitfalls: Equating all black rubbers visually; relying on trade names without confirming polymer chemistry. Final Answer: Polychloroprene

Question 3

Polymethyl methacrylate (PMMA), a transparent thermoplastic used for glazing and lenses, is commonly marketed under which trade/commodity name?

Accepted Answer

Introduction / Context: PMMA is a key optical plastic replacing glass in many applications due to clarity, weatherability, and ease of fabrication. Connecting polymer names to their commercial aliases avoids design errors and ensures correct material specifications for optical and structural components. Given Data / Assumptions: Target polymer: PMMA (polymethyl methacrylate). Applications: signage, lenses, aquaria, glazing. Trade names vary regionally (e.g., Perspex, Plexiglas, Acrylite). Concept / Approach: Perspex (also Plexiglas) denotes PMMA. It offers high light transmission, good surface hardness for a plastic, and good UV resistance, distinguishing it from PTFE (Teflon), melamine/phenolic resins (Bakelite systems), or aliphatic polyamides like nylon-6. Step-by-Step Solution: Identify polymer → PMMA.Map to trade names → Perspex/Plexiglas/Acrylite.Eliminate other well-known but unrelated polymers. Verification / Alternative check: Material datasheets and vendor catalogs list Perspex and Plexiglas as PMMA grades with optical properties near glass level transmission (~92%). Why Other Options Are Wrong: Bakelite: Phenol–formaldehyde thermoset; opaque and brittle. Teflon: PTFE; exceptional chemical resistance and low friction, not a transparent glazing plastic. Nylon-6: Engineering polyamide, not primarily an optical glazing polymer. Common Pitfalls: Assuming any clear plastic is polycarbonate; confusing brand names across regions. Final Answer: Perspex

Question 4

Which thermosetting “amino” resin family results from condensation polymerization of formaldehyde with urea or with melamine and is widely used in laminates, molded ware, and coatings?

Accepted Answer

Introduction / Context: Amino resins are important thermosets in surface finishes, laminates, and molding. Recognizing the condensation pairs (formaldehyde with urea or melamine) clarifies performance traits like hardness, clarity, and heat resistance compared to other resin families such as phenolics, epoxies, and alkyds. Given Data / Assumptions: Monomers: formaldehyde plus urea or melamine. Applications: decorative laminates, dinnerware, coatings crosslinkers. Network-forming condensation creating hard, thermoset structures. Concept / Approach: Urea–formaldehyde (UF) and melamine–formaldehyde (MF) are classic amino resins. They cure to hard, glossy, scratch-resistant networks. Epoxies are formed from epoxides and amines/anhydrides; phenolics from phenol and formaldehyde; alkyds from polyols and polyacids (often oil-modified). Thus the formaldehyde + urea/melamine route uniquely identifies amino resins. Step-by-Step Solution: Match monomer pair → formaldehyde with urea/melamine.Identify resin family → amino (UF/MF).Reject other resin classes with different monomer chemistries. Verification / Alternative check: Coatings and laminate industry references list UF/MF as amino resins, often used as crosslinkers with alkyds/acrylics for baking enamels. Why Other Options Are Wrong: Epoxy: No formaldehyde–urea/melamine condensation. Alkyd: Polyester networks from polyols and acids. Phenolic: Phenol–formaldehyde, not urea/melamine–formaldehyde. Common Pitfalls: Confusing phenolic with melamine formaldehyde due to “formaldehyde” in both; overlooking the amide/amine functionality in amino resins. Final Answer: Amino resins

Question 5

Condensation/transesterification of dimethyl terephthalate (or terephthalic acid) with ethylene glycol yields which polymer product used for fibres and films?

Accepted Answer

Introduction / Context: Identifying monomer pairs is central to polymer synthesis. Dimethyl terephthalate (DMT) or terephthalic acid and ethylene glycol react to form a linear polyester widely used as fibre (Dacron/Terylene) and film/sheet (PET). This question checks accurate mapping between monomers and final polymer identity. Given Data / Assumptions: Aromatic diacid (or its methyl ester): terephthalic unit. Aliphatic diol: ethylene glycol. Condensation proceeds via transesterification and polycondensation. Concept / Approach: Terephthalate units plus ethylene glycol produce polyethylene terephthalate (PET). In fibre form, PET is marketed as Dacron/Terylene; in films/bottles, it remains PET. Other listed polymers arise from different monomer sets: nylon-6 from caprolactam; PVC from vinyl chloride; polycarbonate from bisphenol-A and phosgene or transesterification with diphenyl carbonate. Step-by-Step Solution: Identify diacid and diol → terephthalate + ethylene glycol.Apply condensation chemistry → ester linkages form → PET.Map trade name for fibre → Dacron (Terylene). Verification / Alternative check: Polymer chemistry texts and industrial routes (DMT or PTA processes) confirm PET formation under antimony, titanium, or germanium catalysts. Why Other Options Are Wrong: Nylon-6: Derived from caprolactam ring-opening. Polycarbonate: Requires bisphenol-A and carbonate chemistry. PVC: Chain-growth polymer of vinyl chloride. Common Pitfalls: Confusing PET with general “polyester” answers and creating ambiguity; mixing trade names across polymers. Final Answer: Dacron (polyethylene terephthalate)

Question 6

Chemically, “Neoprene” rubber is the polymer known as which of the following (identify its correct IUPAC-style common name)?

Accepted Answer

Introduction / Context: Different elastomers often serve overlapping applications, but their chemistries yield distinct performance profiles. Accurately identifying Neoprene’s chemical name is important for specifying properties like oil resistance, flame behavior, and weathering stability in seals and belts. Given Data / Assumptions: Neoprene is an elastomeric material. Monomeric unit involves chlorinated diene. Applications require balanced oil, ozone, and weathering resistance. Concept / Approach: Neoprene is polychloroprene (CR), polymerized from chloroprene (2-chloro-1,3-butadiene). The chlorine substituent contributes to flame retardancy and ozone resistance compared to unsaturated hydrocarbon rubbers like polybutadiene or SBR. Polyurethane elastomers are chemically distinct, formed by isocyanate–polyol reactions. Step-by-Step Solution: Identify Neoprene → commercial name for polychloroprene.Exclude hydrocarbon elastomers (BR, SBR) lacking chlorine.Exclude polyurethane (thermoset/TPU chemistry, different synthesis). Verification / Alternative check: Rubber industry resources list Neoprene = CR with grades tailored by crystallization rate and crystallite content for mechanical performance. Why Other Options Are Wrong: Polybutadiene/SBR: No chlorine; different oil/ozone behavior. Polyurethane: Not a polydiene; different curing and properties. Common Pitfalls: Assuming appearance or hardness alone identifies elastomers; overlooking halogenated backbone effects. Final Answer: Polychloroprene

Question 7

In polymer chemistry, identify the correct monomer used to synthesize poly(vinyl chloride) (PVC) via chain-growth polymerization from vinyl monomers.

Accepted Answer

Introduction / Context: PVC (poly(vinyl chloride)) is one of the world’s most widely used thermoplastics. The question tests understanding of monomer–polymer relationships and basic nomenclature in polymer science, which is fundamental for materials selection and processing in chemical engineering and plastics manufacturing. Given Data / Assumptions: PVC is formed by addition (chain-growth) polymerization. Possible precursors include several chlorinated C1–C2 molecules listed in the options. Nomenclature: chloroethene is the systematic name for vinyl chloride. Concept / Approach: In chain-growth polymerization, unsaturated monomers containing carbon–carbon double bonds (like alkenes) add to a growing radical, cation, or anion. PVC specifically arises from polymerization of vinyl chloride, whose IUPAC name is chloroethene (CH2=CH–Cl). Molecules lacking a double bond or being too small/incorrectly substituted cannot serve as the direct monomer for PVC under standard processes. Step-by-Step Solution: Identify which candidates possess C=C unsaturation suitable for chain-growth: chloroethene does; ethyl chloride and chloroform do not; ethylene dichloride is saturated (Cl–CH2–CH2–Cl).Map common names: vinyl chloride ≡ chloroethene.Conclude the correct monomer is chloroethene. Verification / Alternative check: Industrial PVC is produced by bulk, suspension, or emulsion polymerization of vinyl chloride monomer (VCM). The reaction yields –CH2–CH(Cl)– repeating units, matching PVC’s structure. Why Other Options Are Wrong: Ethylene dichloride: A saturated dihalide; used to manufacture VCM via cracking, but not itself the polymerization monomer for PVC. Chloroform: Trihalomethane with no C=C; cannot undergo vinyl addition. Ethyl chloride: Saturated alkyl chloride; no double bond. Common Pitfalls: Confusing feedstock or intermediates (like ethylene dichloride) with the actual monomer. Only the vinyl chloride (chloroethene) molecule polymerizes directly to PVC. Final Answer: chloroethene

Question 8

Celluloid, an early moldable plastic widely used for films and small articles, is primarily composed of which chemically modified form of cellulose?

Accepted Answer

Introduction / Context: Celluloid was among the first commercial plastics, historically used for photographic film, toys, and combs. Recognizing its composition helps distinguish early thermoplastics from later, safer materials and shows how chemical modification of biopolymers creates new properties. Given Data / Assumptions: All options are cellulose derivatives or related materials. Celluloid is often plasticized with camphor. We focus on the principal polymeric component. Concept / Approach: Cellulose can be esterified to make cellulose nitrate (nitrocellulose) or cellulose acetate. Celluloid specifically refers to nitrocellulose plasticized (commonly with camphor), giving a tough, moldable material. This composition also explains the significant flammability associated with celluloid products. Step-by-Step Solution: Identify historical definition: Celluloid = nitrocellulose + camphor + dyes/additives.Compare with alternatives: cellulose acetate and cellulose acetate butyrate were later, safer film bases; regenerated cellulose denotes cellophane/rayon processes.Select cellulose nitrate as the correct base polymer of celluloid. Verification / Alternative check: Museum conservation literature and polymer histories describe celluloid degradation (nitrous off-gassing) consistent with nitrocellulose chemistry, confirming the identification. Why Other Options Are Wrong: Cellulose acetate: Used for safety film; different polymer. Cellulose acetate butyrate: A later mixed ester with improved weatherability. Regenerated cellulose: Produced by viscose/lyocell routes; not celluloid. Common Pitfalls: Assuming all early films were cellulose acetate; early motion pictures used celluloid (nitrocellulose), which contributed to fire hazards. Final Answer: cellulose nitrate

Question 9

In the processing of synthetic plastics, why are plasticizers incorporated into the polymer formulation? Select the most comprehensive reason.

Accepted Answer

Introduction / Context: Plasticizers are low-molecular-weight additives that modify polymer mobility, glass transition temperature, and processability. Understanding their role is central to tailoring properties of PVC, nitrile rubbers, and many other plastics used in cables, flooring, and flexible containers. Given Data / Assumptions: Base resin is relatively rigid or has a high glass transition temperature. Additive is compatible and dispersible within the polymer matrix. Application demands flexibility, ease of shaping, or special performance attributes. Concept / Approach: Plasticizers increase free volume and chain mobility, lowering the glass transition temperature (Tg). This yields softer, more flexible materials, reduces melt viscosity during processing, and can introduce properties like low-temperature flexibility or improved impact resistance when properly formulated. Step-by-Step Solution: Relate molecular effect: plasticizer molecules interpose between polymer chains, weakening intermolecular attractions.Process consequence: reduced Tg and viscosity → easier calendering, extrusion, or molding.Performance effect: flexibility, compliance, and sometimes enhanced durability or low-temperature performance.Thus, plasticizers impart flexibility, improve workability, and help develop enhanced properties. Verification / Alternative check: Empirical PVC data show significant Tg depression with phthalates, adipates, or citrate plasticizers, correlating with measured flexibility and processability improvements. Why Other Options Are Wrong: Single-benefit choices (a), (b), or (c) are incomplete; plasticizers commonly deliver all listed effects when compatibilized. Common Pitfalls: Ignoring compatibility limits and migration; not all plasticizers suit every polymer, and excessive levels can exude or reduce mechanical strength. Final Answer: all (a), (b) and (c)

Question 10

Thermal behavior of engineering polymers: Which listed polymer typically begins to decompose (e.g., dehydrochlorinate) before reaching a clean melting transition under standard processing conditions?

Accepted Answer

Introduction / Context: Different polymers exhibit distinct thermal transitions (glass transition, melting) and stability limits. Recognizing which polymers degrade before melting informs safe processing windows and stabilizer selection, especially for halogen-containing plastics. Given Data / Assumptions: Processing occurs in air or inert atmosphere typical for extrusion/molding. ‘‘Decomposing before melting’’ refers to chemical breakdown that precedes a neat crystalline melt. Commercial stabilizers may extend stability but not alter the fundamental tendency. Concept / Approach: PVC’s backbone contains labile C–Cl bonds. On heating, PVC undergoes dehydrochlorination, forming conjugated polyenes and releasing HCl, often before a well-defined melting event for the polymer backbone. This requires heat stabilizers (e.g., organotin, Ca–Zn) to process safely. In contrast, many nylons melt cleanly before significant decomposition, and polystyrene softens and flows below its degradation threshold in normal processing. Step-by-Step Solution: Evaluate PVC: early onset dehydrochlorination; discoloration (yellow→brown) occurs with HCl evolution.Evaluate Nylon: semi-crystalline polyamide with melting transition typically prior to major decomposition.Evaluate Polystyrene: amorphous thermoplastic softening near Tg; thermal stability adequate for molding.Therefore, PVC is the polymer that tends to decompose before a clean melt, absent stabilizers. Verification / Alternative check: Thermogravimetric analysis and DSC profiles show PVC mass loss and HCl evolution preceding neat melting; industrial practice mandates stabilizers and careful temperature control. Why Other Options Are Wrong: Nylon: Exhibits melting prior to significant degradation under normal conditions. Polystyrene: Processes below its decomposition temperature in standard operations. None of these: Incorrect because PVC fits the described behavior. Common Pitfalls: Assuming additives eliminate decomposition tendency; stabilizers only delay degradation and broaden the processing window. Final Answer: PVC

Question 11

Industrial applications of C4 dienes: Identify the principal industrial use of 1,3-butadiene in large-scale chemical manufacturing.

Accepted Answer

Introduction / Context: 1,3-Butadiene is a key petrochemical building block. Understanding its dominant application highlights connections between monomer markets and end-use sectors like automotive tires, footwear, hoses, and vibration-damping components. Given Data / Assumptions: We consider global bulk usage patterns rather than specialty niche uses. Common copolymerization partners include styrene and acrylonitrile. Evaluation concerns the largest consumption pathway. Concept / Approach: Butadiene’s conjugated diene structure makes it ideal for producing elastomers. The major products are SBR (styrene-butadiene rubber), PBR (polybutadiene rubber), and NBR (acrylonitrile-butadiene rubber). These elastomers dominate tire treads, sidewalls, and impact-modified plastics (e.g., ABS uses butadiene in the rubbery phase). Step-by-Step Solution: List candidate uses: additives in paints/plasticizers vs. elastomer manufacture.Compare market volumes: elastomers represent the overwhelming share of butadiene demand.Select the dominant use: manufacture of synthetic rubber. Verification / Alternative check: Industry reports consistently show SBR and PBR as principal outlets for butadiene, driven by tire production volumes worldwide. Why Other Options Are Wrong: Anti-skimming in paint: Not a primary or large-volume use for butadiene monomer. Plasticizer for unsaturated polyester: Plasticizers are different compounds; butadiene is a monomer for elastomers, not a typical plasticizer. None of these: Incorrect since the elastomer route is correct. Common Pitfalls: Confusing butadiene’s role in ABS (impact modifier phase) with plasticization; it is chemically part of a copolymer, not a free plasticizer. Final Answer: in the manufacture of synthetic rubber

Question 12

Nitrile rubber (NBR): Identify the correct pair of monomers used to produce this oil-resistant elastomer by copolymerization.

Accepted Answer

Introduction / Context: Nitrile rubber (NBR) is valued for its resistance to oils, fuels, and many chemicals. It is ubiquitous in seals, O-rings, fuel hoses, gloves, and gasketing. The question assesses knowledge of the monomer composition underlying these performance traits. Given Data / Assumptions: NBR is a copolymer rather than a homopolymer. Candidate monomers include common vinyl and diene species. Oil resistance correlates with polar nitrile content in the copolymer. Concept / Approach: NBR results from emulsion or solution copolymerization of acrylonitrile (ACN) with 1,3-butadiene. The ACN content (typically 18–50%) tunes polarity and oil resistance: more ACN improves fuel/oil resistance but reduces low-temperature flexibility. The butadiene segments provide elastomeric behavior and processability. Step-by-Step Solution: Identify monomer that introduces nitrile functionality: acrylonitrile.Identify elastomeric diene partner: 1,3-butadiene.Select the pair acrylonitrile & butadiene as the definition of NBR. Verification / Alternative check: Specifications for NBR (e.g., ASTM designations) list ACN content to classify grades, confirming the monomer set. Why Other Options Are Wrong: Acrylonitrile & styrene: Leads to SAN, a rigid copolymer (used in ABS blends) not an oil-resistant elastomer. Isobutylene & isoprene: Forms butyl rubber (IIR), a different elastomer with low gas permeability, not NBR. None of these: Incorrect because option (a) is correct. Common Pitfalls: Assuming all nitrile-named materials are homopolymers of acrylonitrile; NBR is a copolymer with critical composition balance. Final Answer: acrylonitrile & butadiene

Question 13

Tyre reinforcement cords: Which of the following fibres is generally not used as cord material for synthetic-rubber tyre casing? (Assume historical and modern practice in automotive tyres.)

Accepted Answer

Introduction / Context: Tyre casings require strong, fatigue-resistant cords to reinforce the rubber matrix. Materials selection evolved from rayon to nylon and polyester. Understanding which fibres are or have been used is essential for materials engineers working in automotive components and composites. Given Data / Assumptions: The question spans historical and current industrial practice. Dacron denotes polyester (e.g., PET fibre); Nylon denotes polyamide; Cellulose reflects rayon cord. We consider typical passenger and truck tyre constructions. Concept / Approach: Rayon (cellulose), nylon, and polyester have all been used as tyre cords. Rayon was common in early radial tyres; nylon is used for cap plies and some carcasses; polyester (Dacron) is widely used in passenger tyre body plies. Since all listed fibres have been used as cord materials, the correct response is that none are excluded. Step-by-Step Solution: Evaluate Dacron: polyester tyre cord is standard in many body plies.Evaluate Nylon: polyamide cords used in cap plies and high-strength applications; excellent impact/fatigue resistance.Evaluate Cellulose (rayon): historically used and still applied in specific performance tyres; good dimensional stability.Therefore, none of these is ‘‘generally not used’’; all have been used as tyre cords. Verification / Alternative check: Tyre construction references list rayon, nylon, and polyester as common reinforcement fibres; steel cords are used in belts for many modern radials, but textile cords remain essential in carcasses and cap plies. Why Other Options Are Wrong: Dacron (polyester): Actively used; not excluded. Nylon (polyamide): Actively used; not excluded. Cellulose (rayon): Historically and selectively used; not excluded. Common Pitfalls: Assuming only steel belts are used today; textile cords are still critical. Also, confusing brand names with generic polymers can lead to incorrect exclusions. Final Answer: None of these

Question 14

Consumer and building applications: Lavatory cisterns (water closets) are commonly manufactured from which polymer among the choices listed, owing to corrosion resistance and ease of molding?

Accepted Answer

Introduction / Context: Plumbing products must resist water, household chemicals, and impact, while being economical and easy to fabricate. Modern cisterns and fittings often favor thermoplastics that can be injection-molded or blow-molded with integrated features and robust sealing surfaces. Given Data / Assumptions: We focus on common mass-market cisterns (not ceramic tanks). Material needs: corrosion resistance, adequate stiffness, and compatibility with seals/valves. Options include several common polymers with different properties. Concept / Approach: PVC (particularly unplasticized PVC, uPVC) offers good chemical resistance, rigidity, and weldability/glue-ability for plumbing applications. It is widely used in pipes, fittings, and cistern housings. Other listed polymers either lack the necessary toughness/stiffness balance, are more expensive, or are used for different applications (e.g., perspex for glazing, EPS for insulation/packaging). Step-by-Step Solution: Match requirements to materials: water resistance + easy fabrication → PVC.Reject EPS: too brittle/foamed; structural integrity insufficient for tanks under hydrostatic load.Reject perspex: transparent acrylic is more brittle and more expensive for this use.Reject saturated polyester: typically thermoset composites; less common for commodity cistern bodies. Verification / Alternative check: Commercial plumbing catalogs and building-product specifications show uPVC cisterns and uPVC fittings as standard offerings. Why Other Options Are Wrong: Perspex (acrylic): Brittle and costlier; used for windows/displays. Expanded polystyrene: Foam; not suited to pressurized water containment. Saturated polyester: Requires fiber reinforcement and different processing; not typical for cistern bodies. Common Pitfalls: Confusing ceramic/porcelain cisterns with polymer ones; the question specifically targets plastic cisterns. Final Answer: PVC

Question 15

Catalysis in olefin polymerization: A Ziegler–Natta catalyst system of the type AlR3–AlCl3 (representative of organoaluminum/metal halide systems) is classically used to polymerize which monomer to a stereoregular polymer?

Accepted Answer

Introduction / Context: Ziegler–Natta catalysts revolutionized polyolefins by enabling stereoregular (isotactic or syndiotactic) polymers at moderate conditions. Recognizing the monomers most associated with these catalysts is a key concept in polymer reaction engineering and materials selection. Given Data / Assumptions: The catalyst described is representative of Ziegler–Natta systems (organoaluminum + transition metal halide). We look for monomers that yield tactic, crystalline polyolefins under such catalysis. Industrial hallmark product: isotactic polypropylene (iPP). Concept / Approach: Ziegler–Natta catalysts (e.g., TiCl4/MgCl2 with AlR3 cocatalyst) polymerize alpha-olefins like propylene to highly stereoregular polymers. While other monomers can be polymerized with different catalysts, the archetypal success story is propylene → isotactic polypropylene with high crystallinity and excellent mechanical properties. Step-by-Step Solution: Identify alpha-olefin candidate: propylene.Recall classical outcome: isotactic polypropylene production at scale.Eliminate vinylic monomers better suited to radical processes (VCM, styrene, vinyl acetate).Select propylene as the correct monomer. Verification / Alternative check: Process flowsheets and catalyst literature document Ziegler–Natta catalyzed propylene polymerization as a foundational polyolefin technology. Why Other Options Are Wrong: Vinyl chloride, styrene, vinyl acetate: Commonly polymerized by radical routes; Ziegler–Natta is not the standard industrial path. Common Pitfalls: Confusing organoaluminum co-catalysts with the full catalyst system; the key is stereospecific coordination-insertion polymerization of alpha-olefins. Final Answer: propylene

Question 16

Polyester fibres and naming: Which of the following is not a polyester fibre? (Assume Terylene and Dacron are trade names for PET polyester.)

Accepted Answer

Introduction / Context: Many fibre names are trade names or family names. Distinguishing polyester fibres from other synthetic fibres helps in fabric selection, dyeing behavior, and end-use performance (wrinkle resistance, moisture uptake, melting behavior). Given Data / Assumptions: Terylene and Dacron are well-known trade names for PET polyester fibres. PET (polyethylene terephthalate) is the archetypal polyester fibre. Nylon denotes a polyamide, not a polyester. Concept / Approach: Polyester fibres contain ester linkages in the backbone, e.g., PET from ethylene glycol and terephthalic acid. Polyamides (nylons) contain amide linkages (–CONH–) formed from diamines and diacids. Therefore, nylon is chemically distinct and not a polyester. Clarifying names avoids confusion caused by branding and common usage. Step-by-Step Solution: Map names to chemistry: Terylene ≡ PET polyester; Dacron ≡ PET polyester; PET is explicitly a polyester.Identify the outlier: Nylon is a polyamide (e.g., nylon-6,6 from hexamethylene diamine and adipic acid).Therefore, Nylon is not a polyester fibre. Verification / Alternative check: Textile references list polyester (PET) separately from polyamide (nylon) families, with different dye classes, moisture regain, and melting points. Why Other Options Are Wrong: Terylene, Dacron, and PET all denote the same polyester chemistry (PET) used broadly in textiles. Common Pitfalls: Confusing trade names with polymer families; assuming all synthetics are interchangeable despite different chemical backbones. Final Answer: Nylon

Question 17

Polymer chemistry – feedstock for polyamide: Nylon-6 is industrially manufactured from which single-monomer precursor (ring-opening polymerization to caprolactam-derived 6-carbon repeat units)?

Accepted Answer

Introduction: Nylon-6 is a widely used engineering thermoplastic. The question tests understanding of how different nylons are produced and the distinction between single-monomer ring-opening routes and salt/condensation routes used for other polyamides. Given Data / Assumptions: Nylon-6 has a six-carbon repeat unit. Industrial routes prefer economical, high-conversion processes. We compare candidate monomers and their polymerization mechanisms. Concept / Approach: Nylon-6 is manufactured by ring-opening polymerization of ε-caprolactam. In contrast, Nylon-6,6 is produced by step-growth polycondensation of adipic acid with hexamethylene diamine. Recognizing monomer–polymer relationships is key to polymer identification questions. Step-by-Step Solution: Identify Nylon-6 route: ring-opening polymerization of ε-caprolactam produces –[NH–(CH2)5–CO]– units.Differentiate from Nylon-6,6: adipic acid + hexamethylene diamine → salt → condensation polymer.Eliminate unrelated pairs (maleic anhydride or sebacic acid with diamines) which form other polyamides or specialty copolymers, not Nylon-6.Conclude ε-caprolactam is the correct single precursor. Verification / Alternative check: Industrial literature consistently cites ε-caprolactam as the sole precursor to Nylon-6 via ring-opening polymerization under controlled temperatures and catalysts. Why Other Options Are Wrong: Adipic acid + hexamethylene diamine: produces Nylon-6,6, not Nylon-6. Maleic anhydride + hexamethylene diamine: not the commercial route to Nylon-6. Sebacic acid + hexamethylene diamine: leads to Nylon-6,10 type materials. Acrylic acid: unrelated homopolymer produces poly(acrylic acid), not a polyamide. Common Pitfalls: Confusing Nylon-6 with Nylon-6,6 because both have sixes in the name; the first refers to carbon count per repeat from a single monomer, the second to 6 + 6 carbons from two monomers. Final Answer: ε-Caprolactam (caprolactam)

Question 18

Elastomers – comparing SBR (styrene–butadiene rubber) with natural rubber: which combined performance differences are typically observed under service conditions?

Accepted Answer

Introduction: Styrene–butadiene rubber (SBR, Buna-S) is the most widely used synthetic elastomer. This question assesses knowledge of how SBR compares to natural rubber (NR) in key mechanical and dynamic properties under comparable compounding levels. Given Data / Assumptions: SBR and NR are compared at typical, similar filler and cure conditions. Service involves tensile loading and dynamic flexing (heat build-up). We consider general trends, not specialty grades. Concept / Approach: NR exhibits outstanding strain-induced crystallization, giving it higher tensile and tear strength and superior fatigue resistance. SBR lacks the same level of crystallization and typically shows higher hysteresis, leading to more heat build-up under heavy cyclic loads. Step-by-Step Solution: Compare tensile properties: NR > SBR for tensile and tear due to strain-induced crystallization.Assess resistance/aging: NR often shows better cut-growth and fatigue crack resistance; SBR may need reinforcing systems to approach NR.Evaluate dynamic heat: SBR generally exhibits higher hysteresis → greater heat build-up under heavy loading.Hence, all listed differences apply. Verification / Alternative check: Standard rubber handbooks list NR with higher green strength and resilience; SBR is chosen for cost, abrasion resistance, and good wet traction when compounded, but not for superior tensile vs. NR. Why Other Options Are Wrong: Each of (a), (b), (c) is independently true; the comprehensive answer is all of the above. Claiming SBR has universally higher green strength and resilience than NR is incorrect in general practice. Common Pitfalls: Overgeneralizing based on certain oil-extended or solution-SBR grades; base property trends still favor NR in tensile/tear and lower heat build-up. Final Answer: All of the above

Question 19

Applied polymer science: which low-molecular-weight (below about 10^4), soft and waxy polymer is commonly used as a chewing-gum base ingredient?

Accepted Answer

Introduction: Chewing-gum formulations rely on a food-grade, soft, and slightly tacky polymer base. The question checks recognition of PVAc as a classic gum base polymer due to its mouthfeel, film-forming ability, and safety profile in regulated applications. Given Data / Assumptions: Target polymer is soft/waxy and low in molecular weight (sub-10^4 region). Food-contact compliance and taste neutrality are required. Processing involves plasticizers and flavors added to the base. Concept / Approach: Polyvinyl acetate provides suitable viscoelastic properties, acceptable adhesion, and compatibility with plasticizers. Alternatives like PVC or Thiokol are not food-grade choices; cellulose acetate can be film-forming but is not the standard gum base polymer in this context. Step-by-Step Solution: Identify candidate with food use track record: PVAc is widely cited as a gum base.Screen out engineering/industrial polymers (PVC, Thiokol) unsuited for ingestion.Confirm low-MW PVAc grades exhibit the soft, waxy characteristics described.Select PVAc as correct. Verification / Alternative check: Food additive references list PVAc (and certain elastomers) as common chewing-gum base components, blended with plasticizers like triacetin and resins. Why Other Options Are Wrong: Cellulose acetate: used for films/coatings; not the principal gum base polymer. Thiokol: sulfur-based polysulfide rubber with strong odor, not food-grade gum base. PVC and LDPE: unsuitable for chewing gum bases under typical food regulations and performance needs. Common Pitfalls: Assuming any soft thermoplastic can serve as gum base; regulatory and sensory requirements are stringent. Final Answer: Polyvinyl acetate (PVAc)

Question 20

Identify neoprene: in materials terminology, neoprene is best classified as which type of material?

Accepted Answer

Introduction: Neoprene is a trade name historically associated with polychloroprene, a versatile synthetic elastomer. The question evaluates recognition of neoprene’s class and avoids confusion with monomers or thermosets. Given Data / Assumptions: Neoprene is used for wet suits, belts, hoses, and adhesives. Performance involves oil, weather, and ozone resistance. It vulcanizes like other rubbers using cure systems. Concept / Approach: Polychloroprene is formed by polymerizing chloroprene and is categorized as a synthetic rubber. It is not a monomer or a polyester; it can appear in contact adhesives but the base polymer remains an elastomer. Step-by-Step Solution: Link trade name “neoprene” to chemical class: polychloroprene.Note elastomeric properties: flexibility, resilience, and vulcanizability.Exclude alternatives (monomer, thermoset) which do not match neoprene’s behavior. Verification / Alternative check: Materials handbooks and standards list neoprene among general-purpose synthetic rubbers with good weathering resistance. Why Other Options Are Wrong: Monomer/polyester/epoxy labels misclassify neoprene’s chemistry and application form. “None of these” is invalid since the correct class is well-defined. Common Pitfalls: Confusing “neoprene adhesive” (a product form) with the polymer class; the base is still polychloroprene rubber. Final Answer: A synthetic rubber (polychloroprene)

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