Multiple choice question for engineering
Set 1
1. LDPE is more prone to oxidation than HDPE. State true or false.
a) true
b) false
Answer
Answer: a [Reason:] LDPE is more prone to oxidation than HDPE as is contains higher concentration of tertiary hydrogen (at branch sites), given that it is free from metallic impurities. Uncontrolled oxidation leads to countable incorporation of carbonyl and peroxy groups which can make the polymer more prone to degradation due to absorption of heat and light.
2. What does higher melt flow index (MFI) indicates in polymer system and which type of polyethylene belongs to higher MFI value category?
a) lower molecular weight, LDPE
b) higher molecular weight, LDPE
c) lower molecular weight, HDPE
d) higher molecular weight, HDPE
Answer
Answer: a [Reason:] The melt flow index (MFI) helps to differentiate between different grades of polymer. A higher value of melt flow index indicates lower molecular weights, and LDPE falls in a MFI range of (0.3-70), whereas HDPE has a relatively lower value (0.02-2.5).
3. Which of following kind of polyethylene has the highest degree of chain-branching?
a) LDPE
b) HDPE
c) LLDPE
d) cannot be determined
Answer
Answer: a [Reason:] Due to high chain transfer in free radical polymerization effected in high pressure, LDPE has nearly 20-50 branches per 1000 linear carbon atoms in chain molecules, while HDPE contains only about 1-5 branches per 1000 carbon atoms making itself nearly a linear polymer. LLDPE, as the name suggest is a linear polymer.
4. Which of the following category in properties can be considered as a limitation to the application of polyethylene?
a) chemical inertness
b) toxicity
c) softening point
d) insulation properties
Answer
Answer: c [Reason:] The low softening point or heat distortion temperature of polyethylene is a limiting factor for the application of polyethylene. The contributing factors for its application are excellent chemical inertness and electrical insulation properties, and the non-toxic nature of polyethylene.
5. Which of the following is true case when the stress cracking problem in polyethylene is less critical?
a) high molecular weight and high density
b) low molecular weight and high density
c) high MFI and high density
d) low molecular weight and low density
Answer
Answer: a [Reason:] Polyethylenes generally show low environment stress cracking resistance problem. Thus, the stress cracking problem is less critical with relatively high molecular weight or low MFI and high density materials.
6. Which of the following is true, when the density of LDPE is increased?
a) crystallinity decreases
b) permeability to liquid and gas decreases
c) toughness increases
d) all of the mentioned
Answer
Answer: b [Reason:] The crystallinity increases with the density increase of polymer i.e the amount of short chain branching decreases, which on the other hand decreases the toughness and permeability to gas and liquid.
7. Which of the following atom, with its presence in the LDPE chain, can give a rubbery product?
a) Cl
b) S
c) N
d) O
Answer
Answer: a [Reason:] The introduction of chlorine atom in the chain to the extent of one chlorine atom for at least 7 carbon atoms gives a useful rubbery product. The rubbery products formed are among the best chemical resistant rubbers.
8. LDPE has a superior degree of toughness, stiffness, stress cracking resistance and electrical properties than LLDPE. State true or false.
a) true
b) false
Answer
Answer: b [Reason:] LLDPE, a copolymer by definition and design, has a superior degree of toughness, stiffness, stress cracking resistance and electrical properties than LDPE. Even the possibilities for LLDPE to take over 30-350% market of LDPE have also increased.
9. What is the range of melting or softening temperature of high density polyethylene?
a) 125-135 ᵒC
b) 110-117 ᵒC
c) 90-110 ᵒC
d) 118-120 ᵒC
Answer
Answer: a [Reason:] The melting temperature of HDPE (125-135 C) is usually higher in comparison to LDPE and LLDPE, due to the its short and less branching and high density ranges.
10. The films made by copolymer of ethylene and ethyl acrylate are of much better quality than the films made by normal LDPE. State true or false.
a) true
b) false
Answer
Answer: a [Reason:] The films made from the copolymer of ethylene and ethyl acrylate have a great degree of tensile strength, stress cracking resistance, clarity and flexibility at low temperatures in comparison to the films produced by normal LDPE.
Set 2
1. How many initiator fragments are present in the dead polymer formed by combination mode of chain termination?
a) 2
b) 1
c) 3
d) 0
Answer
Answer: a [Reason:] The combination reaction is given by-
R~~~ CH2−∙CHY + YH∙C−CH2 ~~~~~R → R ~~~CH2−CHY─CHY─CH2 ~~~ R.
2. What is the initiator efficiency in chain initiation step of free radical polymerization?
a) fraction of unreacted monomers
b) extent of reaction
c) fraction of radicals actually contributing
d) number of initiator molecules
Answer
Answer: c [Reason:] the initiator efficiency is the fraction of free radicals actually contributing in chain initiation and is less than unity.
3. What is the expression for the rate of chain initiation of free radical chain growth polymerization?
a) fkd[I]
b) 2fkd[I]
c) kd[I]/2
d) kd[I]
Answer
Answer: b [Reason:] The expression is given by-
Ri= 2fkd[I]
where f is the initiator efficiency, and the factor 2 is introduced because for decomposition of one initiator molecule, two initiator radicals are formed.
4. The data for bulk chain polymerization having potassium persulfate as initiator is given-
[I] = 5 mol/m3
[M] = 5.3*103 mol/m3
kp2/kt = 0.85*10-6 m3/ mol-s
What is the initial rate of polymerization, if potassium persulfate decomposes at a rate of 2.2*10-6 m3 s/ mol?
a) 0.012
b) 0.0162
c) 0.05
d) 0.1
Answer
Answer: b [Reason:] The initial rate of polymerization is here, expressed as, Rp=[(kp2/kt)fkd]0.5[I]0.5[M].
Assuming f=1, and substituting all the values, we get Rp as 0.0162 m3/ mol-s.
5. What is the rate chain initiation reaction for initiator efficiency of 0.8, when concentration and decomposition rate of benzoyl peroxide are 4 mol/m3 and 3.24*10-6 m3/ mol-s-1, respectively?
a) 2.07*10-5
b) 1.57*10-5
c) 3.27*10-5
d) 1.03*10-5
Answer
Answer: a [Reason:] The rate expression for chain initiation is given by-
Ri= 2fkd[I]
By substituting the values, rate can be calculated.
6. What is the expression for rate of termination reaction of free radical polymerization?
a) kt[M∙]2
b) 2kt[M∙]2
c) 2fkt[M∙]
d) fkt[M∙]
Answer
Answer: b [Reason:] The rate expression for termination reaction is given by- Rt = 2kt[M∙]2
The factor 2 is used for the disappearance of chain radicals at each incidence of termination reaction.
7. Consider following data for bulk polymerization, with benzoyl peroxide as initiator.
[I] = 6 mol/m3
[M] = 6.56*103 mol/m3
kp2/kt = 1.5*10-6 m3/ mol-s
What is the initiator efficiency if initial rate of polymerization is 0.0256 m3/ mol-s benzoyl peroxide decomposes at a rate of 3.2* 10-6 m3/ mol-s-1?
a) 0.7
b) 0.53
c) 0.26
d) 0.82
Answer
Answer: b [Reason:] The initial rate of polymerization is given by-
Rp =[( kp2/kt)fkd]0.5[I]0.5[M]
Squaring both the sides and then substituting the values given, f is obtained as 0.53.
8. How does polymerization rate at a given monomer concentration vary, if rate of chain initiation is tripled?
a) doubled
b) tripled
c) increment by factor of 30.5
d) remains constant
Answer
Answer: c [Reason:] The rate equation of overall polymerization clears that the polymerization rate at a given monomer concentration is dependent on the square root of rate of chain initiation.
9. Which order kinetics does the rate of polymer formation, in free radical polymerization, follow corresponding to monomer concentration?
a) 1
b) 0
c) 2
d) 3
Answer
Answer: a [Reason:] The rate of polymer formation is given by-
Rp =[( kp2/kt)fkd]0.5[I]0.5[M]
This proves that rate of polymer formation is first order in monomer concentration.
Set 3
1. Which of the following monomer has the highest reactivity towards the styrene radical?
a) styrene
b) vinylidene chloride
c) vinyl acetate
d) butadiene
Answer
Answer: b [Reason:] The relative reactivities of the monomers towards styrene radical is given by-
Styrene=1
Vinylidene chloride= 5.4
Vinyl acetate= 0.019
Butadiene= 1.7
Therefore, vinylidene chloride has the highest reactivity towards the styrene radical.
2. Which of the following factors are responsible for reactivity ratio of monomers?
a) initiation rate
b) reaction medium
c) substituent group on monomer double bond
d) all of the mentioned
Answer
Answer: c [Reason:] The reactivity ratio of monomers is independent of the initiation and termination reaction as well as the reaction medium. The reactivity ratio is dependent on the reactivity of individual monomers and the reactivity of attacking radical, which further depends on the nature of the substituent group on the monomer double bond.
3. Which of the following substituent groups would render greater reactivity of a monomer?
a) ─COOH
b) ─OR
c) ─CH═CH2
d) ─CN
Answer
Answer: c [Reason:] The reactivity order as the effect of substituents is-
─CH═CH2> ─CN> ─COOH > ─OR
Thus the ethylene group would render the highest reactivity to the monomer.
4. Which of the following are more stabilized by the substituents groups?
a) monomers
b) radicals
c) equally stabilized
d) cannot be determined
Answer
Answer: b [Reason:] The substituents that tend to stabilize the radicals also stabilize the monomers, but the degree of stabilization is much less for the monomer as compared to the radical. For example, Styrene monomer is stabilized to 3 kcal/mol whereas styrene radical is stabilized to about 20 kcal/mol.
5. The styrene radical is apparently 500-1000 times less reactive than the vinyl acetate monomer, and also the styrene monomer is 50-100 times less reactive than the vinyl acetate monomer. State true or false.
a) True
b) False
Answer
Answer: b [Reason:] A substituent’s role in enhancing the reactivity of the radical is much greater than its effective role in decreasing the reactivity of the monomer. Thus, vinyl acetate radical is 500-1000 times more reactive than the styrene radical, but the styrene monomer is only about 50-100 times more reactive than the vinyl acetate monomer.
6. Which of the following configurations of the monomer 1,2- dichloroethylene is less reactive towards a radical in copolymerization reaction?
a) cis-isomer
b) trans-isomer
c) equally reactive
d) cannot be determined
Answer
Answer: a [Reason:] The cis-isomer of the monomer 1,2-dichloroethylene is much less reactive than the trans-isomer towards the reaction with a radical in copolymerization because cis-isomer is less stable and also due to its inability to achieve complete coplanar conformation in the transition state during the reaction with a radical, which consequently impairs resonance stabilization of the derived radical by the substituent.
7. Which of the following pairs of monomers will most probably form alternating copolymer?
a) butadiene and acrylonitrile, r1r2=0.0006
b) vinyl acetate and diethyl fumarate, r1r2=0.0049
c) styrene and acrylonitrile, r1r2= 0.016
d) butadiene and styrene, r1r2=0.98
Answer
Answer: a [Reason:] Alternating tendency increases as the product r1r2 approaches zero thus, butadiene and acrylonitrile has the highest alternating tendency.
8. Which of the following monomers have lowest reactivity with butadiene radical?
a) vinyl methyl ether
b) methy methacrylate
c) acrylo nitrile
d) methacrylate
Answer
Answer: a [Reason:] According to the structures of the given monomers-
1. Vinyl methyl ether
CH2═CH─OCH3
2. Methyl methacrylate
CH2═C(CH3)─COOCH3
3. Acrylo nitrile
CH2═CH─CN
4. Methacrylate
CH2═CH─COOCH3
The least reactive monomer is vinyl methyl ether due to the presence of ether group which least stabilizes the monomer.
9. Which of the following monomers is the most reactive with vinyl acetate radical?
a) vinyl chloride
b) vinylidene chloride
c) dichloroethylene
d) tetrachloroethylene
Answer
Answer: b [Reason:] Vinylidene chloride is most reactive as it produces an additive effect on monomer reactivity for the 1,1 disubstituted monomer. Rest dichloroethylene and tetrachloroethylene decreases the reactivity due to steric hindrance.
Set 4
1. What is the melting point of polymer formed by polymerization of tetrafluoroethylene?
a) 100 ᵒC
b) 156 ᵒC
c) 327 ᵒC
d) 533 ᵒC
Answer
Answer: c [Reason:] The melting point of polytetrafluoroethylene is around 327 ᵒC. Polytetrafluoroethylene is a highly temperature stable polymer.
2. What is the nature of the fluoro polymer polytetrafluoroethylene, regarding its crystallinity?
a) highly crystalline
b) highly amorphous
c) cannot be determined
d) atactic
Answer
Answer: a [Reason:] Polytetrafluoroethylene is a highly crystalline polymer with high density, due to its regular chain structure present in the polymer.
3. How is the final product of polymerization of tetrafluoroethylene obtained in the form of?
a) granular
b) granular or aqueous dispersion
c) granular or homogeneous solution
d) suspension
Answer
Answer: b [Reason:] The final polymer product of polymerization of the tetrafluoroethylene, i.e. PTFE is obtained in the form of granules or in the form of aqueous dispersion.
4. Which of the following solvent can dissolve the polymer PTFE at room temperature?
a) propane
b) carbon tetrachloride
c) hexane
d) none of the mentioned
Answer
Answer: d [Reason:] The polymer polytetrafluoroethylene is completely in insoluble in almost all the hydrocarbon solvents. There is no such solvent for PTFE at room temperature.
5. Which of the following is false about the properties of polytetrafluoroethylene?
a) low friction coefficient
b) low dissipation factor
c) high crystallinity
d) low chemical inertness
Answer
Answer: d [Reason:] PTFE has high crystallinity due to its regular chain structure and extremely low dielectric constant and friction coefficient due to its waxy feel. It has an outstanding chemical inertness and is also unaffected by water.
6. Which of the following form of polytetrafluoroethylene can be used for casting films?
a) dispersion form
b) granular form
c) powder form
d) none of the mentioned
Answer
Answer: a [Reason:] The dispersion form of the polytetrafluoroethylene can be used for casting films, dip coating, etc.
7. Which of the following fluoro polymer film is sold under the name of Tedlar by DuPont?
a) polytetrafluoroethylene
b) polyvinyl fluoride
c) polyvinylidene fluoride
d) hexafluoropropylene
Answer
Answer:b [Reason:] Polyvinyl fluoride, with high crystallinity, is available as a tough and flexible film and is sold by the name of Tedlar by DuPont.
8. Polymer A, also available as copolymer with trifluoroethylene, is a crystalline polymer with a melting point greater than 160 ᵒC and is used in coatings and insulation materials. What is the name of polymer A?
a) polyvinyl fluoride
b) polytetrafluoroethylene
c) polyvinylidene fluoride
d) polyvinyl chloride
Answer
Answer: c [Reason:] Polyvinylidene fluoride is a crystalline polymer having melting point of about 176 ᵒC. It is also available as a copolymer with trifluoroethylene which have much higher crystallinity and is used in coatings and insulation on electrical wires and cables.
9. A polymer ‘A’ is formed by the polymerization of monomer B. Monomer B is formed by the pyrolysis of monochlorodifluoromethane in contact with platinum at 700 ᵒC. Monomer is a highly crystalline polymer with excellent insulation properties. What is the name of monomer B?
a) tetrafluoroethylene
b) vinylidene chloride
c) vinylidene fluoride
d) vinyl fluoride
Answer
Answer: a [Reason:] The monomer B is tetrafluoroethylene which polymerizes to give polytetrafluoroethylene which is a highly crystalline polymer with outstanding insulation properties and chemical inertness. Tetrafluoroethylene is formed by the pyrolysis of monochlorodifluoromethane in contact with platinum at 700 ᵒC.
2CHClF2 → CF2═CF2 + 2HCl.
10. What is the approximate density of the polymer polytetrafluoroethylene?
a) 1.8 g/cm3
b) 2.2 g/cm3
c) 0.6 g/cm3
d) 1.5 g/cm3
Answer
Answer: b [Reason:] PTFE his a high density polymer with a density of about 2.2 g/cm3 . Its properties depend on its particle size and molecular weight.
Set 5
1. Which of the following type of fillers are treated with chemicals to improve its attachment with polymers?
a) particulate fillers
b) rubbery fillers
c) mineral fillers
d) fibrous fillers
Answer
Answer: c [Reason:] Mineral fillers are usually treated with specific chemicals to improve wettening and attachment with polymers to fillers. Stearic acid-treated calcium carbonate or amine- or glycol-treated clays are some examples of mineral fillers.
2. Which of the following additives are used in the least amount with polymer in general?
a) plasticizers
b) fillers
c) cross linking agents
d) lubricants
Answer
Answer: d [Reason:] Lubricants are used in the least amount among the other additives. Generally, 1-2 parts by weight of lubricants is used per 100 grams of polymer, while 30-100 and 2-5 parts by weight of plasticizers, fillers and cross-linking agents, respectively are used per 100 parts of polymer.
3. Which of the following filler is used as a reinforcing agent for the polymers?
a) wood flour
b) carbon black
c) silica
d) asbestos
Answer
Answer: a [Reason:] Wood flour is a fibrous filler that is a mixed with polymers to be used as a reinforcing agent.
4. Which property of polymer is enhanced by the use of mica as filler?
a) toughness
b) heat resistance
c) adhesiveness
d) impact resistance
Answer
Answer: b [Reason:] The use of mica, asbestos, glass fibre, etc is used as filler to improve heat resistance of polymers.
5. Which of the following additives are available as high boiling non volatile liquids?
a) fillers
b) plasticizers
c) stabilizers
d) colouring matters
Answer
Answer: b [Reason:] Plasticizers are usually high boiling nonvolatile liquids. They are used in variety of polymers such as cellulosics, acrylics and poly(vinyl) chloride. Fillers are usually solid additives while colouring matters are generally pigments and dyes.
6. What kind of additives prevent the degradation of polymers while their processing and storage?
a) stabilizers
b) cross-linking agents
c) plasticizers
d) fillers
Answer
Answer: a [Reason:] Stabilizers like antioxidants and UV absorbers are used as additives in polymers to protect them from degradation during storage and processing applications under performing conditions.
7. Which of the following stabilizer is capable of preventing the polymer from UV degradation?
a) phenyl napthylamines
b) dilauryl thiopropionate
c) styrenated phenols
d) phenyl salicylates
Answer
Answer: d [Reason:] Phenyl salicylates is a UV absorber which gives protection against UV degradation to polymers while dilauryl thiopropionate, styrenated phenols and phenyl napthylamines are antioxidants that prevent degradation by oxygen attack.
8. What is the use of carbon black in polymer compounding to improve as an additive?
a) as a filler
b) as a colourant
c) as a stablizier
d) all of the mentioned
Answer
Answer: d [Reason:] Carbon black is used as a filler to influence the properties of final product, as a stabilizer UV absorber to avoid UV degradation and also as a colourant in polymer compounding.
9. Which of the following materials work as a polymeric flow promoters?
a) glyceryl stearates
b) calcium stearate
c) stearic acid
d) silicone fluids
Answer
Answer: a [Reason:] Glyceryl stearates are low molecular weight materials that impart better flow properties to the polymer mix under processing conditions without really affecting the bulk properties under service conditions.
10. Which of the following additive can act as curing agent for epoxides?
a) amines
b) sulphur
c) formaldehyde
d) all of the mentioned
Answer
Answer: a [Reason:] Amines and polyamines are used as curing agent for epoxides, sulphur for diene rubbers and formaldehyde for novolacs and polyvinyl alcohols.
11. Which property of polymer is enhanced by adding antimony oxychloride as an additive?
a) flame retardancy
b) buildup of static electricity
c) colour
d) toughness
Answer
Answer: a [Reason:] Antimony compounds like antimony oxychloride work as flame retardants to enhance flame retardancy in plastics. They decompose endothermically and form impervious fire resistant layer on the surface thus preventing access of oxygen to the inner polymer layers.
12. Which of the following compounds are used as antistatic agent?
a) sulphur compounds
b) ammonium compounds
c) chlorinated compounds
d) none of the mentioned
Answer
Answer: b [Reason:] Selected amines and quaternary ammonium compounds are used as antistatic agents while chlorinated paraffins are used as flame retardants in polymer compounding.
13. Which of the following is used as a chemical blowing agent in polymers?
a) trixylyl phosphate
b) azonitriles
c) antimony oxide
d) none of the mentioned
Answer
Answer: b [Reason:] Azonitrile is a commonly used chemical blowing agent while antimony oxide and trixylyl phosphate are used as flame retardants in polymers.
