This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Initiation and Initiator Systems”.
1. Which of the following is a mode for radicals to move out of the cage in decomposition mechanism of initiator?
a) net diffusion of radicals produced
b) release of a small molecule, formed by decomposition of radicals, followed by diffusion
c) all of the mentioned
d) none of the mentioned
View Answer
Explanation: The radicals may undergo a net diffusion through the cage, having walls of solvent molecules, or a release of small molecule, through decomposition of one or both the radicals, is accompanied with the diffusion out of solvent cage.
2. Which of the following factors does initiator efficiency depend on?
a) initiator molecules
b) polymerization condition
c) solvent
d) all of the mentioned
View Answer
Explanation: The initiator efficiency not only depends on initiator molecules but is also affected by condition of polymerization and the solvent used.
3. How is the rate constant ratio kx/kD related to initiator efficiency?
a) kx/kD = (1-f)/f
b) kx/kD = f/(1-f)
c) kx/kD = 1/(1-f)
d) kx/kD = (1-f)/2f
View Answer
Explanation: The relationship between the ratio kx/kD and initiator efficiency, f is given by-
kx/kD = (1-f)/f.
4. Which of the following is required for determination of initiator efficiency, when the approach involves measurement and conversion of polymer production and initiator decomposition?
a) number of polymer molecules formed
b) number of radicals produced
c) mode of termination
d) all of the mentioned
View Answer
Explanation: For determining f, number of polymers molecules formed and number of radicals produced over same period of time, are compared. Along with this, the mode of termination should also be known as it decides how many initiator fragments are trapped as end groups per polymer molecule.
5. When should the measurement of the initiator decomposition be done?
a) before polymerization
b) after polymerization
c) during polymerization
d) independent of time
View Answer
Explanation: The measurement of initiator decomposition is done during actual polymerization, as an independent measurement in the absence of monomer would lead to errors.
6. Which is the most useful approach for evaluating initiator efficiency?
a) analysis of initiator fragments in polymer formed and comparing to initiator consumed
b) measurement and comparison of polymer production and initiator decomposition
c) use of inhibitors
d) dead-end-effect in polymerization
View Answer
Explanation: This technique allows treating the kinetic data obtained under dead-end conditions to evaluate both kd, the rate constant of initiator decomposition reaction and f, the initiator efficiency, which is most useful of all the approaches.
7. What is the mechanism of radical generation by bimolecular initiating systems?
a) electron or charge transfer
b) cleavage of bonds
c) catalyzation
d) all of the mentioned
View Answer
Explanation: Bimolecular initiation systems mostly generate radicals through electron transfer mechanism or via formation of complexes of different degrees of heat or light stability, through charge transfer mechanism.
8. What is the color of the non-radical adduct formed, when the inhibitor diphenylpicrylhydrazyl reacts with other radicals?
a) deep violet
b) light brown yellow
c) dark red
d) black
View Answer
Explanation: The most widely used inhibitor, diphenylpicrylhydrazyl, when reacts with other radicals give a non-radical adduct of light brown yellow color.
9. What has the initiator concentration in the expression for Rp, in bimolecular initiation system, been replaced by?
a) reducing agent concentration
b) oxidising agent concentration
c) product of oxidizing and reducing agent concentration
d) no change
View Answer
Explanation: The initiator concentration in the expression has been substituted by product of oxidizing and reducing agent concentration, and the system is commonly known as redox initiator systems.
10. What is the radical produced in the decomposition of acetyl peroxide?
a) ∙CH3
b) ∙C2H5
c) CO2
d) None of the mentioned
View Answer
Explanation: The reaction is given by-
CH3─C(O)─O─O─C(O)─CH3 → 2CH3─C(O)─∙O → 2∙CH3 + 2CO2.
11. Which molecule is released when AIBN is decomposed to give free radicals?
a) N2
b) HCN
c) NH3
d) None of the mentioned
View Answer
Explanation: The reaction is given by-
(CH3)2─C(CN) ─N═N─(CH3)2─C(CN)→ (CH3)2─C(CN)─N═N∙ + (CH3)2─∙C─CN → 2(CH3)2─∙C─CN + N2.
12. What is the radical produced by decomposition of persulfate ion?
a) S∙O4–
b) SO3∙
c) SO2
d) None of the mentioned
View Answer
Explanation: The decomposition reaction of persulfate ion is given by-
─O3S─O─O─SO3– → 2 S∙O4–.
13. What happens to the metal ion when it reacts with peroxide in a bimolecular initiator system?
a) oxidizes
b) reduces
c) no change
d) none of the mentioned
View Answer
Explanation: The reaction of reducing metal ion and peroxide is given here-
M(m-1)+ + R─O─O─R→ Mm+ +∙OR + OR–.
14. What is the mechanism by which dithionite ion decomposes to give free radical?
a) cleavage of S─O bond
b) cleavage of S─S bond
c) electron transfer
d) cleavage of O─O bond
View Answer
Explanation: Dithionite ion (S2O42-) undergoes decomposition by the cleavage of S─S bond to give ∙SO2–.
15. What happens to copper ion, when it gives out radicals in acidic medium?
a) oxidizes
b) reduces
c) constant charge
d) none of the mentioned
View Answer
Explanation: When copper ion reacts in acidic medium, electron transfer takes place from copper to H+ ion, to give a free radical.
For example,
Cu+ + H+ → Cu2+ + H∙.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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