1. 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
Explanation: The relationship between the ratio kx/kD and initiator efficiency, f is given by-
kx/kD = (1-f)/f.
2. 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
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.
3. When should the measurement of the initiator decomposition be done?
a) before polymerization
b) after polymerization
c) during polymerization
d) independent of time
Explanation: The measurement of initiator decomposition is done during actual polymerization, as an independent measurement in the absence of monomer would lead to errors.
4. 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
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
5. 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
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.
6. 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
Explanation: The most widely used inhibitor, diphenylpicrylhydrazyl, when reacts with other radicals give a non-radical adduct of light brown yellow color.
7. 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
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.
8. What is the radical produced in the decomposition of acetyl peroxide?
a) ∙CH3
b) ∙C2H5
c) CO2
d) None of the mentioned
Explanation: The reaction is given by-
CH3─C(O)─O─O─C(O)─CH3 → 2CH3─C(O)─∙O → 2∙CH3 + 2CO2.
9. Which molecule is released when AIBN is decomposed to give free radicals?
a) N2
b) HCN
c) NH3
d) none of the mentioned
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.
10. What is the radical produced by decomposition of persulfate ion?
a) S∙O4–
b) SO3∙
c) SO2
d) None of the mentioned
Explanation: The decomposition reaction of persulfate ion is given by-
─O3S─O─O─SO3– → 2 S∙O4–.