This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Cationic Polymerization”.
1. Which of the following polymerization mechanism can polymerize the styrene monomer?
a) cationic polymerization
b) radical polymerization
c) anionic polymerization
d) all of the mentioned
View Answer
Explanation: Styrene is capable of polymerizing by radical as well as cationic and anionic mechanisms. It is placed at a low position in each series of reactivity.
2. Which of the following type of termination is not possible in ionic polymerization?
a) bimolecular termination
b) unimolecular termination
c) termination through transfer to monomer or solvent
d) none of the mentioned
View Answer
Explanation: Bimolecular termination is not feasible in the ionic polymerization, as like charges repel each other and cannot come close enough to interact with each other and annihilate together.
3. Which of the following nature of solvent or additives can inhibit the growth in cationic polymerization?
a) basic
b) acidic
c) neutral
d) none of the mentioned
View Answer
Explanation: Basic solvents or additives can inhibit the growth of polymer in cationic polymerization.
4. Which of the following monomer has highest reactivity towards cationic polymerization?
a) isobutylene
b) isoprene
c) vinyl ethers
d) styrene
View Answer
Explanation: The reactivity order for cationic polymerization proposed by Mayo and Walling states-
Vinyl ethers>isobutylene>isoprene>styrene.
5. What kind of substituent groups should be attached to the monomer, readily undergoing cationic polymerization?
a) electron accepting
b) electron releasing
c) all of the mentioned
d) none of the mentioned
View Answer
Explanation: The monomers with electron releasing substituent groups like alkoxy, phenyl, aryl-alkyl, etc. are readily susceptible to cationic polymerization as the it enables easy carbonium formation.
6. How does degree of polymerization affected with increase in temperature of cationic polymerization reaction?
a) increases
b) decreases
c) no change
d) cannot be determined
View Answer
Explanation: Cationic polymerization generally occurs around -100ᵒC temperature. So, the rate and degree of polymerization drops sharply with rise in the temperature.
7. How is the rate of polymerization dependent on the concentration of catalyst in cationic polymerization?
a) proportional to first power
b) proportional to half power
c) proportional to second power
d) no dependence
View Answer
Explanation: The rate of cationic polymerization is given by-
Rp= (kikp/kt)[C][M]2
Thus, Rp is proportional to the first power of catalyst concentration.
8. What is true about the degree of cationic polymerization when termination occurs by monomer transfer?
a) constant
b) proportional to monomer concentration
c) proportional to catalyst concentration
d) proportional to square of monomer concentration
View Answer
Explanation: The degree of polymerization for transfer reaction is given is a constant which is given by-
Xn= kp[M+][M]/ktr[M+][M] Xn= kp/ktr
Where kp and ktr are propagation and termination constants.
9. What does the binding energy between the propagating ion and the gegen ion depend on?
a) nature of reaction media
b) nature of gegen ion
c) temperature of reaction
d) all of the mentioned
View Answer
Explanation: The binding energy between the propagating ion and the gegen ion is dependent on the nature of the reaction media and the gegen ion and on the temperature of the reaction.
10. What is the range of activation energy of overall polymerization of cationic polymerization?
a) -10 to +10 kcal/mol
b) -100 to +100 kcal/mol
c) -500 to +500 kcal/mol
d) -25 to +25 kcal/mol
View Answer
Explanation: The activation energy for the overall rate is given by [(Ei+Ep)-Et] and it ranges between -10 to +10 kcal/mol.
11. The magnitude of the negative activation energy for degree of polymerization is higher for true termination than that for the termination by transfer reactions. State true or false.
a) true
b) false
View Answer
Explanation: The activation energy for degree of polymerization is given by (Ep-Et) and Et>Ep giving always a negative value. Since Etr (for transfer reaction) is generally greater than Et (for true termination), the magnitude of negative activation energy is higher for the termination by transfer reactions than for the true termination.
12. BF3 is ineffective to induce cationic polymerization in isobutylene when the reactants are moisture free. State true or false.
a) true
b) false
View Answer
Explanation: BF3 is very effective in the presence of traces of moisture as a co-catalyst as it reacts with traces of moisture to form a complex (BF3∙H2O) which can readily induce polymerization.
13. How is the rate of cationic polymerization reaction affected with the increase in the dielectric constant of the reaction medium?
a) increase
b) decreases
c) may increase or decrease
d) no effect
View Answer
Explanation: The increase in dielectric constant of reaction medium increases the initiation rate constant, ki by decreasing the energy required for charge separation and simultaneously, it decreases the termination constant, kt by increasing the energy required for arrangement or combination of ion pair. Since, Rp is directly proportional to the ratio ki/kt, an increase in the dielectric constant of reaction medium will increase the rate of reaction.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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