1. 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
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.
2. How the termination in anionic polymerization most probably does take place?
a) unimolecular termination
b) bimolecular
c) termination by solvent transfer
d) all of the mentioned
Explanation: The termination reaction in anionic polymerization most probably takes place by the chain transfer involving solvent or some other additive used such as water, alcohol, etc.
3. Which of the following monomer has the least reactivity towards anionic polymerization?
a) acrylonitrile
b) methyl metharylate
c) butadiene
d) methacrylonitrile
Explanation: According to the reactivity order given by Mayo and Walling,
Acrylonitrile>Methacrylonitrile>Methyl methacrylate>butadiene
This order is decided on the basis of the electronegativity of the electron-withdrawing substituent groups.
4. Which of the following nature of solvent can inhibit the growth of polymer in anionic polymerization?
a) acidic
b) basic
c) neutral
d) none of the mentioned
Explanation: Acidic solvents or additives inhibit the growth in anionic polymerization
5. What kind of substituent groups should be attached to the monomer, readily undergoing anionic polymerization?
a) electron accepting
b) electron releasing
c) all of the mentioned
d) none of the mentioned
Explanation: The monomers with electron accepting substituent groups like nitrile, carboxyl, ester groups, etc. are readily susceptible to anionic polymerization as the it enables easy carbanion formation.
6. Which of the following can assist as a catalyst in anionic polymerization?
a) Sulphuric acid
b) Boron trifluoride
c) grignard reagent
d) all of the mentioned
Explanation: The basic compounds like amides, aryls, alkoxides and Grignard reagents (R-MgX) are used as catalysts for anionic polymerization.
7. What does the effectiveness of the catalyst in the initiation process of anionic polymerization depend on?
a) acidity of the monomer
b) basicity of the catalyst
c) all of the mentioned
d) none of the mentioned
Explanation: The effectiveness of the catalyst in the initiation process of anionic polymerization depends on its basicity as well as the acidity of monomer.
8. Styrene is polymerized using amide catalyst in liquid ammonia, anionically. How will the rate of reaction change, if the monomer concentration is doubled (keeping rest other things constant)?
a) doubled
b) halved
c) quadrupled
d) No change
Explanation: According to the rate expression for overall rate
Rp α [M]2
So the rate is quadrupled, if the monomer concentration is doubled.
9. Which of the following monomers is more prone to form low-molecular weight polymer when polymerized in liquid ammonia?
a) acrylonitrile
b) metha acrylonitirile
c) styrene
d) methyl methacrylonitrile
Explanation: Styrene contains the phenyl group which is less electronegative than the nitrile group (-CN) attached to the other three monomers, so it is more susceptible to proton transfer from ammonia. And transfer reactions generally yield low-molecular weight polymers.Styrene contains the phenyl group which is less electronegative than the nitrile group (-CN) attached to the other three monomers, so it is more susceptible to proton transfer from ammonia. And transfer reactions generally yield low-molecular weight polymers.
10. How is the degree of polymerization affected with the increase in concentration of both monomer and liquid ammonia, when a monomer is polymerized anionically in liquid ammonia?
a) increases
b) decreases
c) no change
d) cannot be determined
Explanation: According to the expression for degree of polymerization,
Xn α [M]/[NH3]
Since the degree of increase in the concentration of both monomer and liquid ammonia is not known, we cannot determine that whether the degree of polymerization will increase or decrease.