250+ TOP MCQs on Structure and Reactivity of Monomers and Radicals

Polymer Engineering Questions on “Structure and Reactivity of Monomers and Radicals”.

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: b
Clarification: 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: c
Clarification: 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: c
Clarification: 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: b
Clarification: 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: b
Clarification: 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: a
Clarification: 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: a
Clarification: 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: a
Clarification: 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: b
Clarification: 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.