This set of Polymer Engineering Quiz focuses on “Binary Copolymerization of Vinyl Monomers by Free Radical Mechanism”.
a) step-growth mechanism
b) free radical mechanism
c) cationic mechanism
d) all of the mentioned
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Explanation: Copolymers can be produced by both step-growth mechanism and chain- growth mechanism, which can occur by free radical as well as ionic mechanisms.
2. How is the reactivity of a chain radical practically determined in a free radical copolymerization?
a) number of the monomers present
b) free radical bearing terminal monomer unit
c) size of the monomer unit
d) chemical nature of monomer unit
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Explanation: The reactivity of a chain radical in free radical polymerization is practically determined by the free radical bearing terminal monomer unit. The size and chemical nature of the part preceding the radical bearing terminal unit is of very little significance.
3. How many propagation reactions occur simultaneously in a binary copolymerization process?
a) 2
b) 4
c) 1
d) 3
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Explanation: In binary copolymerization, there are two different chain radicals which can add both the monomers, though not necessarily with same ease, the system characterizes four simultaneous propagation reactions.
4. What does the copolymer composition depend upon, in binary copolymerization?
a) feed monomer composition
b) initiator concentration
c) rate of polymerization
d) all of the mentioned
View Answer
Explanation: It is clear from the copolymer equation that copolymer composition is dependent on the feed monomer composition.
{[M1]/[M2]}copolymer = {[M1/[M2]}(r1[M1]+[M2])/(r2[M2]+[M1])
Also, there is absence of initiator and termination rate constants in the copolymer equation, which makes the composition independent of these terms.
{[M1]/[M2]}copolymer = {[M1/[M2]}(r1[M1]+[M2])/(r2[M2]+[M1])
What does the term [M1] on the right hand signify here?
a) absolute molar concentration of monomer M1
b) molar concentration of monomer M1 in feed
c) molar concentration of monomer M1 in copolymer
d) none of the mentioned
View Answer
Explanation: The term [M1] on the right hand side is the molar concentration of monomer M1 in the feed or reaction mixture.
6. In most cases, the copolymer composition is not measurably affected due to the presence of solvents and additives. State true or false.
a) True
b) False
View Answer
Explanation: The composition is controlled by the kinetic factors, i.e. the reactivity ratios, r1 and r2, which are not affected by the initiator concentration, rate of polymerization and presence of solvents or additives. So the copolymer composition remains unaffected by such factors.
7. Which of the following has more priority, in binary copolymerization involving monomers M1 and M2, if the reactivity ratio r1 is greater than 1?
a) chain radical ∙M1 to add monomer M1
b) chain radical ∙M1 to add monomer M2
c) chain radical ∙M2 to add monomer M1
d) chain radical ∙M2 to add monomer M2
View Answer
Explanation: The reactivity ratio r1 is given by-
r1= k1,1/k1,2
i.e. the ratio of homo-propagation rate constant to cross propagation rate constant, involving the chain radical ∙M1. When r1 is greater than 1, it signifies that chain radical ∙M1 has a preference to add monomer M1.
8. The values of reactivity ratios, r1 and r2 are independent of the change in the mechanism of chain propagation, form radical to ionic mechanism. State true or false.
a) True
b) False
View Answer
Explanation: The values of reactivity ratios significantly change for a drastic change in the mechanism of chain propagation from free radical to ionic, and even from cationic to anionic mode of chain propagation.
a) sequentially
b) alternatively
c) randomly
d) all of the mentioned
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Explanation:In general, the monomer units in a copolymer structure are arranged in a random manner.
10. Where is the copolymer equation of binary copolymerization not applicable?
a) free radical systems
b) cationic systems
c) anionic systems
d) none of the mentioned
View Answer
Explanation: The copolymer equation is relevant and applicable to radical, cationic and anionic systems, despite variations in values of reactivity ratios depending on the mode of chain propagation.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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