This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Techniques of Polymerization-2”.
1. What is the size of the monomer droplets in suspension polymerization?
a) 25-30 mm
b) 0.1-5 mm
c) 15-20 mm
d) 50-60 mm
View Answer
Explanation: The size of the monomer droplets is generally in the range of 0.1-5 mm.
2. Which of the following feature of water as a solvent helps in purity of polymer?
a) low cost
b) non-toxic nature
c) convenient boiling temperature
d) zero chain transfer constant
View Answer
Explanation: The special feature of water as a solvent is that it provides us with a medium characterized by zero chain transfer constant.
3. Which of the following compounds can minimize the fluctuations in surface tension of emulsion in emulsion polymerization?
a) soaps
b) cetyl alcohol
c) dextrin
d) peroxides
View Answer
Explanation: Cetyl alcohol plays the role of a surface tension regulator and minimizes the fluctuations in the emulsion as the polymerization progresses.
4. Which of the following compounds is used to control the polymer chain length in emulsion polymerization?
a) cetyl alcohol
b) buffer solutions
c) dodecyl mercaptan
d) gelatin
View Answer
Explanation: Dodecyl mercaptan is used as a chain length regulator or chain transfer agent of high transfer constant to control the chain length of the polymer.
5. Which of the following cannot be a protective colloid for emulsion polymerization?
a) Carboxymethyl cellulose
b) Cetyl alcohol
c) gelatin
d) poly vinyl alcohol
View Answer
Explanation: The water soluble polymers like carboxy-methyl cellulose, PVA and gelatin stabilizes the emulsion and prevents emulsion break down with progress of polymerization, so these can be called as a protective colloid for emulsion.
6. How is the polymerization rate in emulsion polymerization dependent on the rate of radical generation?
a) directly proportional
b) inversely proportional
c) no dependence
d) cannot be determined
View Answer
Explanation: The polymerization rate per cubic centimeters of aqueous phase is given by- Rp= kp (N/2)[M] Thus the rate Rp is independent of rate of radical generation, Ri.
7. How is the rate of polymerization affected with the change in surfactant concentration in emulsion polymerization?
a) increases with increase in concentration
b) decreases with increase in concentration
c) no effect
d) cannot be determined
View Answer
Explanation: The rise in surfactant concentration increases the number of polymer formed per cubic centimeters of the aqueous phase, which consequently increases the rate of polymerization rate, as the polymerization rate is given by-
Rp= kp (N/2)[M].
8. How is the degree of emulsion polymerization related to the monomer concentration, [M] and the rate of radical generation, Ri?
a) directly proportional to [M], inversely proportional to Ri
b) inversely proportional to Ri, directly proportional to [M].
c) directly proportional to Ri, independent of [M].
d) directly proportional to [M], independent of Ri
View Answer
Explanation: The degree of polymerization is given by-
Xn = Ʋp/Ʋi = kpN[M]/Ri
So, clearly the degree of emulsion polymerization is proportional to first power of [M] and negative first power of Ri.
9. Which of the following polymerization technique allows the increase in both the rate and degree of polymerization simultaneously by increasing a certain parameter?
a) bulk polymerization
b) solution polymerization
c) suspension polymerization
d) emulsion polymerization
View Answer
Explanation: The emulsion polymerization technique allows the increase in both the rate and degree of polymerization simultaneously by increasing the number of polymer particles, N at a fixed rate of initiation.
10. What is the average equilibrium radical concentration in the aqueous medium in emulsion polymerization?
a) 108 radical/cm3
b) 1013 radical/cm3
c) 105 radical/cm3
d) 1015 radical/cm3
View Answer
Explanation: The equilibrium radical concentration in the aqueous medium, [Raq∙] is measured to be about 108 radical/cm3.
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