This set of Polymer Engineering Assessment Questions and Answers focuses on “Equilibrium in Chain Polymerization”.
1. Which of the following is not dependent on result of equilibrium condition of polymerization reaction?
a) degree of polymerization
b) chain length distribution
c) limiting monomer conversion
d) none of the mentioned
View Answer
Explanation: The result of equilibrium condition is felt on degree of polymerization, chain length distribution and also on the conversion of monomer to polymer.
2. How the increase in temperature to higher values, does affect the equilibrium state of propagation reaction?
a) shifts forward
b) shifts backwards
c) remains constant
d) none of the mentioned
View Answer
Explanation: The shifting of equilibrium takes place in reverse reaction as the propagation reaction is exothermic. Initially the effect of reverse reaction rate constant, kdp is not felt, but it increases progressively with higher temperatures and at a critical temperature, the overall polymerization reduces to zero.
3. What is the value of overall rate of polymerization at ceiling temperature?
a) exceptionally high
b) exceptionally low
c) zero
d) cannot be determined
View Answer
Explanation: When the temperature is initially increased from a low level, rate increases due to gain in the value of kp. Initially the effect of reverse reaction rate constant, kdp is not felt, but it increases progressively with higher temperatures and at a critical temperature, the rate of propagation is equal to rate of de-propagation and the overall polymerization reduces to zero.
4. What is the critical temperature Tc called, if ∆Hᵒ and ∆Sᵒ are both negative in radical polymerization?
a) ceiling temperature
b) floor temperature
c) theta temperature
d) all of the mentioned
View Answer
Explanation: If both ∆Hᵒ and ∆Sᵒ are negative, then the critical temperature is called the ceiling temperature, above which it is thermodynamically impossible to convert monomer to polymer.
5. What is the critical temperature called, if ∆Hᵒ and ∆Sᵒ are both positive in radical polymerization?
a) ceiling temperature
b) floor temperature
c) theta temperature
d) all of the mentioned
View Answer
Explanation: If both ∆Hᵒ and ∆Sᵒ are positive, then the critical temperature is called the floor temperature, below which it is thermodynamically impossible to convert monomer to polymer.
6. What is the approximate ceiling temperature of tetrahydrofuran?
a) 70ᵒC
b) 160ᵒC
c) 300ᵒC
d) none of the mentioned
View Answer
Explanation: Tetrahydrofuran shows a ceiling temperature of 70ᵒC above which its polymerization does not take place.
7. How does the viscosity of molten sulphur vary near 160ᵒC and above it?
a) goes minimum and then rises sharply
b) goes maximum and falls rapidly
c) remains constant
d) cannot be determined
View Answer
Explanation: The viscosity of molten sulphur passes through minimum at approximately 160ᵒC and the rises sharply. The hemolytic cleavage of S8 ring yield diradical and gives rise to free radical polymerization of further heating.
8. Which of the following does not affect the critical temperature, Tc?
a) heat of polymerization
b) conditions affecting monomer concentration
c) reaction medium
d) none of the mentioned
View Answer
Explanation: Tc is affected by the conditions affecting monomer concentration, the heat of polymerization and the reaction medium.
9. What does the intersection point of kdp and kp[M] curves give, where kp and kdp are the rate constants of propagation and depropagation reaction, respectively, when kdp and kp[M] are plotted against temperature of reaction?
a) critical monomer concentration
b) critical ceiling temperature
c) kp/kdp
d) all of the mentioned
View Answer
Explanation: The intersection point of the given curves in the plot of kdp and kp[M] against the temperature, gives the value of ceiling temperature, at which the rate of polymerization is zero.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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