1. What is the approximate ceiling temperature of tetrahydrofuran?
a) 70ᵒC
b) 160ᵒC
c) 300ᵒC
d) none of the mentioned
Explanation: Tetrahydrofuran shows a ceiling temperature of 70ᵒC above which its polymerization does not take place.
2. 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
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.
3. 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
Explanation: Tc is affected by the conditions affecting monomer concentration, the heat of polymerization and the reaction medium.
4. 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
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.
5. Which of the following is not a reason for non-ideal kinetics of radical polymerization?
a) initiator-monomer complexation
b) unimolecular termination
c) degradative initiator transfer
d) none of the mentioned
Explanation: All the three mechanisms cause non-ideality and kinetic deviations in the radical polymerization.
6. Consider initiator-monomer complexation in polymerization reaction, and a straight line is plotted between [M]3/Rp2 and [M]. What is the value of quotient of slope and the intercept?
a) equilibrium rate constant of monomer complexation reaction, K
b) termination rate constant, kt
c) propagation rate constant, kp
d) initiator concentration
Explanation: The transformed rate equation, considering initiator monomer complexation, is given by-
[M]3/Rp2 = (kt/kp2 kd K[I0]) + (kt[M]/ kp2 kd [I0])
Thus, the slope of the straight line plotted is, kt/ kp2 kd [I0] and the intercept is kt/kp2 kd K[I0]. Therefore, the quotient is calculated as K.
7. What is the order of reaction with respect to initiator, considering exclusive case of unimolecular termination?
a) 1
b) 0
c) 2
d) 0.5
Explanation: For exclusive unimolecular termination,
Rt = kt1 [M∙] Thus, the overall rate of polymerization is expressed as
Rp = kp/kt1 (2fkd) [I] [M] Therefore, the initiator order is equal to 1.
8. Which of the following can restrict the bimolecular termination?
a) high monomer concentration
b) insolubility of polymer formed in monomer
c) presence of solvents, additives
d) none of the mentioned
Explanation: Bimolecular termination is restricted in heterogeneous polymerization, where the polymer formed is insoluble in the monomer solvent media and unimolecular termination shows prominence.
9. What are the initiator and monomer orders, in limiting case of exclusive primary radical termination?
a) 0, 2
b) 1, 2
c) 1, 1
d) 2, 0
Explanation: The rate of polymerization, taking into account exclusive primary radical termination mechanism, is given by
Rp = kp (ki/kprt)[M]2
where kprt is the rate constant for primary radical termination.
Thus, the initiator and monomer orders are 0 and 2, respectively.
10. What is the order of dependence of monomer concentration on Rp, in the exclusive case of degradative initiator transfer process?
a) 1
b) 0
c) 2
d) 0.5
Explanation: The overall rate maintains first order dependence on monomer concentration and the rate equation is given by-
Rp =( kp/kt’)(2fkd) [M].