# Polymer Engineering Questions and Answers – Determination of Absolute Rate Constant of Propagation

This set of Polymer Engineering MCQs focuses on “Determination of Absolute Rate Constant of Propagation”.

a) ratio of the steady state radical concentration and the rate of its termination
b) ratio of termination of the radical and its steady state concentration
c) ratio of steady state radical concentration and the rate of propagation
d) cannot be determined

Explanation: The average lifetime of a growing radical under steady state is given by the ratio of the steady state radical concentration and the rate of its termination, and is expressed as-
τs = kp[M]/2kt[Rp]s.

2. What is the intensity received by the system in rotating sector technique, under the limiting case of very fast flashing?
a) I0
b) I0/2
c) 2I0
d) 3I0

Explanation: Under the limiting case of very fast flashing so as to have a little fluctuation in the radical concentration, only 50% of the irradiation is received by the system i.e. continuous illumination of intensity I0/2 is obtained.

3. Which of the following cannot affect the average lifetime of a radical in a photo-initiated polymerization?
a) rate of polymerization, Rp
d) none of the mentioned

Explanation: The average lifetime of the radical is proportional to the rate of polymerization, which on the other hand is dependent on frequency and intensity of incident light. Thus the average lifetime can get affected by all the given factors.

4. What is the proportionality order for the average rate of polymerization for steady conditions and continuous illumination, with respect to intensity of illumination?
a) ½
b) 1
c) -½
d) -1

Explanation: For steady state conditions and continuous illumination,(Rp)s α (I0)1/2.

5. Which of the following is correct regarding the proportionality of average rate for intensity of illumination, if there is very fast blinking with equal light and dark periods?
a) ( Rp) α ½ (I0)1/2
b) ( Rp) α (I0/2)1/2
c) ( Rp) α (I0)1/2
d) ( Rp) α 2(I0)1/2

Explanation: For very fast blinking with equal light and dark periods, the average rate shows following proportionality for intensity of illumination, (Rp) α (I0/2)1/2.
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6. What is the relative rate of polymerization, under steady conditions to that of slow blinking, when the dark period is 4 times longer than the light period?
a) 1/4
b) 1/5
c) 1/51/2
d) 1/2

Explanation: The relative rate for the slow blinking condition is given by,(Rp)s/(Rp) = 1/(r+1), where r is ratio of dark period to the light one. Thus, the relative rate is obtained as 1/5.

7. How many times is the lighter period shorter than the darker one, if the steady state rate is one third of the average rate for very fast blinking?
a) 4
b) 8
c) 2
d) 3

Explanation: If the steady state rate is one third of the average rate for very fast blinking, then (Rp)s/(Rp)= 1/3, and for fast blinking
(Rp)s/(Rp)= 1/(r+1)1/2
1/3 = 1/(r+1)1/2
r=8.