Engineering Questions with Answers - Multiple Choice Questions
Polymer Engineering MCQ’s – Kinetics of Step – Growth Polymerization
1 - Question
What is the order of a self-catalyzed polyesterification reaction?
a) 2
b) 3
c) 1
d) 4
View Answer
Explanation: For each step of reaction between a –COOH group and –OH group, a second functional group –COOH acts as a catalyst in the reaction. Therefore, the reaction follows the third order kinetics.
2 - Question
How is the reactivity of a specific functional group, in general, dependent on the size of the molecule to which it is attached, in a polycondensation reaction?
a) increases with increase in molecular size
b) decreases with decrease in molecular size
c) independent of molecular size
d) cannot be determined
View Answer
Explanation: The reactivity of functional is independent of the size of the molecule to which it is attached
3 - Question
Which of the following is true about polymer systems in polycondensation?
a) have higher viscosity than small non-polymeric molecules
b) insoluble beyond a critical molecular weight
c) all of the mentioned
d) none of the mentioned
View Answer
Explanation: The medium viscosity in polymer systems is much higher than the systems of small non-polymeric molecules. Besides, there tend to become insoluble after a certain range of chain length or molecular weight.
4 - Question
Which order kinetics does a strong acid catalyzed polyesterification reaction follow?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: This reaction is achieved by addition of a strong acid catalyst, which is not utilized in the reaction as in self catalyzed reaction. So, the reaction clearly, follows second order kinetics.
5 - Question
What is the slope of the line plotted between square of the average degree of polymerization and time for a self catalyzed polyesterification?
a) 2c02k
b) 2c0k
c) c0k/2
d) c02k
View Answer
Answer: a
Explanation: The rate of disappearance of carboxyl groups is given by, -dc/dt = kc3 (due to self catalyzation, second COOH group acts as catalyst, and reaction follows third order kinetics)
On integration we get,
2kt = 1/c2 – constant
On substituting c=c0(1-p), we get
2c02kt = 1/(1-p)2 – constant
This equation gives the slope equal to 2c02k.
6 - Question
What factors may be responsible for deviation in the high conversion region of self-catalyzed polycondensation?
a) loss of reactants
b) cyclization
c) other side reactions
d) all of the mentioned
View Answer
Explanation: The deviation from linearity in the high conversion region may have arisen due to the factors including loss of reactants, cyclization or other side reactions.
7 - Question
What is true about an end functional group, having a terminal reactive centre, of a polymer molecule?
a) has a greater mobility than the polymer molecule as a whole
b) has a lower mobility than the polymer molecule as a whole
c) same as polymer molecule
d) cannot be determined
View Answer
Explanation: The functional group at a free end has a good degree of mobility to collide and faster reaction to take place.
8 - Question
How does the reaction rate vary with increasing extent of reaction beyond 94% conversion in self catalyzed reaction?
a) decreases
b) increases
c) remains same
d) none of the mentioned
View Answer
Explanation: The reaction rate decreases with increasing extent of reaction beyond 94%. The factors responsible are loss of reactants, difficulty in removal of byproduct molecule due to high viscosity and other side reactions.
9 - Question
What is the average degree of polymerization for a complete polycondensation reaction in a bifunctional system?
a) infinity
b) 0
c) 1
d) none of the mentioned
View Answer
Explanation: For a bifunctional system, average functionality, f=2 and for a complete reaction, extent of reaction, p=1. So the expression for extent of reaction reduces to, p = [1-(1/Xn)] where, Xn is the average degree of polymerization. Therefore, Xn=∞. Although it is possible only in hypothetical situation.
10 - Question
How is the extent of reaction, p, of a polycondensation reaction related to the average functionality, f, of the system?
a) proportional to f
b) proportional to 1/f
c) proportional to f2
d) proportional to 1/f2
View Answer
Explanation: The term for extent of reaction is given by, p = (2/f)[1-(1/Xn)] Therefore, it is inversely proportional to f.
11 - Question
The average functionality of a polyfunctional system is 2.4. What will be the average degree of polymerization for 80% completion of reaction?
a) 20.55
b) 27.67
c) 50.3
d) 2.97
View Answer
Explanation: Using the formula, p = (2/f)[1-(1/Xn)] and putting the values of f=2.4 and p=0.8, we get the value of Xn as 27.67.