1. 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
Explanation: The term for extent of reaction is given by,
p = (2/f)[1-(1/Xn)] Therefore, it is inversely proportional to f.
2. 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
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.
3. Which of the following expressions correctly represents the number distribution function for a linear polycondensation reaction?(Here N0 and p are total number of initial monomer molecules and extent of reaction initially)
a) Nn=N0(1-p)2pn-1
b) Nn=N0(1-p)pn-1
c) Nn= N0pn-1
d) Nn0n(1-p)2pn
Explanation: The probability Pn of formation of polymer molecule with n degree of polymerization is given by,
Pn=pn-1(1-p)
Where, Pn= Nn/N, and also N= N0(1-p), so the value on Nn comes out to be, Nn= N0(1-p)2pn-1.
4. Find the value of number average degree of polymerization for a mixture of polymers at 90% completion of reaction?
a) 0.1
b) 10
c) 100
d) 1.1
Explanation: The expression for Xn is given by,
Xn= 1/(1-p)
= 1/0.1
= 10
Thus, the value of number average degree of polymerization is 10.
5. What does the ratio of number to weight average degree of polymerization for a bifunctional system represent?
a) degree of polymerization
b) breadth of molecular size
c) extent of reaction
d) none of the mentioned
Explanation: The ratio, commonly, is used to represent the molecular size distribution, which is given by (1+p).
6. What are the values of number and weight average degree of polymerization for a bifunctional system at 95% completion of reaction?
a) 20, 39
b) 10,39
c) 2,3.9
d) 25,35
Explanation: The expressions for number and weight average degree of polymerization are given by,
Xn= 1/(1-p)
Xw= (1+p)/(1-p)
By putting the value of p, value of Xn and Xw can be calculated.
7. 80 moles of monomers react to prepare Nylon 12. After completion of 8 hrs, 4 moles of monomers are still left. What is the weight average molecular weight of polymer system?
a) 1263
b) 197
c) 3940
d) 7683
Explanation: The extent of reaction is-
p= 80-4/80 = 0.95
Thus, Xw= (1+p)/(1-p) = 39
Mw= Xw Mo= 197*39= 7683.
8. What are the number average molecular weights of Nylon 66 and Nylon 11, when the conversion is 90%?
a) 2260, 1830
b) 4294, 3477
c) 2586, 1830
d) 3477, 4200
Explanation: The value of Xn is given by,
Xn= 1/(1-p) = 1/(1-0.9)
= 10
Thus, for Nylon 66, Mn= 226*10=2260
For Nylon 11, Mn= 183*10= 1830
(226 and 183 are the molecular weights of the repeating units of polymer Nylon 66 and Nylon 11, respectively).
9. What is the maximum attainable degree of polymerization for 5% stoichiometric imbalance?
a) 52
b) 41
c) 63
d) 56
Explanation: For 5% impurity, the maximum attainable degree of polymerization will be,
Xn= [1+(100/105)]/[1-(100/105)] Thus, Xn will be equal to 41.
10. Hydroxy caproic acids are used to polyester molecules. Due to improper purification of reactants, 2% of acid impurity was found. What is the number average degree of polymerization for 95% completion of reaction?
a) 2526
b) 1280
c) 1912
d) 1270
Explanation: For 2% acid impurity, r= 100/102= 0.98
Then, Xn is given by,
Xn= (1+r)/(1+r-2rp)
= 16.78
Thus, Mn= 114*16.78= 1912.