This set of Polymer Engineering Interview Questions and Answers focuses on “Multichain Step – Growth Polymers and Molecular Weight Distribution in Multifunctional Systems”.
1. What is the molecular distribution breadth for polymerization reaction of trifunctional monomers, if the conversion is 90%?
a) 0.344
b) 1.344
c) 0.33
d) none of the mentioned
View Answer
Explanation: The distribution breadth for polyfunctional system is expressed as,
Xn/Xw= 1+ fp/(fp+1-p)2
And p=0.9, f=3
Thus, distribution breadth is 1.344.
2. Hydroxyacid is allowed to polymerize in the presence of another trifunctional monomer containing carboxylic groups. What kind of structure is formed at the end of the reaction?
a) linear
b) branched
c) cross-linked
d) none of the mentioned
View Answer
Explanation: At the end of the reaction only branched structure is formed and no cross-linked structures can be formed since no bifunctional hydroxyl monomers are present to combine the branches.
3. Which of the following monomer molecule’s presence could lead to the formation of cross linking polymer, when hydroxyl caproic acid and carboxyl acid monomers (f>2) are polymerized together?
a) glycol
b) ethanol
c) diamines
d) none of the mentioned
View Answer
Explanation: Glycol is a bifunctional monomer having hydroxyl groups which will establish cross-links by combining two branches.
4. How does weight fraction distribution vary with increasing functionality at constant conversion?
a) gets broader
b) gets narrower
c) remains constant
d) none of the mentioned
View Answer
Explanation: The weight fraction distribution broadens with increasing functionality at comparable conversion values.
5. What is true about the branching system involving trifunctional monomers?
a) weight fraction of monomer lower than other species
b) weight fraction of bigger species become higher progressively
c) weight fraction of monomer always larger than other species
d) none of the mentioned
View Answer
Explanation: The weight fraction of the monomer is always greater than any of the other species and the weight fraction of larger species being lower, progressively, in such a gelling system involving trifunctional monomers.
6. How does the weight distribution vary with increasing conversion and constant trifunctionality?
a) gets broader
b) gets narrower
c) remains constant
d) none of the mentioned
View Answer
Explanation: The distribution broadens as the extent of reaction is increased, keeping the functionality same.
7. At 100% completion of reaction, only gel is present and the distribution breadth, Xw/Xn becomes infinite. State true or false.
a) True
b) False
View Answer
Explanation: At p=1, the whole system is converted into an insoluble and infusible mass of one giant molecule and distribution breadth becomes equal to unity.
8. Which is the correct expression for number average degree of polymerization for the non-linear multi-functional systems?
a) 1/{1-(pf/2)}
b) (1+p)/{1-(f-1)p}
c) 1-(pf/2)
d) 1/(pf/2)
View Answer
Explanation: The general expression for Xn for non-linear multi-functional system is given by,
Xn= 1/{1-(pf/2)}.
9. Before the interaction of W3 and W4 curves in the given figure, the system consists of most weight abundant species. State true or false.
a) true
b) false
View Answer
Explanation: The gel formed comprises of the most weight abundant species, beyond the intersection of the the curves W3 and W4.
10. What is the weight average degree of polymerization for non-linear trifunctional system, if the conversion is 0.3?
a) 2.35
b) 3.25
c) 5.5
d) 1.82
View Answer
Explanation: The expression for Xw, for non-linear trifunctional system is given by,
Xw = (1+p)/{1-(f-1)p}
Substituting the values we get, Xw as 3.25.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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