This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Step Reaction Polymerisation”.
1. Which of the following is true about Step-growth polymerisation?
a) radical, coordination, anionic, or cationic polymerization, depending on the type of initiation
b) polymerization that is catalysed by transition metal salts and complexes
c) monomers react by eliminating small molecules like H2O, NH3, CH2O and NaCl in a repetitive manner, Indefinite growth of the polymer occurs at both ends
d) monomers react to form first dimers, then trimmers, longer oligomers and eventually long chain polymers
View Answer
Answer: d
Explanation: Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimmers, longer oligomers and eventually long chain polymer.
2. Which of the following is not true about step growth polymerisation?
a) Molar mass of backbone chain increases rapidly at early stage and remains approximately the same throughout the polymerization
b) Similar steps repeated throughout reaction process
c) Initiator are required for the step growth polymerisation
d) Rapid loss of monomer early in the reaction
View Answer
Answer: c
Explanation: Initiator is not required for the step growth polymerisation. Step-Growth polymerization occurs by consecutive reactions in which the degree of polymerization and average molecular weight of the polymer increase as the reaction proceeds.
3. Which of the following is polymer formed by step-growth polymerization is not classified under condensation polymerisation?
a) Polyester
b) Polyurethane
c) Polysiloxane
d) Polyamide
View Answer
Answer: b
Explanation: Most step-growth polymers are classified as condensation polymers, but not all step-growth polymers. Polyurethanes formed from isocyanate and alcohol bifunctional monomers) release condensates; in this case, we talk about addition polymers.
4. Which monomers are required for the formation of Bakelite via a typical step-growth polymerization?
a) phenol and formaldehyde
b) isocyanate and alcohol
c) diamine and formaldehyde
d) ester and phenol
View Answer
Answer: a
Explanation: The synthesis of first truly synthetic polymeric material, Bakelite, was announced by Leo Baekeland in 1907, through a typical step-growth polymerization fashion of phenol and formaldehyde.
5. Formation of polytriazole polymers via step-growth polymerization is produced from which of the following monomers?
a) Compound which bears both alkyne and azide functional group
b) Compound which bears both alkene and azide functional group
c) Compound which bears both alkane and azide functional group
d) Compound which bears both vinyl and azide functional group
View Answer
Answer: a
Explanation: Poly-Triazole polymers are produced from monomers which bear both an alkyne and azide functional group. The monomer units are linked to each other by the a 1,2,3-triazole group; which is produced by the 1,3-Dipolar cycloaddition, also called the Azide-alkyne Huisgen cycloaddition.
6. 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) first increases than decreases
View Answer
Answer: a
Explanation: The kinetics of the step-growth polymerization can be described with Flory’s equal reactivity principle. If the polymerization is carried out in the presence of a strong acid (sulfonic acids) and if the catalyst concentration is kept constant throughout the process the average degree of polymerization increases linearly with the reaction time, which is a much more favorable situation for obtaining high average molecular weight polymers than the weak-acid catalyzed third-order reaction.
7. What is the trend in the molecular weight of step growth polymer at lower conversion and higher conversion respectively?
a) Increase then decrease
b) Decreases an increases
c) Remains same
d) Can’t say about molecular weight
View Answer
Answer: b
Explanation: Step-growth polymers increase in molecular weight at a very slow rate at lower conversions and reach moderately high molecular weights only at very high conversion (i.e., >95%).
8. Which of the following is not prepared by Ziegler-Natta coordination polymerisation?
a) High density Polyethylene (HDPE)
b) Ultrahigh molecular weight Polyethylene (UHMWPE)
c) Ethylene-1-alkenebcopolymer (linear low density polyethylene, LLDPE)
d) Polyvinyl acetate (PVAc)
View Answer
Answer: d
Explanation: Vinyl chloride is polar olefins and such alkenes do not polymerize in the presence of Ziegler-Natta or Kaminsky catalysts.
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