This set of Polymer Engineering test focuses on “Poly(vinyl Acetate)”.
1. Which is the most widely used polymerization technique to produce polyvinyl actate?
a) bulk polymerization
b) solution polymerization
c) emulsion polymerization
d) all of the mentioned
Explanation: Poly vinyl acetate is generally used as emulsion, and therefore emulsion polymerization is widely employed for the production of poly vinyl acetate. Bulk polymerization of vinyl acetate poses difficulties at high conversions due to its high exothermic nature.
2. What is the nature of commercially used poly vinyl acetate?
d) none of the mentioned
Explanation: The commercially used poly vinyl acetate is atactic and hence, amorphous in nature. It has a poor dimensional stability.
3. In which of the following solvents, is polyvinyl acetate immiscible?
Explanation: PVA is soluble in benzene and acetone, and methanol. It is immiscible in ethanol.
4. Why is vinyl alcohol not polymerized to give Poly vinyl alcohol?
a) tautomerism of vinyl alchol
b) free state existence
c) infeasible reaction
d) water insoluble
Explanation: The monomer, vinyl alcohol, does not exists in free state and being unstable, it forms a stable tautomer, acetaldehyde. This is why, polyvinyl acetate is used as the starting material for production of polyvinyl alcohol.
5. Polyvinyl alcohol is atactic in nature and hence amorphous. Therefore, it cannot be used as crystalline fibres. State true or false.
Explanation: Although polyvinyl alcohol has atactic chain structure and hence it is amorphous in nature. However, it can be stretched into crystalline fibre due to small size OH groups which lets it fit into the crystal lattice.
6. Which of the following pair lead to the formation of polyvinyl acetals?
a) Polyvinyl alcohol + aldehydes
b) Polyvinyl alcohol + esters
c) Polyvinyl chloride + aldehydes
d) Polyvinyl acetate + ester
Explanation: Polyvinyl acetals are formed by the interaction of polyvinyl alcohol and various aldehydes. The reaction usually involves condensation between I,3- hydroxyl groups and aldehyde group.
7. Which among the following is the important commercial use of polyvinyl butyral?
a) film forming technology
b) safety glass interlayer
c) textile and paper treatment
d) decorative laminates
Explanation: The commercial importance of polyvinyl butyral is its use as a safety glass interlayer, particularly because of its excellent clarity, toughness and exceptional adhesion o glass.
8. Why is reaction between polyvinyl alcohol and butyraldehyde for the formation of polyvinyl butyral, which is to be used for safety glass application, is stopped at about 75% conversion?
a) high heat is generated
b) polyvinyl butyral precipitates out
c) certain amount of monomer should be left unreacted
d) none of the mentioned
Explanation: For the purpose of safety glass application, the reaction is stopped at about 75% conversion, so that nearly 25% monomer is left unreacted which would provide the required strength and adhesion to the glass.
9. What happens when the degree of alcoholysis of polyvinyl alcohol is increased beyond 90%?
a) water solubility increases
b) water solubility decreases
c) decolouration occurs
d) water insolubility
Explanation: The polymer of vinyl alcohol having a degree of alcoholysis beyond 90%, its water solubility then follows an increasing trend with increasing degree of alcoholysis.
10. Which of the following is used as a catalyst in the formation of polyvinyl butyral?
Explanation: The reaction between polyvinyl alcohol and butyraldehyde requires the presence of acid catalyst like H2SO4 for the formation of polyvinyl butyral.
Sanfoundry Global Education & Learning Series – Polymer Engineering.
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