1. How much would the unsaturation of cyclized rubber reduce to its original when it forms polycyclic structure?
a) 57-60%
b) 20-30%
c) 40%
d) 70%
Explanation: Cyclization reaction of rubber leading to the formation of bi- or even polycyclic structures result in the reduction in unsaturation to 20-30% of the original rubber, while the formation of monocyclic structure lead to the drop in unsaturation by 57% of original.
2. What kind of product is obtained on chlorination of natural rubber?
a) elastomer
b) thermoplastic
c) resinous
d) none of the mentioned
Explanation:The chlorinated rubber formed by chlorination of natural rubber is resinous in character while natural rubber is elastomeric in nature.
3. Which solvent is used to dissolve rubber pieces in the process of chlorination of natural rubber?
a) carbon tetrachloride
b) acetone
c) benzene
d) toluene
Explanation:In the process of chlorination, rubber small pieces of rubber are dissolved in carbon tetrachloride in presence of a small amount of benzoyl peroxide which act as a depolymerizing agent and lowers the solution viscosity.
4. Which of the following information about chlorinated rubber is wrong?
a) it resists concentrated nitric acid
b) it is used as heat sealable package for dry food
c) it has flame retardant characteristics
d) it is resinous in character
Explanation: Hydrochlorinated rubber is used as heat sealable package for dry foods whereas chlorinated rubber is used in formulation of paints, lacquers, adhesives and printing inks.
5. Which solution is used for hydrochlorination of natural rubber with HCl gas?
a) benzene
b) toluene
c) carbon tetrachloride
d) acetone
Explanation: Hydrochlorinated rubber is conveniently obtained by hydrochlorination with gaseous HCl using rubber in benzene solution.
6. Which synthetic rubber is also commonly known as hypalon?
a) polychloroprene rubber
b) chloro-sulphonated polyethylene
c) styrene-butadiene rubber
d) nitrile rubber
Explanation: Chlorosulphonated polyethylene (CSP) is commonly known in the trade as Hypalon.
7. What kind of synthetic rubbers are commonly known as thiokols?
a) polyurethane rubbers
b) polysulphide rubbers
c) fluorocarbon rubbers
d) polyacrylic rubbers
Explanation: Polysulphide rubbers are commonly known as Thiokols due to the presence of thio group in their structure.
8. What is the cis content of polybutadiene rubber obtained by emulsion polymerization using redox catalyst?
a) <40%
b) >10%
c) >92%
d) None of the mentioned
Explanation: Polybutadiene prepared by emulsion polymerization in the presence of redox catalysts is lower in cis content i.e. below 10%.
9. Which of the following catalyst is used to obtain polybutadiene of cis content <40%?
a) coordination catalyst based on Ni, Co
b) redox catalyst
c) zeiglar natta catalyst
d) butyl lithium catalyst
Explanation:When polybutadiene is prepared using butyl lithium catalyst, rubber of lower cis content (<40%) is formed. Using coordination catalyst, high cis content (>90%) polybutadiene is obtained.
10. Which synthetic rubbers are blended with BR to make its extensive use in tyres?
a) NR and SBR
b) NBR and SBR
c) NR and NBR
d) NR, NBR and SBR
Explanation:BR is blended with natural rubber and SBR in the manufacture of tyres for improved milling, wet skid resistance, while BR imparts excellent abrasion resistance to car and truck tyres.