1. Which of the following is not true about photo-sensitizer in photo-polymerization?
a) easily gets excited on exposure to light
b) carries energy absorbed to initiator or monomer
c) helps in both catalyzed and uncatalyzed polymerizations
d) gets excited and decomposes to give radicals
Explanation: Photo-sensitizer gets easily excited on exposure to light, and the carries adsorbed light to initiator and monomer molecules so that they undergo homolysis to reduce chain-initiating radicals.
2. What happens to overall rate of catalyzed photo-polymerization, when the initiator concentration is quadrupled?
a) doubled
b) quadrupled
c) tripled
d) remains same
Explanation: According to the rate expression of related photo-polymerization, we have
Rp α [I]0.5
Therefore, Rp gets doubled.
3. What does the ratio Rp/Ri represent in polymerization?
a) chain length
b) monomer concentration
c) initiator concentration
d) none of the mentioned
Explanation: The kinetic chain length is viewed as the ratio of rate of propagation to the rate of initiation or termination, since Ri = Rt.
4. The kinetic chain length represents the average number of monomer molecules in a polymer molecule. State true or false
a) true
b) false
Explanation: The kinetic chain length represents the average number of monomer molecules consumed by a primary radical, from its initiation to termination.
5. What is the expression for kinetic chain length for a purely thermal polymerization??
a) kp/2(kikt)0.5
b) kp/2(ki/kt)0.5
c) kp2/2(kikt)0.5
d) kp/(kikt)0.5
Explanation: For pure thermal polymerization, Rp is given by-
Rp = kp(ki/kt)0.5[M]2
And the chain length is given by-
v =( kp2/2kt) ([M]2/Rp)
So, for pure thermal polymerization, the expression for kinetic chain length is given by,
v = kp/2(kikt)0.5
6. The kinetic chain length expression given by, v=( kp2/2kt)([M]2/Rp) is applicable to all cases of termination, irrespective of the mechanism involved. State true or false.
a) true
b) false
Explanation: The kinetic chain length expression given by, v=( kp2/2kt)([M]2/Rp) is applicable to all cases of termination, irrespective of the mechanism involved, combination or disproportionation and also irrespective of the nature of initiation mechanism.
7. For vinyl acetate polymerized at 50ᵒC, the value of the ratio kp2/kt is 0.0138 l/mol-s. What is the value of chain length, when monomer concentration is 6.53 mol/l and rate of polymerization is 2.0*10-4mol/l-s?
a) 1471
b) 2942
c) 500
d) 225
Explanation: The expression for kinetic chain length is-
v=( kp2/2kt)([M]2/Rp)
Substituting the values, we get v as 1471.
8. What are the relative chain lengths of vinyl chloride and styrene, polymerized at 60ᵒC, having the values of ratio kp2/kt as 0.126 l/mol-s and 0.0034 l/mol-s, respectively?
a) 37
b) 74
c) 50
d) 100
Explanation: Assume the rate of polymerization and monomer concentration same for both the cases.
vvc/vs = ( kp2/kt)vc/( kp2/kt)s
= 0.126/0.0034
= 37.
9. What is the degree of polymerization for polyvinyl chloride, having kinetic chain length as 400 and terminated by coupling mechanism?
a) 400
b) 800
c) 200
d) none of the mentioned
Explanation: For termination by combination,
Xn = 2v
So, the value of degree of polymerization is 800.
10. For styrene polymerized at 70ᵒC, monomer concentration is 7.85mol/l and the value of the ratio (kp2/kt) is 0.0015 l/mol-s. What is the rate of polymerization reaction, if the chain length is 300?
a) 0.092
b) 0.046
c) 0.08
d) 0.072
Explanation: The kinetic chain length expression is given by,
v= (kp2/kt)([M]2/Rp)
Substituting the values we get, Rp as 0.046.