This set of Polymer Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Photo Initiaton of Polymerization”.
1. What is the mechanism of uncatalyzed photo-initiation of polymerization, when light of specific wavelength falls on monomer?
a) monomer directly decomposes to give radicals
b) monomer generates excites species by absorbing light quanta and then decompose into radicals by homolysis
c) photo-initiator is added to monomer and decomposes to radicals by photolysis
d) all of the mentioned
View Answer
Explanation: The monomer, on photo-activation, generates excited species M*, by absorbing the light quanta of specific wavelength and the subsequently decomposes to give radicals by homolysis.
2. What has the terms kd[I] in the overall rate equation of uncatalyzed photo-polymerization been replaced by?
a) intensity of light radiation absorbed
b) intensity of incident light
c) number of pairs of chain radicals formed per quantum of light absorbed
d) monomer concentration
View Answer
Explanation:The term kd[I] is replaced by the intensity of active radiation absorbed, Ia and f is replaced by φ that stands for number of pairs of chain radicals formed per quantum of light absorbed.
3. What does the intensity of active radiation absorbed in uncatalyzed photo-polymerization, not depend on?
a) thickness of reaction mixture
b) intensity of incident radiation
c) monomer concentration
d) none of the mentioned
View Answer
Explanation: The intensity of incident light does not vary measurably with the thickness of reaction mixture, while it is proportional to the product of intensity of incident radiation and monomer concentration.
4. How does the overall rate of uncatalyzed photo-polymerization vary, when the monomer concentration is quadrupled, rest all the terms remain same?
a) two fold increase
b) eight fold increase
c) remains same
d) two fold decrease
View Answer
Explanation: According to the rate expression of uncatalyzed photo-polymerization, we have
Rp α [M]1.5
Therefore, when monomer concentration is quadrupled, Rp increases by 8 times.
5. Which of the following initiator system works on the mechanism of photo-activation?
a) hydrogen halide
b) nitrobenzene complexes
c) hydrogen sulphide
d) oxalate complex of transition metals
View Answer
Explanation: The cleavage of H─S bond in hydrogen sulphide takes place by photo-activation, which then gives H∙ and HS∙ radicals.
6. Photo-activation allows the use of a wide range of chemicals as polymerization initiators in comparison to the thermal catalyzed process. State true or false.
a) true
b) false
View Answer
Explanation: This happens because of the high selectivity of photolytic homolysis in most compounds.
7. What is the expression for rate of initiation in catalyzed photo-polymerization? ( I0 and φ are the intensity of incident light and number of pairs of chain radicals formed per quantum of light absorbed, respectively and ε be the molar absorption coefficient )
a) 2φεI0[I]
b) φεI0[M]
c) 2φεI0[M]
d) φεI0[I]
View Answer
Explanation: The rate of initiation in catalyzed photo-polymerization, when a photo-initiator, I is used, is given by-
Ri = 2φεI0[I].
8. 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
View Answer
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.
9. What happens to overall rate of catalyzed photo-polymerization, when the initiator concentration is quadrupled?
a) doubled
b) quadrupled
c) tripled
d) remains same
View Answer
Explanation: According to the rate expression of related photo-polymerization, we have
Rp α [I]0.5
Therefore, Rp gets doubled.
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