Question

In a set of copolymerization reactions, the following monomer reactivity ratios (\(r_1\) and \(r_2\)) were found for different cases: \[ \begin{array}{|c|c|c|} \hline \text{Case} & r_1 & r_2 \\ \hline I & 0.1 & 10 \\ II & 0.003 & 0.02 \\ III & 3.4 & 5.6 \\ IV & 51 & 0.01\\ \hline \end{array} \] Which option(s) correctly identify/identifies the type of copolymerization corresponding to each Case?

• A. I - Ideal copolymerization
• B. II - Azeotropic copolymerization
• C. III - Block copolymerization
• D. IV - Alternating copolymerization

Hint:

Rule of thumb: - \(r_1 = r_2 = 1 \Rightarrow\) Ideal, - \(r_1 r_2 = 1 \Rightarrow\) Azeotropic, - Both \(\gg 1 \Rightarrow\) Block, - Both \(\ll 1 \Rightarrow\) Alternating.

Answer 1

The Correct Option is A, C

Case	r1	r2
I	0.1	10
II	0.003	0.02
III	3.4	5.6
IV	51	0.01

In copolymerization, the monomer reactivity ratios (r₁ and r₂) determine the nature of the copolymer. Four main types can occur:

• Ideal copolymerization: r₁ and r₂ are near 1, indicating both monomers have similar reactivity towards each other, resulting in a random copolymer.
• Azeotropic copolymerization: This results in the composition being fixed at a particular ratio due to both r values being equal.
• Block copolymerization: Large values for both r₁ and r₂ indicate preference for homopolymer formation leading to blocks.
• Alternating copolymerization: r₁r₂ is close to zero, suggesting strong preference for alternate copolymer configuration.

Analyzing each case: 

• Case I: r₁=0.1, r₂=10. This represents ideal copolymerization as neither tries to form a homopolymer alone.
• Case II: Values are low, indicating neither monomer strongly prefers adjacent sequences, but not distinct.
• Case III: Both r₁=3.4 and r₂=5.6 are large, favoring block formation.
• Case IV: r₁=51 is very high but r₂ is quite low, thus does not fit alternating pattern well.

Correct identification is:

• Case I: Ideal copolymerization
• Case III: Block copolymerization