Question

1. Free radical polymerization

Styrene is polymerized by free radical polymerization in solution. The initial monomer and initiator concentration are 1 M (mol L^-1) and 0.001M, respectively. At the polymerization temperature of 60°C, the initiator efficiency is 0.30. The rate constants at the polymerization temperature are as follows:

k_d = 1.2*10^-5 s^-1

k_p= 176 M^-1 s^-1

k_t= 7.2*10⁷ M^-1s^-1

Given this information determine the following

(a) Rate of initiation at 1 min and 16.6 min

(b) Steady state free radical concentration

(c) rate of polymerization at 1 min

(d) number-average degree of polymerization at 1 min

(e) average free-radical lifetime, τ, at 1 min, where τ is defined as the radical concentration divided by the rate of termination

(f) Why is the information to determine the rate of polymerization and number-average degree of polymerization at 1 min important? What will change if the polymerization has been carried out for several hours already? Give qualitative answers!

(e) To what percentage is the molecular weight reduced at a polymerization time of 1 min when we add a chain transfer agent (0.001 M) with a chain transfer constant of C_s= 40. How would this change if we polymerize over several hours to 100% monomer conversion? Give a qualitative answer!

2. Free radical copolymerization

Styrene (1) and acrylonitrile (2) are copolymerized (r₁= 0.29, r₂= 0.02). Calculate the polymer composition F₁ for f₁= 0.01, 0.02. 0.03, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95.

• Determine the azeotropic composition from the F₁ vs f₁
• Calculate the azeotropic point and compare the result to (a)

(c) How does your composition change when you have an initial composition of f₁= 0.2 or an initiator composition of f₂= 0.8 and you polymerize to a monomer conversion of 100%?

3. RAFT polymerization

(a) How has the following polymer been prepared? Outline the mechanism!

(b) Imagine now that you take this polymer and mix it with styrene. The macroRAFT agent acts now similar to a RAFT agent and the PMMA chain is now the leaving group R. What structure would your final polymer have? What kind of polymer did you create? Outline the mechanism of the process!

(c) The molar ratio between styrene and thiocarbonylthio (RAFT group) is 500. The macroRAFT agent has a molecular weight of 20,000 g mol^-1. We polymerize styrene to 80%. What would your final molecular weight be?

4. Polycondensation

(a) Assume a polyesterification is conducted in the absence of solvent or catalyst and that the monomers are present in stoichiometric ratios. Calculate the time (min) required to obtain a number-average degree of polymerization of 50given that the initial dicarboxylic acid concentration is 3 mol L^-1 and that the polymerization rate constant is 10^-2 L mol^-1 s^-1.

(b) Plot the maximum number-average degree of polymerization X_n against various molar ratios r of carboxylic acid and alcohol for a range of different ratios. (Choose the sensible ratios r yourself)

(c) We add now various amounts of the following compounds to the mixture:

• What structure would your polymer have?
• What do you need to consider if you want to achieve high molecular weights?
• How does the amount of this multifunctional compound influence the structure and solubility of the final product?

5. Ionic Polymerisation

How would you go about making an A-B-A triblock copolymer consisting of dimethyl siloxane and isoprene such that all of the following criteria were fulfilled:

• High cis-1,4 addition of the isoprene monomer
• The isoprene unit is the A block
• The A block consisted of 50 monomer units and the B block consisted of 200 monomer units
• The chain ends are capped with carboxylic acid moieties
• The final polymer chain concentration is 0.1 M

Use any initiating system you require to obtain this polymer. However, you’re answer should include a full mechanism for the system, complete with conditions, AND concentrations for the main steps.

6. Heterogeneous Polymerisation

The emulsion and suspension polymerisations of styrene are useful for the formation of polystyrene latexes and foams. Contrast the two systems and describe the major differences between the two.

Summary

These questions belong to Chemical Engineering and they are deal with polymerization. Various questions such as free radical polymerization, free radical copolymerization, RAFT polymerization, polycondensation, ionic polymerization and heterogeneous polymerization have been answered in detail in the solution.

Total Word Count 1029

 

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