Step-Growth Polymerization

Part l: Step-Growth Polymerization [14 marks]

1.In the kinetic treatment of step-wise polymerizationcovered in this course, it was

assumed that the reactivities of all functionalgroups are equal and that there is no dependence of reactivity on chainlength.If there is chain-length dependence, how do you think this would influence a plot of number-average degree of polymerization vs time? Explain your answer. (2 marks)

2. Consider aninterfacial polymerization such as that in the"Nylon Rope Trick".

(a)Which is the most obvious way to increase the rate of polymerizationin an

interfacial polymerization? (1 mark)

(b) Explain how/why this approach leads to a higher polymerization rate.(1 mark)

3. You conduct a polyesterification reaction involving a diol and a diacid in equimolar

proportions in a closed system.You take samples asa function of time and measure the number-average molecular weight (Mn).When plotting Mnvs time, you notice that after a certain polymerization time, the M,values plateau and do not increase further.

(a) What is the reason for this plateau? (2 marks)(b) What can be done to overcome this problem? (1 mark)

4. You synthesize a polyamide by reaction between a diacid and a diamine in

equimolar proportions.You run the exact same polymerization twice, the only difference being the polymerization time. At the end of each polymerization, you conduct GPC analysis and find that the polymerizations give molecular weight dispersities of 1.56 and 1.87. Which of the dispersities is associated with thelonger polymerization time? Explain. (2 marks)

5. A polyesterification is conducted using the following monomers:

0

HO、

OH 0

2.02 M HO、 OH 1.98 M

The initial concentrations are as listed under each monomer in units of M.

(a)If the final conversion of functionalgroups of the limiting reagent is 98%,what is

the final Mn? (3 marks)

(b) In the example in(a), what would happen(qualitatively) to the final M, if a mono-

functional carboxylic acid were added? Explain. (2 marks)

Part II: Radical Polymerization [20 marks]

1. Radical polymerization of methyl methacrylate (100 g/mol) in solution ([M]o = 5.0 M) is conducted to low conversion at 70 °C initiated by AIBN using four different concentrations of a thiol chain transfer agent: 0, 0.05, 0.13, and 0.19 M. The corresponding values of M_n (measured by GPC) are 80000, 25030, 14000 and 10000 g/mol. We know that the value of the propagation rate coefficient k_P is 1050 M 's」.

(a) What is the value of the rate coefficient for chain transfer (for) (4 marks)?

(b) If the activation energy for the propagation step is 30 kJ/mol and the activation energy for the transfer step is 17 kJ/mol_z how would the molecular weight change (qualitatively) if the reaction temperature was reduced to 60 °C? (2 marks)

(c) What would happen to the molecular weight if the AIBN concentration was

increased by 40%? Explain. (2 marks)

2.(a)What two main factors dictate the copolymer composition at low monomer

conversion in a binary copolymerization? (2 marks)

(b)Why arer andrz usually determined at very low conversions?(1 mark)(c) In a binary copolymerization, we have:r=1.82 and rz=0.55.Draw(schematically)the copolymer composition F as a function of monomer feed composition (fi). What type of copolymerization is this?(3 marks)

3.Styrene is polymerized using three different approaches: (i)Emulsion

polymerization;(ii)Suspension polymerization;(ii)Solution polymerization.The experimental conditions of (i), () and (i) are comparable.

(a)Which system would give the highest molecular weight polymer? Why?(2 marks(b) Which system would polymerize the fastest? Why? (2 marks)

4. You wish to polymerize a very water insoluble vinyl monomer in an aqueous

heterogeneous(dispersed system).Would you choose an emulsion polymerization or a miniemulsion polymerization? Explain. (2 marks)

PartIIl: lonic Polymerization [27 marksl

1. A researcher wants to synthesise a diblock copolymer containing a poly(butyl

methacrylate) block and a poly(styrene) block by anionic polymerization.

(a) Describe a synthesis method for the preparation of such a block copolymer,

including the reaction steps (monomer addition) and conditions involved.(3 marks)

(b)Explain why anionic polymerization is asuitable technique to prepare such a block

copolymer. Can such a block copolymer be prepared via conventional (or non- living) radical polymerization or cationic polymerization? (1 mark)

(c) Describe the potential side reactions for the anionic polymerization of BMA.How

can you prevent these side reactions? (1 mark)

(d) The researcher wants to prepare 70 g of a diblock copolymer containing 70/30

mol-% of BMA/St with a molecular weight of 100,000 g/mol.N-butyl lithium is used as the initiator.Justify the choice of this initiator. (1 mark)

(e) Calculate the molar amount and mass of initiator required if each step is carried

out to a conversion of 100%[BMA MW=142g/mol, n-BuLi MW=64g/moland St MW = 104 g/mol. (2 marks)

(f) Indicate the molar amount and mass of BMA and St needed to perform this

polymerization. (2 marks)

(g) How can the researcher introduce a hydroxyl group at the chain end of this block

copolymer? Indicate the type of compound which needs to be added. (1 mark

(h) Calculate the molar amount and mass of this compound to functionalize the

diblock copolymer prepared in the previous question. (1 mark)

2. High molecular weight poly(ethylene oxide)-block-poly(styrene)-block-poly(ethylene

oxide) triblock copolymer is produced industrially using an anionic polymerization process.A researcher wants to produce 10g of this triblock with a molecular weight of 50 000 g/moland a composition of styrene/ethylene oxide=30/70 in mol-%.

a)Indicate if a specific monomer addition needs to be used for the preparation of

this triblock copolymer. (1 mark)

b)Calculate the molar amount and mass of initiator to prepare this block copolymer

if sodium/naphthalene is employed as initiator.(1 mark)

c) Calculate the molar amount and mass of styrene and ethylene oxide needed in

this synthesis(ethylene oxide MW= 54 g/mol) assuming that full monomer conversion is obtained in each step. (2 marks)

d)Asmall amount of methanol is present in the ethyleneoxide (0.1 wt-%).What wil

be the consequence on the molecular weight for this triblock copolymer? Provide an explanation.Calculate the expected molecular weight of thetriblockcopolymer(3 marks)

3. A researcher wants to prepare a pentablock copolymer containing one block each of

polystyrene, poly(butadiene), poly(2-vinyl pyridine), poly(methyl methacrylate)and poly(ethylene oxide) via anionic polymerization.Indicate if there is a specific polymerization order for the synthesis of this pentablock copolymer. Justify your response by explaining the criteria of selection. (2 marks)

4. A researcherwants to prepare 200gof poly(tetrahydrofuran)with a molecular weight

of 12,000 g/mol via cationic ring-opening polymerization of tetrahydrofuran. The polymerization is performed at 0℃ using boron trifluoride etherate as catalyst, water as cocatalyst, and ethylene dichloride as solvent.

a) Calculate the molar amount and mass of boron trifluoride to prepare this polymer

assuming that the efficiency of the initiator is 90%.Using chemical drawings,show the initiation mechanism. (2 marks)

b) Calculate the mass and molar amount of tetrahydrofuran required if the expected

monomer conversion is 90%. (2 marks)

c)At the end of the polymerization, a monomer conversion of 95% was observed.

Calculate the expected molecular weight of the polymer. (2 marks)