POLY3000 / CEIC8104THE UNIVERSITY OF NEW SOUTH WALES TERM 2, 2020 POLY3000 / CEIC8104 Polymer Science / Topics in Polymer Technology DURATION OF EXAMINATION: 24 hours NUMBER OF PAGES: 5 NUMBER OF QUESTIONS: 10 TOTAL NUMBER OF MARKS: 64 MARKS FOR EACH QUESTION ARE AS INDICATED YOU ARE REMINDED OF THE UNSW STUDENT CODE OF CONDUCT AND ADVISED THAT COMMUNICATION WITH OTHERS DURING THE EXAM IS NOT PERMITTED Page 1Page 2 Part I: Step-Growth Polymerization [19 marks] 1. The polyamide Nylon-6,6 is prepared by the reaction of a diamine with a diacid using equal concentrations of both reactants of 1 M in an open (driven) system. (a) Draw (free hand, no need to calculate data points) how the number-average molecular weight would increase with monomer conversion. Explain the general shape of the curve. (2 marks) (b) What is the meaning and purpose of an “open (driven) system”? (2 marks) (c) The following measurements were obtained to track the polymerization. From the data, calculate p, ����, ����, Ð for each reaction time. (6 marks) Time (min) [COOH] (mol dm-3) 30 0.5 60 0.33 120 0.2 240 0.1 480 0.01 (d) Determine the highest value of ���� that can be reached if the same polymerization is performed in a closed reactor with an equilibrium constant of 400. (2 marks) 2. A polyesterification is conducted using the following monomers: 2.00 M 1.97 M The initial concentrations are as listed under each monomer in units of M. (a) If the final conversion of functional groups of the limiting reagent is 97%, what is the final number-average degree of polymerization? (3 marks)(b) Explain in words (not equations) why the final number-average degree of polymerization in a stepwise polymerization is lower when non-stoichiometric ratios of AA and BB type monomers are used (compared to equimolar amounts of AA and BB). (2 marks) (c) In the example in (a), what would happen (qualitatively) to the final number average degree of polymerization if a mono-functional carboxylic acid were added? Explain. (2 marks) Part II: Radical Polymerization [18 marks] 3. Radical polymerization of styrene (104 g/mol) in bulk ([M]0 = 8.7 M) is conducted to low conversion at 70 °C initiated by benzoyl peroxide using four different concentrations of a thiol chain transfer agent: 0, 0.05, 0.13, and 0.19 M. The corresponding values of Mn (measured by GPC) are 80000, 25030, 14000 and 10000 g/mol. We know that the value of the propagation rate coefficient kp is 480 M-1s-1. (a) What is the value of the rate coefficient for chain transfer (ktr) (4 marks)? (b) If the activation energy for the propagation step is 32.5 kJ/mol and the activation energy for the transfer step is 18 kJ/mol, 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 benzoyl peroxide concentration was increased by 50%? Explain. (2 marks) 4. (a) What two main factors dictate the copolymer composition at low monomer conversion in a binary copolymerization? (2 marks) (b) Why are r1 and r2 usually determined at very low conversions? (1 mark) (c) In a binary copolymerization, we have: r1 = 1.90 and r2 = 0.53. Draw (schematically) the copolymer composition F1 as a function of monomer feed composition (f1). What type of copolymerization is this? (3 marks) Page 35. Styrene is polymerized using three different approaches: (i) Emulsion polymerization; (ii) Suspension polymerization; (iii) Solution polymerization. The experimental conditions of (i), (ii) and (iii) 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) Part III: Ionic Polymerization [27 marks] 6. What are the criteria to define a living polymerization? Explain and comment on the benefits of a living polymerization process in comparison to a conventional (or non living) radical polymerization. A detailed response is expected. (6 marks) 7. A researcher wants to prepare a pentablock copolymer containing one block each of polystyrene, poly(isoprene), poly(2-vinyl pyridine), poly(ethyl 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) 8. A researcher wants to synthesise a poly(methyl methacrylate)-block-poly(styrene) (PMMA-b-PS) diblock copolymer by anionic polymerization. (a) Describe a synthesis method for the preparation of such a PMMA-b-PS block copolymer, including the reaction steps (monomer addition) and conditions involved. (3 marks) (b) Describe the side reactions for the anionic polymerization of MMA? How can you prevent the side reactions. (1 mark) (c) We want to prepare 100 g of a diblock copolymer containing 40/60 wt-% of PMMA/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) Page 4(d) Calculate the molar amount and mass of initiator required if each step is carried out to a conversion of 100% [MMA MW = 100 g/mol, n-BuLi MW = 64 g/mol and S MW = 104 g/mol]. (2 marks) (e) Indicate the mass of MMA and St needed to perform this polymerization. (2 marks) (f) How can the researcher introduce a carboxyl acid group at the chain end? Indicate the type of compound which needs to be added. Calculate the molar amount of this compound to functionalize the diblock copolymer prepared in the previous question. (2 marks) 9. High molecular weight poly(styrene)-block-poly(butadiene) is produced industrially using an anionic polymerization process. A researcher wants to produce 10g of poly(styrene)-block-poly(butadiene) with a molecular weight of 150 000 g/mol and a composition by weight of styrene/butadiene = 30/70 in wt-%. Calculate the molar amount and mass of styrene and butadiene needed in this synthesis (butadiene MW = 54 g/mol) assuming that full monomer conversion is obtained in each step. Give a potential application for this diblock copolymer (justify your response). (4 marks) 10. A scientist wants to prepare 200 g of poly(ethylene oxide) with a molecular weight of 5,000 g/mol via cationic ring-opening polymerization of ethylene oxide. The polymerization is initiated using boron trifluoride. Calculate the molar amount and mass of boron trifluoride required. (4 marks) END OF EXAM |