CHM6204 CHM6204 1 TURN OVER Ancillary material: Chemistry data booklet Molecular model kits are permitted DEPARTMENT OF CHEMISTRY Spring Semester 2019-2020 Smart Polymers and Polymeric Materials 1 hour 30 minutes There are two questions. Answer both questions. Answer each question in a separate answer booklet. Registration Number: Question identifiers Question 1: A. Iraqi – Smart Polymers and Polymeric Materials [L6.I.1] Question 2: C.J. Crook – Smart Polymers and Polymeric Materials [L6.P.5] CHM6204 CHM6204 2 CONTINUED CHM6204 CHM6204 3 TURN OVER Answer all parts of this question. 1. (a) The structures of polymers P1-P2, along with their absorption (Abs), photoluminescence (PL) and electroluminescence (EL) data in the solid state, are shown in the table below: Polymers Structure max(Abs) /nm max(PL) /nm max(EL) /nm P1 R R n 370 439 441 P2 R R S n 442 476 478 (i) Explain the differences that are observed in the absorption and photoluminescence data of the two polymers. [3 marks] (ii) Provide an explanation for the red shift of the photoluminescence spectra relative to the absorption spectra for these polymers and explain why the PL and EL spectra have similar maxima. [3 marks] (b) Draw the structures of regioregular and regiorandom poly(3-alkylthiophene), and explain the effect of regioregularity on the band gap of the materials, their electronic conduction in the doped state and their charge mobilities in the neutral state. [4 marks] (c) Suggest synthetic methods that could be used to prepare the two different samples outlining the mechanisms involved. [4 marks] (d) Explain the lack of processability of polyacetylenes and outline a synthetic method allowing exploitation of these polymers in electronic devices. [4 marks] (e) With the aid of a diagram, explain the design and operation of an organic based bulk heterojunction solar cell. [6 marks] CHM6204 CHM6204 END OF QUESTION PAPER Answer all parts of this question. 2. (a) Thermo-responsive surfaces have been used to facilitate the culture and harvesting of mammalian cells. The polymer most commonly used for this purpose is poly(N- isopropyl acrylamide), which has a Lower Critical Solution Temperature (LCST) of approximately 32 ° C. (i) How does the hydrophilicity of the polymer-coated surface change when the polymer is heated above its LCST in an aqueous environment? [2 marks] (ii) Explain this change in the behaviour of poly(N-isopropylacrylamide) in terms of its structure and conformation and the trade-off between enthalpy and entropy. [4 marks] (iii) Describe the protocol used to encourage cells to adhere to poly(N- isopropylacrylamide)-coated surfaces for cell growth and their subsequent release. [2 marks] (b) The phenomenon of Maxwell stress is observed in insulating materials when an electric field is applied. (i) Describe the mechanism of Maxwell stress. [4 marks] Maxwell stress is particularly marked for dielectric elastomers, such as silicones and acrylics, especially when combined with flexible electrodes. (ii) What properties of dielectric elastomers make them particularly useful for applications as smart devices? [2 marks] (iii) Briefly describe how these materials can be used to make a linear actuator (artificial muscle). [4 marks] (c) An application requires the delivery of a hydrophobic anti-cancer drug doxorubicin (DOX) which has some significant unpleasant side-effects. Cancer cells are known to generate both CO2 and lactic acid, which lowers the pH around them. Propose a drug delivery system, based on smart polymers, to release the drug specifically in the presence of cancer cells. Your proposal should clearly state the role that the polymer is playing, and the processes taking place in the mechanism of release. [6 marks]
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