Synthesis of MEH - PPV lab report PDF

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Procedure and Analysis of a synthesized MEH-PPV polymer...

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Lab 10 Report: Synthesis of MEH - PPV Lab Section: 3522 FQ9 Prof. Mark Wlodarczyk By: Hamzah Sibil Partner: Leyla Yashaeva

Date/time: 4/30/20 Fri. 9:30-12:50 am

Abstract In this lab we synthesize polymer the MEH-PPV via Gilch polymerization of 2,5bis(bromomethyl)-1-methoxy-4-(2-ethylhexyloxy)benzene (monomer 2), in order to investigate a polymer’s photophysical properties, and to understand the mechanism of the polymerization reaction. The reaction involves involves the addition of a strong base such as potassium tertbutoxide to an α,α’-dihalogenated p-xylene monomer which is our monomer 2. The Strong base is able deprotonates the acidic benzylic protons which generates an intermediate. Dimerization of that intermediate is followed by radical polymerization to generate a saturated intermediate. And finally Elimination of that macromolecular intermediate through the base-catalyzed removal of HX yields our desired product. This product was then weighed to get a yield of 2.41g which can be used to determine the percent conversion. Additional test of fluorescent under UV light was also taken as well Observations 1. After adding potassium tert-butoxide to the reaction mixture, we observe a color change into an orange/red solution. This is significant as it indicates the initiation of the polymerization 2. After washing with methanol, our product was subjected to vacuum filtration. We left with a reddish gel-like product. This is likely the desire product MEH-PPV. 3. Under a UV lamp, the polymer emits a orange light. This indicates that our polymer possesses a fluorescent property. Results After obtaining a yield of 2.41g. We can calculate the percent conversion of our polymer product Theoretical Yield (0.20g of Monomer 2 / 333.31 g/mol of Monomer 2) x [333.31 g/mol of Monomer 2 – 2(80.91 g/mol of HBr)] = 0.102g of product Actual yield 2.41 g of product

Percent conversion 2.41 g of product / 0.102g of product x 100% = 2362.7 % Its clear that this percent conversion is impossible. An experimental error had occur which could explain why this percent error doesn’t make sense. Errors that could explain this include, incorrect measurements of the reagent Monomer 2, using a higher yield of reagent, or a glassware not being properly dried which could result in contamination of the product. The most likely error that could have occurred is probably the using a higher yield of reagent such as using 5.00 g of monomer 2. If were to assume this, then our yields would drastically change. (5.00 of Monomer 2 / 333.31 g/mol of Monomer 2) x [333.31 g/mol of Monomer 2 – 2(80.91 g/mol of HBr)] = 2.57g of product Thus are Percent conversion would be 2.41 g of product / 2.57g of product x 100% = 93.7 % This would suggest that most of reactant was used up to form the polymer. This is more believable % conversion as it would suggest that most of monomer was used to form the polymer We also tested for the fluorescent of product. Under a UV lamp, we observed the polymer emit an orange light. Here’s a graph of the standard UV absorbance of MEH-PPV in chloroform solution

When the electrons of the polymer move from the ground to the excited state, its emits a wavelength of roughly 635–590 nm. This is a result of an extended π conjugation, which lowers the HOMO-LUMO gap. The fact that wavelength is large it suggest that the distance between HOMO and LUMO is smaller, and electrons can move more easily to the excited state requiring

less energy compare to the wavelength of blue or violet. Therefore they can also move more easily back to the ground state. Questions 1. What is the percent conversion that you obtained in the polymer synthesis? Why is it hard to measure a percent yield for polymer synthesis? If starting material was 5.00 of Monomer 2, we obtain a percent conversion of 93.7%. It hard to measure a percent yield for polymer synthesis since we don’t know the exact molecular weight of polymer since we can’t tell how long are the side chains or how many monomers we used to form the polymer. 2. Can you correlate the color of the polymer with its absorbance spectrum? The absorbance of the polymer is around 590 nm, which correlates the wavelength of orange light. This was observed with our polymer as well. Conclusion In summary, we were able to successfully synthesize the polymer, MEH-PPV. We were able to study the mechanisms and utilities of Glich polymerization that was involved in producing such product. We able to observe and interpret the photoluminescent properties of polymers as result of π conjugation and the excitation of electrons moving from LUMO to HOMO. This lab helps reinforce concepts of molecular orbitals as well conjugation of complex polymers....