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Use of Nuclear Magnetic Resonance Spectroscopy in Polymer Science

Use of Nuclear Magnetic Resonance Spectroscopy in Polymer Science. Christine Fernyhough. Why use NMR for polymers?. Because you like broad peaks? Maybe not.... Composition of copolymers End-group analysis and determination of M n

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Use of Nuclear Magnetic Resonance Spectroscopy in Polymer Science

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  1. Use of Nuclear Magnetic Resonance Spectroscopy in Polymer Science Christine Fernyhough

  2. Why use NMR for polymers? • Because you like broad peaks? Maybe not.... • Composition of copolymers • End-group analysis and determination of Mn • Reactions e.g. hydrogenation, hydrolysis, addition of functional groups to main chain • Microstructure (cis, trans), tacticity • Branch points if have a really powerful machine!

  3. Available techniques • Bruker machines in department 250, 400 & 500MHz. • Many deuterated solvents available from stores – cheaper than Aldrich! • Variable temperature on 500MHz NMR – useful for polymers which are insoluble at RT • 1H, 13C, 31P • Solid state NMR: EPSRC facility at Durham • Registered users: Sarah, Masa and Lewis • Programs: Win NMR TopSpin

  4. Composition Aromatic protons: 5 styrene Aliphatic protons: 3 styrene + 14 poly(t-butyl methacrylate) Use signal integration to find out the resonance per proton Area due to each aromatic proton = 1/5 = 0.2 Area due to PS resonances = 0.2 x 8 = 1.6 Area for each t-BuMA proton = Total area – Area for PS = (4.03-1.6)/14=0.17 Mole fraction PS = 0.2/(0.2+0.17) = 0.54 Weight fraction PS = (0.2x104)/(0.2x104)+(0.17x142)=0.46

  5. End-group analysis Sec-Butyl end group:6 protons d0.7. Integral per proton=0.167 Ethylene oxide termination CH2-OH 2 protons d3.3 Integral per proton=0.165 Styrene aliph. 3 protons d1.2-2.6 Integral per proton=11.46 Degree of Polymerisation =11.46/0.167 = 68 Mn polymer = 68x104=7100g/mol Styrene aliphatic protons CH3 initiator CH2-CH2-OH End functionalisation %= (0.165/0.167)x100=99%

  6. hPB85-20 in Tol @70deg 50,000g/mol polybutadiene prior to hydrosilylation 5.6 5.4 5.2 5.0 4.8 (ppm) 1.0000 0.0609 5.8 5.4 5.0 (ppm) 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 (ppm Integral 1.0000 0.0609 12.0 10.0 8.0 6.0 4.0 2.0 0.0 (ppm) Reactions • Example – Hydrogenation of poly(butadiene) High T measurement in d8-toluene RT measurement in CDCl3

  7. Further references • http://ccias.dept.shef.ac.uk/nmr.php • http://ccias.dept.shef.ac.uk/nmrdetails.php • http://www.epsrc.ac.uk/ResearchFunding/FacilitiesAndServices/OtherEPSRCSupportedServices.htm • Spectroscopic Methods in Organic Chemistry D. H. Williams & I. Fleming • Barry Hunt & John Ebdon’s “Polymer Characterization” courses

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