Molecular weight of polymers. Molecular weight of polymers. Molecular weight of polymers. Molecular weight of polymers. H i

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1 Gel Permeation Chromatography (GPC) : Size Exclusion Chromatography GPC : 1. Chromatogram (V R vs H) H i Detector response Baseline N i M i Elution volume (V R ) (counts) Microporous gel particle : (material) Styrene and divinyl benzene copolymer(pore size) 0.5~10 5 nm, (MW) 100~4x10 7 (diameter) 3~20μm [η]m GPC : 2. Universal Calibration V R vs [η]m of Polystyrene GPC gives information about polymer sizes Calibration between Sizes and MW is necessary. Universal calibration approach is based on the fact that the product is proportional to the hydrodynamic volume of a polymer molecule in solution Polystyrene (linear) Polystyrene (comb) Polystyrene (star) Heterograft copolyner Poly (methyl methacrylate) Poly (vinyl chloride) Styrene-methyl methacrylate graft copolymer Poly (phenyl siloxane) (ladder) Polybutadiene GPC : 3. V R vs [η]m MW of each fractions (of Polystyrene) [η]m Universal calibration can be used if the MHS constants are known for both the standard and unknown polymer samples in the same solvent and at the same temp. M Elution volume (V R ), 5 ml counts, THF solvent) 115 Elution volume (V R ) Elution volume (V R ) 116

2 GPC : 4. MW of PS MW of polymer samples GPC : 5. M vs H Molecular weight distribution M p [η] s M s = K s M s a s +1 a p +1 [η] p M p = K p M p [η] s M s = [η] p M p to be combined MHS equation H a K p M p +1 a p = K s M s +1 s 1 logm p = ( 1 + ap K )log( s Kp ) + ( 1 + a s )logm s 1 + ap M GPC : 6. Tabulation of M, N and NM 2 M n, M w, & PDI GPC : Calibration Elution volumes of the polymers with the same MW could be different due to the difference in Hydrodynamic volumes M p M n, M w, & PDI

3 Size-exclusion chromatography setup Size-exclusion chromatography hardware Injection of polymer of unknown MW characteristics Pump eluent Columns of defined characteristics for column packing: diameter, exclusion limit, pore size distribution Detector signal = f(elution volume) calibration curve with standards: elution volume = f(mw) PUMP INJECTOR COLUMNS MALLS DEGASSER SOFTWARE MAREK MW characteristics (MWD, M w, M n ) of polymer RI The first GPC columns are packed with materials referred to as gels, hence gel permeation. detector exclusion calibration curve MW Distribution signal log M separation signal Rheodyne inj. or Waters Autosampler elution volume permeation elution volume M 121 Degasser Pump Waters 515 Columns MALLS SLD7000 DRI Detector Waters 2410 WinGPC 7.4 Software M n M w M z M Molecular weight: characterization techniques techniques related to colligative properties (dependence on the number of molecules) membrane osmometry (> g/mol) vapor pressure osmometry (< g/mol) mass spectrometry electrospray ionization mass spectrometry (ESI MS) matrix assisted laser desorption/ionization (MALDI) size exclusion chromatography static laser light scattering analytical ultracentrifuge size exclusion chromatography static laser light scattering analytical ultracentrifuge size exclusion chromatography viscometry size exclusion chromatography w i M n M i M w M z Mass spectrometry : If something is moving and you subject it to a sideways force, instead of moving in a straight line, it will move in a curve - deflected out of its original path by the sideways force Atoms can be deflected by magnetic fields - provided the atom is first turned into an ion. Electrically charged particles are affected by a magnetic field although electrically neutral ones aren't. 124

4 Mass spectrometry : In a typical MS procedure, Stage 1: Ionization The atom is ionized by knocking one or more electrons off to give a positive ion. Mass spectrometers always work with positive ions. Mass spectrometry : A full diagram of a mass spectrometer Electromagnet Stage 2: Acceleration The ions are accelerated so that they all have the same kinetic energy. Stage 3: Deflection The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected. The amount of deflection also depends on the number of positive charges on the ion - in other words, on how many electrons were knocked off in the first stage. The more the ion is charged, the more it gets deflected. Vaporized sample To vacuum pump amplifier Stage 4: Detection The beam of ions passing through the machine is detected electrically. 125 chart recorder 126 Mass spectrometry : Mass spectrometry : Conventional mass spectrometer for low MW compound The signal is processed into the singular spectrum of the masses of the particles of that sample. Mass spectrometry works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios. Relative abundance Formation of gas phase samples ion is an essential prerequisite to the mass sorting and detection process that occur in a mass spectrometer. However, macromolecules can not be vaporized!!

5 Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS or MALDI-TOF) Polymers can be vaporized with the help of low MW molecules and can be analyzed by using a mass spectroscopy Matrix-Assisted Laser Desorption Ionization (MALDI) Laser Sample plate hn AH + 1. Sample (A) is mixed with excess matrix (M) and dried on a MALDI plate. 2. Laser flash ionizes matrix molecules. 3. Sample molecules are ionized by proton transfer from matrix: MH + + A M + AH +. polymers are imbedded by UV laser absorbable organic compound containing Na and K kv Variable Grid Ground Grid 130 Time of Flight Mass Analyzer : Calibration of the mass scale MALDI Mass Spectrum of Low Molecular Weight PMMA (flight tube) Source Ions are formed in pulses. Small ions reach the detector before large ones. Measures the time for ions to reach the detector. t = Drift time D = Drift length m = Mass z = Number of charges on ion Drift time is proportional to the square root of its mass-to-charge ratio (m/z ) of an ion

6 Features of MALDI-TOF MALDI-TOF, which simply refers to combining a matrix-assisted laser desorption/ionization source with a time-of-flight mass analyzer Instrument costs are relatively high MW averages as well as the molecular weight distribution are obtained quickly and generally more accurately than the more traditional separation methods. Easy to use and maintain, no water or gas hook ups required High sensitivity, superior mass resolution and accuracy Up to M=400,000 for monodisperse polymers 133