Macromolecular Chemistry

Transcription

1 Macromolecular Chemistry Vacuum Degasser Pump and Pulse Controller Autosampler Solvent and Filter In-Line Filter Column Oven and Columns Injection Loop Sample Source Detector 1 Detector 2 Detector 3 Waste Lecture 9

2 Midterm Exam Where: Right here.in the lecture room WEL When: Next Tuesday 2/24/09 at 3:30 5PM What: Covers lectures through Thursday 2/18 Bring: Pencil, eraser, Calculator only closed book! Do: Study lecture notes, homework, reading assignments and graduate presentations Do not: Memorize the free radical kinetics equations but do know the principles! Go over homework problems. Please: Do a good job!

3 Measuring Molecular Weight Membrane Osmometry Alfredo Vapor Phase Osmometry Linda Viscometry GW Gel Permeation Chromatography Size exclusion Chromatography Light Scattering MALDI GW Others GW End group analysis You

4 MALDI Mass Spectrum of a Synthetic Polymer CH 3 -(CHO) n -OH+Na n

5 High Performance Liquid Chromatography Vacuum Degasser Pump and Pulse Controller Autosampler Solvent and Filter In-Line Filter Column Oven and Columns Injection Loop Sample Source Detector 1 Detector 2 Detector 3 Waste

6 Typical Instrument

7 Autosampler

8 Columns the heart of the tool

9 Reverse phase HPLC Partition Coefficient K = Solubility in mobile phase Solubility in stationary phase K > K

10 Column packing materials C-18 Silica gel

11 Refractive Index Detection Snell s Law

12 . HPLC

13

14 UV-Detector Absorbance time

15 Remarkable Separations! 2. O S NH 2 O

16 All of the amino acids resolved!

17 POLYMERS Size Exclusion Chromatography Gel Permeation Chromatograpy

18 Size Exclusion Chromatography

19

20

21

22 Calibration Run

23 Calculation of MW s Log (Molecular Weight) M i Number Average (Mn) (Weights Low Molecular Weights) Mn = ci c i / M i RI Height (Weight Fraction) c i Retention Volume Weight Average (Mw) (Average Molecular Weight) Mw Mi c = ci i

24 Setting the Standard for GPC. Advantages of Conventional Calibration 1) Simple Setup. (Only one Detector Required - RI or UV) 2) Solution Concentration Not a Variable. (Approximate Concentrations are Good Enough) 3) Excellent Precision (Repeatability) (Related to Column and Pump Performance) Disadvantages of Conventional Calibration 1) Mw Values Only Accurate for One Sample Type (Can Only Get True Molecular Weights of Polymers Which are the Same Type as the Calibrant.) 2) Ignores Structural Differences (Such as Branching, Aggregation and other structural modifications)

25 Setting the Standard for GPC. Overlay of Conventional Calibration Curves Each Polymer has a Unique Size to Weight Relationship. 6.5 Log (Molecular Weight) PS PAMS PMMA PIP PBD PPG Retention Volume (ml)

26 Setting the Standard for GPC. Classical Determination of MW Viscometry Common terms of of expressing viscosity Relative Viscosity η r =η/η 0 Reduced Viscosity η red =η sp /C Intrinsic Viscosity [η]=η sp /C 0 Specific Viscosity η sp = (η - η 0 ) /η 0 Inherent Viscosity η inh =lnη r /C

27 Setting the Standard for GPC. Intrinsic Viscosity (IV) is Determined By Extrapolating Ubbelohde Tube Measurements Down to Zero Concentration. η sp c GPC Concentration Range concentration GPC Measurements Are Made Two Orders of Magnitude Lower in Concentration Than Ubbelohde Measurements.

28 Setting the Standard for GPC. Interpretation of Intrinsic Viscosity Mark-Houwink Relationship The Mark-Houwink equation is an empirical equation relating intrinsic viscosity and molecular weight, and is generally valid for linear polymers, at least above 10,000 MW: [ η] = KM a

29 Setting the Standard for GPC. Universal Calibration and Differential Viscometry Developed by by W. W. Yau, Yau, Carrier Liquid Pump Bath Pulse Dampener Reference Capillary and Transducer Dilution Column Analytical Capillary and Transducer Sample Loop RI Detector DuPont PSM Columns Waste P R Differential Log Amplifier P A Dual Dual Capillary Viscometer log η rel

30 Setting the Standard for GPC. Detector Responses for Narrow Standards Detector Response (mv) Viscometer Polystyrene 850,000 Detector Responses VISC IV x C RI dn/dc x C Refractometer Polystyrene 30, Retention Volume (ml)

31

32

33 Grubisic, Rempp & Benoit, JPS Pt. B, 5, 753 (1967)

34 Setting the Standard for GPC. Universal Calibration All Polymers Fall on the Same IV x MW Curve. Log [η] M ELUTION VOLUME Universal Calibration was first demonstrated and proven by Benoit in 1967, who showed that a wide range of polymer structures eluted on the same calibration curve when the intrinsic viscosity is included. PS Comb PS PS Star Hetero-Graft Copolymer PolyMethylMethacrylate PolyVinylChloride Graft Copolymer: PS/PMMA PolyPhenylSiloxane Polybutadiene It does not matter whether the polymer is linear, branched, block copolymer, heterogeneous copolymer, or whatever...

35

36 Setting the Standard for GPC.

37 SEC Deficiencies 45 o C at 8 am and 50 o C at noon, etc? Non-size exclusion mechanisms: binding. Big, bulky and slow (typically 30 minutes/sample). Temperature/harsh solvents no fun. You learn nothing by calibrating. Columns are expensive, easily damaged. 37