analysis of molecular weight of polymers
TRANSCRIPT
Analysis of molecular weight of polymers
Asst.Prof.Dr. Jatuphorn Wootthikanokkhan
Division of Materials Technology, School of Energy and Materials, King Mongkut’s University of Technology Thonburi,
Thailand
Polymer contains molecules with a variety of chain length
• Diversity in terms of molecular weight is an inherent
characteristic of the natural polymers
• For synthetic polymers, this is attributed to many factors
including uncontrollable terminations
Disproportionation
Combination
น ำ้หนักโมเลกลุพอลเิมอร์ จะสัมพนัธ์โดยตรงกบัควำมหนืด Effect of molecular weight on Newtonian viscosity
M.P. Stevens, Polymer Chemistry, 1991
จุดวกิฤต (Mc) เก่ียวขอ้งกบัการเก่ียวพนักนั
(entanglement) ของโมเลกลุพอลิเมอร์
Once molecular weight of polymer exceed a critical value (Mc), entanglement
between chains occur
Effects of Molecular Weight
• Higher Mw increases tensile strength
– Tension force cause polymers to align and reduce the number of
entanglements. If the polymer has many entanglements, the force
would be greater.
• Higher Mw increases toughness
– Toughness is increased with longer polymer chains because energy is transmitted down chain
• Higher Mw increases melting temperature – Melting point is a measure of the amount of energy necessary to
have molecules slide freely past one anotherใ
– If the polymer has many entanglements, the energy required would be greater.
กำรวดัค่ำดชันีกำรไหล Melt Flow Indexer
• ใชน้ ้าหนกั กดอดัพอลิเมอร์ ณ อุณหภมิูตามท่ีก าหนด
• Melt flow index (MFI) = น ้าหนกัตวัอยา่งท่ีไหลออก ในเวลา 10 นาที
• หน่วย เป็น (กรัม/10 นาที)
14/08/55 Dr. Jatuphorn Wootthikanokkhan, KMUTT
สภำวะในกำรทดสอบ MFI ตำมมำตรฐำน ASTM Test conditions for some plastics (ASTM D 1238)
Condition Temperature ( C) Total load (g) Materials A 125 325 PE B 125 2,160 PE D 190 325 Nylon. PE E 190 2,160 Nylon, PE F 190 21,600 Nylon, PE G 200 5,000 PS L 230 2,160 PP
14/08/55 Dr. Jatuphorn Wootthikanokkhan, KMUTT
Factors affecting result from MFI test
• Preheat time (Cylinder should be preheated to ensure uniform temperature)
• Moisture (Moisture in the plastic deviate the MFI
• Packing (Plastic should be pack properly be pushing the rod to expel the entrapped
air)
• Volume of the sample (keep constant for a good reporducibility)
• Type of Melt Indexer ( L/D of cylinder and Die, Die shape)
• Type of sample (No cross-comparison between different plastics)
ขอ้จ ากดัของเทคนิค MFI
• ค่าท่ีได ้สมัพนัธ์กบัความหนืดและน ้าหนกัโมเลกลุ แต่ไม่ใช่ค่าเฉล่ียน ้าหนกัโมเลกลุท่ีแทจ้ริง
• ค่าท่ีได ้บ่งบอกถึงความยากง่าย ในกระบวนการผลิตข้ึนรูป • ควรใชเ้ปรียบเทียบพอลิเมอร์ ชนิดเดียวกนัเท่านั้น
Mn MFI (g/10min)
100,000 10.0
150,000 0.30
250,000 0.05
Results from MFI test of polystyrene at 200 ºC
ความสามารถในการผลติ Ethylene Octene Copolymer 2 เกรด ทีม่คีา่ MFI ตา่งกนั
Effect of MFI and die temperature on polymer process-ability
145 C 125-135 C
115 C Low MFI polymer cannot be extruded,
regardless of the processing temperature Higher MFI polymer can be
extruded at a suitable temperature
Un-melted polymer Degradation at the die zone
Calculations of Average Molecular Weight of Polymer
Polydispersity index = Mw/Mn
(L.H. Sperling, Introduction to physical polymer science, 1992, John Wiley & Sons, NY)
Some k- and a- constants ทีม่า J. Brandrup and E.H. Immergut, Eds., Polymer Handbook, 2 nd ed., Wiley-Interscience, NY, 1975
kaพอลิเมอร ์ ตวัท ำละลำย อณุหภมิู ( C) k x 103 a
ซสิ พอลบิวิตะไดอนี เบนซนี 30 33.7 0.715
ไอโซแทคตคิ พอลพิรอพลินี คลอโรแนพธาลนี 139 21.5 0.67
พอลเิอธลิอะครเิลต อะซโิตน 25 51 0.59
พอลเิมธลิเมธาครเิลต อะซโิตน 20 5.5 0.73
พอลไิวนิลอะซเิทต เบนซนี 30 22 0.65
พอลสิไตรนี บวิธาโนน 25 39 0.58
พอลไิสตรนี ไซโคลเฮกเซน (-solvent) 34.5 84.6 0.50
พอลเิตตระไฮโดรฟิวแรน โทลอูนี 28 25.1 0.78
เฮกเซน (-solvent) 31.8 206 0.49
Effects of polydispersity
• Broader MWD decreases tensile strength – Broad MWD represents polymer with many shorter
molecules which are not as entangled and slide easily.
• Broader MWD decreases impact strength – Shorter chain do not transmitted as much energy
during impact
• Broader MWD decreases melting point – Broad MWD represents polymer with many shorter
molecules which are not as entangled and melt sooner
– Broader MWD yield an easier processed polymer
Methods of determining polymer molecular weight
Method Type Molar mass range (g/mol)
Average value
Membrane osmometry A 104 – 105 Mn
End group analysis E < 104 Mn
Light scattering A 103 - 107 Mw
Viscometry R 102 -107 Mv
Size exclusion
chromatography (SEC) or GPC
R 102 -107 Mn, Mv, Mw, PDI
Molecular weight analysis techniques
• A = Absolute method (polymer Mw is directly calculated from the experimental data, without additional information on the chemical structure of the polymer.
• E = Equivalent method (chemical structure of polymer
must be known for a calculation of polymer Mw).
• R = Reference method (data must be calibrated with samples of known Mw)
Light scattering (LS) technique
• The basis of the LS is the measurement of intensity of scattered light, I() at various angle
• From the I(o) and I(), Rayleigh ratio [R()] at various angle can be calculated using the following equation;
R() = I() r2 / I(o) V
where
V = scattering volume
r = distance between detector and sample cell
I()
I(o)
D
Light scattering (LS) technique
• Rayleigh ratio is related to molecular weight of polymer through the below equation;
kc/R() = 1/(Mw) P() + 2A2C
where
k = an optical constant (related to RI of solvent, of incident light, and concentration).
P() = particle scattering function or form factor (which is equal to 1 at very low angle (), ~ 0 – 2°)
R() = R() solution - R() solvent
A2 = second varial coefficient, describing polymer - solvent interactions.
Light scattering (LS) technique
• Low angle lasers light scattering (LALLS) use He-Ne lasers
as a light source.
• This high intensity of the lasers permits scattering to be
measured at a much smaller angle than conventional LS
• Usually < 7 º (Jeng et al., J.Appli Polym Sci., 49(1993)1359)
• The equation can be re-written as
kc/R() = 1/(Mw) + 2A2C
Multiple Angle Laser Light Scattering (MALLS) technique
By measuring the I() at
various polymer solution
concentration (c),
a Zimm plot can be obtained.
From the Zimm plot, by performing “double extrapolation” ( = 0) and
c = 0, Y-intercept of the Zimm plot is equal to 1/ Mw
kc/R() = 1/(Mw) P() + 2A2C
Size Exclusion Chromatography (SEC)
(Gel Permeation Chromatography, [GPC] )
GPC apparatus
1. Injection port
2. Column(s)
3. Detector
4. Collector flask
5. Chart recorder
6. Solvent reservoir 7. Pump with pressure gauge
GPC solvent and injection system
• THF is normally used for the non-aqueous phase GPC. Sometime non UV grade THF is used if the UV detector was used
• Polymer sample prepared in a solution (0.1 -0.2 % g/ml)
• The sample must be filtered before injection
• Typical injection volume ~ 0.1 L
• Flow rate ~ 1 ml/min
Detectors
• UV visible spectrometer (measure the absorption of eluted polymer solution), A = elc – Suitable grade of solvent must be used
• Differential refractometer (detect differences in RI between pure solvent and polymer solution)
GPC columns
• Column packing material is
basically small porous beads.
Generally made from crosslinked
PS
• Pore diameter ranged between 10 – 107 ºA
Column packing materials
ผูผ้ลิต ช่ือกำรค้ำวสัดท่ีุเป็น packing
วสัดท่ีุใช้
Polymer Laboratories PL gel Styrene-divinylbenzene copolymer
Waters Styragel Styrene-divinylbenzene copolymer
Shodex Asahipak GF HQ Highly crosslinked poly(vinyl alcohol) *
Protein KW Silica *
Chitopak KQ Chitosan *
(Ref: H. Pasch and B. Trathnigg in HPCL of Polymers, Springer1999)
GPC experiment and GPC chromatogram (From L.H. Sperling in Introduction to Physical Polymer Science, John Wiley & Sons, 1992),
Resolution is affected by
the column characteristics and the flow rate
www.viscotek.com/images/Theory/separate.jpg
Typical GPC chromatogram (plot of retention volume vs signal strength [conc])
Reco
rded
sig
nal str
en
gth
Retention volume (ml)
Basic steps in obtaining MWD curve from a chromatogram
(Ref: H. Pasch and B. Trathnigg in HPCL of Polymers, Springer1999)
(1)
(2) (3)
(4)
(Calibration curve)
Narrow molecular weight calibration curve
(H. Pasch and B. Trathnigg, HPLC of Polymers, Springer, Berlin, 1999)
Polymer standards for establish a calibration curve
Polymers Suppliers Number of standards
Lowest Mw
Highest Mw
Polystyrene Polymer Laboratories 29 162 15,000,000
Polymer standard service 18 500 4,000,000
Water Corp. 20 400 20,000,000
PMMA Polymer Laboratories 20 500 1,500,000
Polymer standard service > 70 102 1,200,000
Water Corp. 10 1,000 15,000,000
Polyisoprene Polymer Laboratories 11 1,000 3,000,000
Water Corp. 10 1,000 3,000,000
Polybutadiene Polymer Laboratories 11 1,000 1,000,000
Polymer standard service 4 5,000 80,000
Polyethylene Polymer Laboratories 10 170 120,000
(ท่ีมำ H. Pasch and B. Trathnigg, HPLC of Polymers, Springer, Berlin, 1999)
Note: there are many more, see the reference
Universal calibration
[]M hydrodynamic volume, regardless of the polymer type
Universal calibration
Universal calibration curve
Membrane Osmometer
(from M.P. Stevens in Polymer Chemistry, John Wiley & Sons, 1990, NY)
Osmotic pressure is related to molecular weight by the van’t Hoff equation
Plot of /c versus c for PMMA dissolved in three different solvents
; (a) toluene, (b) acetone and (c) acetonitrile
พอลิเมอร ์ ตวัท ำละลำย อณุหภมิู (องศำเซลเซียส)
(ซสิ) พอลบิวิตะไดอนี n-haptane (-1)
พอลเิอธลินี Biphenyl 125
พอลบิวิธลิอะครเิลต Benzene/methanol (52/48) 25
พอลสิไตรนี Cyclohexane 34
Toluene
Acetone
Acetonitrile
solvent ของพอลเิมอรช์นิดต่างๆ
The osmotic pressure data for cellulose tricaproate in DMF at three temperatures. The Flory -temperature was determined to be 41 ±1 °C
(from L.H. Sperling, Introduction to physical polymer science, 1992, John Wiley & Sons)
Schematic representation of a molecular coil. r = end-to-end distance, s = radius of gyration
Unpurturbed dimension (mean-square average)
Expansion factor
will be greater than 1 in a good solvent.
The lowest temperature at which = 1 is called the theta () temperature
and the solvent is then called a theta solvent.
The theta state is that in which the polymer is on the brink of becoming insoluble. The solvent is having a minimal solvation effect.
Viscometers
Some useful equations
Some useful equations
Poiseville’s equations
Some k- and a- constants ทีม่า J. Brandrup and E.H. Immergut, Eds., Polymer Handbook, 2 nd ed., Wiley-Interscience, NY, 1975
kaพอลิเมอร ์ ตวัท ำละลำย อณุหภมิู ( C) k x 103 a
ซสิ พอลบิวิตะไดอนี เบนซนี 30 33.7 0.715
ไอโซแทคตคิ พอลพิรอพลินี คลอโรแนพธาลนี 139 21.5 0.67
พอลเิอธลิอะครเิลต อะซโิตน 25 51 0.59
พอลเิมธลิเมธาครเิลต อะซโิตน 20 5.5 0.73
พอลไิวนิลอะซเิทต เบนซนี 30 22 0.65
พอลสิไตรนี บวิธาโนน 25 39 0.58
พอลไิสตรนี ไซโคลเฮกเซน (-solvent) 34.5 84.6 0.50
พอลเิตตระไฮโดรฟิวแรน โทลอูนี 28 25.1 0.78
เฮกเซน (-solvent) 31.8 206 0.49
Determination of k- and a- constants (from Introduction to physical polymer science, L.H. Sperling, 1992)
End-group analysis
Exercise 1. What is the DP of a sample of
polyester prepared from 4-hydroxy benzoic acid if the acid number determined with standard KOH solution is 11.2 ?
Note: Acid number = mg of base used to neutralize 1 g of the polymer
2. A 0.5 g sample of unsaturated polyester resin was reacted with excess acetic anhydride. Titration of the reaction mixture with 0.0102 M KOH required 8.17 ml to reach the end point. What is the number average molecular weight of the polyester? Would this method be suitable for determining any polyester?
• Determination of the amount of functional groups at the chain ends by using some techniques such as – Titration
– UV spectroscopy – Elemental analysis
แบบฝึกหดั
(260,000, 420,000)
Mw of each fractions Mole
50,000 1
100,000 4
200,000 5
500,000 3
700,000 1
Determine Mn, Mw and PDI using data from the table above