National Science Foundatio WHERE DISCOVERIES BEGIN National Science Foundation WHERE DISCOVERIES BEGIN Controlling Polymer Rheological Properties Using Long-Chain Branching PI: Ronald Larson Univ. of Mich., Dept of Chem. Eng., Macromolecular Science and Engineering Program Possible co-PI: Michael Solomon Univ. of Mich., Dept of Chem. Eng., Macromolecular Science and Engineering Program Possible co-PI: Jimmy Mays Univ. of Tennessee, Dept of Chemistry
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National Science Foundation WHERE DISCOVERIES BEGIN Controlling Polymer Rheological Properties Using Long-Chain Branching PI: Ronald Larson Univ. of Mich.,
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Controlling Polymer Rheological Properties Using Long-Chain Branching
PI: Ronald LarsonUniv. of Mich., Dept of Chem. Eng., Macromolecular Science and
Engineering ProgramPossible co-PI: Michael Solomon
Univ. of Mich., Dept of Chem. Eng., Macromolecular Science and Engineering Program
Possible co-PI: Jimmy MaysUniv. of Tennessee, Dept of Chemistry
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Industrial Relevance
“The flow behavior (‘rheology’) [of polymers] is enormously sensitive to LCB [long chain branching] concentrations far too low to be detectable by spectroscopic (NMR, IR) or chromatographic (SEC) techniques. Thus polyethylene manufacturers are often faced with ‘processability’ issues that depend directly upon polymer properties that are not explainable with spectroscopic or chromatographic characterization data. Rheological characterization becomes the method of last resort, but when the rheological data are in hand, we often still wonder what molecular structures gave rise to those results.”
< 1 LCB’s per million carbons significantly affects rheology!
branched thread-like micelles
branched polymers
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Project Goals
• Develop industrially useful tools for inferring long-chain branching levels from rheology
• Develop optimization strategies for improving processing and product properties through control of long-chain branching
• Provide software tools and training as needed for industrial applications
Innovation through Partnerships
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Objectives & Research Methods• Measure rheology of commercial polymers • Combine this with conventional
characterization by SEC, light scattering, and knowledge of reaction kinetics
• Use “Hierarchical model”, a computational tool, to determine a long-chain branching profile of commercial polymers.
• Determine how changes in the long-chain branching profile could alter rheological properties in desirable ways.
Innovation through Partnerships
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Hierarchical Model
Larson et al., (2001, 2006, 2011)
comb
H
star
linear
• A complex commercial branched polymer is represented by an ensemble of up to 10,000 chains.
• This ensemble represents the range of branching structures and the molecular weight distribution of the commercial polymer.
•The ensemble is generated from a combination of GPC characterization, knowledge of reaction kinetics, and rheology.
•The ensemble is fed into the “Hierarchical Code,” and a prediction of the linear rheology (G’ and G”) emerges.
Das, Inkson, Read, Kelmanson, J. Rheol. (2006)
Relaxation of each molecule is tracked in the time domain, as it relaxes from the tips of the branches, inwards towards the backbone. At long times, branches act as drag centers, slowing down motion of the branch or backbone to which they are attached. The contributions of all molecules in the ensemble to the rheology are combined, and converted to the frequency domain to predict G’ and G’’.
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Example 1: Characterization of Anionically Synthesized “H” Polymer
Synthesized by Rahman and Mays
LinearMw/Mn=1.01
StarMw/Mn=1.03
HMw/Mn=1.07
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Chemically Likely Structures
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Identification of Structures
0 5 10 15 20 25 30 35
n (
a.u
.)
tR (min)
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T (
oC)
Mw 38.5k
54.8k
73.6k
Unfractionated Star
0 5 10 15 20 25 30
n (a
.u.)
tR (min)
T (oC
)
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32Fractionated H
71k
129k95k
114k
Star (Semi-H):
H:
TGIC from Hyojoon Lee and Taihyun Chang
Using TGIC: Temperature Gradient Interaction Chromatography
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Identification of Structures
0 5 10 15 20 25 30 35
n (
a.u
.)
tR (min)
17
18
19
20
21
22
T (
oC)
Mw 38.5k
54.8k
73.6k
Unfractionated Star
0 5 10 15 20 25 30
n (a
.u.)
tR (min)
T (oC
)
14
16
18
20
22
24
26
28
30
32Fractionated H
71k
129k95k
114k
Star (Semi-H):
H:
TGIC from Hyojoon Lee and Taihyun Chang
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Comparisons of theoretical predictions and experimental measurements
Reaction kinetics of LCB PE using single-site catalyst
Algorithm for Monte Carlo simulation of LCB PE using
single-site catalyst
Monte Carlo probabilities
Costeux et al., Macromolecules (2002)propagation probability
monomer selection probability
Generating an Ensemble of Chains for a Commercial Single-Site Metallocenes
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A Priori Predictions of Commercial Branched Polymer Rheology
101
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PL1880_60
PL1880_40PL1880_80
G
' & G
'' (P
a)
AFFINITYTM PL1880
10-2 10-1 100 101 102101
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10-2 10-1 100 101 102101
102
103
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PL1880_20
PL1880_05
G' &
G''
(Pa)
(rad/s)
10-2 10-1 100 101 102101
102
103
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105
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108
Exact3128
PL1880_02
(rad/s)
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Outcomes/Deliverables• Measurements of rheological properties of
commercial polymers• Measurement of SEC curves for select commercial
polymers• Computer software and training for predicting
rheological properties• Assessment of impact of changing • branching structure on rheology
Innovation through Partnerships
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Impact
• Improved ability to design and control polymer processing properties
• Ability to infer likely branching characteristics from rheology
• Develop methods of extracting “hidden” features of molecular structure through rheology of samples blended with simpler linear polymers
Innovation through Partnerships
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Project Duration and Proposed Budget
• 1-4 years, depending on polymer to be tackled, number of samples to be studied, availability of industrial data, such as GPC data, and the solvents/conditions required for characterization