BEGIN
BEGIN
DISCOVERIES
DISCOVERIES
WHERE
WHERE
Foundation
Foundation
Science
Science
National
National
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
WHERE DISCOVERIES BEGIN
National Science Foundation
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.”
Janzen and Colby, J. Molecular Structure, 1999
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6
10
5
10
4
10
G' (Pa)
WHERE DISCOVERIES BEGIN
National Science Foundation
Rheology, Processing and LongChain Branching
TM
AFFINITY PL1880
PL1880_80
PL1880_60
PL1880_40
PL1880_20
PL1880_05
PL1880_02
Exact 3128
3
10
2
10
1
10 -2
10
-1
10
0
10
 (rad/s)
1
10
2
10
< 1 LCB’s
per million
carbons
significantly
affects
rheology!
branched polymers
branched thread-like micelles
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WHERE DISCOVERIES BEGIN
National Science Foundation
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
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National Science Foundation
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.
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National Science Foundation
Hierarchical Model
comb
H
star
linear
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’’.
• 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.
Larson et al., (2001, 2006, 2011)
Das, Inkson, Read, Kelmanson, J.
Rheol. (2006)
Titration
s-BuLi
Butadiene
Example 1: Characterization of Anionically
Synthesized “H” Polymer
Cl
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National Science Foundation
Li
Si
Si
Cl
CH3
CH3
(CH3)2SiCl2
Li
Linear
Mw/Mn
=1.01
Star
Mw/Mn
=1.03
H
Mw/Mn
=1.07
Synthesized by
Rahman and Mays
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National Science Foundation
Chemically Likely Structures
Unfractionated Star
Fractionated H
22
114k
54.8k
32
30
21
28
95k
22
129k
o
n (a.u.)
24
20
Mw 38.5k
71k
18
73.6k
T ( C)
19
n (a.u.)
26
20
o
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Using TGIC: Temperature Gradient Interaction Chromatography
T ( C)
National Science Foundation
Identification of Structures
18
16
0
5
10
15
20
tR (min)
Star (SemiH):
H:
25
30
17
35
0
5
10
15
20
25
14
30
tR (min)
TGIC from
Hyojoon Lee and
Taihyun Chang
Fractionated H
22
114k
54.8k
32
30
21
28
95k
22
129k
o
n (a.u.)
24
20
Mw 38.5k
71k
18
73.6k
18
16
0
5
10
15
20
tR (min)
Star
(SemiH):
H:
25
30
17
35
0
5
10
15
20
T ( C)
19
n (a.u.)
26
20
o
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Unfractionated Star
T ( C)
National Science Foundation
Identification of Structures
25
14
30
tR (min)
TGIC from
Hyojoon Lee and
Taihyun Chang
1.E+06
1.E+05
H
1.E+04
G', G'' (Pa)
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National Science Foundation
Comparisons of theoretical predictions and
experimental measurements
Xue Chen
1.E+03
Star (semi-H)
1.E+02
1.E+01
blend
Me=1620,Gn0=1.095MPa, tau_e=5E-7
from Chen, Rahman, Mays,
Lee, Chang, Larson
1.E+00
1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04
11
Freq (rad/s)
National Science Foundation
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12
Example 2: Blends of Linear Exact 3128 and
Branched PL1880 Polyolefins
Sample name
AFFINITY™
PL 1880
PL1880_80
PL1880_60
PL1880_40
PL1880_20
PL1880_05
PL1880_02
Exact 3128
AFFINITY™
PL1880
(branched)
Exact
LCB
3128
(n/1000C)
(linear)
nc
Mw
(kg/mol)
100%
0%
0.0177
0.0482
116
80%
60%
40%
20%
5%
2%
100%
20%
40%
60%
80%
95%
98%
0%
0.0142
0.0106
0.00709
0.00355
0.000887
0.000355
0
0.0502
0.0521
0.0541
0.0560
0.0575
0.0578
0.0580
116
116
116
115
115
115
115
X.Chen, C. Costeux, R. Larson. J. of Rheology 54(6) 1185-1206, 2010
6
10
T=150C
5
10
4
10
G' (Pa)
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National Science Foundation
Rheology of Blends of Linear Exact 3128 and
Branched PL1880 Polyolefins
Increasing LCB
TM
AFFINITY PL1880
PL1880_80
PL1880_60
PL1880_40
PL1880_20
PL1880_05
PL1880_02
Exact 3128
3
10
2
10
0.3 LCB’s
per million
carbons!
1
10 -2
10
13
-1
10
0
10
 (rad/s)
1
10
2
10
Algorithm for Monte Carlo
simulation of LCB PE using
single-site catalyst
Reaction kinetics of LCB PE
using single-site catalyst
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National Science Foundation
Generating an Ensemble of Chains for a Commercial Single-Site Metallocenes
k
p
Px,n + M ¾¾
® Px +1,n
Start
monomer addition
=
LCB
Px,n + Dy,m
¾k¾
¾® Px +y,n +m +1
Generate random
number R: U(0,1)
addition of unsaturated chain
+
CTA
Px,n + CTA ¾k¾
¾® Dx,n
+ P1,0
NO
Propagation
generation of dead structured chain
YES
R>pp
Termination
k
b
=
Px,n ¾¾
® Dx,n
+ P1,0
Generate random
number R: U(0,1)
-hydride elimination
NO
Monte Carlo probabilities
pp =
Rp + RLCB
Rp + RLCB + RT
propagation
probability
lp =
Rp
R>lp
Add monomer
Save molecule
YES
Add macromonomer
Rp + RLCB
monomer selection
probability
Costeux et al., Macromolecules (2002)
8
8
10
7
10
10
TM
AFFINITY
7
10
PL1880
G' & G'' (Pa)
6
10
5
5
10
10
4
4
10
10
3
10
3
PL1880_80
10
2
1
1
10 -2
10
8
10
8
10
7
PL1880_20
1
10
2
10
PL1880_02
6
10
5
5
10
4
4
10
10
3
3
10
PL1880_05
2
10
Exact3128
2
10
10
1
15
0
10
10
10
10 -2
10
-1
10
7
10
6
PL1880_40
2
10
10
10
PL1880_60
6
10
10
G' & G'' (Pa)
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National Science Foundation
A Priori Predictions of Commercial Branched
Polymer Rheology
1
-1
10
0
10
(rad/s)
1
10
10
2
-2
10 10
-1
10
0
10
 (rad/s)
1
10
2
10
WHERE DISCOVERIES BEGIN
National Science Foundation
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
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National Science Foundation
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
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WHERE DISCOVERIES BEGIN
National Science Foundation
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
• Budget: $75,000/year
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