1. Determination of Short-Chain Branching Distribution of Polyethylene via IR5-GPC
Youlu Yu* and Paul J. DesLauriers
Chevron Phillips Chemical Company LP
Bartlesville Research & Technology Center
Bartlesville, Oklahoma 74006
February 27 – March 2, 2011
International Polyolefins Conference 2011
Hilton Houston North, Houston, Texas

2. Outline Introduction Instrumentation Methodology Practical Aspects
Data handling/processing
Calibration
Error analysis
Practical Aspects
Comparison with Other Techniques
Conclusions

3. Conventional Techniques for PE SCB Distributional Determination
SGF-NMR
Classic method
SGF Fractionation + NMR
Off-line technique
Tedious & labor intensive
Limited resolution
Large quantity of solvent/waste
On-line SEC-FTIR
Pioneered by DesLauriers et al. (DesLauriers, Rohlfing, Hsieh, 2002, Polymer, 43, 159)
On-line technique
Fast turn-around
Chemometrics for data analysis
Liquid nitrogen needed
Batch mode

4. SGF-NMR vs. Online SEC-FTIR
SGF-NMR takes days of operation for one sample
SEC-FTIR takes hours of operation for one sample
DesLauriers, Rohlfing, Hsieh, Polymer, 43, 2002, 159

5. Desired Improvements in Online SCB Determination Technique
With today’s PE business environment where safer, faster, and cheaper operations are required, there are still rooms for improvements with the Online SEC-FTIR SCB determination technique in the following areas:
Eliminating liquid nitrogen usage
Less human intervention
Less system upsets
Easier operation
System suitable for continuous operations
Reduced human intervention
Improved productivity
Easy/straight forward data processing

6. IR5 Detector
Manufactured by Polymer Characterization, S.A. Spain (J. Montesinos, R. Tarin, A. Ortin, B. Monrabal, 1st Internantional Conference of Polyolefins Characterization, 2006, Houston)
A fixed-band IR spectrometer with five optical filters for detection of adsorbance in five different mid-IR bands
Thermoelectrically-cooled MCT detector
Advanced optics to achieve high energy throughput
High temperature capability
Specifically designed for polyolefins characterization
Minimal mixing in cell (cell volume 11.3 uL)
No liquid N2 needed
Suitable for continuous GPC and high-throughput GPC applications

7. IR5-GPC Instrumentation
Computer A
Computer B
IR5
Pump
Columns
Injector
Solvent Reservoir
Waste
Data Box

8. SCB Calibration and Calculation
SCB calculation based on intensity ratios
Two intensity ratios tested: ICH3/ICH2 and ICH3/Iall C-H
Chain-end effect correction based on polymer chemistry (# CE/molecule)
Calibration curve (i.e. intensity ratio as a function of SCB content) needed
Polymers of known SCB contents and with flat SCB distribution employed
Data points influenced by chain-end effect excluded from the calibration
MW/MWD determined by the relative method using the integral calibration method and broad MWD PE standard
Both the “compensate” and “un-compensate” modes explored
All data processing performed using in-house developed software

9. SCB Calibration and Calculation (E/H Copolymers)

10. Error Analysis
Uncertainty defined by signal to noise ratio (S/N)

11. Simulated SCB Error Map
28% 5%
Detection 0.5 – 1 SCB/1,000 TC if CH2 S/N at 2,000 – 3,000

12. Error bars significantly larger at the two ends where S/N poorer
SCB Distributional Profile via IR5-GPC (4 columns; flowrate=1.0 mL/min; conc. =1.5 mg/mL; inj vol=400 uL)
Error bars significantly larger at the two ends where S/N poorer

13. Reducing Determination Uncertainty
Minimize low-frequency noise
Stable power voltage
Good environmental control
Room temperature affecting results significantly
Increase signal intensity
Increase sample concentration
Increase injection volume
Increase flow rate
Reduce number of columns 
Increase injection volume
Increase flow rate
Reduce number of columns

14. Concentration Effect Separation efficiency and signal S/N trade-off
Too high a polymer concentration causing MWD and SCBD distortion

15. Practical Aspects Environment control Chain ends effect
Both detection accuracy and precision affected by environment temperature
Chain ends effect
Imperfect separation at the low MW end causing significant errors in SCB contents

16. Comparison with NMR
IR5-GPC results generally in very good agreement with NMR results
Calibration less accommodating to branching types than Chemometrics

17. Comparison with SEC-FTIR
IR5-GPC
4 columns; 1.0 mL/min; 0.4 mL; 1.5 mg/mL
SEC-FTIR
2 columns; 1.0 mL/min, 0.5 mL; 2.0 mg/mL
IR5-GPC results in very good agreement with SEC-FTIR

18. Conclusions IR5-GPC a robust SCB distribution determination technique
No liquid N2 needed
Continuous process
No human intervention between samples
Easy operation and simple data processing
SCB precision determined by IR5 signal S/N
ICH3/ICH2 gives better results
GPC column fractionation efficiency and SCB precision trade off
Too high a polymer concentration can cause MWD and SCBD distortion
No significant difference found between the “compensate” mode and the “un-compensate” mode
Results in good agreement with NMR and SEC-FTIR
SCB at LMW end significantly affected by column separation efficiency and the presence of impurity/contamination
Maintaining stable instrument environment essential for data accuracy and precision