Determination of Short-Chain Branching Distribution of Polyethylene via IR5-GPC

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 • 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, 1stInternantional 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. Waste IR5-GPC Instrumentation Computer A Computer B Solvent Reservoir Data Box Pump Injector Columns IR5

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 limit @ 0.5 – 1 SCB/1,000 TC if CH2 S/N at 2,000 – 3,000

12. SCB Distributional Profile via IR5-GPC(4 columns; flowrate=1.0 mL/min; conc. =1.5 mg/mL; injvol=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. PracticalAspects • Environment control • 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