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

Outline

Introduction Instrumentation Methodology

– Data handling/processing– Calibration– Error analysis

Practical Aspects Comparison with Other Techniques Conclusions

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

SGF-NMR vs. Online SEC-FTIR

DesLauriers, Rohlfing, Hsieh, Polymer, 43, 2002, 159

9

10

11

12

13

14

4.5 4.7 4.9 5.1 5.3 5.5

Log M

SCB

/1,0

00 T

C

From fractionation/NMR

From SEC-FTIR

4.0 5.0 6.0

Log M

Weighted MWD's of fractions

0.0

0.1

0.2

0.3

0.4

0.5

Wtf

*dW

/d(

Log

M

)

0.74 wt% 18.53 Me/1000C 6.92 15.6416.54 13.9015.86 12.75 6.72 12.1712.54 11.59 9.91 11.01 9.11 10.43 6.67 9.85 3.20 9.27 9.97 7.53 3.17 6.38 1.37 3.48

SGF-NMR takes days of operation for one sample

SEC-FTIR takes hours of operation for one sample

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

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

IR5-GPC Instrumentation

IR5Pump ColumnsInjector

Solvent Reservoir

Waste

Computer A Computer B

Data Box

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

SCB Calibration and Calculation (E/H Copolymers)

Error Analysis

Uncertainty defined by signal to noise ratio (S/N)

Simulated SCB Error Map

28%

5%

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

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

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

Concentration Effect

Separation efficiency and signal S/N trade-offToo high a polymer concentration causing MWD and SCBD distortion

Practical Aspects

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

Comparison with NMR

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

Comparison with SEC-FTIR

IR5-GPC4 columns; 1.0 mL/min; 0.4 mL; 1.5 mg/mL

SEC-FTIR2 columns; 1.0 mL/min, 0.5 mL; 2.0 mg/mL

IR5-GPC results in very good agreement with SEC-FTIR

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