Controlling Polymer Rheological Properties Using Long-Chain Branching

1. 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

2. 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 Innovation through Partnerships

3. Rheology, Processing and Long-Chain Branching < 1 LCB’s per million carbons significantly affects rheology! branched polymers branched thread-like micelles Innovation through Partnerships

4. 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

5. 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

6. comb H star linear Hierarchical Model • 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. 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’’. Larson et al., (2001, 2006, 2011) Das, Inkson, Read, Kelmanson, J. Rheol. (2006)

7. Example 1: Characterization of Anionically Synthesized “H” Polymer Linear Mw/Mn =1.01 Star Mw/Mn =1.03 H Mw/Mn =1.07 Synthesized by Rahman and Mays

8. Chemically Likely Structures

9. Fractionated H Unfractionated Star 114k 54.8k 95k 129k 71k Mw 38.5k 73.6k Identification of Structures Using TGIC: Temperature Gradient Interaction Chromatography TGIC from Hyojoon Lee and Taihyun Chang Star (Semi-H): H:

10. Fractionated H Unfractionated Star 114k 54.8k 95k 129k 71k Mw 38.5k 73.6k Identification of Structures TGIC from Hyojoon Lee and Taihyun Chang Star (Semi-H): H:

11. Comparisons of theoretical predictions and experimental measurements H Xue Chen Star (semi-H) blend from Chen, Rahman, Mays, Lee, Chang, Larson

12. Example 2: Blends of Linear Exact 3128 and Branched PL1880 Polyolefins X.Chen, C. Costeux, R. Larson. J. of Rheology 54(6) 1185-1206, 2010

13. Rheology of Blends of Linear Exact 3128 and Branched PL1880 Polyolefins T=150C Increasing LCB 0.3 LCB’s per million carbons!

14. Generating an Ensemble of Chains for a Commercial Single-Site Metallocenes Start Generate random number R: U(0,1) NO YES R>pp Propagation Termination Generate random number R: U(0,1) Save molecule NO YES R>lp Add monomer Add macromonomer Algorithm for Monte Carlo simulation of LCB PE using single-site catalyst Reaction kinetics of LCB PE using single-site catalyst monomer addition addition of unsaturated chain generation of dead structured chain -hydride elimination Monte Carloprobabilities propagation probability monomer selection probability Costeux et al., Macromolecules (2002)

15. A Priori Predictions of Commercial Branched Polymer Rheology

16. 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

17. 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

18. 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 Innovation through Partnerships