National Science Foundation WHERE DISCOVERIES BEGIN 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

National Science Foundation WHERE DISCOVERIES BEGIN 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 Partnerships2

National Science Foundation WHERE DISCOVERIES BEGIN Rheology, Processing and Long- Chain Branching Innovation through Partnerships3 < 1 LCB’s per million carbons significantly affects rheology! branched thread-like micelles branched polymers

National Science Foundation WHERE DISCOVERIES BEGIN 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 Partnerships4

National Science Foundation WHERE DISCOVERIES BEGIN 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 Partnerships5

National Science Foundation WHERE DISCOVERIES BEGIN Hierarchical Model Larson et al., (2001, 2006, 2011) comb H star linear 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. Das, Inkson, Read, Kelmanson, J. Rheol. (2006) 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’’.

National Science Foundation WHERE DISCOVERIES BEGIN Example 1: Characterization of Anionically Synthesized “H” Polymer Synthesized by Rahman and Mays Linear Mw/Mn =1.01 Star Mw/Mn =1.03 H Mw/Mn =1.07

National Science Foundation WHERE DISCOVERIES BEGIN Chemically Likely Structures

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

National Science Foundation WHERE DISCOVERIES BEGIN Identification of Structures Mw 38.5k 54.8k 73.6k Unfractionated Star Fractionated H 71k 129k 95k 114k Star (Semi- H): H: TGIC from Hyojoon Lee and Taihyun Chang

National Science Foundation WHERE DISCOVERIES BEGIN 11 Comparisons of theoretical predictions and experimental measurements Star (semi-H) H blend from Chen, Rahman, Mays, Lee, Chang, Larson Xue Chen

National Science Foundation WHERE DISCOVERIES BEGIN 12 Example 2: Blends of Linear Exact 3128 and Branched PL1880 Polyolefins X.Chen, C. Costeux, R. Larson. J. of Rheology 54(6) , 2010

National Science Foundation WHERE DISCOVERIES BEGIN 13 Rheology of Blends of Linear Exact 3128 and Branched PL1880 Polyolefins T=150C Increasing LCB 0.3 LCB’s per million carbons!

National Science Foundation WHERE DISCOVERIES BEGIN Start Generate random number R: U(0,1) R>pp PropagationTermination Save molecule Add monomerAdd macromonomer Generate random number R: U(0,1) R>lp NOYES NOYES monomer addition addition of unsaturated chain generation of dead structured chain  -hydride elimination Reaction kinetics of LCB PE using single-site catalyst Algorithm for Monte Carlo simulation of LCB PE using single-site catalyst Monte Carlo probabilities Costeux et al., Macromolecules (2002) propagation probability monomer selection probability Generating an Ensemble of Chains for a Commercial Single-Site Metallocenes

National Science Foundation WHERE DISCOVERIES BEGIN 15 A Priori Predictions of Commercial Branched Polymer Rheology

National Science Foundation WHERE DISCOVERIES BEGIN 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 Partnerships16

National Science Foundation WHERE DISCOVERIES BEGIN 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 Partnerships17

National Science Foundation WHERE DISCOVERIES BEGIN 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 Partnerships18