Northwestern Events Calendar

May
31
2018

ChBE Seminar Series: Rick Register

recurring see all events in this series

When: Thursday, May 31, 2018
9:00 AM - 10:00 AM CT

Where: Technological Institute, M345, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Public - Post Docs/Docs - Graduate Students

Cost: Free

Contact: Elizabeth Rentfro   (847) 491-2773

Group: McCormick-Chemical and Biological Engineering (ChBE)

Category: Academic

Description:

Rick Register
Princeton University

Title:
Polyethylene Block Copolymers: Synthesis, Miscibility, and Properties

Abstract:
Polyethylene (PE) is the world’s most widely produced synthetic polymer: 92 million tons in 2016, or about 35% of total thermoplastics production. Yet the mechanical properties of PE (relatively low stiffness and yield strength, poor creep resistance, etc.)—even for the most-crystalline “high density” linear PE—are limiting for many applications. Polymer properties are commonly tuned either through copolymerization, or through blending, but very few polymer species have been identified with sufficiently weak repulsive interactions against PE to yield block copolymers with disordered (homogeneous) melts, or PE-containing miscible blends at high molecular weights. Moreover, most suitably miscible candidates are chemically similar to PE, such as copolymers of ethylene with an α-olefin; these polymers also have low glass transition temperatures (Tg) and thus do not ameliorate the limiting properties outlined above.
We have found that several members of another family of hydrocarbon polymers—hydrogenated substituted polynorbornenes—are substantially miscible with PE in the melt, yielding symmetric block copolymers with homogeneous melts at molecular weights exceeding 100 kg/mol, tunable through the substituent attached to the polynorbornene repeat unit. The polymers are synthesized by “living” ring-opening metathesis polymerization (ROMP) of cyclopentene, as the precursor to perfectly linear PE, and various 5-substituted norbornene monomers (alkyl, cycloalkyl, aryl), yielding narrow-distribution polymers of targeted molecular weight and composition. We characterize the interaction energy density X (proportional to the Flory interaction parameter, ) by measuring the order-disorder transition temperature of near-symmetric diblocks via small-angle x-ray scattering or dynamic mechanical thermal analysis. These values of X are then compared against various mixing rules proposed to describe the mixing energy in terms of pure-component properties, starting with the classical regular mixing (solubility parameter) treatment of Hildebrand, as employed originally for polymer solutions by Flory. Despite the relatively simple nature of the dispersive interactions in these all-hydrocarbon polymers, they do not quantitatively obey regular mixing, nor do entropic contributions from chain stiffness nor free volume mismatches appear to be responsible for the observed deviations from regularity. Instead, the interactions within this family of polymers can be satisfactorily described by an empirical mixing rule of the form X = (Δγ)1.5, where X is the interaction energy density and γ is a pure-component quantity, operationally analogous to a solubility parameter, with a distinct value for each polymer. Attaching relatively short blocks of hydrogenated poly(norbornylnorbornene), with Tg = 115C, to PE effectively doubles its modulus and yield strength, while retaining an easily-processed single-phase melt.

Biography:
Richard A. Register is Eugene Higgins Professor in the Department of Chemical and Biological Engineering at Princeton University. His research interests revolve around micro- and nanostructured polymers, such as block copolymers, polymer blends, semicrystalline polymers, and ionomers, ranging across their synthesis, physics, properties, and applications. He served as chair of his department from 2008-2016, and as Director of the Princeton Center for Complex Materials from 2005-2008. He received the Charles M.A. Stine Award from the American Institute of Chemical Engineers in 2002, and was honored with the Graduate Mentoring Award from Princeton University in 2008. He is a Fellow of the American Physical Society, of the American Chemical Society, and of the American Institute of Chemical Engineers.

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