1. Comonomers Included or Excluded from Polymer Crystals Richard A. Register, Princeton University, DMR 1003942 polymer chain must pack into a highly-regular crystal lattice, any “irregular” units, such as comonomers, hamper the crystallization process. Usually such co- units are strongly excluded from the crystals, but in some cases– when they are similar in size and shape to the “regular” units– they can be partially incorporated into the crystals. We have recently investigated[1] model copolymers based on hydrogenated polynorbornene (hPN); like PE and PP, hPN homopolymer is highly crystalline. Co-units bearing a six-carbon (hexyl) branch were strongly excluded from hPN crystals, causing the crystallinity to fall off rapidly with comonomer content. But when the co-units instead carried a one-carbon (methyl) branch, roughly 3 of every 4 co-units could enter the crystals. The degree of crystallinity, which controls the material’s stiffness, and the melting point, differed dramatically between the two copolymer cases, revealing a versatile way to tune polymer properties. TOP: chemical structures of the repeat units in the hPN copolymer systems: hPN (black, crystallizable) majority units, and methyl (MeN, red, included) and hexyl (HxN, blue, excluded) norbornene comonomer units. BOTTOM: exclusion of HxN units causes the degree of crystallinity and crystal thickness t c to fall off rapidly with comonomer content, while the decrease is fourfold more gradual for MeN units, which are extensively included into the hPN crystals. [1] M.T. Showak, A.B. Burns, A.J. Stella, and R.A. Register, “Counit Inclusion in Hydrogenated Polynorbornene Copolymer Crystals”, Macromolecules, 46, 9288−9295 (2013). tctc exclusioninclusion  3-50 nm Many polymers– including polyethylene (PE) and polypropylene (PP), the two largest- volume commercial polymers in the US and worldwide– are capable of crystallization, which changes the material from a soft rubber to a stiff plastic. Since the units making up the

2. Stars of Materials Science: Amazing Polymers Richard A. Register, Princeton University, DMR 1003942 On March 29, 2014, the Register Group inaugurated the new “Stars of Materials Science” public science outreach series, sponsored by the Princeton Center for Complex Materials and in the tradition of Michael Faraday’s famous Christmas Lectures. The PI, four Ph.D. students, and staff from the Chemistry Department and the Cotsen Children’s Library performed two well-rehearsed 90-minute interactive shows on “Amazing Polymers” to nearly 300 attendees, in Princeton’s new Taylor Auditorium. Those in attendance learned about the science, technology, and history behind rubbers and other crosslinked polymers, such as superabsorbent gels, as well as thermoplastic elastomers based on block copolymers. TOP: PI Richard Register describes Charles Goodyear’s 1839 discovery of vulcanization (crosslinking), which transforms a viscoelastic liquid (like Silly Putty) into an elastic solid. RIGHT: audience members watch intently as the story unfolds.