Rubbers that Melt but Don’t Dissolve Richard A. Register, Princeton University, DMR 0505940

1. Rubbers that Melt but Don’t DissolveRichard A. Register, Princeton University, DMR 0505940 Conventional rubbers, like those in rubber bands or rubber tires, get their strength from “vulcanization” (crosslinking)–- but the drawback is that once a material is vulcanized, it cannot be reshaped (remolded, recycled). “Thermoplastic elastomers” (TPEs) are materials which behave like vulcanized rubbers at room temperature, but can be shaped or reshaped at high temperatures using the same processes employed for making plastic objects (extrusion, injection molding). However, a major drawback of most TPEs is that they are dissolved by common organic liquids, and so cannot be used in applications such as gaskets and hoses. Recently, we1 synthesized a TPE with crystallizable segments, which make the material insoluble while allowing it to be easily shaped above its melting point. With judicious materials design, a semicrystalline TPE can be created which has both the softness and excellent recovery from deformation desired in a rubber. True Stress (MPa) Percent Strain Main figure: Stress-strain curve for a semicrystalline TPE, measuring the force required to stretch the material to a given length. Inset: Dogbone-shaped test specimen, after stretching to three times its initial length, recovers nearly completely. TPE is a triblock copolymer with crystalline linear polyethylene endblocks (12 kg/mol) and rubbery hydrogenated poly(n-hexylnorbornene) midblock (93 kg/mol), synthesized by ring-opening metathesis polymerization. [1] S.B. Myers, and R.A. Register, “Extensibility and Recovery in a Crystalline-Rubbery-Crystalline Triblock Copolymer”, Macromolecules, ASAP Article (July 2009).

2. Polymers at West Windsor – Plainsboro Family Science DayRichard A. Register, Princeton University, DMR 0505940 Many students lose interest in science and technology during their middle-school years, making this group a critical target for science outreach. On January 31, 2009, the West Windsor-Plainsboro Education Foundation organized the first WW-P Family Science Day at Thomas R. Grover Middle School in West Windsor. The day featured auditorium shows on materials science performed by staff of the Liberty Science Center in Jersey City, and demonstration tables including one hosted by the Register Group, focused on the unusual properties of polymers: swelling and deswelling of a superabsorbent polymer gel; rubber elasticity, in vulcanized or themoplastic elastomers; and the creation of “gak” and “slime”.  Roughly 300 students and 300 parents from across the WW-P School District enjoyed the Saturday morning event. PI Rick Register (right foreground) explains the dramatic swelling of polyelectrolyte gels (the “active ingredient” in superabsorbent diapers) to middle school students at the inaugural WW-P Family Science Day, with graduate students Bryan Beckingham and Sheng Li (center background). Photo by Mary Iuvone for the Trenton Times.