 normalize substituent length by number of backbone carbons per mer, N

1. Structuring Polymer Crystals Through Macromolecular ArchitectureRichard A. Register, Princeton University, DMR-0505940 In semicrystalline homopolymers, the crystal thickness and melting points typically assume nonequilibrium values dictated by the specimen’s crystallization history. By incorporating the crystallizable material into a block copolymer architecture, an equilibrium degree of chain folding is induced, thus decoupling crystal thickness and melting point from the processing history. “Living” ring-opening metathesis polymerization (ROMP) is an excellent means of synthesizing such block copolymers, but unfortunately, the monomers amenable to ROMP typically yield polymers with high glass transition temperatures (Tg) which are unsuitable as elastomers. But we have found that alkyl-substituted norbornenes polymerize smoothly by ROMP to yield amorphous polymers, with Tg values as low as -40oC after hydrogenation. Lengthening the alkyl substituent leads to “internal plasticization” whose effect is quantitatively similar to that in conventional polymers once the difference in backbone structure are accounted for.  normalize substituent length by number of backbone carbons per mer, N = 2 for vinyl polymers = 5 for PaN, hPaN  compare magnitude of internal plasticization as Tg/Tgm (absolute units), where Tgm = Tg of methyl member of homologous series

2. Structuring Polymer Crystals Through Macromolecular ArchitectureRichard A. Register, Princeton University, DMR-0505940 Outreach: On March 21, Princeton University hosted its third Science and Engineering Expo (SEE), which brought approximately 1000 local middle-school children to campus. Studies have shown that the middle-school years are when many students lose interest in science and technology, especially girls; the goal of the SEE is to reinforce that interest, by presenting a number of “hands-on” demonstration tables where students can experience firsthand the excitement of science and technology (and, for our group, particularly the science and technology of polymers!). The photo at right shows the PI and five students and postdocs demonstrating eye-catching and technologically important aspects of material behavior, all with their roots in polymer physics: the unparalleled water-swelling capacity of polyelectrolyte gels (foreground); the glass transition temperature and its influence on polymer mechanical behavior; and elastic fluids and transient physical crosslinking in Silly Putty and Slime. The event was covered in local print and broadcast media to reach an even wider audience. Some of these demonstrations are currently being incorporated into a “materials science show” under development by the staff of the Liberty Science Center, with assistance from the PI and students.