#1: Chemistry in the Novak Group: Our polymer program currently encompasses projects concentrated in several major areas in materials chemistry: macromolecular chirality, designing molecular motors, the synthesis of organic-inorganic hybrid materials that display mixing near the molecular level; the design of organometallic complexes for use in living polymerizations; the development of transition metal catalysts for the polymerization of functional olefins; the catalytic formation and polymerization of thermodynamically unstable monomers; and the development of photoactive materials for applications ranging from photolithography to reversible molecular switching.

" … Never shall I forget the hours passed in the laboratory of Gay-Lussac. When we finished a successful analysis (you know without me telling you that the method and the apparatus described in our joint memoir were entirely his), he would say to me, 'Now you must dance with me just as Thenard and I always danced together when we had discovered something new.' And then we would dance."

Justus Liebig

Come Dance with us!

#2: Chiral Polymers. Examples of chirality influencing biological chemistry are ubiquitous and essentially uncountable. Less clear, however, are the affects of chirality on synthetic materials. In the cases of random-coil polymers (i.e., most synthetic polymers: polystyrene, PMMA, PVOH, etc.) the affects are non-existent. However, when you build order into the polymer structure chirality can have pronounced influence over their properties. In order to explore this unusual area of polymer science, we have been studying polymers that adopt regular, helical structures by decorating them with chiral side chains. Solid state, dilute solution, concentrated solution and thin film properties have all been studied. These chiral helical polymers have numerous applications that include reversible molecular switches and sensors, optoelectronic components, chiral separations media, and synthetic protein mimics.

#3: This picture shows the uses of helical polymers. The helix motif is a versatile structure that has applications in a number of important technological areas which include optical devices (reversible information storage, nonlinear optics, selective diffraction gratings), chiral separations and sensors (chiral separation media, amplified chemical sensors), asymmetric catalysis (chiral supports, acid/base catalysts), high strength materials (liquid crystalline polymers, thermoplastic elastomer hard segments, O/I composites, rigid rod fibers), recyclable/degradable polymers (activation by chiral-achiral switching, reversible monomer-polymer cycles), and finally, biomimetic polymers (artificial proteins, ion channels, controlled drug delivery, antibacterial/viral agents).

#4: This picture shows the chemical structure of the polyquanidines and the 6/1 helical conformation that they can adopt. Steric interactions force polyguanidines adopt an approximate 6/1 helical conformations in both solution and the solid state. This helical pitch will depend on side chain interactions.

#5: Polyguanidines can be prepared by the transition-metal catalyzed polymerization of carbodiimides at room temperature. This picture shows a representative polymerization. Our mechanistic studies to date, show that initiation is effected by the insertion of one of the nitrogen-carbon double bonds of a carbodiimide into a metal -OR or -NR2 bond to form an metal-amindate. Propagation then proceeds in an analogous manner by reversible insertions into the propagating amidinate metal complex.

#6: This slide shows the concept of a helix sense-selective polymerization of an achiral carbodiimide with a chiral catalyst. The molecular structure of a single handed poly(di-n-hexylguanidine) is also shown.

#7. We have synthesized a number of chiral binaphthal catalysts that can be used to polymerize carbodiimides to form polymers that adopt primarily a single screw-sense. The structures of some of these titanium catalysts are shown in this picture.

#8: The binapthol catalysts are successful at enantioselective (single screw-sense) polymerizations of achiral carbodiimides. Shown in this picture is a carbodiimide possessing an anthracene group was polymerized with one of our chiral catalysts. The polymer shows an optical rotation of -550°.

#9: These chiral anthracene polymer are very resistant to racemization (i.e., 80° C for > 100 hrs). However, at lower temperatures, they act as very sensitive switches by inverting the sign of their optical rotations over very small temperature ranges and solvent polarities. This picture shows the racemization plot the anthracene polymer at 80° C.

#10: This picture shows the low temperature reversible switching that these polymers are capable of undergoing. These single screw-sense polyguanidines show optical rotations (and Cotton effects in the CD) that are extremely sensitive to temperature and polarity.

#11: This picture shows the reorientation of the anthracene groups on the helical polyguanidine backbone. These optical switching properties arise from reorientation of the anthracene dipoles relative to the helix directorate via a simple, cooperative wagging motion. This switching becomes the basis for a variety of molecular switches, sensors and motors.