Autonomously healing materials that utilize thiol−ene polymerization initiated by an environmentally borne reaction stimulus are demonstrated by puncturing trilayered panels, fabricated by sandwiching thiol−ene− trialkylborane resin formulations between solid polymer panels, with high velocity projectiles; as the reactive liquid layer flows into the entrance hole, contact with atmospheric oxygen initiates polymerization, converting the liquid into a solid plug. Using infrared spectroscopy, we find that formulated resins polymerize rapidly, forming a solid polymer within seconds of atmospheric contact. During high-velocity ballistics experiments, additional evidence for rapid polymerization is provided by high-speed video, demonstrating the immediate viscosity increase when the thiol−ene−trialkylborane resins contact atmospheric oxygen, and thermal imaging, where surface temperature measurements reveal the thiol−ene reaction exotherm, confirming polymerization begins immediately upon oxygen exposure. While other approaches for materials self-repair have utilized similar liquid-to-solid transitions, our approach permits the development of materials capable of sealing a breach within seconds, far faster than previously described methods.

Metamaterials or artificial negative index materials (NIMs) have generated great attention because of their unique electromagnetic properties. The main challenge in current NIM development is creating a homogenous NIM without the need of complex geometric architectures consisting of capacitors and inductors or aggregated fillers, but possessing a tunable plasma frequency. A natural material that can exhibit negative values for permittivity and permeability simultaneously has not been found, or discovered. If one can design a negative dielectric constant material with a tunable plasma frequency of interest, implementing negative permeability into the material or system would be much more readily achievable to create a metamaterial. In this regard, a novel negative dielectric constant material, which is an essential key to creating the NIMs, was developed by doping ions into a polymer, a protonated poly(benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at frequencies of kHz to MHz because of its reduced plasma frequency and an induction effect. As temperature increased, the dielectric spectrum changed from a relaxation to a resonance behavior and exhibited a larger magnitude of negative dielectric constant at a lower frequency. The conductivity of the doped PBI measured as a function of both temperature and frequency followed the same trend as the dielectric constant. With respect to the dielectric constant and the conductivity data, it can be assumed that the origin of the negative dielectric constant is attributed to the resonance behavior of the highly mobile ions at elevated temperatures and high frequencies.

Poly(2-methoxystyrene)s (P2MS) were synthesized using n-BuLi in THF and toluene at various temperatures. At -20 degrees C and higher temperatures, toluene was an effective polymerization solvent for synthesizing poly(2-methoxystyrene). Under these conditions, polymers with good yields and reasonable molecular weight distributions were obtained. Polymers synthesized under all conditions were isotactic; the most highly isotactic polymer was obtained in toluene at -20 degrees C. The m (isotactic dyad) content of the polymers synthesized in toluene at 0 degrees C and -20 degrees C was 0.65 and 0.74, respectively. Optically active helical (+) and (-) P2MS were synthesized by asymmetric polymerization utilizing (+) or (-) [2,3-dimethoxy1,4(dimethylamino)butane] (DDB)/tolyl lithium initiating complex in toluene. Asymmetric polymerizations were also carried out at 0 degrees C to synthesize optically active polymers. The optical rotations of the polymers were found to be dynamic and reversible, strongly suggesting contribution of the chiral higher ordered structure to the overall optical rotation. Geometry optimization carried out using various force fields such as MM+, AMBER and CHARMM suggests that isotactic P2MS form low energy stable helical conformations. HeLa cells showed better growth on surfaces prepared using chiral polymers compared to the surfaces prepared with achiral polymers. Similarly, chiral P2MS surfaces were also more effective as supports for mouse and human osteoblast cells. The cell attachment and growth data demonstrate that chiral P2MS surfaces were better supports compared to achiral P2MS surfaces. Atomic force microscopy (AFM) studies on surfaces prepared using chiral poly(2-methoxystyrene) showed more discrete topography features compared to surfaces prepared with achiral polymers. Thus, the surface topography may play a role in determining polymer-cell interactions.

As part of a program to develop more survivable aircraft, flame-retardant epoxy resins were investigated for their potential as fire-resistant exterior composite structures for future subsonic commercial and general aviation aircraft. Four different poly(phosphonamide)s were prepared by low temperature NMR condensation and characterized by Fourier transform infrared spectroscopy, 1H-NMR spectroscopy, 31P-NMR, differential scanning calorimetry, viscometry and gel-permeation chromatography. The poly(phosphonamides) were used as toughening agents (with 4,4'-diaminodiphenyl sulfone) to partially cure a commercially available unmodified liquid epoxy resin. The resulting cured epoxy formulations were evaluated for water uptake, flame retardance and fracture toughness. The formulations show good flame retardation with phosphorus content as low as 1.6% by weight, but exhibited high moisture uptake compared to the baseline epoxy. The fracture toughness of the cured formulations showed no detrimental effect due to phosphorus content (∼ 1.5% P). The heat of combustion of the pyrolysis gases, hc = 23.5 ± 1.3 kJ g—1 for the poly(phosphonamide) formulations were essentially the same as the N, N, N', N'-tetraglycidylether of -4,4'-methylene dianiline/4,4'-diaminodiphenyl sulfone epoxy formulation, hc = 24 kJ g—1.