William W. Lai

Renewable thermosetting resins and thermoplastics from vanillin

Two cyanate ester resins and a polycarbonate thermoplastic have been synthesized from vanillin. The bisphenol precursors were prepared by both an electrochemical route as well as by a McMurry coupling reaction. 1,2-Bis(4-cyanato-3-methoxyphenyl)ethene (6) had a high melting point of 237 °C and did not cure completely under a standard cure protocol. In contrast, the reduced version, 1,2-bis(4-cyanato-3-methoxyphenyl)ethane (7) melted at 190 °C and underwent complete cure to form a thermoset material with Tg = 202 °C. 7 showed thermal stability up to 335 °C and decomposed via formation of phenolics and isocyanic acid. A polycarbonate was then synthesized from the reduced bisphenol by a transesterification reaction with diphenylcarbonate. The polymer had Mn = 3588, Mw/Mn = 1.9, and a Tg of 86 °C. TGA/FTIR data suggested that the polycarbonate decomposed via formation of benzodioxolones with concomitant elimination of methane. The results show that vanillin is a useful precursor to both thermosetting resins and thermoplastics without significant modification.

Nanofiber waveguides and photophysics of an organic dye

Abstract. We present previously unreported properties of the organic molecular dye compound, 2,3,7,8-tetracyano-5,10-dimethyl-5,10-dihydrodipyrazino[2,3-b:2’,3’-e]pyrazine (DMTC-pyrazine) (CAS Reg. No. 150960-11-5), including photophysical properties with particular emphasis on optical waveguiding. We show that DMTC-pyrazine can self-assemble into monoclinic crystals that are thermally stable over 300°C. Through shape-engineering, optimized growth conditions produced high yields of nanofiber (aspect ratio >6) crystals. No photobleaching of this dye was observed in air even after hours of on-resonant illumination. Excitation of photoluminescence within the DMTC-pyrazine nanofibers propagates in tightly confined guided modes (up to 25  μm). The finesse, end-facet reflectance, and group refractive index of nanofiber DMTC-pyrazine Fabry-Pérot cavities are reported.