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  1. We report on the use of visible light as the driving force for the intramolecular dimerization of pendant anthracene groups on a methacrylic polymer to induce the formation of single-chain nanoparticles (SCNPs). Using a 532 nm green laser light source and platinum octaethylporphyrin as a sensitizer, we first demonstrated the use of TTA-UC to dimerize monomeric anthracene, and subsequently applied this concept to dilute poly((methyl methacrylate)- stat -(anthracenyl methacrylate)) samples. A combination of triple-detection size-exclusion chromatography, atomic force microscopy, and UV-visible spectroscopy confirmed the formation of the SCNPs. This report pioneers the use of TTA-UC to drive photochemical reactions in polymeric systems, and showcases the potential for TTA-UC in the development of nanoobjects.
  2. Since the inception of carbon fiber-reinforced polymers (CFRPs) they have steadily gained in popularity due to their light weight, high tensile strength and modulus, and environmental toughness. However, curing of CFRPs of the thermosetting type generally must be performed within an autoclave, whose fixed, physical dimensions effectively limit the maximum size of the part. Alternative curing chemistries may potentially eliminate the requirement for an autoclave, which would allow creation of much larger panels. This project seeks to develop a thermoset composite matrix that is radiation-curable using the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. Previously, Storey et al.(1,2) reported that the azide-modified epoxy resin, di(3-azido-2-hydroxypropyl) ether of bisphenol-A (DAHP-BPA), could be cured by reaction with polyfunctional alkyne crosslinkers under mild conditions using Cu(I) catalysis. In the absence of reducing agents, Cu(II) compounds are catalytically inactive; however, upon exposure to ultraviolet light, they are reduced to Cu(I), which then catalyzes the reaction, allowing it to progress to a high degree of cure at room temperature. Herein, we report the kinetics of photo-induced CuAAC polymerization of the DAHP-BPA and several polyfunctional propargyl amine based crosslinkers, monitored by real-time FTIR as well as mechanical properties of fully cured materials. Polymerizations were studied as amore »function of Cu(II) compound type, Cu(II) concentration, UV light (365 nm) intensity, and duration of irradiation.« less
  3. This research investigates how reaction induced phase separation (RIPS) of thermoplastic, which occurs during glassy polymer network cure, is determined by viscosity. Utilizing high Tg engineering thermoplastics in high viscosity thermoset systems, dissolution of multiple loading levels of thermoplastic and thermoset pre-polymer conversion will be achieved through use of a high shear continuous reactor. Samples will be cured using various isothermal curing profiles and characterized for morphology type and domain size as well as rheologically to determine minimum viscosity, time to gelation, time from phase separation to gelation, and average viscosity. The influence of cure conditions, thermoplastic loading levels, thermoplastic composition, and molecular weight on structural morphology will be resolved, establishing a well-defined rheological well during cure that leads to tunable and controllable phase separated morphologies, from dispersed droplet to co-continuous. By controlling viscosity of thermoplastic dispersed network pre-polymers through phase composition, cure schedule, molecular weight, directed phase separation will be achieved. Rheological profiles will be related to resulting network structure, which will lead to the ability to control and direct complex thermoplastic filled thermoset systems to targeted unique morphologies.