Spencer L. Giles

Characterization of immiscibly blended polyurethane coatings part 1: selective staining for enhanced micro-Raman spectroscopy

Raman spectroscopy (RS) mapping of the selective infiltration of styrene monomer has been developed as a protocol for polymeric phase identification in resin-blended thermoset powder coatings. Blends of incompatible acrylic polyols, with low and high hydroxyl contents, combined with matting agents and pigments, were crosslinked to produce unique low gloss thermosets. The low reflectance originated from a synergistic effect between the polymeric phase separation and the incorporation of the matting agents and pigments. RS conclusively identified the phases within the blended film using polyester-embedded cross-section samples. Further analysis has revealed that monomeric styrene from the polyester-embedding resin produced the spectroscopic handle necessary for domain identification. Preferential infiltration of styrene was therefore investigated through dip and vapor staining of the blended and individual resin films. The spectroscopic handle had manifested through the consistent infiltration of styrene within the low hydroxyl film. The contamination in the cross-sections was eliminated when an epoxy-embedding resin was utilized, which produced no such marker peak in the ensuing spectra. These observations led to the development of the described selective staining protocol for micro-Raman analysis, which enabled very reproducible results for enhanced chemical mapping of phase-separated coatings.

Delineating crosslink density gradients via in-situ solvation of immiscibly blended polyurethane thermosets

AbstractThe cure of a blended resin thermoset coating comprised of two immiscible acrylic polyols, and an isophorone diisocyanate (IPDI) compatibilizer was analyzed via vibrational spectroscopy and TEM. The polyol reactants differed in their relative quantities of OH groups (referred to as high OH and low OH), which rendered them incompatible. The reaction yielded a coating with a surface roughened by droplet domains. Previous analysis revealed that domains consisted of the high OH resin. Carbonyl peaks originating from IPDI exhibited intensities commensurate with IPDI concentration for single resin coatings. However, commensuration was absent from the blend phases due to a diffusion gradient. The gradient is evidenced by the domains’ resistance toward in-situ caprolactam and introduced styrene monomer. These conclusions support the theory that caprolactam acts an internal solvent to reduce the coating viscosity for even application on a substrate. Domains are less solvated due to their higher crosslink density. Graphical abstractᅟ

Air Activated Self-Decontaminating Polydicyclopentadiene PolyHIPE Foams for Rapid Decontamination of Chemical Warfare Agents

The threat of chemical warfare agents (CWA) compels research into novel self-decontaminating materials (SDM) for the continued safety of first-responders, civilians, and active service personnel. The capacity to actively detoxify, as opposed to merely sequester, offending agents under typical environmental conditions defines the added value of SDMs in comparison to traditional adsorptive materials. Porous polymers, synthesized via the high internal phase emulsion (HIPE) templating, provide a facile fabrication method for materials with permeable open cellular structures that may serve in air filtration applications. PolyHIPEs comprising polydicyclopentadiene (polyDCPD) networks form stable hydroperoxide species following activation in air under ambient conditions. The hydroperoxide-containing polyDCPD materials react quickly with CWA simulants, Demeton-S and 2-chloroethyl ethyl sulfide, forming oxidation products as confirmed via gas chromatography mass spectrometry. The simplicity of the detoxification chemistry paired with the porous foam form factor presents an exciting opportunity for the development of self-decontaminating filter media.