Organic nanoparticles are synthesized by partial imidization of high-molecular weight styrene(maleic-anhydride) with 26 to 34 mol% maleic anhydride, in aqueous environment and presence of ammonium hydroxide. The nanoparticle dispersions have a maximum solid content of 35 wt% and good stability that critically depends on the ratio of imidized and ammonolyzed maleic anhydride moieties. The deprotonated residual maleic anhydride moieties provide dispersion stability at pH > 4, while protonation at pH < 4 causes nanoparticle sedimentation. After presentation of the synthesis conditions, the imidization reaction is characterized by FT-IR and Raman spectroscopy, followed by thermal analysis (TGA, DSC), and morphological characterization (DLS, SEM, TEM, AFM). The reaction conditions were optimized by physical characterization of various dispersions, and finally nanoparticles could be obtained with a maximum degree of imidization of 77% in dispersed conditions, or 90 to 95% after drying that are favorable for coating applications.

Different vegetable oils including soy oil, high-oleic sunflower oil, corn oil, castor oil (CO), rapeseed oil, and hydrogenated CO were added to the imidization reaction of poly(styrene-maleic anhydride) or SMA, with ammonium hydroxide in aqueous medium. The oils favorably reduce viscosity during ammonolysis of the anhydride moieties and increase the maximum solid content of the dispersed imidized SMA to at least 50 wt%, compared to a maximum of 35 wt% for pure imidized SMA. The viscosity of imidized SMA with polyunsaturated oils was generally larger than for monosaturated oils, but it was highest for COs due to high contents of hydroxyl groups. Depending on the oil reactivity, homogeneous or core-shell nanoparticles with 20-60 nm diameters formed. The interactions of oil and organic phase were studied by Fourier-transform infrared spectroscopy, indicating qualitative variances between different oils, the fraction imidized SMA and remaining fraction of ammonolyzed SMA without leakage of oil upon diluting the dispersion and precipitation at low pH. A quantitative analysis with calculation of imide contents, amounts of reacted oil and chemical interactions was made by Fourier-transform-Raman spectroscopy suggesting that most interactions take place around the unsaturated oil moieties and ammonolyzed anhydride

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Celluloses are preferred renewable substrates, but hydrophilicity and porosity disfavor their water resistance. We present here an ecofriendly application of imidized nanoparticles and a method to flexibly tune the surface wettability of papers. The soft nanostructured coating is sensitive to thermal curing, which affects both the surface chemistry and morphology. The thermal stability of the coating is first investigated with conventional and modulated differential scanning calorimetry, revealing influences of the imide content and an endotherm reaction below the glass transition temperature at 120-150 °C. The latter is studied in detail for an appropriate selection of the copolymer precursors. According to diffuse reflection infrared spectroscopy, Raman spectroscopy, and UV/vis spectroscopy, the endotherm corresponds to an imidization reaction. The morphology of the coatings is followed at various scale levels by contactless roughness measurements and atomic force microscopy. Finally, the experimental values are fitted to the parameters of the Wenzel wetting model, and so-called calibration curves for the relation between contact angles, surface roughness, and surface chemistry are presented. They allow the prediction of the water contact angle of coated papers from the hydrophilic to the hydrophobic range, with a maximum in hydrophobicity after increasing the imide content at 120-150 °C curing.