The encapsulation of photolabile 2-oxoacetates in core-shell microcapsules allows the light-induced, controlled release of bioactive compounds. On irradiation with UVA light these compounds degrade to generate an overpressure of gas inside the capsules, which expands or breaks the capsule wall. Headspace measurements confirmed the light-induced formation of CO and CO2 and the successful release of the bioactive compound, while optical microscopy demonstrated the formation of gas bubbles, the cleavage of the capsule wall, and the leakage of the oil phase out of the capsule. The efficiency of the delivery system depends on the structure of the 2-oxoacetate, the quantity used with respect to the thickness of the capsule wall, and the intensity of the irradiating UVA light.

Poly(maleic acid monoester)-based β-mercapto ketones were synthesized and investigated as potential delivery systems for the controlled release of bioactive, volatile, α,β-unsaturated enones (such as damascones and damascenones) by retro 1,4-addition. The bioconjugates were prepared in a one-pot synthesis using 2-mercaptoethanol as a linker. The thiol group of 2-mercaptoethanol adds to the double bond of the enone to form a β-mercapto ketone, which was then grafted via nucleophilic ring-opening of the remaining alcohol function onto a series of alternating copolymers of maleic anhydride and 1-octadecene, ethylene, isobutylene, and methyl vinyl ether. The influence of copolymer backbones on the release of δ-damascone was investigated in buffered aqueous solution as a function of pH and time. In the presence of a cationic surfactant, the polymer conjugates were transferred from an aqueous medium to a cotton surface. The deposition and the release of δ-damascone from the cotton surface as a function of the polymer backbone structure were measured by fluorescence spectroscopy and dynamic headspace analysis, respectively. All polymer conjugates were found to deliver higher amounts of the volatile into the headspace than the reference consisting of unmodified δ-damascone. Polymers with a hydrophobic backbone were generally efficiently deposited on the cotton surface, but released δ-damascone only moderately in solution. Conjugates with a more hydrophilic backbone release the active compound more efficiently in water, but are deposited to a lower extent onto the target surface. A good balance of the hydrophobicity and hydrophilicity of the polymer backbone is the key factor to maximize the deposition of the conjugates on the target surface and to optimize the release of the bioactive volatiles.

Natural daylight is suitable for controlling the release of volatile compounds, such as fragrances, from different surfaces. Upon UVA irradiation, 2-oxoacetates (α-ketoesters) fragment in a Norrish type II reaction to form aldehydes and ketones. To profit from the stabilising effect of polymers in an aqueous environment, we extended our previous work on 2-oxoacetate profragrances to two alternative polymeric delivery systems. We thus compared the light-induced release of fragrance aldehydes from 2-oxo-2-phenylacetates encapsulated into melamine-formaldehyde core-shell microcapsules, on the one hand, with latex nanoparticle dispersions obtained by radical (co-)polymerisation of fragrance-releasing 2-oxo-2-(4-vinylphenyl)acetate monomers, on the other hand. We could demonstrate that microcapsules prepared with a minimum amount of resin in their shell performed best, while the size of the latex nanoparticles influenced the deposition of the delivery systems from aqueous media onto the target surface. Furthermore, dynamic headspace analysis above cotton showed that both systems are alternative and reliable techniques to control the light-induced delivery of fragrances in practical applications under natural daylight conditions.

The release of volatile bioactive molecules, such as fragrances, can be controlled by microencapsulation in core-shell polymeric delivery systems. Currently, most of the available polymers are based on melamineformaldehyde materials, and the release is generally triggered by the rupture of the brittle and stiff shell.However, formaldehyde-based chemistry may often be undesirable in applications for consumer goods such as personal care products or detergents for fabrics, and there is a strong need for formaldehydefree microcapsules in these applications. In this article, formaldehyde is successfully substituted by glyoxal and its derivatives to allow the polymerization of melamine and other amines to prepare oligomers as starting point for core/shell polymerization. The oligomer synthesis is optimized via the reactant composition and towards an enhanced potential cross-linking density. The formulations with the most branched oligomers are applied at the interface of oil-in-water emulsions to prepare microcapsules. Their capacity to retain volatile molecules is measured by thermogravimetry and their mechanical properties are measured by micromechanical testing using compression-retraction cycles on multiple individual microcapsules. The results reveal an excellent retention capacity for volatile molecules and tunable mechanical properties that make these capsules highly suitable as a formaldehyde-free alternative to conventional aminoplast microcapsules.