Primary amine functionalized microgels
- Mikrogele mit primärer Amin-Funktionalisierung
Meurer, Richard Achim; Pich, Andrij (Thesis advisor); Schwaneberg, Ulrich (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2019
The present work focuses on the synthesis, characterization and application of aqueous microgels functionalized with a high content of primary amine functions. Primary amine functionalized microgels are particularly interesting due to the tremendous amount of possible post-modification reactions. The first part of the thesis shows the synthesis of poly(N-vinylcaprolactam) based microgels containing three different 2-aminoethyl methacrylate derivates as primary amine co-monomers by precipitation polymerization. Colloidally stable temperature and pH double-responsive microgels are obtained, with good control over spatial distribution of the primary amine functions, hydrodynamic radius, and size distribution. The accessibility of the primary amine functions is demonstrated by post-modification with a fluorescent dye.The second part of this work shows the synthesis of aqueous poly(allylamine) microgels by precipitation polymerization. Inorganic acid salts of allylamine are polymerized with crosslinkers of different reactivity at high solid content. Colloidally stable pH-responsive microgels with tunable hydrodynamic radius and crosslink density are obtained. Furthermore, a similar network- forming reaction is carried out in inverse-miniemulsion to obtain higher microgel yield due to compartmentalization resulting in pH responsive microgels with extremely high swelling degrees. The inverse-miniemulsion method is further used to obtain microgels by utilizing the base-catalyzed crosslinking of preformed poly(allylamine hydrochloride) with crosslinkers of different reactivity as network-forming reaction. Microgels with tunable hydrodynamic radius, size distribution and crosslink density are successfully synthesized. Particularly, the microgel synthesis can be performed at room temperature with very short reaction times in quantitative yield due to the independence of the polymerization rates of the compounds. Again, the accessibility of the primary amine functions is demonstrated by post-modification with a fluorescent dye. In the last part of this thesis, a possible application of the synthesized microgels as foliar delivery system of micronutrients for plants is presented and the versatile post-modification ability of the microgels is demonstrated. For this, the microgels from the second part are modified in two different ways: 1) the interior is functionalized with a strong chelating agent for selective loading of a model micronutrient and 2) the surface of the microgels is decorated with tailor-made anchor peptides for improved adhesion to the leaf surface of a model plant. Controllable loading degree of the micronutrient and strong binding to the leaf cuticle is achieved. Finally, the proof-of-concept is fulfilled by ’re-greening’ of micronutrient deficient model plants indicating the bioavailability of the micronutrient originating from the developed microgels. The microgels are bio-compatible and non-phytotoxic, the fertilizer system involves no auxiliaries and is loadable, storable, and applicable from aqueous dispersion.