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PN-II-RU-TE-2014-4-0654 |
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Unprecedented polyesters as coating for solid surfaces with application in medicine and nanotechnology |
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Results for Objective 2 |
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O2. Synthesis of PAHCA I by ring opening polymerization (ROP) in the presence of magnetic nanoparticles or solid materials and characterization of the materials
In objective 2 of the project, the main activities were focused on the preparation of new polymers, magnetic nanoparticles and the preparation of materials based on new polymers. A significant discovery within this objective was obtained using 4-hydroxymandelic acid as a monomer for a presumed lactide synthesis. This approach led us to a new type of polymer with interesting properties. 4-Hydroxymandelic acid as a typical α-hydroxy acid was polymerized by thermal treatment. Instead of the commonly observed polyester formation (e. g. in case of lactic acid or mandelic acid), C-C bond connection between the phenolic units of 4-hydroxymandelic acid by Friedel-Crafts alkylation occurred giving rise to polymers containing carboxylic and phenolic moieties. In addition, lactone formation took place giving rise to benzofuranone units. Thus the final polymer is poly(benzofuran-co-arylacetic acid) (PHMA), a novel type of organic polymers. Detailed analysis of this PHMA by spectroscopic methods revealed oligomer formation up to about 15-mers. In most cases, the oligomers occur with several extents of lactonization. The three reactive units (acid, phenol, lactone) of PHMA provide orthogonal reactivity, i. e. they can be addressed independently in linking applicatory entities to the polymer. We could demonstrate the functionality of each reactive groups selectively and obtain many types of new polymers with more than one applicatory function in this way. The preparation of materials using either the ring opening polymerization of lactides (3,6-dioxo-1,4-dioxane-2-carboxylic acid, diallyl 3,3'-(3,6-dioxo-1,4-dioxane-2,5-diyl)dipropanoate) initiated on the surface of magnetic nanoparticles resulted in an nanostructure which was further on functionalized. Another important achievement in this objective was the synthesis of poly(tartronic-co-glycolic acid) [poly(TA-co-GA)], which was obtained by straightforward thermal treatment of tartronic acid under controlled conditions as a novel type of polyester. It is worth mentioning that the poly(TA-co-GA) is formed just from one precursor while copolymers such as the well-known poly(lactic-co-glycolic acid) usually are synthesized from a mixture of the single components. This fact is attributed to partial decarboxylation of the tartronic acid. The copolymer ratio can be affected to a certain extent by variation of the heating time. Following the same procedure for the tartaric acid, we obtained in a non-catalytic, solvent free synthesis polytartaric acid. In this case, it turned out that the decarboxylation reaction is only a minor reaction as compared with tartronic acid. Magnetic nanoparticles with tailored properties have found various important applications in nanomedicine, electronics, separation technology, catalysis, etc. By stabilization of the magnetic nanoparticles with different stabilizers we found interesting results connected to the type of stabilizer. Furthermore, hitherto unknown changes of the average crystallite sizes with changing exposure times were observed, giving evidence for a new mechanism of coating of magnetic nanoparticles with stabilizers. Instead of the hitherto accepted simple anchoring of the stabilizers to the magnetite nanoparticle surfaces, a more complex recrystallization mechanism is likely to occur including re-dispersing magnetite moieties from the nanoparticles and re-deposition. The results lead to important insights in the mode of interaction of stabilizers with magnetite nanoparticles and provide important information to the manufacturing and application of magnetic nanoparticles in different areas. A significantly increased saturation magnetization was obtained in particular with hydroxyl acids such as glycolic acid, malic acid, or mandelic acid. Based on the new polymers synthesized in this project and solid supports (magnetic nanoparticles) we obtained interesting materials which can be easily functionalized and tailored for specific applications. All the nanostructures and polymers prepared where careful investigated in terms of structure, morphology and physical properties.
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