| dc.description.abstracteng | Well-defined, end-functional polyethylene (PE) was synthesized in a catalyzed chain growth (CCG) polymerization and applied in novel synthetic routes for PE modified surfaces as well as in the manufacturing of multifunctional charged PE.
Polyethylene was covalently attached to the surface of prefunctionalized wood particles via different coupling reactions. Amine and azide end-functional polyethylene was grafted onto the surface via an amide-coupling or [3+2]-cycloaddition, respectively. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy of treated wood particles confirmed their successful modification. Differential scanning calorimetry (DSC) revealed the formation of a crystalline polyethylene layer with a decreased melting temperature range compared to non-bound PE. The decomposition temperature of PE modified wood shows combined characteristics of both components examined by thermogravimetric analysis TGA. Caused by the permanent attachment of polyethylene, a strong enhancement of the surface’s hydrophobicity was achieved and validated by water contact angle (WCA) measurements and dynamic vapor sorption (DVS) analysis. Based on the developed strategies, surface modifications of silica nanoparticles were performed. TGA and dynamic light scattering (DLS) analysis confirmed the successful modification, further underlining the versatility of the designed system.
A novel route for the fabrication of polyethylene grafted gold- and silver nanoparticles (AuNPs and AgNPs) was developed by an efficient ligand exchange procedure using trithiocarbonate and thiol end-functional PE. DLS analysis revealed a strong increase in the hydrodynamic diameter of the nanoparticles caused by the strongly attached polyethylene-shell. The stability of the grafted nanoparticles over a wide temperature and time range was confirmed by DLS and UV-vis analysis. A perfect separation of the formed polyethylene-nanoparticle hybrids was observed and vali-
dated by transmission electron microscopy (TEM). Furthermore, these hybrid materials were well dispersible into a PE matrix even at high particle contents. Polyethylene capped AuNPs and AgNPs exhibited a reversible temperature-dependent aggregation/disaggregation behaviour, entirely attributed to the critical solution temperature of the attached polyethylene layer. The complete reversibility and the corresponding critical disaggregation temperature were confirmed by UV-vis analysis, demonstrating polyethylene’s potential as thermoresponsive polymer. The investigated approach was subsequently transferred to palladium nanocrystals to further expand the field of polyethylene-noble metal nanohybrids.
The synthesis of charged end-functional polyethylene was performed based on iodo terminated PE in combination with an efficient nucleophilic substitution using various amines. The introduction of a permanent cationic end-group enables matrix-assisted laser desorption/ionization (MALDI) and electrospray ionisation (ESI) mass spectrometry of the investigated compounds, extending the field of PE end-group characterization via mass spectrometry. Mass spectra with excellent signal-to-noise ratios were obtained without the addition of any auxiliary metal salt. Caused by the introduction of an additional hydroxyl group, further transformation reactions on charged polyethylene were conducted. For this purpose, an alkyl-bromide moiety was introduced, resulting in a PE-based charged macroinitiator which was applied in a controlled radical polymerization, leading to the formation of a block copolymer. Moreover, the developed charged end-functional PE was applied in phase transfer catalysis. The results obtained by NMR spectroscopy revealed similar or superior activities compared to well-established phase transfer catalysts. In addition, the PE-based catalyst was completely recovered by simple filtration due to the solution properties of PE. Based on the phase transfer properties, an anionic dye could be introduced efficiently into cationic polyethylene. Caused by strong ion-ion interactions, the designed material showed an excellent solvent resistance without observing any migration of the incorporated compound. | de |