Functional Nanostructured Materials: Synthetic Aspects and Properties Evaluation

In this dissertation, the synthesis of functional nanostructured materials including stimuli responsive nanomat composites, nanoparticles and biodegradable polyester nanofibers are presented. Further the novel properties such as controlled water absorption/desorption, fast thermo responsive properties and potential applications in biomedical and microelectronic fields were investigated. In chapter 4.1, photoresponsive superabsorbent nanomat composites were prepared by combination of hydrophilic polyurethane nanofibers with crosslinked photoresponsive superabsorbent particles, the properties of nanocomposites were highly dependent upon the amount of the superabsorbent photochromic particles added. The composite nanomats had a high water absorption capacity of 40 g/g and reached to the maximum absorption in two minutes which was faster than the conventional superabsorbers. The elastic polyurethane served as a substrate to capture most of the particles and provided good mechanical properties for the nanocomposties. Such nanocomposites could be of utility for drug release and sensor applications. Also stimulus responsive antibacterial cationic segmented block copolyurethane nanoparticles with upper critical solution temperature (UCST) behavior was synthesized in chapter 4.2 by polyaddition of 2,4-toluene diisocyanate, diethanol-N-methylamine and polyethylene glycol (PEG) in two steps. Stable dispersions were prepared by facile heating up to 90 °C and cooled down to room temperature. The introduction of PEG segments was found to favor the formation of stable dispersion and keep the antibacterial activity, the particle size and UCST could be adjusted by the PEG contents and concentration of the dispersions. Such novel antibacterial dispersion had a big potential to be used for drug encapsulation and controlled release for various therapeutic application. Followed the previous research on functional stimuli responsive nanostructured materials, biodegradability functionality was introduced and investigated in the following two chapters. Chapter 4.3 describes a fast degrading odd-odd aliphatic polyester synthesis and degradation behavior with and without enzyme. Due to the odd-odd structure of the main chain, the polyester-5,7 had a relative low crystallinity and possessed a faster degradation rate compared to commercial poly(ε-caprolactone) (PCL). The degradation was started in the amorphous region and on the surface with change in surface morphology which was confirmed by SEM and optical polarized microscopy. It would be an addition to the class of biodegradable aliphatic polyesters having its own profile for different biomedical applications. Based on this study, poly(hexamethylene adipate)-PEO (PHA-b-PEO) block copolymers were synthesized and processed to aqueous suspensions with high solid contents. This suspension was mixed with a small amount of high molecular weight PEO and electrospun into corresponding nanofibers. The stable nanofibers of PHA-b-PEO were obtained after extraction by water. Such concepts of utilizing electrospinning of biopolymers from aqueous suspensions avoiding harmful organic solvents are suggested to be “green electrospinning” and offer novel perspectives for application in actual medicine, pharmacy and agriculture. In the last part of this dissertation, utilizing the characteristics of electrospun nanofibers (e.g. high surface to volume ratio and rough surface structures), fluorinated polyimides were processed into nanomats by electrospinning techniques. The corresponding nanofibers have a low dielectric constant, high thermo-oxidative stability and hydrophobicity which could be of high use as insulating material in interlayer dielectrics besides their use in filter and composite industry.