Preparation, Properties And Applications Of Stimuli-responsive Polymeric Materials

Stimuli-responsive polymers are a class of polymer materials that can perceive and respond small physical or chemical changes of the external environments. These external environmental changes mainly include temperature, solvent, pH. magnetic and electric fields, ionic strength and light, etc. They would cause changes in the intermolecular interactions and various energies, and changes of polymer chain structures at a molecular level, or the interactions of polymer molecular chains and between polymers and solvents. Stimuli-responsive polymers can be divided into temperature-sensitive, gas-sensitive and pH-responsive polymer materials etc, according to the environmental factors. They have been widely applied in drug controlled release, environmental protection and biological engineering in recent years. Especially, they have been attracted much attention in both the drug release and organic gas detection, becoming one of the hottest research topics. This thesis has carried out a significative exploration in organic gas sensitive composite materials and temperature sensitive block copolymers. The main research contents and results obtained are as follows.1. Synthesis, characterization and self-assembly of thermosensitive PNIPAM-b-epoHTPB-b-PNIPAM block copolymersThermoresponsive poly(N-isopropyl acrylamide)-block-hydroxy-terminated polybutadine-block-PNIPAM triblock copolymers were synthesized by atom transfer radical polymerization; this was followed by the in situ epoxidation reaction of peracetic acid. The copolymers were characterized by 1H-NMR, Fourier transform infrared spectroscopy, and size exclusion chromatography measurements, and their physicochemical properties in aqueous solution were investigated by surface tension measurement, fluorescent spectrometry, ultraviolet-visible transmittance, transmission electron microscopy observations, dynamic light scattering, and so on. The experimental results indicated that the epoxidized copolymer micelle aggregates retained a spherical core-shell micelle structure similar to the control sample. However, they possessed a decreased critical aggregate concentration(CAC), increased hydrodynamic diameters, and a high aggregation number and cloud point because of the incorporation of epoxy groups and so on.2. Biomedical applications of thermosensitive block copolymer micellesThermosensitive PNIPAM-b-epoHTPB-b-PNIPAM block copolymer micelles were used toload anticancer drug,10-hydroxycamptothecin (HCPT), and deliver HCPT from the prepared micelle-based drug formulations. The experimental results indicated that the epoxidized copolymer micelles assumed an improved loading capacity and entrapment efficiency of the drug, a preferable drug-release profiles without an initial burst release, and a low cytotoxicity. Therefore, they were more suitable for the loading and delivery of the hydrophobic drug as a controlled release drug carrier.3. Preparation and characterization of organic gas sensitive PVK-g-MWCNTs conductive polymer nanocompositesNovel multiwalled carbon nanotubes grafted with poly(N-vinylcarbazole) electroconductive polymer nanocomposites(PVK-g-MWCNTs) were prepared via a nucleophilic reaction using PVK as electron donors and MWCNTs as electron acceptors in the presence of sodium hydride. The covalent interaction between PVK and MWCNTs and the dispersion properties of the prepared compositeswere evaluated through different characterization techniques like Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet visible spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The studies showed that the nucleophilic grafting could significantly promote dispersion properties of MWCNTs, and PVK could be well enwrapped on the surface of MWCNTs.4. Assembly of gas sensitive PVK-g-MWCNTs conductive polymer nanocomposites and their applications in gas sensingThe PVK-g-MWCNTs conducting polymer nanocomposites were fabricated into thin films to detect the response toward various organic solvent vapors, especially THF vapor. The response dependence on the contents of carboxyl groups and organic gas concentrations was investigated for the conducting composite thin films. The experimental results indicated that the electroconductive nanocomposite film sensors exhibited good response and reproducibility toward THF vapor. Particularly, the chemically grafted PVK-g-MWCNTs sensor has the advantage of fast response and preferable recoverability over the physically mixed one. The sensing properties hinged upon the carboxyl contents and solvent vapor concentrations. The conductive nanocomposite sensors have a satisfactory linear relationship and a relatively low detection limit up to 50 ppm, which ensured that the covalently linked PVK-g-MWCNTs nanocomposites could be used to fabricate gas sensors for monitoring the environmental gaseous pollutants.