Study On The Environment Stimuli-responsive Polymers Based Poly

Stimuli-responsive polymers are able to undergo relatively large and abrupt, physical or chemical changes in response to small external changes in the environmental conditions. They are of fundamental importance in many scientific areas and have been proposed for use in a variety of applications such as in drug delivery, biotechnology, sensors, catalyst supports, and dispersants. In the early studies, single stimuli-responsive polymers had attracted considerable attention due to the theory of theirs aqueous solution behavior. However, there are many different stimulis in the practical applications, and the interest in the multi stimuli-responsive polymers has grown greatly. The stimuli-responsive polymers containing poly(ethylene oxide) (PEO) segments have been focused on due to its hydrophilicity, solubility in organic solvents and biocompatibility. Up to now, most polymers containing PEO were synthesized by using PEO macroinitiators or vinyl end-capped PEO macromolecules. These reactive processes are usually multistep, and catalysts or initiators are necessary to these reactions. So it is very important to develop new synthesis ways of stimuli-responsive polymer. In this thesis a novel way was been developed. A new multi-responsive polymer, poly(ether ter-amine) (PEA) were synthesized by nucleophilic addition/ring-opening reaction. These polymers exhibit sharp response to temperature,pH and ionic strength. Some potential applications were also investigated.Multi-stimuli responsive copolymers were prepared by free-radical copolymerization of methacrylamide end-capped PEO macromonomer (PEO-MA) and 4-vinylpyridine (4-VP). The copolymer displayed sharp response to temperature and pH. The more PEO was induced into the macromolecule, the higher lower critical solution temperature (CP) of copolymer was observed. And the CP decreased with increasing pH dure to the deprotonation of the pyridine ring. In addition, the CP of P4VP-g-PEO9 presented a unique phase transition behavior with varying salt concentration, showing a minimum with 1 M NaCl solution at pH 6.0,but itsΔT showed a maximum. 1H NMR spectra data showed that the hydrophobic segment of P4VP formed the core and the hydrophilic PEO side chain composed the corona. The TEM images showed that P4VP-g-PEO formed micelles with a diameter of 35-45 nm at pH 5.0 and room temperature. At high temperature, the copolymer formed mesoglobules with a diameter of 300-500 nm.Three series of PEA, multi-block poly(ether ter-amine) (PEA), grafted poly(ether ter-amine) (gPEA) and amphiphilic poly(ether ter-amine) (agPEA) were successfully synthesized by nucleophilic addition / ring-opening reaction. These poly(ether ter-amine)s exhibit very sharp response to temperature, pH and ionic strength with tunable cloud point (CP). They displayed rapid phase transition withΔT < 3 oC,and gPEA and agPEA have smallerΔTs than PEA. Their CPs increased with increasing the PEO content or decreasing pH, and they presented largeΔTs under low pH and PEO content. The critical micelles concentration (CMC) of these poly(ether ter-amine) was determined by using prene as a fluorescent probe. The CMCs were less than 31.2×10-6 mol/L, and increased with increasing PEO content. The results obtained from TEM and DLS revealed that poly(ether ter-amine)s were dispersed as uniform sized nano-micelles in aqueous at room temperature, which can further aggregate into mesoglobules of complex structure at high temperature (> CP). 1H NMR spectra data showed that the tertiary amino groups undergo different changes at different conditions. At lower pH, the tertiary amino groups were protonized and caused the split of the peaks of its neighboring protons. At higher pH, the tertiary amino groups were deprotonized and do similar inductive effect to its neighboring protons, so these protons peaks associated together and showed a single peak. Increasing temperature, two peaks replaced the single peak, which indicated that the tertiary amino groups exited in two different environments of hydrophilic and hydrophobic phase. In the presence of these obtained agPEAs, hydrophobic dye Nile red can be dispersed into aqueous solution and polar dye methyl orange can be dispersed into non-polar toluene. The agPEAs are expected to be potential in application such as encapsulation and controlled release of drugs, due to their simple synthesis, amphiphility and multi-stimuli response.We further investigated a pyrene-labeled poly(ether ter-amine) (pePEA), which was synthesized by nucleophilic addition / ring-opening reaction of 2-methylamine pyrene and Jeffamine L100 with poly(ethylene glycol) diglycidyl ether. It CP decreased with increasing pH. pePEA formed uniform sized nano-micelles in aqueous at room temperature, which can further aggregated into mesoglobules at high temperature (>CP). The fluoscence intensity of pePEA532 decreased with increasing pH. The ratio of excimer emission intensity to monomer emission intensity (IE/IM) increased at pH 6.0~8.0. IE/IM of pePEA showed a maximum with increasing temperature which can be used to confirm the phase transition temperature. TEM images at pH 7.0 showed that pePEA formed nano-micelles at low temperature and mesoglobules at high temperature. At pH 6.0, pePEA532 formed 200-750 nm micelles, and these micelles were linked by copolymer fiber. 1H NMR spectra data showed that the hydrophobicity of PO units of the macromolecule increased with increasing temperature. These PO units gathered together and formed core of self-assemblies which were wraped by the hydrophilic corona of L100. MWNT was noncovalent functionalized by pePEA211 and the functionalized MWNT can be dispersed well in water. TEM image revealed that pePEA had wrapped the MWNT. TGA data indicated that the complex contained 20.4 wt% pePEA.