Synthesis And Micellization Of Temperature-responsive Polymers

With the development of polymer and material sciences,new requirements for basic synthetic technologies,such as controllabilty,high efficiency,high selectivity etc are presented.According to these requirements,those newly developed techniques,such as controlled free radical polymerization and "click chemistry", have been poured great passion by the scientists.They provided the scientists with powerful methods to synthesize various special-structured polymers as well as various organic & inorganic materials.Smartly application of these techniques in polymer synthesis and material modification is one of the most important topics in the field of chemistry.Based on the research of the precursors,this dissertation describes several interesting research in the synthesis and micellization of polymers, as well as the modification of carbon nanotubes.The main results obtained in this thesis are as follows:1.Hetero-arm star polymer PSt-PNIPAM-PDMAEMA was synthesized by "clicking" the alkyne group at the junction of PSt-b-PNIPAM diblock copolymer onto the azide end-group of PDMAEMA homopolymer via 1, 3-dipolar cycloaddition.PSt-PNIPAM-PDMAEMA micelles with PSt block as core and PNIPAM and PDMAEMA blocks as shell were formed when adding the copolymer solution in THF into ten folds of water.Lower critical solution temperature(LCST) of PNIPAM and PDMAEMA homopolymer is 32℃for PNIPAM and 40-50℃for PDMAEMA,respectively.Upon continuous heating through their LCSTs,PSt-PNIPAM-PDMAEMA core-shell micelles exhibited two-stage thermally induced collapse.2.Hetero-arm star polymer PEG-PNIPAM-PLys was synthesized by "clicking" the azide group at the junction of PEG-b-PNIPAM diblock copolymer with the alkyne end-group of poly(L-lysine)(PLys) homopolymer via 1,3-dipolar cyeloaddition.Polyelectrolyte complex(PEC) micelles with the ion-bonded PLys/PAA chains as core and the PEG and PNIPAM chains as shell were formed by mixing the synthesized polymer with poly(acrylic acid)(PAA) in water.Dynamic light scattering(DLS) was used to confirm the thermally induced collapse of the PEC micelles.3.Poly(styrene-b-N-isopropylaerylamide)(PSt-b-PNIPAM) with dithiobenzoate terminal group was synthesized by reversible addition-fragmentation-transfer polymerization.The dithiobenzoate terminal group was converted into thiol terminal group with NaBH₄,resulting thiol-terminated poly(styrene-b-N-isopropylacrylamide) (PSt-b-PNIPAM-SH).After PSt-b-PNIPAM-SH assembled into core-shell micelles in aqueous solution,gold nanoparticles were in-situ surface-linked onto the micelles through the reduction of gold precursor anions with NaBH₄.Changing the temperature of PSt-b-PNIPAM-Au micelles led to the shrinkage of PNIPAM shell and allowed to tune the distance between gold nanoparticles.Ultraviolet-visible(UV-vis) spectroscopy clearly showed the reversible modulation of UV-vis absorbance of PSt-b-PNIPAM-Au micelles upon heating and cooling.4.A surface-initiated ring-opening polymerization approach was used to functionalize multiwalled carbon nanotubes(MWNTs) with linear poly(L-lysine) (PLL).The successful grafting was confirmed by Fourier transform infrared spectroscopy,thermal gravimetric analysis,X-ray photoelectron spectroscopy, elemental analyses,high-resolution transmission electron microscopy and field-emission scanning electron microscopy.The as-prepared MWNT-g-PLL exhibited excellent ability to disperse homogeneously in water.5.PLL-g-PEG compolymer was synthesized by grafting PEG to the chain of PLL via Michael Addition Reaction.Highly sulfonate polystyrene(PSt(SO₃H)) was prepared by treating PSt obtained from anion polymerization with sulfuric acid. Polyelectrolyte complex(PEC) micelles were formed by mixing PLL-g-PEG with highly sulfonated polystyrene in a phosphate buffer solution.The influence of mixing molar ratio to the formation of PEC micelles was studied by Laser light scattering(LLS) and Transmission Electron Microscopy(TEM).