Micellization Of Amphiphilic Fluorosilicone-containing Block Copolymers And Their Applications In Producing Gold Nanoparticles

The micelles of amphiphilic block copolymers can exhibit thermodynamic andKinetic stability and therefore have been used as nanoreactors for the syntheses ofinorganic nanoparticles. However, the morphology of self-assembled copolymeraggregates is governed primarily by core-chain stretching, interfacial energy, andintercoronal chain interactions. That is, the composition of amphiphilic blockcopolymers will have important effect on the morphology of aggregates as well as thelaw of micellization.As we know, amphiphilic siloxane copolymers have low surface tensions (20–30mN/m) and can be self-assembled and form micelles in water or solvent. If somefluorinated groups incorporated into amphiphilic siloxane copolymers, thesegment-segment interaction would be changed, which would influence themicrostructure of aggregates and the micellization behaviour. In this work, thesynthesis and micellization of novel amphiphilic block copolymers of fluorosiliconeand poly[(meth)acrylic acid] were demonstrated, and then, their applications inproducing gold nanoparticles (AuNPs) were also presented. The main results wereshown as follows:1. A series of well-defined poly[methyl(3,3,3-trifluoropropyl)siloxane]-b-poly[(meth)acrylic acid](PMTFPS-b-P(M)AA) block copolymers were synthesizedin this work.(a) A series of well-designed poly[methyl(3,3,3-trifluoropropyl)siloxane]-b-poly(tert-butyl (meth)acrylate)(PMTFPS-b-PtB(M)A) diblock copolymers weresynthesized by a combination of anionic ring-opening polymerization (ROP) of1,3,5-trimethyl-1,3,5-tris(3′,3′,3′-trifuoropropyl)cyclotrisiloxane (F3), and atomtransfer radical polymerization (ATRP) of tert-butyl (meth)acrylate (tB(M)A). (b) The tert-butyl ester groups on PMTFPS-b-PtB(M)A diblock copolymers weresuccessfully hydrolyzed in dry dichloromethane using NaI/(TMS)Cl Method.PMTFPS-b-P(M)AA diblock copolymers were obtained and the tert-butyl estergroup in block copolymers was found to be as high as84.6%hydrolysed. Thetert-butyl ester group was not fully hydrolysed in order to protect the ester group inthe backbone of block copolymers.2. The micellization of novel amphiphilic PMTFPS-b-P(M)AA block copolymerswere carried out and some self-assembled morphologies of spheres, pear-necklaceaggregates or vesicles were obtained.(a) The critical micelle concentration (CMC) of PMTFPS-b-PAA was measured byfluorescence spectroscopy using pyrene as a fluorescence probe. The results showedthat the estimated CMC value of PMTFPS21-b-PAA11block copolymers is ca.0.05wt%.(b) The micellization behavior of PMTFPS-b-PAA block copolymers inacetone/water would be significantly influenced by the copolymer composition,polymer concentration, water content in solution or the time of water addition.Spheres or pear-necklace aggregates could be obtained by carefully controlling themicellization condition of self-assembly system.(c) For the self-assembly of PMTFPS-b-PMAA block copolymers in acetone/water,spheres or pear-necklace aggregates could also be obtained by controlling the polymerconcentration, water content or other conditions. However, vesicles or compoundvesicles were formed when the mixture of dioxane/water was used as the co-solventof micellization.3. An approach for rapidly producing and stabilizing small-size AuNPs in themicelles of PMTFPS-b-P(M)AA block copolymers in the presence of PEOhomopolymers was provided.(a) AuNPs could be produced and stabilized by using the micelles ofPMTFPS-b-PAA block copolymers as “micro/nano-reactors” and using PEO homo-polymers as reducing and stabilizing additives. The AuNPs have the particle diameters in about2–6nm and the colloidal solution have good stability.(b) The results showed that HAuCl4could be rapidly converted into AuNPs in themicelles of PMTFPS-b-PAA block copolymers in the presence of PEO. However,only part of gold salts was reduced to Au by PEO homopolymers in the solution ofacetone/water. That is, PMTFPS-b-PAA block copolymer micelles could provideappropriate micro-environment for the rapid reduction of gold salts when using PEOas the reductant.(c) Fluorescent AuNPs in the block copolymer micelles were presented by a directmonitoring of the micelle shape and the solution optical properties, using the methodsof steady-state fluorescence studies and confocal laser scanning microscopy (CLSM).(d) Furthermore, AuNPs synthesized by the chemical reduction of gold salts usingsodium citrate were also successfully encapsuled and stabilized in the micelles ofPMTFPS-b-PMAA block copolymers.