The Effect Of Inorganic Salts On Micellar Morphology Of Crystalline Block Copolymer And Preparation Of Silver Nanoparticles In The Presence Of Block Copolymer

This dissertation focuses on the morphology of poly(ethylene glycol) b-poly(ε-caprolactone)block copolymers micelle in water,effect of inorganic salt on the micellar morphology,and preparation of silver nanoparticles in the presence of block copolymer micelle.First we synthesized two series of poly(ethylene glycol)-b-poly (ε-caprolactone)block copolymers(PEG₄₄PCL_n and PEG₁₁₃PCL_n)with different molecular weights but narrow polydispersity with a salicylaldimine-aluminum complex in the presence of monomethoxy poly(ethylene glycol)and the block copolymers were characterized by ¹H NMR and GPC.Next,the morphology of the block copolymers micelle in aqueous solution was studied.The morphology of the block copolymer micelle in aqueous solution was strongly influenced by the composition of PEG-b-PCL. When W_PCLis low,only spherical micelles were found.With further increase in W_PCL,rod,wormlike and lamellae micelles were observed.The micellar morphology of the PEG-b-PCL block copolymers was correlated with the reduced tethering density.When the reduced tethering density was smaller than 3 the morphology of micelle was lamellae and when the reduced tethering density was larger than 8,the morphology of micelle was sphere.The effect of inorganic salt on the morphology of PEG-b-PCL micelle was also studied.The micelle solution with inorganic salt was prepared by two different methods:directly dialysis of the block copolymer's THF solution by sodium nitrite solution;addition of sodium nitrite or sodium chloride into the aqueous micelle solution.Since the length of PEG block in PEG₄₄PCL_n is shorter than that in PEG₁₁₃PCL_n,the morphology of PEG₄₄PCL_n micelle is more intensely influenced by the inorganic salt,and at a lower concentration of inorganic salt,the change of morphology can be observed.At the same concentration of sodium nitrite and sodium chloride,the morphology of PEG-b-PCL micelle is more intensely influenced by sodium nitrite.The morphology transformation of PEG-b-PCL micelle in inorganic salt solution can be explained in terms of the dehydration of the PEO chains in the micelle corona by inorganic salt.Finally,silver nanoparticles were prepared by reduction of silver nitrate with sodium borohydride or vitamin C at the presence of the micelle of PEG-b-PCL.The silver nanoparticles were characterizd by TEM and UV. When the W_PCLis moderate,the size of silver nanoparticles is uniform,and the morphology is spherical.The size of silver nanoparticles increases with when prepared by PEG₄₄PCL_n but decreases with when prepared by PEG₁₁₃PCL_n with sodium borohydride as reducing agent.Comparing the W_PCLin PEG₄₄PL_n and PEG₁₁₃PCL_n at the smallest size of silver nanoparticles,we speculated that when the W_PCLis 69%,the size of silver nanoparticles may be the smallest.In addition,silver ion can be eliminated by dialysis,and the size of silver nanoparticles becomes smaller and more uniformly when sodium nitrite is added.The size of silver nanoparticles was larger with vitamin C as reducing agent and became aggregated.Short rod silver nanomaterial was found in PEG₁₁₃PCL₆₁aqueous micelle solution,so the morphology of micelle and reduction speed may influence the morphology of silver nanoparticles.