Preparation And Characterization Of Several Block Copolymer Nanocomposites

The designed amphiphilic block copolymers,Polyacrylonitrile-block-poly(ethylene glycol)-block-Polyacrylonitrile and poly(styrene-block-acrylic acid),were synthesized by atom transfer radical polymerization as described in this paper.After that,several kinds of organic/inorganic composites were fabricated by using the block copolymer acting as the template. In addition,loading of CdSe nanoparticles on MWNTs' surfaces was carried out using the copolymer as linker molecules.The morphologies,crystal structures and optical properties were investigated and the factors-features relations were discussed.The research work could be divided into four parts as the following:It is well known that -CN acts as a stronger coordination group and can be used to immobilize metal ion due to the chelation effect.The amphiphilic block copolymer containing polyacrylonitrile chains in selective solvents for one of the block copolymers generally yield colloidal aggregates of various morphologies by self-assembly.In this study,the block copolymer PAN-b-PEG-b-PAN with -CN group were synthesized by ATRP method.ZnSe nanoparticles were prepared in-situ by using the PEA assembly of micelles in DMF/H₂O solvents based on the flexibility of the copolymer chains and the complex effect of-CN in the polyacrylonitrile with Zn²⁺.It had been confirmed that the nanoparticles can be dispersible uniformly in the matrices,where aggregation and agglomeration phenomena are suppressed.The results of XRD and TEM analyses demonstrated that the products were spherical and homogeneous with cubic structure,which are about 60 nm in diameter.The corresponding UV-vis absorption peaks showed a blue shift compared to bulk ZnSe.In this part,surface functionalization of multi-walled carbon nanotubes(MWNTs) with block copolymer PEI-b-PAN by combining electrostatic adsorption and atom transfer radical polymerization was achieved.That is functionalization of MWNT surface with polymer and for attachment of CdSe nanocrystals to the modified MWNTs uniformly.The presence of copolymer plays an important part in the formation of CNT/CdSe nanocomposites.The roles of the concentrations of polymers,metal cations in the formation of products and the size of nanoparticles were also investigated.The block copolymer PS-b-PAA was synthesized by ATRP technology in this part and the self-assembly of the diblock copolymer in H₂O solutions generally results in micelles of a core-shell structure with PS as the core and PAA as the shell,in which the carboxyl groups provide a certain number of negative charge sites for Polyelectrolyte.In this study,Ag nanoparticles were prepared by in-situ reduction after surface modification of PS-b-PAA with PEI-Ag⁺ by electrostatic assembly. The size of prepared silver nanoparticles could be controllable by the change of AgNO₃ concentration,a possible mechanism,which is the model of recognition-reduction-limited nucleation and growth,was also proposed to account for the formation of Ag nanoparticles.The synthesis of PS-CTA(chain transfer agent) has been achieved successfully by RAFT method in DMF solvent at 60℃,using prepared dibenzyl trithiocarbonate(DBTTC) as chain transfer agent (CTA),AIBN as initiator.Then the block copolymer PS-b-P4VP-b-PS was synthesized using as macro-CTA the obtained homopolymers PS.The block copolymer structure was confirmed by FF-IR and ¹H NMR.