Silver Nanocomposites Based On Block Copolymers And Pectinase Immobilized

The self-assembling of block copolymer takes on extensive potential in the application of optics, electronics,information,chemistry and biology.In selective solvents,polymeric micelles are formed via the association of amphiphilic block copolymers into nanoscopic core/shell structures at or above the critical micelle concentration,the drugs entrapped in the inner core of the micelles by physical entrapment,static or chemical conjugation.Temperature and pH sensitive block copolymers are some macromolecules connected by temperature or pH sensitive monomers with some biological materials according to a certain sequence,or polymerized themselve.On the basis of pertinent documents,the development of pH and temperature sensitive biodegradable block copolymers was introduced,involving their mechanism of action and potential application.The thermo-sensitive amphiphilic block copolymers have drawn much attention due to their potential applications.In the field of drug controlled-delivering system,the polymeric micelles based on such block copolymers show several preferable unique characteristics when used as drug carriers.Polymeric micelles comprising block copolymers would achieve target sides by passive targeting mechanism.If thermo-responsive segment was introduced into block copolymer,active targeting mechanism would be achieved,the molecular design,synthesis and self-assemble behavior of the block copolymer is an important task in this field.In this paper,the diblock copolymer poly(styrene-b-N-isopropylacrylamide)(PS-b-PNIPAM) was synthesized by atom transfer radical polymerization(ATRP) and triblock copolymer PS-b-PMIPAM-b-PS was synthesized by reversible addition fragmentation chain transfer(RAFT) methods.The support materials designed for the purpose were elaborated by the self-assembly technique,preparation of new kind nanoparticles and immobilization enzyme through combining nanotechnology.The relative experiments and results are summarized as follow:1.Atom transfer radical polymerization of styrene was studied using ethyl 2-bromopropionate as functional initiator.The resulted polystyrene with a bromo-terminal in macromonomer chain PS-Br(PS polystyrene) as expected.A novel amphiphilic block PS-b-PNIPAM macromonomer was synthesized by using the obtained PS-Br as macromolecule initiator,which initiated ATRP of N-isopropylacrylamide(NIPAAM).The structure of synthesized PS-b-PNIPAM was characterized by means of FTIR and ~1H NMR.2.Unprotected Ag nanoparticles are susceptible to irreversible aggregation in solution due to their small size and shape.Therefore,organic-inorganic composites were prepared with Ag nanoparticles embedded within colloidal particles of an amphiphilic,thermally responsive polymer. To promote the incorporation of unaggregated Ag nanoparticles,temperature responsive microspheres of poly(N-isopropylacrylamide) block with polystyrene were synthesized. Polyethyleneimine(PEI) could act as the linker between Ag ions(Ag nanoparticles) and PS-b-PNIPAM colloids and the reducing agent in the formation of Ag nanoparticles.The product was characterized by X-ray diffraction(XRD) and transmission electron microscope(TEM).The silver crystal was monocrystalline with a face-centered cubic structure,as confirmed by XRD and Electron diffraction.The results revealed that the size and size distribution of the resulting silver nanoparticles prepared based on the copolymer were strongly dependent on the ratio of initial concentration of the copolymer solution to silver ion.This work provides a simple route for the in situ synthesis of Ag nanoparticles on block copolymer colloids.3.Well-defined amphiphilic block copolymers PS-b-PNIPAM with controlled block length were synthesized using ATRP method.Pectinase enzyme was immobilized on the well-defined amphiphilic block copolymers PS-b-PNIPAM.The amidocyanogen on the amphiphilic PS-b-PNIPAM diblock copolymers present a very simple,mild,and time-saving process for enzyme immobilization.Various characteristics of immobilization pectinase such as the pH,thermal stability and storage stability were valuated.Among them the pH optimum and temperature optimum of immobilization enzyme were found to be pH 4.64 and 60℃.One important feature is that the composite microspheres can be separated from the hydrolyzed products by temperature-change and used recyclably as PNIPAM was used as a temperature-sensitive spacer between an enzyme molecular and a particle.4.The synthesis of PS-CTA(chain transfer agent) has been achieved successfully by RAFT method at 110℃,using prepared dibenzyl trithiocarbonate(DBTTC) as chain transfer agent(CTA), AIBN as initiator.Then the block copolymer PS-b-PNIPAM-b-PS was synthesized using as macro-CTA the obtained homopolymers PS.The block copolymer structure was confirmed by FT-IR and ~1H NMR.