The Synthesis And Self Assembly Of Amphiphilic Thermo-sensitive Block Copolymers

Thermosensitive amphiphilic block copolymers could self-assemble to micelle in aqueous solutions,which have attracted a great deal of interest in drug release,separate extraction,enzyme immobilization,chemical machinery valves,tissue engineering,and other fields due to their unique temperature responsive nature.In this paper,octadecyl acrylate(ODA)as hydrophobic monomer and N-isopropylacryamide(NIPAAm)as hydrophilic monomer,2,2-Azobis(isobutyronitrile)as initiator and S,S'-Bis(?,?'-dimethylaceticacid)-trithiocarbonate(TTC)used as chain transfer agent were chosen to synthetize a series of amphiphilic thermo-sensitive block copolymers PNIPAAm-b-PODA-b-PNIPAAm(ABA-type)and PODA-b-PNIPAAm-b-PODA(BAB-type)via reversible-addition-fragmentation chain transfer(RAFT)polymerization.The thermo-sensitivity and micellization of the two kinds of block copolymers in aqueous solution were investigated systematically,and Sudan Red was used as model drug to investigate the drug loading capacity of the block copolymers.1.The structure of ABA-type block copolymer was characterized by IR and 1H NMR,showing that the ABA-type block copolymers had been successfully synthetized.2.The GPC measurement results showed that the larger the content of NIPAAm was,the greater the ABA-type block copolymer molecular weight and molecular number would be.The polymerization dispersion index of block copolymer(Mw/Mn)was always controlled within 1.50(1.3~1.49),illustrating that the RAFT polymerization process of ABA-type block copolymer was controllable and the molecular weight distribution was uniform.3.Both of the two kinds of block copolymers were shown to be surfactive in aqueous solutions using the automatic surface tension meter.The CMC values of ABA type block copolymers were greater than that of BAB-type block copolymers which had the same proportion of hydrophilic and hydrophobic chains.The longer the hydrophilic chain of ABA-type block copolymer was,the smaller the CMC values were;the rule of CMC values of BAB-type block copolymers was opposite to that of ABA-type block copolymer: the longer the hydrophilic chain was,the greater the CMC values were.4.The measured light transmittance of the different micelle solutions of two block copolymers with the increasing of temperature showed that both of the block copolymer solutions were double thermo-sensitive.LCST values became higher with the increasing content of hydrophilic NIPAAm segment.The drop rate of the light transmittance of the first LCST of BAB-type block copolymer was quicker than that of ABA-type block copolymer,while the second falling rate of light transmittance of BAB-type block copolymer near the LCST was slower,and the total decreased light transmittance was less than that of ABA-type block copolymer in total light transmittance.5.The micellar particle size and size distribution(PdI)of different block copolymers were determined by dynamic light scattering(DLS)with the increasing of temperature,the micellar particle size and distribution of ABA-type block copolymer remained a certain value before the LCST;when the temperature reached higher than the LCST,ABA-type block copolymers aggregated while BAB-type block copolymer did not aggregate.In addition,the PdI values(< 0.7)of the BAB-type block copolymer were small which showed that the particle size distribution was narrow and uniform.6.The core-shell structure of the amphiphilic block copolymer micelle could be used as the potential carrier for liposoluble drug,the micelle size increased obviously after loading drugs(Sudan Red as model),showing that the drug was encapsulated into the micelles.