Synthesis And Properties Of ABC Triblock Copolymers With PEO As The Middle Block

Amphiphilie and functional ABC triblock copolymers have attracted more interests in the last decades for their widely application in self-assembly field.Among them, poly(ethylene oxide)(PEO) was the most widely used component due to its outstanding properties such as biocompatibility,crystallizability and well dissolvability in water and most organic solvent.That's why PEO was always considered as one of the blocks when scientists design new ABC triblock copolymers. However,mostly the PEO block introduced in ABC triblock copolymer was located in the first or third block,and only few papers reported the synthesis of triblock copolymers with PEO as the middle block.And for this reason,effect of PEO position on the properties of ABC triblock eopolymers was rarely investigated.In this paper,the triblock copolymers(PS-b-PEO-b-PtBA and PS-b-PEO-b-PAA) were synthesized by a combination of living anionic polymerization, Nitroxide-Mediated Radical Polymerization(NMRP) and Atom Transfer Radical Polymerization(ATRP).The main results are shown as follows:(1) The PEO prepolymer with the 2,2,6,6-tetramethylpiperidinyl-1-oxy(TEMPO) end group was obtained by anionic ring-opening polymerization of ethylene oxide using 4-hydroxyl-2,2,6,6-tetramethylpiperidinyl-1-oxy and Diphenylmethyl-potassium (DPMK) as co-initiation system.The product was characterized in detail(2) The TEMPO mediated radical polymerization of St was carried out using BPO as initiator in the presence of TEMPO-PEO,and a series of PEO-b-PS with different PS block chains was obtained.The products were characterized in detail(3) The diblock copolymers PS-b-PEO-Br macromolecular initiator for ATRP was obtained by the reaction of 2-bromoisobutyryl bromide with the hydroxyl at the end of PS-b-PEO,then it initiated the polymerization of tBA in the present of copper bromide(CuBr) and N,N,N′,N″,N″-pentamethy-ldiethylenetriamine(PMDETA). (4) The obtained PtBA block in copolymer PS-b-PEO-b-PtBA was hydrolyzed by triflluor oacetic acid,so another triblock copolymer PS-b-PEO-b-PAA was prepared. The self-assembly of desired triblock copolymers in the dilute solution was investigated.(5) By means of comparasion of thermo-properties of PS-b-PEO-b-PtBA with PEO-b-PS-b-PtBA and self-assembly of PS-b-PEO-b-PAA with PEO-b-PS-b-PAA,it was found that the location of PEO block in the copolymers exerted great effect on the glass transition temperature(T_g) and self-assembly of copolymers.