The Study Of Self-Assembly Behavior Of Poly(L-lactide)-Poly(Ethylene Glycol)-Poly(L-lactide) Triblock Copolymer

Molecular solution of an amphiphilic block copolymer may act as oil phase by dispersing into an aqueous micellar system of small-molecular surfactant,forming oil-in-water(O/W)emulsion droplets.And amphiphilic block copolymers can self-assembly by different kinds of methods.In this paper,Poly(L-lactide)-polyoxyethylene-poly(L-lactide)(PLLA-PEG-PLLA)were synthesized with different EO/LA ratios by ring-opening polymerization of L-lactide using PEG and Sn(Oct)2 as the macroinitiator and catalyst,respectively.They were PLLA20PEG227PLLA20,PLLA53PEG227PLLA53,PLLA109PEG227PLLA109,End PLLA53PEG454PLLA53.For the preparation of copolymer emulsion,PLLA-PEG-PLLA was first dissolved in tetrahydrofuran(THF)and then added into aqueous micellar solution of nonaethylene glycol monododecyl ether(AEO-9),forming the relatively stable emulsion system after 30 min stirring.In the PLLA-PEG-PLLA emulsion system,the amphiphilic backbones themselves experienced solution-based self-assembly to form inverted core-corona aggregates within an oil-phase domain along with the gradually increasing of the concentration of PLLA-PEG-PLLA molecules caused by the volatilizing of THF.For the core-corona structure,PEG segments formed the core and PLLA segments formed the corona.More importantly,anisotropic coalescence of adjacent O/W emulsion droplets could be occurred accompanying with the further volatilizing of THF,then both the hydrophilic block crystallization of core-forming PEGs and the hydrophobic chain stretch of corona-forming PLLAs induced the formation of rodlike intermediates with an average diameter of 300-800 nm.Finally,with the repetition of these processes and oriented alignment of crystallized PEG segments,copolymers fibers could be formed with an average diameter of?2.0 pm?For this paper,the formation mechanism of copolymer fibers was studied by different characterization methods.The copolymers were characterized by 1H NMR,GPC and FT-IR.The copolymer fibers could be observed by SEM and TEM test.Crystallization properties and segments interaction could be achieved by XRD,POM and FT-IR tests.The variation of melting points of copolymers and copolymer fibers were observed by DSC.Furthermore,these novel copolymer fibers could be formed by the emulsification/solvent evaporation method,and it would provide an access to aqueous solution crystallization of these copolymers hydrophilic segments.