Amphiphilic Multi-arm Star Copolymer: Synthesis, Characterization And Application

This paper was mainly studied on the synthesis, modification, self-assemble behavior of theamphiphilic multi-arm star copolymer polyethylenimine-block-poly(Lactide)(PEI-b-PLA) andtheir encapsulation and release property as guest molecules delivery. The detail was asfollows:1. Synthesis, modification and characterization of the amphiphilic multi-arm star copolymerpolyethylenimine-block-poly(Lactide)(PEI-b-PLA)Catalyzed by the Tin(II)2-ethylhexanoate (Sn(Oct)2), hyperbranched polyethylenime(PEI1.2K, Mw/Mn=1.04and PEI10K, Mw/Mn=2.5）have successfully iniatiated ring-openingpolymerization of the lactide(DLLA,LLA,DLA), to obtain the amphiphilic multi-arm starcopolymer with polylactide as shell and polyethylenime (PEI) as core.These polymers werecharacterized by DSC, NMR and GPC. The influences of different reaction conditions(polymerization temperature, reaction time and the amount of catalyst) to initiation efficiency,dispersity and molecular weight were discussed.The PEI inner core of polymers (PEI-b-PLA) were quaternized with HCl、HBr、H2SO4、HIand CH3I and the PLA arms were esterified with aliphatic acid（propionic acid,valeric acid andOctylic Acid）. In the same time, the polymers (PEI-b-PLA) of different arm density were got bypart amino protection of PEI with paranitrobenzaldehyde and were characterized by NMR.2. Study of guest encapsulation and release behavior of the amphiphilic multi-arm star copolymerpolyethylenimine-block-poly(Lactide)(PEI-b-PLA)Due to the polar difference of the PLA arms and the PEI inner core, the obtained starcopolymer could act as the unimolecular micelle to encapsulate the water-soluble guests. Theirguest (MO、EY、FS and EBT）encapsulation behaviors have similar laws:Increasing the size of thehydrophilic PEI core and the hydropholic PLA arm length are two effective ways toenhance;Whereas their hydrophilic guest encapsulation capacity of the weight ration mainlydepends on the arm length and has little releration with PEI core.The longer the arm, the smallerguest encapsulation capacity. No obvious difference of their hydrophilic guest encapsulationcapacity was observed between the polymers (PEI-b-PDLLA) and the polymers (PEI-b-PLLA). Inthe same time, their hydrophilic guest encapsulation capacity related with concentration of thepolymers and the guest molecules and the size of guest molecules.The guest encapsulation capacity of PEI-b-PLA was pH sensitive, which reached the maximum loading at pH≦5.5and reduced quickly at pH≧7.0. When the PEI inner core ofpolymers (PEI-b-PLA) were quaternized with HCl、HBr、H2SO4、HI and CH3I, their hydrophilicguest encapsulation capacity increased obviously. Whereas when the PLA arms were esterifiedwith valeric acid, their hydrophilic guest encapsulation capacity decreased. It can be seen that thedecentralized state of the Polymers in chloroform changed from original200nm to less than2nmwhen characterized by DLS.Increasing the size of the hydrophilic PEI core and the hydropholic PLA arm length are twoeffective ways to slow down the realease rate of the encapsulated guest molecules. Moreover, therealease rate of the encapsulated guest molecules of the polymers (PEI-b-PDLLA) was faster thanthat of the polymers (PEI-b-PLLA).