Preparation And Characterization Of Nanoparticles Based On Amphiphilic Star-branched Spla-b-pdmaema Copolymers

The star-branched amphiphilic copolymer composed of polylactide(PLA) hydrophobic core and positive poly(N, N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) hydrophilic shell was synthesized by"arm-first"method. For the synthesis of the copolymers, the hydrophilic arms formed by acetylene terminated PDMAEMA were obtained through the atom transfer radical polymerization of DMAEMA, employing butynl 2-bromoisobutyrate, which was synthesized through the esterification of 3-Butyn-1-ol with 2-bromoisobutyryl bromide, as initiator. The hydrophobic arms consisted of PLA with azide end-caps were prepared via the ring-opening polymerization of D, L-lactide under the initiation of pentaerythritol triazide. The super-branched star copolymers with symmetric A3(B3)3 structures were obtained by the"assembly process"as firstly conjugation of PLA onto the 1, 3, 5-benzenetricarboxylic acid chloride followed by the click reaction between the azide end-caps of PLA and the acetylene end-groups of PDMAEMA. The 1H NMR measurement demonstrated the perfect structure of the acquired copolymers.The copolymers exhibited amphiphilic behavior in the aqueous solution, and the critical aggregated concentration (CAC) were determined by fluorescence spectrum. The CAC of the copolymer, which ranged from 1.54?10-3 mg/ml to 4.63?10-3 mg/ml, increased with the length of the PDMAEMA arms.The copolymers nanoparticles were prepared via solvent evaporation method and dialysis method. The morphologies and the size of the nanoparticles were measured through transmission electron microscopy and dynamic light scattering, respectively, and the zeta potential was also measured. The results showed that the copolymers aggregated into spheres in aqueous solution, but both the sizes and the zeta potential were depended on the prepare method and the length of the PDMAEMA segments. The nanoparticles prepared via dialysis method possessed a size larger than 50 nm, while those obtained from solvent evaporation method exhibited diameters ranged from 10 nm to 40 nm. Lengthening of the PDMAEMA arms resulted in the increase in size of the nanoparticles. The nanoparticles of A3(B3)3 super-branched star copolymers with the PDMAEMA8000 segments exhibited a highest zeta potential +35.0 mV, suggesting their potential as the carrier for the co-delivery of chemotherapeutic drugs and gene.