(617c) Amphiphilic Block Copolymers and Their Self-Assembled Thermosensitive and Crystallizable Nanoparticles

A facile and nontoxic approach to synthesize amphiphilic block copolymers and nanoparticles in aqueous medium was demonstrated. This method exploited the variation of polymer upon Volume phase transition temperature (VPTT), because its solubility and oil-water partition are all greatly changing with temperature. Rising temperature could effectively increase the incorporation of PNIPAM oligomers into oil phase and set the stage for direct copolymerization of hydrophobic and hydrophilic monomers by emulsion polymerization. The results of ¹H, ¹³C NMR, DSC and TEM proved the successfully formation of block structure of copolymer. The triads sequence and average block length are analyzed to determine the sequence distribution of copolymers. Volume phase transition temperature of PNIPAM copolymer was first increased to nearly 40 °C with hydrophobic monomer rather than hydrophilic monomer. PSMA exhibit a ‘jump’ in permeability at the T_m of the side-chain lengths, which is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. 

The PNIPAM moiety is swelling and could dissolve in water and PSMA moiety can crystallize into ordered domain at 25 °C, showing as nano-lamellae. When heating, PNIPAM moiety will curl up and PSMA moiety is turning to amorphous state, which shows as nanoparticles.  In addition, hydrophilic property of copolymer was studied to understand further applications. These amphiphilic block copolymers show great potential in the controlled delivery system for drugs. The application performances of loading and releasing hydrophobic/hydrophilic model drugs were studied using ultraviolet–visible spectrophotometer, which showed a quite different thermal response and loading capability of hydrophilic and hydrophobic drugs in nanoparticles, and supposed to be used in extended and controlled delivery system of drugs.