SYNTHESIS OF PSt-b-PAA-b-PSt AMPHIPHILIC BLOCK COPOLYMERS VIA RAFT POLYMERIZATION AND THEIR SELF-ASSEMBLY IN IONIC LIQUID [BMIM] [PF6]

The Block copolymer polystyrene-b-poly(acrylic acid)-b-polystyrene (PSt-b-PAA-b-PSt) was synthesized via reversible addition-fragmentation chain transfer polymerization by using styrene as the first monomer. The architectures of the macr-chain transfer agent PSt-CTA and the block copolymers were confirmed by FTIR and H-1-NMR. GPC analysis was used to estimate the molecular weight and the molecular weight distribution of the copolymers, the number-average molecular weight of macro-chain transfer agent PSt-CTA was 8320, and the molecular weight distribution was 1.05. The number-average molecular weight of three block copolymers was 13050, 11130, and 9760, respectively, and the corresponding molecular weight distribution was 1. 356, 1. 430, 1. 365. The block copolymers with different molecular weights were self-assembled by co-solvent method in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The nanostructures of the PSt-b-PAA-b-PSt micelles formed in the ionic liquid were observed by TEM (transmission electron microscopy) and DLS (dynamic light scattering). The self-assembled morphologies of the copolymers are strongly dependent on the length of PAA block chains when the chain length of PSt is fixed. With the decrease of molecular weight of PAA in block copolymers, the resulting aggregates are spheres with diameter of about 50 nm. With further decrease of PAA molecular weight in copolymers, the sphere morphology is turned to core-shell sphere micelles with diameters not more than 100 nm. Compared with the aqueous solutions of the same copolymers. [BMIM][PF6] solutions exhibit some distinct features, such as temperature-independent micellar morphologies between 25 degrees C and 100 degrees C.