Core-Shell Nanoaggregates from Stimuli Responsive Block Copolymers in Aqueous Solutions 

P BAHADUR

Chemistry Department

Veer Narmad South Gujarat University, Surat -395007, India;

E-mail address: pbahadur2002@yahoo.com

Block copolymers have two distinct incompatible moieties in their molecule and thus behave like surfactants (i.e., adsorb onto interfaces and self-assemble to form nano-size aggregates). The advances in polymerization techniques and their several emerging applications viz in the preparation of mesoporous materials/ nanoparticles and as vehicles for delivery systems in addition to conventional performance based surfactant applications such as wetting/dispersing/solubilizing/emulsifying/foaming agents/ rheology modifiers have made block copolymers useful substances. Block copolymers with one stimuli-responsive block have an additional feature as the properties can be tuned by an external factor.

Heat- and salt-induced core-shell nanoaggregates from aqueous solutions of water soluble block copolymers (AB, ABA and ABC) will be described. Special attention will be focused on our studies on amphiphilic triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, (Pluronic^®) and  double hydrophilic diblock copolymer  poly[sodium 2-(acrylamido)-2-methylpropanesulfonate] -poly(N-isopropylacrylamide), PAMPS-PNIPAM. Aggregation and the size/shape of core-shell aggregates, thermoreversible phase behaviour and adsorption characteristics in aqueous solution as modulated by their molecular characteristics, temperature, pH and in the presence of additives like salts, cosolvents, hydrotropes and low molecular weight surfactants will be discussed.

 The formation and characteristics of pH responsive core-shell-corona nanosized aggregates from a water soluble ABC triblock copolymer polystyrene-poly(2-vinylpyridine)-poly(ethylene oxide) (with one hydrophobic, one hydrophilic and one pH responsive blocks) will also be discussed.

Key words: Nanoaggregates, Block copolymers, Micelles, Surfactants