Self-assembly of stimuli-responsive block copolymers in aqueous solutions: an overview

The review reports an aqueous solution behavior of commercially available and easy-to-use polymers, i.e., Pluronics^®- and PNIPAM-based block copolymers. Both the polymers are stimuli responsive in nature. The present review covers the different aspects of aggregation behavior of Pluronics^®- and PNIPAM-based block copolymeric micelles. Here, a comparison of physical properties such as EO–PO block, CP, CMC and CMT is made. Such physical parameters can be modulated with ease by the presence of external stimuli, viz. electrolytes, organic additives such as alcohols, phenols, amides and acids, different types of surfactants and water-soluble polymers, and also by modification of end groups of Pluronics^®. But in this review, our main focus is to study the addition of salts and non-electrolytes on the aggregation behavior of Pluronics^®. With the help of above parameters, users can get idea about the stability, partition coefficient, solubilization capacity, etc. In analogy with Pluronics^®, PNIPAM is also a thermo-responsive polymer with ~ 32 °C lower critical solution temperature (LCST). However, the LCST is independent of the degree of polymerization, i.e., molecular weight of homopolymer. However, the LCST can be tuned in the presence of external stimulus. PNIPAM-based di-block copolymers form various morphologies in different environments. An inverted morphology by double-hydrophilic-block copolymers is also possible. According to US and British Pharmacopoeia, some of the Pluronics^® and PNIPAM are recognized as pharmaceutical excipients. Therefore, they have been extensively used for various pharmaceutical formulations. The other applications of these polymers are tissue engineering, bioseparation devices, active membranes, biosensors, rheological modifier, lithium batteries, etc.