PH and temperature-responsive POSS-based poly(2-(dimethylamino)ethyl methacrylate) for highly efficient Cr(VI) adsorption

Abstract

Sixteen-arm star-shaped polymer of s-POSS-(PDMAEMA)16 was synthesized by octakis(dibromoethyl) polyhedral oligomeric silsesquioxane (POSS-(Br)16) initiating 2-(dimethylamino)ethyl methacrylate (DMAEMA) via atom transfer radical polymerization (ATRP) process. The obtained s-POSS-(PDMAEMA)16 showed controllable and reversible pH-responsive behavior at pH = 1–12 and thermoresponsive behavior at 20–60 °C. Typical core/shell micelles (100–130 nm) were formed by s-POSS-(PDMAEMA)16 at pH = 7.8 and transformed into 450–600 nm snowflake-shaped micelles at pH = 6, 400 nm butterfly-shaped micelles at pH = 3, and 20–40 nm spherical particles at pH = 10 due to the different interactions between the PDMAEMA chains and the aqueous solution. When the pH of the solution decreased from 10 to 3, 350–400 nm butterfly-shaped micelles were reformed, demonstrating the reversibility of this process. The soluble-insoluble transition temperature for s-POSS-(PDMAEMA)16 was located between 20 and 60 °C. Furthermore, equilibrium adsorption indicated that s-POSS-(PDMAEMA)16 could adsorb Cr(VI) due to strong electrostatic interactions between its tertiary amines and Cr(VI).