Thermo- and pH-responsive POEGMA-b-PDMAEMA-b-POEGMA triblock copolymers

Abstract

A series of thermo- and pH-responsive triblock copolymers based on poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) and poly(N, N-dimethylaminoethyl methacrylate) (PDMAEMA) were synthesised by RAFT polymerisation. The kinetics of the polymerisation of OEGMA and DMAEMA have been studied. The effect of the degree of polymerisation (DP) of the OEG side chain of the POEGMA block and the PDMAEMA block, temperature, pH, solvent, and concentration on the phase behaviour of the POEGxMAy-b-PDMAEMAz-b-POEGxMAy copolymers solutions were investigated comprehensively. At pH 5, the self-assembly of POEG5MA17-b-PDMAEMAz-b-POEG5MA17 copolymers induced by heating was driven by the POEG5MA dehydration, resulting in structures with hydrodynamic radii RH > 100 nm. On the other hand, at pH 9, 1H NMR studies showed that both blocks, PDMAEMA and POEG5MA, dehydrated with increasing temperature, forming stable aggregates with RH ≈ 20 nm, at a concentration of 0.125 mg mL−1. However, by increasing the concentration to 5 mg mL−1, these aggregates precipitated above 70 °C. The increase in the DP of the PDMAEMA block caused a decrease in the RH of aggregates at pH 7 and 9 at 25 °C. This effect was gradually attenuated by the increase in the DP of the OEG side chain and accompanied by an increase in the Tcp of the PDMAEMA block. Cryo-TEM images showed that the copolymers self-assembled as spherical and elongated micelles depending on their concentration and temperature. The copolymers were capable of Reichardt’s dye incorporation at pH 9, demonstrating the hydrophobic nature of the PDMAEMA core of the self-assembled structures.