Tailoring supramolecular ionic azo triblock copolymers by partial quaternization and complexation

Abstract

A series of azo-containing triblock copolymer complexes with a majority poly(n-butyl acrylate) (PnBA) middle block and minority outer blocks composed of quaternized poly(dimethylaminoethyl methacrylate) (PDM) complexed with methyl orange (MO) were prepared from a single parent PDM-PnBA-PDM block copolymer (BCP) by varying the degree of PDM quaternization and supramolecular ionic complexation. The parent BCP was prepared by atom transfer radical polymerization (ATRP), making use of the halogen exchange technique along with various adjustments to the previously reported synthesis procedure, to obtain a well-defined, monodisperse triblock. Phase separation between the high-Tg outer blocks and low-Tg middle block for the series was confirmed by DSC, AFM and SAXS. The outer (hard) block Tg, between 175 and 130 °C, decreases with decreasing degree of ionization regardless of the nature of the counterion (I− or MO), attributed to plasticization by the unionized PDM units. The block copolymer structure ranges from a predominantly inverted-phase spherical morphology for the fully quaternized and complexed triblock (37 wt % hard block content), reflecting distortion of usual BCP phase diagrams caused by the ionic block, to normal-phase cylindrical-type morphologies for the least quaternized and complexed triblocks (25–28 wt % hard block content). This correlates with mechanical properties that range from rigid plastic to elastomeric materials. The liquid crystal (smectic A) character of the hard block phase was perturbed by partial quaternization and complexation, indicative of the statistical character of the reactions.