Synthesis of well-defined PPV containing block polymers with precise endgroup control by a dual-initiator strategy

Poly(2,5-bis(2-ethylhexyloxy)p-phenylene vinylene)-b-poly(tert-butyl acrylate) (BEH-PPV-b-P(t-BuA)) block copolymers with various block compositions have been synthesized by a dual initiator strategy. PPV polymerizations are performed via the anionic polymerization mode of the so-called sulfinyl precursor synthesis route with a dedicated initiator carrying a moiety that is able to reinitiate polymer chains under the conditions of a single electron transfer living radical polymerization (SET-LRP). In order to prove that such a route can be taken, a detailed study on the initiator efficiency in the anionic polymerization based on post-mortem analysis of materials with ESI-MS is presented. Low molecular weight PPVs in the range of 2000 Da are synthesized by means of high initiator to monomer concentrations with the use of two differently functionalized anionic initiators. Almost quantitative incorporation of the initiator in the alpha position of the chains is confirmed. Block copolymers are subsequently obtained from a BEH-PPV building block with an apparent M_n of 5300 g mol^-1. Block copolymers with apparent M_n between 6800 and 25000 g mol^-1 are synthesized. Hydrolysis of the acrylate ester block yields amphiphilic block copolymers with a poly(acrylic acid) block, which can be self-assembled in methanolic solution to form micelles with a mean diameter of 81 nm. The micelles respond to changes in pH and ionic strength, leading to significant expansion of the micelles in both cases.