ABC Triblock Copolymer Micelle-Like Aggregates in Selective Solvents for A and C

Interesting self-assembly behavior of an ABC triblock copolymer in selective solvents for the terminal A and C blocks is reported. The triblock copolymer consists of poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(glyceryl monomethacrylate) or PtBA-b-PCEMA-b-PGMA, with 107 tBA units, 193 CEMA units, and 115 GMA units. The solvents used are pyridine/methanol with methanol volume fraction f(MeOH) between 80 and 100%. While pyridine is a good solvent for all of the three blocks, methanol is selective for PtBA and PGMA. At f(MeOH) = 80% and f(MeOH) = 90% and at 50 degrees C, spherical and cylindrical micelles with PtBA and PGMA coronal chains are formed. Atf(MeOH) = 95%, vesicles are formed. Grafted on the outer surface of the vesicles are mostly the PGMA chains and some PtBA chains. The PtBA chains are found by atomic force microscopy and transmission electron microscopy to segregate from the PGMA chains to form circular patches. Atf(MeOH) = 100%, tubular micelle-like aggregates (MAs) coexisted with vesicular MAs. While there have been many reports on morphologies of block copolymer MAs, reports on MAs of ABC triblock copolymers in selective solvents for A and C are rare. Also, there have been very few reports on tubular MAs and MAs with segregated Surface chains. These combinations make results of this study unique.