Twisted ABC Triblock Copolymer Cylinders with Segregated A and C Coronal Chains Jiwen Hu, Gabriel Njikang, and Guojun Liu* Department of Chemistry, Queen’s UniVersity, 90 Bader Lane, Kingston, Ontario, Canada K7L 3N ReceiVed July 18, 2008; ReVised Manuscript ReceiVed September 5, 2008 ABSTRACT: The formation of twisted cylinders with segregated A and C coronal chains from an ABC triblock copolymer in a block-selective solvent for the A and C blocks is reported. Such cylinders consisted of left- and right-handed helical sections (3D twisting) connected by wriggling (2D twisting) sections after aspiration on a solid substrate. The copolymer used was poly(glyceryl monomethacrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(tert-butyl acrylate) or PGMA-b-PCEMA-b-PtBA consisting of 310 PGMA units, 130 CEMA units, and 110 tBA units. Twisted cylinders were prepared from the dialysis of an aqueous solution of the triblock copolymer against methanol. In water, the copolymer formed core-shell-corona cylinders with the insoluble PtBA and PCEMA blocks making up the core and shell and the soluble PGMA block making up the corona. The cylinders with PCEMA cores twisted in water/methanol with high methanol contents, e.g., >90 vol%, probably to create more space to accommodate the segregated PGMA chains, which were longer, better solvated, and more crowded than the PtBA chains. Also investigated is the mechanism for the morphological transition from the core-shell-corona cylinders in water to the twisted cylinders in water/methanol. I. Introduction The association of block copolymers in block-selective solvents yields micelle-like aggregates (MAs) with shapes ranging from spheres 1 to vesicles, 2–5 nanotubes, 6 linear cylin- ders, 7,8 branched cylinders, 9 looped cylinders, 3,10,11 and seg- mented cylinders etc. 12,13 The shape diversity of such aggregates facilitates their applications in nanofabrication, 14–16 lithogra- phy, 17–19 cell culturing, 20,21 and drug delivery. 22,23 Most past morphological studies of MAs were performed for diblock copolymers. 1 When ABC linear triblock copolymers were studied, solvents selective for one terminal block (A or C) or two consecutive blocks (A and B or B and C) were typically used. 24 With rare exceptions for ABC linear triblock copoly- mers 25,26 and exceptions for ABC mikto-star triblock copoly- mers, 27,28 the use of such solvents led to the formation core-shell-corona spheres 29–33 or core-shell-corona cylin- ders. 14,34–36 We report in this paper the preparation of MAs from an ABC triblock copolymer in a block-selective solvent for the A and C blocks and the discovery of a novel MA morphology, which consists of twisted B cylinders covered by segregated A and C coronal chains. Such cylinders contain both left- and right- handed helical (3D twisting) sections connected by wriggling (2D twisting) sections after aspiration on a solid substrate. Specifically, the triblock copolymer used in this study was poly(glyceryl monomethacrylate)-block-poly(2-cinnamoyloxy- ethyl methacrylate)-block-poly(tert-butyl acrylate) or PGMA- b-PCEMA-b-PtBA. This polymer was targeted because methanol could be used as a block-selective solvent for the PGMA and PtBA blocks. With PGMA being hydrophilic and PtBA hydrophobic, we suspected that the two terminal blocks should be highly incompatible and segregate in the corona of the MAs formed. PCEMA was used because it could be photocrosslinked to lock in the structure of the MAs 34,37,38 to facilitate their structural elucidation. Single-handed helical cylinders with many pitches have been prepared from the self-assembly in block-selective solvents of diblock copolymers containing a chiral block. 39,40 These helical cylinders twisted single-handedly for the chirality and thus the oriented packing of the chiral block. Recently, Pochan, Wooley, and co-workers 25 reported formation of helical cylinders from a triblock copolymer, poly(acrylic acid)-block-poly(methyl methacrylate)-block-polystyrene or PAA-b-PMMA-b-PS, in water/tetrahydrofuran (THF) containing triethylenetetramine or other multiamines. Here, the water/THF mixture was selective for PAA. For lack of chiral centers, the cylinders were not single-handed. The PS-PMMA core-shell cylinders twisted presumably for the uniaxial compression of the cylinders along the cylinder axis, and the compression forces were thought to arise from complex formation between the multiamines and PAA. Aside from being in block-selective solvents, the helical morphology has been observed also in block copolymer solids. For example, Krappe et al. 41 discovered the formation of helical cylinders from the B block in an ABC triblock copolymer solid. Helical cylinders have been observed also for the A block of an AB diblock copolymer that had undergone self-assembly in the confinement of the tubular pores of an anodized alumina membrane. 42 The cylindrical PCEMA core of the PGMA-b-PCEMA-b- PtBA MAs twisted in water/methanol with high methanol contents, e.g., >90 vol%, probably to create more space for the segregated PGMA chains, which were longer, better solvated, and more crowded than the PtBA chains. Our twisted cylinders (TCs) were formed for a mechanism that was different from those that have been reported. They were unique in structure for the segregation of their coronal chains. While the segregation of different polymers in the solid state 43 or in concentrated polymer solutions 44 is well-known, the observation of segregation of solvated coronal chains on the surfaces of MAs or polymer nanoparticles has rarely been observed. 45–47 * To whom correspondence should be addressed. E-mail: guojun.liu@ chem.queensu.ca. 7993 Macromolecules 2008, 41, 7993-7999 10.1021/ma801626y CCC: $40.75  2008 American Chemical Society Published on Web 10/14/2008