Novel Phase Morphologies in a Microphase-Separated Dendritic Polymer Melt

Equilibrium phase morphologies of two different dendritic block copolymer melts are calculated and compared. These copolymers have a pitchfork-like architecture and consist of three distinct blocks that correspond roughly to the handle, the connecting middle dendron structure, and the attached tines of a pitchfork. The first melt considered consists of a copolymer that has a simple Y-junction middle block, and it connects the handle to two tines. The second is similar except its dendritic middle block branches twice to connect to four tines. Polymeric segments are modeled as flexible Gaussian threads and interactions between dissimilar blocks are all contact-like, Flory−Huggins repulsions. All calculations are done for incompressible melts in the context of self-consistent mean-field theory. We find that several morphologies compete for stability depending on the architecture and lengths of the blocks as well as their incompatibilities. As many as four stable two-dimensional phases appear in the phase diagram including: columnar square, rectangular and hexagonally packed structures. A long handle and a moderate length of the dendron are essential for stabilizing the square phases, and the four tine copolymer shows a larger region of stability for these phases compared to the Y-junction middle block system. A remarkable continuous phase transition between the square and rectangular phases is also found and investigated.