Selectivity- and size-induced segregation of molecular and nanoscale species in microphase-ordered triblock copolymers.

Microphase-ordered block copolymers serve as model systems to elucidate the potential of molecular self-assembly and organic templates to fabricate functionalized polymeric materials. Both aspects are related to the incorporation of secondary species such as low-molar-mass compounds or nanoparticles within the copolymer matrices. Since the resulting properties of such functionalized copolymers critically depend on the morphology of the blend or composite, the nonrandom distribution of such inclusions within the copolymer matrix must be understood.

Molecularly asymmetric triblock copolymers as a single-molecule route to ordered bidisperse polymer brushes.

The conditions signaling the formation of bidisperse brushes in ordered block copolymers are investigated as an A(2) block is progressively grown onto an A(1)B diblock copolymer to form a series of molecularly asymmetric, isomorphic A(1)BA(2) triblock copolymers. Small-angle scattering and self-consistent field theory confirm that the microphase-ordered period decreases when the A(2) block is short relative to the A(1) block, but then increases as A(1)+A(2) bidisperse brushes develop. The mechanical properties systematically follow the spatial distribution of the A(2) block.

Phase behavior of triblock copolymers varying in molecular asymmetry.

The transformation from A(1)B diblock copolymer to A(1)BA(2) triblock copolymers varying in molecular asymmetry is investigated as the A(2) end block is progressively grown via chemical synthesis. Dynamic rheological measurements show that the order-disorder transition (ODT) temperatures of two copolymer series differing in composition and molecular weight decrease when the A(2) block is short relative to the A(1) block, and then increase as the length of the A(2) block is increased further. The resultant ODT minimum, predicted by mean-field theory, is attributed to mixing between long B and short A(2) blocks.