(133b) Structure and Dynamics of Model Tapered Diblock Polymers

Tapered diblock polymers are akin to AB diblock polymers but contain a region with a gradient in composition inserted between the pure A and B blocks. We consider polymers in which the taper is a linear gradient from pure A to pure B, or B to A in the case of inverse tapers, and can be from 0% (diblock) to 100% (gradient copolymer) in length. We aim to show how adjusting the taper length and direction controls the interfacial and microphase structure, as well as the impacts on dynamics. Self-consistent field theory (SCFT) was used to study phase behavior while coarse-grained molecular dynamics (MD) simulations showed details of polymer conformations and diffusion, including diffusion of small molecule penetrants that have a favorable chemical interaction with only one of the polymer phases. In accordance with experimental results, adding a taper increases the interfacial region and decreases the order to disorder transition temperature of block copolymers. Interestingly, the region of the phase diagram where the bicontinuous double gyroid phase is preferred is widened significantly for short to medium length normal tapers, but not for inverse tapers. Inverse tapered polymers can stitch back and forth across the interface as would be expected of ABâ??Aâ??B type tetrablock copolymers, however, due to the mixed taper region, this behavior depends strongly on segregation strength. The interesting inverse tapered polymer conformations lead to nonintuitive trends in the domain spacing and dynamics, and in certain systems penetrans can diffuse faster through inverse tapered polymers than diblocks even while the polymer diffusion is slower.