Distinct alignment of benzene derivatives in stretched polystyrene and polybutylacrylate gels: Specific polymer-solute interactions.

We have measured the alignment of a range of benzene derivatives in cross-linked polystyrene and poly(butyl acrylate) using a small number of residual dipolar couplings and simple geometric considerations. For apolar solutes in polystyrene and protic solutes in poly(butyl acrylate), the preferred molecular orientation does not coincide with the longest molecular axis (steric aligment). This behavior may be explained by specific π-π and hydrogen bonding interactions between solute and polymer, respectively, the latter being confirmed by molecular dynamics simulations.