A small number of associating groups incorporated onto a polymer backbone have dramatic effects on the mobility and viscoelastic response of the macromolecules in melts. These associating groups assemble, driving the formation of clusters, whose lifetime affects the properties of the polymers. Here, we probe the effects of the interaction strength on the structure and dynamics of two topologies, linear and star polymer melts, and further investigate blends of associative and non-associating polymers using molecular dynamics simulations. Polymer chains of approximately one entanglement length are described by a bead–spring model, and the associating groups are incorporated in the form of interacting beads with an interaction strength between them that is varied from 1 to 20 kBT. We find that, for all melts and blends, interaction of a few kBT between the associating groups drives cluster formation, where the size of the clusters increases with increasing interaction strength. These clusters act as physical crosslinkers, which slow the chain mobility. Blends of chains with and without associating groups macroscopically phase separate for interaction strength between the associating groups of a few kBT and above. For weakly interacting associating groups, the static structure function S(q) is well fit by functional form predicted by the random phase approximation where a clear deviation occurs as phase segregation takes place, providing a quantitative assessment of phase segregation.
Ionizable
block copolymers with distinctive block characteristics
display the diversity crucial for the design of macromolecules for
targeted applications. In contrast to van der Waals copolymers, their
interfaces, which are critical to their function, consist of nanodomains,
each of a different nature and thus unique interfacial behavior. Here,
the interfacial response of a symmetric block copolymer with a sulfonated
polystyrene polyelectrolyte center, tethered to polyethylene-r-propylene and terminated by poly(t-butyl
styrene) is probed as polymer films are exposed to three polar solvents,
water, propanol, and tetrahydrofuran (THF), using molecular dynamics
simulations. Each of the solvents captures a distinctive interaction
with the individual blocks. We find that at the film boundary, the
interfacial response is initially dominated by that of the hydrophobic
blocks to all solvents. At later times, the solvent distribution among
the blocks, where water molecules associate predominantly with the
sulfonated groups and propanol and THF reside at multiple different
sites, determines the chemical composition and the polymer conformation
at the interface. Overall, these simulations provide the first direct
molecular insight into the interfacial response of ionizable copolymers.
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