Mechanically interlocking cyclic star polymers quenches solvent-dependent properties

Abstract

We simulate star polymers with cyclic arms formed via click reactions and study the effects of solvent quality on the resulting mechanical interlocking complexity and radius of gyration. We find that polymers with sufficiently long arms cyclized in a poor solvent present a higher degree of interlocking among arms with respect to those cyclized in a good solvent. Furthermore, when a polymer cyclized in a poor solvent is moved to a good solvent, its radius of gyration is smaller than that of star polymers cyclized in a good solvent, indicating that cyclization can quench a solvent-dependent property. Importantly, we show that the number of arms—or functionality, f—affects the degree of interlocking in poor solvents. Due to an asymmetric collapse transition, if f is sufficiently small, all arms phase separate to one side of the star’s central core; they can hence all interact with each other, increasing interlocking. When f is large enough, the entire surface of the core is covered by the arms, hindering interactions between faraway arms and decreasing interlocking. We identify a critical grafting density for the transition via a geometric argument, and we set a criterion for the formation of a single mechanically interlocked blob, that is, the arm’s length must be larger than half of the core’s circumference.