Adding small amounts of ring polymers to a matrix of their linear counterparts is known to increase the zeroshear-rate viscosity because of linear-ring threading. Uniaxial extensional rheology measurements show that, unlike its pure linear and ring constituents, the blend exhibits an overshoot in the stress growth coefficient. By combining these measurements with ex-situ small angle neutron scattering and nonequilibrium molecular dynamics simulations, this overshoot is shown to be driven by a transient threading-unthreading transition of rings embedded within the linear entanglement network. Prior to unthreading, embedded rings deform affinely with the linear entanglement network and produce a measurably stronger elongation of the linear chains in the blend compared to the pure linear melt. Thus, rings uniquely alter the mechanisms of transient elongation in linear polymers.

Processing ionomers is complicated by their ability to exhibit brittle fracture even in the melt state. This work introduces a new strategy for providing ionomers with good flowability, extensibility, and superior strain hardening. Diamineneutralized entangled poly(styrene-co-4-vinylbenzoic acid) ionomers were studied using small-amplitude oscillatory shear and nonlinear uniaxial extension measurements. The parent molecule, poly(styrene-co-4-vinylbenzoic acid), has a molar mass of 85,400 g/mol, well above the entanglement molar mass of polystyrene (13,300 g/mol). Neutralization was performed using "Jeffamine" type diamines with different molar masses. The resulting neutralized ionomers presented relaxation processes similar to entangled polymers but with faster terminal relaxation, suggesting negligible ionic cluster formation and indicating a diluting effect of the introduced diamines. This feature provides the ionomers with good flowability and facilitates their processing. In extensional measurements, these ionomers displayed superior strain hardening compared to the parent molecule, which also proved to be adjustable via changing diamine length. The stress growth curves showed a maximum stress, followed by stress overshoot and steady state at larger strain. The stress maximum and overshoot were correlated with ionic sticker disassociation, as evidenced by phase separation-induced color change during filament stretching. At high stretch rates, the stickers disassociate abruptly to accommodate the strain, so that the sticker disassociation time decreased with increasing stretch rates. Good extensibility (up to Hencky strain 7) was achieved via ionic sticker reassociation and entanglements.

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