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We have measured the dynamics of completely monodisperse (PDI = 1.0) ultrahigh-molecular-weight linear lambda (λ) DNA solutions as a function of concentration. Due to the very high molecular weight of the DNA, M n = M w > 30 million g/mol, we were able to study the dynamic properties of well-entangled systems even in very dilute (low-concentration) conditions. We report the linear rheology by conducting dynamic oscillatory measurements well into the entanglement regime (11 < C* < 90), where C* is the overlap concentration. The tests are reported in good solvent conditions. Upon comparing our results with previously reported data in the literature by Teixeira et al. [Macromolecules 2007, 40 (7), 2461−2476 and reproducing their data, we can confirm their measurements to have been conducted in the nonlinear regime. This leads to the conclusion that the lambda DNA exhibits extreme strain sensitivity in the observed dynamics, and this induces the earlier onset of nonlinearity as the angular frequency decreases. The time−concentration superposition (TCS) was found to be valid in the terminal zone, which permitted the evaluation of ∼9 decades of dynamics in the mastercurve. The concentration dependence of the time− concentration shift factors (vertical and horizontal) was found to be in good agreement with the plateau moduli and the crossover frequency scaling. A concentration dependence of plateau modulus G N 0 ∼ C 2.29 is obtained from the dynamic tests. The plateau modulus scaling is consistent with the blob model for entangled polymer solutions. The terminal relaxation time shows a change like the unentangled-to-entangled crossover in synthetic polymer solutions from τ d ∼ C 1.1 and τ d ∼ C 3.53 at around 1 mg/mL (24C*). A very high concentration dependence of the zero-shear viscosity, η 0 ∼ C 5.5 , is estimated for the high-concentration samples. We interpret the concentration-dependent scaling to be in an entangled regime observed only in very high molecular weight solutions at sufficiently high concentrations. A Likhtman−McLeish model was used to fit the LVE with the constraint release parameter, c ν , fixed at 1 and 10. The Likhtman−McLeish model does not seem to capture all of the physical processes in the dynamics, and a good fit was not obtained, particularly for the higher-concentration samples though the fit quality improved with the greater constraint release parameter magnitude. Entanglement density predicted by the Likhtman−McLeish model scaled linearly with the entanglement density calculated by the blob model for solutions. The entangled dynamics is possibly nonreptative as reptation or its derivative models do not predict the observed strong nonlinearity and the high susceptibility of the system to strain.

Bulk rheology measurements on concentrated monodisperse ring−linear DNA mixtures are reported for the first time. The entanglement behavior of the ring−linear DNA mixtures (with 15 and 50% linear chain fractions, ϕ Lin ) over a range of total DNA concentration, ϕ Tot , from ∼0.8 mg/mL (20C*) to 2 mg/mL (50C*) is reported. A discussion on the current problems in the reported ring dynamics/scaling is included. The concentration-dependent dynamics of the ring−linear DNA mixtures are compared with the dynamics of 100% linear DNA at the same linear chain degree of entanglement, Z. Dynamic oscillatory tests were conducted to understand the bulk rheological behavior of the ring−linear DNA blends. The blends showed a broadening of the rubbery plateau region compared with that of the pure linear counterpartsnot reported in any previous works on ring polymers. However, the final plateau moduli, G N 0 , of the ring−linear mixtures were found to be lower than for the pure linear DNA at the same total concentration. The plateau moduli for the mixtures followed a 2.2−2.3 power law dependence with total concentration, ϕ Tot , similar to the scaling seen in the 100% linear analogue. G N 0 for the blends scaled as G N 0 ∼ (ϕ Tot ) 2.2−2.29 (ϕ Lin ) 0.7−0.8 for the two linear chain percentages and the range of concentrations studied. The blends at the same total concentration exhibited much higher viscosities relative to the linear counterparts than reported by prior works on synthetic ring melt systems. This is consistent with very long terminal relaxation times most likely due to linear chain threading of these very large macrocycles. The zero shear viscosities for the blends with only 15% linear chain fraction could not be obtained at shear rates as low as 10 −5 s −1 . The Cox−Merz rule was found to hold for the ring−linear blends. Linear chains seem to dictate the dynamics and the entanglement scaling of the blends even at low linear chain fraction of 15%.

Extrusion film casting (EFC) is an important melt processing operation which is extensively used to make polypropylene (PP) films. Linear PP shows significant amount of necking and draw resonance during EFC. One of the ways to reduce necking is to introduce long chain branches (LCB) on the polymer backbone. The long branches impart extensional strain hardening behavior thereby stabilizing the melt flow. In this work, we investigate the influence of long chain branching in polypropylene on the extent of necking in the EFC process. Laboratory scale EFC experiments were performed on homopolymer PP of linear and long chain branched architectures. Simulations of the EFC process were carried out using the one‐dimensional flow model of Silagy et al., Polym. Eng. Sci., 36, 2614 (1996) into which we incorporate two different multi‐mode molecular constitutive equations namely, the ‘eXtended Pom‐Pom’ equation (XPP, for long chain branched PP) and the ‘Rolie‐Poly’ equation (RP‐S, for linear PP). Our experimental data confirm that presence of long chain branching in PP reduces the extent of necking and our numerical predictions show qualitative agreement with experimental data, thereby elucidating the role of chain architecture on the extent of necking. POLYM. ENG. SCI., 55:1977–1987, 2015. © 2014 Society of Plastics Engineers

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