@article{denton_koh_simon_mckenna_2024, title={On the glass transition temperature of TNT}, volume={736}, ISSN={["1872-762X"]}, DOI={10.1016/j.tca.2024.179733}, abstractNote={In prior work (N. Shamim, Y. P. Koh, S. L. Simon and G. B. McKenna, "The glass transition of trinitrotoluene (TNT) by flash DSC," Thermochimica Acta, 620, 36-39 (2015)) results for the glass transition temperature Tg of TNT based on measurements using a rapid chip calorimeter were reported. In that work a silver paste was used to contain the liquid TNT on the chip sensor. In the present work we show that there was an interaction between the paste and the TNT that cause the reported Tg to be approximately 10°C higher than what we find for the material when placed directly on the chip calorimeter sensor. The reasons for the differences in Tg values and similarities in the glassy fragility index m from the different sample preparations are presented and discussed.}, journal={THERMOCHIMICA ACTA}, author={Denton, Aric A. and Koh, Yung P. and Simon, Sindee L. and Mckenna, Gregory B.}, year={2024}, month={Jun} }
 @article{el banna_mckenna_2023, title={AFM dilatometry measurements on ultra-stable fluoropolymer glasses: Further evidence of extreme fictive temperature reduction}, ISSN={["2642-4169"]}, DOI={10.1002/pol.20230478}, abstractNote={Abstract}, journal={JOURNAL OF POLYMER SCIENCE}, author={El Banna, Amer A. and McKenna, Gregory B.}, year={2023}, month={Oct} }
 @article{el banna_mckenna_2023, title={Challenging the Kauzmann paradox using an ultra-stable perfluoropolymer glass with a fictive temperature below the dynamic VFT temperature}, volume={13}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-023-31074-0}, abstractNote={Abstract}, number={1}, journal={SCIENTIFIC REPORTS}, author={El Banna, Amer A. and McKenna, Gregory B.}, year={2023}, month={Mar} }
 @article{banik_mckenna_2023, title={Extremely early onset of nonlinear viscoelasticity in dynamic shear of ideally monodisperse DNA}, ISSN={["2642-4169"]}, DOI={10.1002/pol.20230014}, abstractNote={Abstract}, journal={JOURNAL OF POLYMER SCIENCE}, author={Banik, Sourya and McKenna, GregoryB B.}, year={2023}, month={Apr} }
 @article{molnar_pillai_chen_kaszas_mckenna_kornfield_puskas_2023, title={Investigation of the structure, filler interaction and degradation of disulfide elastomers made by Reversible Radical Recombination Polymerization (R3P)}, volume={191}, ISSN={["1873-1945"]}, DOI={10.1016/j.eurpolymj.2023.112033}, abstractNote={In this paper we report the synthesis and analysis of cyclic polydisulfides, their redox depolymerization as well as their interaction with carbon black. Cyclic poly(3,6-dioxa-1,8-octanedithiol)s (pDODT) were synthesized by Reversible Radical Recombination Polymerization (R3P). R3P is a scalable “green” polymerization process using triethylamine (TEA), H2O2 and air for the polymerization of dithiol monomers. pDODTs were synthesized in 5 and 20 g batches. The effect of peroxide concentration (3, 5, 10, 20, 30 %) was investigated. It was found that the molecular weights increased exponentially with increasing peroxide concentrations. At 30 % peroxide concentration pDODTs with Mn up to 400,000 g/mol and polydispersity of 2 were obtained. 700 and 800 MHz NMR were used for investigating the chemical structure of the polymers. The absence of thiol end group signals in polymers made with > 10 wt % H2O2 and Mn < 100,000 g/mol, including a sample of a fractionated polymer with starting Mn = 600,000 g/mol, verified cyclic structures. Dithiothreitol reduced the polymers to monomer and a small percentage of oligomers. Carbon black was shown to increase the moduli of high molecular weight pDODTs. Swelling tests in chloroform showed that polymers made with 20 and 30 w% peroxide swelled 14 and 10 times of their starting weight without dissolving, indicating chemical interaction between the polymers and carbon black. Further analysis of these interesting elastomers, available at the 20 g scale, is in progress.}, journal={EUROPEAN POLYMER JOURNAL}, author={Molnar, Kristof and Pillai, Aswathy Sasidharan and Chen, Dongjie and Kaszas, Gabor and McKenna, Gregory B. and Kornfield, Julia A. and Puskas, Judit E.}, year={2023}, month={Jun} }
 @article{chen_molnar_kim_helfer_kaszas_puskas_kornfield_mckenna_2023, title={Linear Viscoelastic Properties of Putative Cyclic Polymers Synthesized by Reversible Radical Recombination Polymerization (R3P)}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.2c00892}, abstractNote={Linear viscoelastic properties in both melt and solution states are reported for a series of poly(3,6-dioxa-1,8-octanedithiol) (polyDODT) made by reversible radical recombination polymerization (R3P) under conditions designed to produce linear (LDODT), cyclic (RDODT), and linear–cyclic mixtures (LRDODT). PolyDODT is amorphous (Tg < −50 °C) and highly flexible (entanglement molecular weight Me,lin ≈ 1850 g/mol for LDODT). PolyDODT’s low Tg and low Me,lin enable characterization over a wide dynamic range and a wide range of dimensionless weight-average molecular weight Zw = Mw/Me,lin. Measurements at temperatures from −57 to 100 °C provide up to 18 decades of reduced frequency, which is necessary to characterize RDODT melts with Zw from 23 to 300. The two highest-molecular-weight polymers in the present RDODT series have such high Mw (406k and 556k g/mol) that mass spectrometry, NMR spectroscopy, and even chemical assays for chain ends are unable to rule out up to 2 mol % of linear contaminant. By studying the samples in solution (using dilution to reduce Zw), we could compare their dynamics with those of previously established high-purity polystyrene (PS) rings (limited to Zw ≤ 13.6). RDODT solutions with Zw < 15 (concentrations <5 wt % for RDODT-406k and 556k) have dynamic moduli G* that accord with LCCC-purified PS rings in terms of the frequency dependence (including the absence of a plateau), the progression of shapes of G* as a function of Zw, and the linear scaling of their zero-shear viscosity η0 with Mw. The shape of G* as a function of Zw for solutions of RDODT-406k and -556k also accords with lower Mw RDODT melts (which have ≤1.3 mol % of linear contaminant). Thus, the measurement of the linear viscoelastic properties of appropriate concentrations of high Mw (>200k g/mol) putative cyclic polymers, in which linear chains evade spectroscopic detection, may provide an alternative means (though not fully proven) of validation of sample purity. When Zw > 15 (including all seven RDODT melts and eight of their solutions), G* has a rubbery plateau. This suggests that the onset of entanglement-like behavior in rings requires 4–5-fold greater Zw than is required for linear chains. Further, the plateau moduli of RDODT samples are indistinguishable from GNo of the corresponding LDODT (melt or matched-concentration solutions). In entangled linear polymers, the observation that GNo is independent of Zw follows from limitations on lateral fluctuations due to neighboring chains becoming independent of position along a given chain. The present results for RDODT suggest that this holds for sufficiently long endless chains, too. While the RDODTs have the same GNo as entangled LDODTs, when Zw > 60, the terminal relaxation, if reached at all, of RDODT extends to orders of magnitude lower frequency than an entangled linear polymer of the same Zw. Consequently, the viscosity of RDODT with Zw > 60 increases with Zw much more strongly than the 3.4 power observed for entangled linear polymers. Finally, these novel polymers, with a disulfide-linked backbone and broad relaxation time distribution, may prove important in relation to biodegradable elastomers and materials with exceptional low-frequency dissipation, extending at least 12 decades below the onset of the rubbery plateau.}, journal={MACROMOLECULES}, author={Chen, Dongjie and Molnar, Kristof and Kim, Hojin and Helfer, Carin A. and Kaszas, Gabor and Puskas, Judit E. and Kornfield, Julia A. and McKenna, Gregory B.}, year={2023}, month={Jan}, pages={1013–1032} }
 @article{kong_meng_mckenna_2023, title={Searching for the ideal glass transition: Going to yotta seconds and beyond}, volume={606}, ISSN={["1873-4812"]}, DOI={10.1016/j.jnoncrysol.2023.122186}, abstractNote={Here we report results for the dynamics of a 50-million-year-old (geologically) aged Fushun amber that had a fictive temperature Tfapproximately 193 K below its glass transition temperatureTg in the thermally rejuvenated state. The density of this ultra-stable amber was found to be 14% greater than the post-rejuvenation value. Length change dilatometry was used to map the Tf by performing de-aging experiments and equilibrium state dynamics were obtained by making measurements at T=Tf. Time-Temperature Superposition was applied to the frequency dependent storage and loss modulus measurements both along the equilibrium line and in upper-bound conditions where T>Tf. We find that the relaxation times cover >1027s (1 ronna second), i.e., thousands of yotta seconds but do not follow the "expected" Vogel-Fulcher-Tammann (VFT) type of super-Arrhenius type of temperature dependence. Rather the deep glassy state equilibrium dynamics show no evidence of divergence at a finite temperature for temperatures that would be expected to be far below the ideal glass temperature Tg,ideal. In addition, at constant fictive temperature, we find that the relaxation times vary very strongly with specific volume v whereas, in isothermal conditions, the relaxation times are only weakly dependent on v. These results evidence that the deep glass state behavior presents a challenge to current ideas about glasses and the glass transition.}, journal={JOURNAL OF NON-CRYSTALLINE SOLIDS}, author={Kong, Dejie and Meng, Yan and McKenna, Gregory B.}, year={2023}, month={Apr} }
 @article{koh_fondren_denton_simon_mckenna_2022, title={Amorphization and Crystallization of Hexanitroazobenzene (HNAB) Using Conventional DSC and Flash DSC}, ISSN={["1521-4087"]}, DOI={10.1002/prep.202100366}, abstractNote={Abstract}, journal={PROPELLANTS EXPLOSIVES PYROTECHNICS}, author={Koh, Yung P. and Fondren, Zachary T. and Denton, Aric A. and Simon, Sindee L. and McKenna, Gregory B.}, year={2022}, month={Aug} }
 @article{jin_mckenna_2022, title={Anomalous structural recovery in the near glass transition range in a polymer glass: Data revisited in light of temperature variability in vacuum oven-based experiments}, ISSN={["1548-2634"]}, DOI={10.1002/pen.25911}, abstractNote={Abstract}, journal={POLYMER ENGINEERING AND SCIENCE}, author={Jin, Shuang and McKenna, Gregory B.}, year={2022}, month={Feb} }
 @article{jin_mckenna_2022, title={Comment on Comment on "Anomalous structural recovery in the near glass transition range in a polymer glass: Data revisited in light of temperature variability in vacuum oven-based experiments"}, ISSN={["1548-2634"]}, DOI={10.1002/pen.26055}, abstractNote={Abstract}, journal={POLYMER ENGINEERING AND SCIENCE}, author={Jin, Shuang and McKenna, Gregory B.}, year={2022}, month={Jul} }
 @article{kong_meng_mckenna_2022, title={Determination of the molecular weight between cross-links for different ambers: Viscoelastic measurements of the rubbery plateau}, ISSN={["1548-2634"]}, DOI={10.1002/pen.25903}, abstractNote={Abstract}, journal={POLYMER ENGINEERING AND SCIENCE}, author={Kong, Dejie and Meng, Yan and McKenna, Gregory B.}, year={2022}, month={Feb} }
 @article{mangalara_mckenna_2022, title={Large-amplitude oscillatory shear to investigate the nonlinear rheology of polymer glasses - PMMA}, ISSN={["1573-2738"]}, DOI={10.1007/s11043-021-09529-6}, journal={MECHANICS OF TIME-DEPENDENT MATERIALS}, author={Mangalara, Satish Chandra Hari and McKenna, Gregory B.}, year={2022}, month={Jan} }
 @article{molnar_kim_chen_helfer_kaszas_mckenna_kornfield_yuan_puskas_2022, title={PolyDODT: a macrocyclic elastomer with unusual properties}, ISSN={["1759-9962"]}, DOI={10.1039/d1py01426a}, abstractNote={Reversible Radical Recombination Polymerization (R3P) using triethylamine (TEA), H2O2 and air is a scalable and green method for the synthesis of biodegradable polysulfides.}, journal={POLYMER CHEMISTRY}, author={Molnar, Kristof and Kim, Hojin and Chen, Dongjie and Helfer, Carin A. and Kaszas, Gabor and McKenna, Gregory B. and Kornfield, Julia A. and Yuan, Chunhua and Puskas, Judit E.}, year={2022}, month={Jan} }
 @article{kong_banik_san francisco_lee_anderson_schroeder_mckenna_2022, title={Rheology of Entangled Solutions of Ring-Linear DNA Blends}, volume={55}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.1c01672}, abstractNote={: Bulk rheology measurements on concentrated monodisperse ring − linear DNA mixtures are reported for the fi rst 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 (20 C * ) to 2 mg/mL (50 C * ) is reported. A discussion on the current problems in the reported ring dynamics/scaling is included. The concen-tration-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 fi nal 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%.}, number={4}, journal={MACROMOLECULES}, author={Kong, Dejie and Banik, Sourya and San Francisco, Michael J. and Lee, Megan and Anderson, Rae M. Robertson and Schroeder, Charles M. and McKenna, Gregory B.}, year={2022}, month={Feb}, pages={1205–1217} }
 @article{mckenna_chen_mangalara_kong_banik_2022, title={Some open challenges in polymer physics}, ISSN={["1548-2634"]}, DOI={10.1002/pen.25938}, abstractNote={Abstract}, journal={POLYMER ENGINEERING AND SCIENCE}, author={McKenna, Gregory B. and Chen, Dongjie and Mangalara, Satish Chandra Hari and Kong, Dejie and Banik, Sourya}, year={2022}, month={Mar} }
 @article{zhao_cheng_koh_kelly_mckenna_simon_2021, title={Prediction of the Synergistic Glass Transition Temperature of Coamorphous Molecular Glasses Using Activity Coefficient Models}, volume={18}, ISSN={["1543-8392"]}, DOI={10.1021/acs.molpharmaceut.1c00353}, abstractNote={The glass transition temperature (Tg) of a binary miscible mixture of molecular glasses, termed a coamorphous glass, is often synergistically increased over that expected for an athermal mixture due to the strong interactions between the two components. This synergistic interaction is particularly important for the formulation of coamorphous pharmaceuticals since the molecular interactions and resulting Tg strongly impact stability against crystallization, dissolution kinetics, and bioavailability. Current models that describe the composition dependence of Tg for binary systems, including the Gordon-Taylor, Fox, Kwei, and Braun-Kovacs equations, fail to describe the behavior of coamorphous pharmaceuticals using parameters consistent with experimental ΔCP and Δα. Here, we develop a robust thermodynamic approach extending the Couchman and Karasz method through the use of activity coefficient models, including the two-parameter Margules, non-random-two-liquid (NRTL), and three-suffix Redlich-Kister models. We find that the models, using experimental values of ΔCP and fitting parameters related to the binary interactions, successfully describe observed synergistic elevations and inflections in the Tg versus composition response of coamorphous pharmaceuticals. Moreover, the predictions from the NRTL model are improved when the association-NRTL version of that model is used. Results are reported and discussed for four different coamorphous systems: indomethacin-glibenclamide, indomethacin-arginine, acetaminophen-indomethacin, and fenretinide-cholic acid.}, number={9}, journal={MOLECULAR PHARMACEUTICS}, author={Zhao, Xiao and Cheng, Sixue and Koh, Yung P. and Kelly, Brandon D. and McKenna, Gregory B. and Simon, Sindee L.}, year={2021}, month={Sep}, pages={3439–3451} }