@article{truitt_white_2009, title={In-situ NMR studies of isobutane activation and exchange in zeolite beta}, volume={35}, ISSN={["1527-3326"]}, DOI={10.1016/j.ssnmr.2008.12.002}, abstractNote={1H solid-state NMR techniques have been used to simultaneously detect the reactivity of both catalyst and alkane reactant protons in an in-situ experimental design. Specifically, the activation of isobutane C–H bonds by the solid acid zeolite H-Beta is directly observed while the reaction is in progress, and the rate of proton transfer between the solid catalyst surface and gaseous isobutane is quantitatively measured using isotopic 1H/2H exchange methods. Arrhenius analysis of isothermal kinetic runs revealed an apparent activation barrier of 70 kJ/mole for the exchange process between isobutane and the 12-membered ring H-Beta, which exceeds our previously determined value of 57 kJ/mole for isobutane in the 10-membered ring H-ZSM-5 (JACS 2006, v. 128, p. 1848). Estimation of true activation energies using heat of adsorption data from the literature combined with the experimentally measured apparent Ea suggests that the true activation barrier differs by only 6–7 kJ/mole in the two catalysts. We discuss the possibility that subtle shape selectivity, or inverse shape selectivity, and lattice solvation differences between the two catalysts account for the enhanced solvation of the isobutane transition state in HZSM-5 compared to the larger channel H-Beta. In all experiments, the isobutane reagent was treated to eliminate any unsaturated impurities that might serve as initiators for carbenium-ion mechanisms, and the active catalyst was free of any organic contaminants that might serve as a source of unsaturated initiators.}, number={2}, journal={SOLID STATE NUCLEAR MAGNETIC RESONANCE}, author={Truitt, Matthew J. and White, Jeffery L.}, year={2009}, month={Apr}, pages={100–103} }
 @misc{white_truitt_2007, title={Heterogeneous catalysis in solid acids}, volume={51}, number={2}, journal={Progress in Nuclear Magnetic Resonance Spectroscopy}, author={White, J. L. and Truitt, M. J.}, year={2007}, pages={139–154} }
 @article{sremaniak_whitten_truitt_white_2006, title={Weak hydrogen bonding can initiate alkane C-H bond activation in acidic zeolites}, volume={110}, ISSN={["1520-6106"]}, DOI={10.1021/jp0658703}, abstractNote={Ab initio calculations at the Hartree-Fock self-consistent field/single determinant (SCF) and configuration interaction multi-determinant (CI) expansion levels have been used to show that isobutane primary C-H bond activation occurs via direct protium exchange with the zeolite surface via a weakly hydrogen-bonded complex. The calculated 15 kcal/mol activation barrier agrees with the 13.7 kcal/mol value from a recently reported experimental study (J. Am. Chem. Soc. 2006, 128, 1847-1852). Overall, the mechanism described in this contribution demonstrates that weak C-H to O hydrogen bonding leads to complexes at the zeolite acid site that can facilitate C-H bond activation.}, number={42}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Sremaniak, Laura S. and Whitten, Jerry L. and Truitt, Matthew J. and White, Jeffery L.}, year={2006}, month={Oct}, pages={20762–20764} }
 @article{wolak_white_2005, title={Factors that allow polyolefins to form miscible blends: polyisobutylene and head-to-head polypropylene}, volume={38}, ISSN={["1520-5835"]}, DOI={10.1021/ma052162r}, abstractNote={Solid-state CODEX NMR experiments directly probe chain dynamics in pure polyisobutylene (PIB), head-to-head polypropylene (hhPP), and their binary blend. The conclusions we draw from the results of the CODEX experiments, which are conducted over a temperature range of 210−300 K and which probe frequencies of 5−10 Hz, indicate that the overall chain dynamics of the blend system exceeds that of the two unmixed polymers. This is in agreement with our previous work on miscible PIB/polyethylene-co-butene blends [Macromolecules 2003, 36, 4844−4850], in which configurational entropy was shown to increase for miscible polyolefins. The CODEX experiments on PIB/hhPP, which offer the advantage of direct and simultaneous observation of both chains in the blend, show that conformational reorientation in hhPP increases significantly upon blending with PIB, while PIB chain dynamics are relatively unchanged. Rotating frame spin−lattice relaxation experiments support this conclusion. The benefits of direct chain observati...}, number={25}, journal={MACROMOLECULES}, author={Wolak, JE and White, JL}, year={2005}, month={Dec}, pages={10466–10471} }
 @article{porbeni_shin_shuai_wang_white_jia_tonelli_2005, title={Morphology and dynamics of the poly(epsilon-caprolactone)-b-poly(L-lactide) diblock copolymer and its inclusion compound with alpha-cyclodextrin: A solid-state C-13 NMR study}, volume={43}, ISSN={["1099-0488"]}, DOI={10.1002/polb.20490}, abstractNote={Abstract}, number={15}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Porbeni, FE and Shin, ID and Shuai, XT and Wang, XW and White, JL and Jia, X and Tonelli, AE}, year={2005}, month={Aug}, pages={2086–2096} }
 @article{jia_wang_tonelli_white_2005, title={Two-dimensional spin-diffusion NMR reveals differential mixing in biodegradable polymer blends}, volume={38}, ISSN={["1520-5835"]}, DOI={10.1021/ma047838h}, abstractNote={Length scales of mixing in amorphous blends of solid PCL (polycaprolactone) and PLLA (poly-l-lactic acid) were investigated as a function of preparation method. A recently described two-dimensional heteronuclear correlation (Hetcor) spin-diffusion technique (Jia et al. Macromolecules 2003, 36, 712) revealed that PCL/PLLA blends with shorter length scales of mixing, relative to solution blending, could be prepared using inclusion-compound coalescence methods (Rusa et al. Macromolecules 2000, 33, 5321). These biocompatible and biodegradable polymer blends provide a clear example of the utility of the 2D Hetcor spin-diffusion method for quantitative miscibility and phase analysis in amorphous macromolecules and their blends. The rates for intrapolymer polarization transfer vs interchain/interdomain polarization equilibration were easily differentiated using the 2D technique for either blend. As a result, spin-diffusion coefficients and miscibility length scales could be calculated by direct measurement on th...}, number={7}, journal={MACROMOLECULES}, author={Jia, X and Wang, XW and Tonelli, AE and White, JL}, year={2005}, month={Apr}, pages={2775–2780} }
 @misc{rusa_wei_bullions_rusa_gomez_porbeni_wang_shin_balik_white_et al._2004, title={Controlling the polymorphic behaviors of semicrystalline polymers with cyclodextrins}, volume={4}, ISSN={["1528-7505"]}, DOI={10.1021/cg049821w}, abstractNote={We present a review of our initial studies concerning the control of polymorphism in semicrystalline polymers with cyclodextrins (CDs). CDs are cyclic starch oligomers with six (α-CD), seven (β-CD), and eight (γ-CD) α-1,4-linked glucose units possessing bracelet structures with hydrophobic and hydrophilic interiors and exteriors, respectively. They are able to act as hosts to form noncovalent inclusion compounds (ICs) with a large variety of guest molecules, including a wide range of high molecular weight guest polymers. In polymer-CD-ICs, the CD host crystalline lattice consists of hexagonally packed CD stacks with guest polymers occupying the narrow channels (∼0.5−1.0 nm) extending down the interiors of the stacked CDs. As a consequence, the included guest polymers must adopt highly extended conformations and are segregated from neighboring guest polymer chains. When the host CDs are appropriately removed from polymer-CD-ICs, the included guest polymers are forced to coalesce into a pure polymer solid, ...}, number={6}, journal={CRYSTAL GROWTH & DESIGN}, author={Rusa, CC and Wei, M and Bullions, TA and Rusa, M and Gomez, MA and Porbeni, FE and Wang, XG and Shin, ID and Balik, CM and White, JL and et al.}, year={2004}, pages={1431–1441} }
 @article{truitt_toporek_rovira-hernandez_hatcher_white_2004, title={Identification of an adsorption complex between an alkane and zeolite active sites}, volume={126}, ISSN={["0002-7863"]}, DOI={10.1021/ja046729f}, abstractNote={Direct observation of the Bronsted acid site signal in an active zeolite catalyst following adsorption of stoichiometric quantities of isobutane reveals the presence of a specific adsorption complex. Independent polarization transfer experiments in which magnetization originates with either the catalyst or the adsorbed isobutane confirm this assignment. The initial steps in alkane reactivity are poorly defined, and this experimentally verified complex is proposed as a route to C-H bond activation in solid acids.}, number={36}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Truitt, MJ and Toporek, SS and Rovira-Hernandez, R and Hatcher, K and White, JL}, year={2004}, month={Sep}, pages={11144–11145} }
 @article{wachowicz_wolak_gracz_stejskal_jurga_mccord_white_2004, title={Length scales which perturb chain packing in amorphous polymers}, volume={37}, ISSN={["1520-5835"]}, DOI={10.1021/ma049263u}, abstractNote={Direct spectroscopic probes of individual chain conformation and free volume are used to measure the increasing perturbation in the local glass-transition temperature of one polymer chain with decreasing length scale of mixing in binary polyolefin blends. Solid-state 2H and 129Xe NMR experiments reveal a compositional miscibility window in side-chain concentration for polyisobutylene (PIB)/poly(ethylene-co-butene) (PEB) blends. A combination of pulsed-field gradient and chemical shift data for xenon gas absorbed in these polymer blends indicates that the presence of polymer chains within a radius of ∼35 nm of a different chain structure will perturb the intermolecular packing contribution to the total conformational energy of that chain, thereby changing its Tg.}, number={12}, journal={MACROMOLECULES}, author={Wachowicz, M and Wolak, J and Gracz, H and Stejskal, EO and Jurga, S and McCord, EF and White, JL}, year={2004}, month={Jun}, pages={4573–4579} }
 @article{wolak_knutson_martin_boyle_sargent_white_2003, title={Dynamic disorder and conformer exchange in the crystalline monomer of polycarbonate}, volume={107}, ISSN={["1520-5207"]}, DOI={10.1021/jp036527q}, abstractNote={Direct measurement of chemical exchange events in the crystalline polycarbonate monomer 4,4‘- isopropylidenediphenol (bisphenol A, BPA) via 2D 13C solid-state NMR reveals slow, large-amplitude aromatic ring reorientations. X-ray diffraction, however, indicates a static crystalline structure. Experiments with multiple exchange times show that ring flips occur in all of the three unique conformers found in the crystalline unit cell of this compound, but in specific cases, two of the three unique molecules actually switch conformations. Kinetic analysis of the exchange data indicates that the average rate constant kex = 0.01 s-1 for ring flips and conformer interchange at room temperature. Differential scanning calorimetry and variable-temperature powder diffraction studies indicate a systematic volume expansion that accompanies this motion but no first-order phase transition. All room-temperature exchange events may be quenched at 213 K, at least on the time scale (up to several seconds) probed in this work...}, number={48}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Wolak, JE and Knutson, J and Martin, JD and Boyle, P and Sargent, AL and White, JL}, year={2003}, month={Dec}, pages={13293–13299} }
 @article{jia_wolak_wang_white_2003, title={Independent calibration of H-1 spin-diffusion coefficients in amorphous polymers by intramolecular polarization transfer}, volume={36}, ISSN={["0024-9297"]}, DOI={10.1021/ma0215316}, abstractNote={We report a general method, based on intramolecular spin diffusion, for the measurement and calculation of spin-diffusion coefficients in amorphous polymers and their blends using only NMR data. The basic structural unit that defines 1H polarization density in polymers is the monomer unit. Using appropriately selected internal reference distances calculated from energy-minimized chain dimension simulations, time scales for the redistribution of 1H polarization within amorphous homopolymers may be used to independently calculate maximum values of the spin-diffusion coefficients D. This strategy represents an attractive alternative to current methods employed for domain size measurements in polymer blends, which require calibration of spin-diffusion coefficients based on comparisons of similar NMR data obtained on model compounds analyzed previously using scattering or microscopy techniques. In this way, many more polymer systems become amenable to study by NMR spin-diffusion methods, since X-ray scattering...}, number={3}, journal={MACROMOLECULES}, author={Jia, X and Wolak, J and Wang, XW and White, JL}, year={2003}, month={Feb}, pages={712–718} }
 @article{wolak_jia_gracz_stejskal_white_wachowicz_jurga_2003, title={Polyolefin miscibility: Solid-state NMR investigation of phase behavior in saturated hydrocarbon blends}, volume={36}, ISSN={["0024-9297"]}, DOI={10.1021/ma0301449}, abstractNote={Chain-level mixing in polyolefins is investigated for blends of polyisobutylene (PIB) and polyethylene-co-1-butene (PEB). Previous reports suggest that PIB exhibits unusual mixing behavior in certain saturated blends relative to other polyolefins, even though it is immiscible with most. Variable-temperature 1H, 2H, 13C, and 129Xe NMR experiments are used to characterize local PIB chain dynamics in blends with PEB in which the concentration of 1-butene comonomer units is 23 or 66 wt %. Results from 1D and 2D solid-state 13C exchange experiments, 1H relaxation measurements, and 2H line shape analysis indicate that local conformational dynamics of the PIB CH2 group in the polymer backbone increase significantly in blends with PEB copolymers containing 66 wt % butene comonomer (PEB-66). Even though the PEB-66 is a higher Tg polymer than PIB, PIB exhibits a lower effective Tg when the blend is formed relative to its pure state. Similar perturbations are not observed in the PIB/PEB-23 blend, indicating that thi...}, number={13}, journal={MACROMOLECULES}, author={Wolak, J and Jia, X and Gracz, H and Stejskal, EO and White, JL and Wachowicz, M and Jurga, S}, year={2003}, month={Jul}, pages={4844–4850} }
 @article{wolak_jia_white_2003, title={The  glass transition time scale and configurational entropy in polymers: An experimental molecular view}, volume={125}, DOI={10.1021/ja037736b}, number={45}, journal={Journal of the American Chemical Society}, author={Wolak, J. E. and Jia, X. and White, J. L.}, year={2003}, pages={13660–13661} }
 @misc{wang_white_2002, title={Intramonomer polarization transfer: Calibrating spin diffusion coefficients in mobile polyolefins and their blends}, volume={35}, number={10}, journal={Macromolecules}, author={Wang, X. W. and White, J. L.}, year={2002}, pages={3795–3798} }
 @article{wei_davis_urban_song_porbeni_wang_white_balik_rusa_fox_et al._2002, title={Manipulation of nylon-6 crystal structures with its alpha-cyclodextrin inclusion complex}, volume={35}, ISSN={["0024-9297"]}, DOI={10.1021/ma020765m}, abstractNote={We successfully formed an inclusion complex between nylon-6 and α-cyclodextrin and attempted to use the formation and subsequent disassociation of the nylon-6/α-cyclodextrin inclusion complex to manipulate the polymorphic crystal structures, crystallinity, and orientation of nylon-6. Formation of the inclusion complex was verified by Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and CP/MAS 13C NMR. After obtaining the inclusion complex of nylon-6 and α-cyclodextrin, the sample was treated in an acid environment to remove the host α-cyclodextrin and coalesce the nylon-6 guest polymer. Examination of as-received and IC coalesced nylon-6 samples showed that the α-form crystalline phase of nylon-6 is the dominant component in the coalesced sample. X-ray diffraction patterns demonstrate that the γ-form is significantly suppressed in the coalesced sample. Along with the change in crystal form, an increase in crystallinity of ∼80% wa...}, number={21}, journal={MACROMOLECULES}, author={Wei, M and Davis, W and Urban, B and Song, YQ and Porbeni, FE and Wang, XW and White, JL and Balik, CM and Rusa, CC and Fox, J and et al.}, year={2002}, month={Oct}, pages={8039–8044} }
 @article{wang_coleman_jia_white_2002, title={Quantitative investigations of acidity, and transient acidity, in zeolites and molecular sieves}, volume={106}, number={19}, journal={Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical}, author={Wang, X. W. and Coleman, J. and Jia, X. and White, J. L.}, year={2002}, pages={4941–4946} }
 @article{bullions_wei_porbeni_gerber_peet_balik_white_tonelli_2002, title={Reorganization of the structures, morphologies, and conformations of bulk polymers via coalescence from polymer-cyclodextrin inclusion compounds}, volume={40}, ISSN={["1099-0488"]}, DOI={10.1002/polb.10152}, abstractNote={Abstract}, number={10}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Bullions, TA and Wei, M and Porbeni, FE and Gerber, MJ and Peet, J and Balik, M and White, JL and Tonelli, AE}, year={2002}, month={May}, pages={992–1012} }
 @article{white_wang_2002, title={Structural investigations of solid proteins at natural abundance using 2D multiple-pulse NMR}, volume={35}, ISSN={["0024-9297"]}, DOI={10.1021/ma012067s}, abstractNote={Results from multiple-pulse 2D 1H−13C correlation experiments are described for natural proteins in the solid state. Detailed HETCOR experiments on the complex silk fibroin proteins Samia cynthia ricini (S. c. ricini) and Bombyx mori (B. mori) demonstrate that while the expected dipolar-mediated 13C and 1H correlations are observed, additional chemical shift and coupling information involving amide linkages and dilute peptides are also detected indirectly. This is an important result since we show that the 1H chemical shifts for −NH groups in S. c. ricini are not resolved in the CRAMPS experiments, thereby preventing their direct measurement. Chemical shifts via dipolar couplings (two-spin and multiple-spin interactions) are also detected for dilute peptides in the silk fibroins, again providing key structure information for these functional residues that is completely absent in the CRAMPS data. Relative dynamics of bulky side groups from dilute amino acid residues are apparent from the 2D multiple-pulse ...}, number={7}, journal={MACROMOLECULES}, author={White, JL and Wang, XW}, year={2002}, month={Mar}, pages={2633–2639} }