Graft copolymers via ROMP and Diels–Alder click reaction strategy

Anthracene‐functionalized oxanorbornene monomer and oxanorbornenyl polystyrene (PS) with ω‐anthracene end‐functionalized macromonomer were first polymerized via ring‐opening metathesis polymerization using the first‐generation Grubbs' catalyst in dichloromethane at room temperature and then clicked with maleimide end‐functionalized polymers, poly(ethylene glycol) (PEG)‐MI, poly(methyl methacrylate) (PMMA)‐MI, and poly(tert‐butyl acrylate) (PtBA)‐MI in a Diels–Alder reaction in toluene at 120 °C to create corresponding graft copolymers, poly(oxanorbornene)‐g‐PEG, poly(oxanorbornene)‐g‐PMMA, and graft block copolymers, poly(oxanorbornene)‐g‐(PS‐b‐PEG), poly(oxanorbornene)‐g‐(PS‐b‐PMMA), and poly(oxanorbornene)‐g‐(PS‐b‐PtBA), respectively. Diels–Alder click reaction efficiency for graft copolymerization was monitored by UV–vis spectroscopy. The dn/dc values of graft copolymers and graft block copolymers were experimentally obtained using a triple detection gel permeation chromatography and subsequently introduced to the software so as to give molecular weights, intrinsic viscosity ([η]) and hydrodynamic radius (R_h) values. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Sequential double polymer click reactions for the preparation of regular graft copolymers

In this study, graft copolymers with regular graft points containing polystyrene (PS) backbone and poly(methyl methacrylate) (PMMA), poly(tert‐butyl acrylate) (PtBA), or poly (ethylene glycol) (PEG) side chains were simply achieved by a sequential double polymer click reactions. The linear α‐alkyne‐ω‐azide PS with an anthracene pendant unit per chain was produced via atom transfer radical polymerization of styrene initiated by anthracen‐9‐ylmethyl 2‐((2‐bromo‐2‐methylpropanoyloxy)methyl)‐2‐methyl‐3‐oxo‐3‐(prop‐2‐ynyloxy) propyl succinate. Subsequently, the azide–alkyne click coupling of this PS to create the linear multiblock PS chain with pendant anthracene sites per PS block, followed by Diels–Alder click reaction with maleimide end‐functionalized PMMA, PtBA, or PEG yielded final PS‐g‐PMMA, PS‐g‐PtBA or PS‐g‐PEG copolymers with regular grafts, respectively. Well‐defined polymers were characterized by ¹H NMR, gel permeation chromatography (GPC) and triple detection GPC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Periodic mesoporous hydridosilica--synthesis of an "impossible" material and its thermal transformation into brightly photoluminescent periodic mesoporous nanocrystal silicon-silica composite

There has always been a fascination with "impossible" compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these "impossible" materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such "impossible" material is periodic mesoporous hydridosilica (meso-HSiO(1.5)). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO(1.5) can be synthesized by template-directed self-assembly of HSi(OEt)(3) under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO(2), a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.     

Hochschild homology and split pairs

We study the Hochschild homology of algebras related via split pairs, and apply this to fiber products, trivial extensions, monomial algebras, graded-commutative algebras and quantum complete intersections. In particular, we compute lower bounds for the dimensions of both the Hochschild homology and cohomology groups of quantum complete intersections.     

Multiplicity theory for multivariate wide sense stationary generalized processes

It is shown that the representation theory of a multivariate, purely nondeterministic, wide sense stationary generalized process can be reduced to a study of some isomorphism results established for commutation relations occurring in quantum mechanics. Using this simplification a multiplicity theory is developed. The time domain and spectral representation of the process are investigated in this context, and the concept of a generalized innovations process is introduced.     

The bonded water molecule3ĪII: 180° Flips and diffusion

The proton spin-lattice relaxation time, T₁, is measured as a function of temperature in α -(COOH)₂·-2H₂O, K₂HgCl₄· H₂O and LiCHO·H₂O. The relaxation is caused by 180° flips of the water molecules about their 2-fold axes and good agreement is obtained between calculated and observed values of T₁. Empiricly the flip rate follows a classical Arrhenius equation: P· exp $\text{(? ΔH}\text{(RT))}$. A literature survey of values of P and ΔH obtained from similar investigations on other hydrates is given. The survey shows that the preexponential factor, P, is a function of the activation enthalpy, ΔH. P increases from 10¹² to 10¹⁷ Hz when ΔH changes from 2 to 17 $\text{kcal}\text{mole}$. Using a dynamical rate theory as formulated by Feit, we find the flip rate is given by: K₂· √(ΔH)· exp (K₁ΔH)· exp $\text{(?ΔH}\text{(RT>))}$. This expression can be fitted to the observed data using K₁ = 0.69 $\text{mole}\text{kcal}$ and K₂ = 2 × 10¹¹ Hz · $\text{(kcal}\text{mole)}$$\text{?1}\text{2}$. Thus both the frequency factor, K₂√ (ΔH), and the entropic factor, exp (K₁ΔH), have been obtained for flipping water molecules in hydrates. The values of K₁ and K₂ are shown to be physically reasonable.     

Radiation-induced changes in phosphorus T1values in human melanoma xenografts studied by P-MRS

³¹P-magnetic resonance spectroscopy (MRS) has been shown to be a promising method for monitoring tumor response to radiation therapy. The purpose of the work reported here was to investigate whether the usefulness of ³¹P-MRS might be enhanced by measurement of spin-lattice relaxation times (T₁s) in addition to resonance ratios. The work was based on the hypothesis that tumors having a high probability of being controlled locally would show shortened T₁s during the treatment course due to reoxygenation and development of necrosis. BEX-t human melanoma xenografts, which show efficient reoxygenation and development of necrosis following single dose irradiation, were used as tumor models. Tumors were treated with single doses of 5.0 or 15.0 Gy and the T₁s of the inorganic phosphate and nucleoside triphosphate β resonances were measured as a function of time after irradiation by using the superfast inversion recovery method. Fractional tumor water content was determined by drying excised tumors at 50°C until a constant weight was reached. The T₁s in irradiated tumors were either longer than or not significantly different from those in unirradiated control tumors. The increase in the T₁s following irradiation coincided in time with a radiation-induced increase in tumor water content, suggesting a causal relationship. The effects of reoxygenation and development of necrosis on T₁s were probably overshadowed by the effects of tumor water content. Consequently, the usefulness of ³¹P-MRS in monitoring tumor response to radiation therapy might not be significantly enhanced by measurement of T₁s.     

Optimization methods for pipeline transportation of natural gas with variable specific gravity and compressibility

In this paper, the problem of flow maximization in pipeline systems for transmission of natural gas is addressed. We extend previously suggested models by incorporating the variation in pipeline flow capacities with gas specific gravity and compressibility. Flow capacities are modeled as functions of pressure, compressibility and specific gravity by the commonly-used Weymouth equation, and the California Natural Gas Association method is used to model compressibility as a function of specific gravity and pressure. The sources feeding the transmission network do not necessarily supply gas with equal specific gravity. In our model, it is assumed that when different flow streams enter a junction point, the specific gravity of the resulting flow is a weighted average of the specific gravities of entering flows. We also assume the temperature to be constant, and the system to be in steady state. Since the proposed model is non-convex, and global optimization hence can be time consuming, we also propose a heuristic method based on an iterative scheme in which a simpler NLP model is solved in each iteration. Computational experiments are conducted in order to assess the computability of the model by applying a global optimizer, and to evaluate the performance of the heuristic approach. When applied to a wide set of test instances, the heuristic method provides solutions with deviations less than 10% from optimality, and in many instances turns out to be exact. We also report several experiments demonstrating that letting the compressibility and the specific gravity be global constants can lead to significant errors in the estimates of the total network capacity.