Porous monodisperse poly(methacrylic acid-co-ethylene dimethacrylate) and poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads, which can be used as a platform for the production of separation media, polymeric reagents, and supports, have been prepared using the staged templated suspension polymerization process. Since the direct polymerization of methacrylic acid, which would lead to beads bearing carboxyl groups in a single step, is not compatible with the preparation technique, poly(tert-butyl methacrylate-co-ethylene dimethacrylate) beads were prepared and then selectively deprotected. In contrast, beads containing aliphatic hydroxyl groups can be prepared directly despite the high solubility of 2-hydroxyethyl methacrylate in water. The degree of functionalization and porous properties of the beads are largely controlled by the monomer composition in the polymerization mixture. One application for the functionalized beads is the preparation of very selective chiral separation media for HPLC of enantiomers.
Abstract The porous structure of monodisperse macroporous beads can be controlled by using soluble polymers with well‐defined structural characteristics as part of the porogenic mixture. In general, the use of linear polystyrene as a porogen in the preparation of poly (styrene‐co‐divinylbenzene) beads shifts the pore size distribution towards larger pores. While a direct correlation between pore size and molecular weight of the porogen has been established, the chemical composition of the polymer porogen has no effect on the porous and chromatographic properties of the beads. These findings suggest that the average molar volume of the porogenic system is important while the miscibility of the polymer porogen with the crosslinked polymer that is formed is of little relevance. © 1994 John Wiley & Sons, Inc.
© 2014 American Chemical Society. A hybrid quantum mechanics/molecular mechanics (QM/MM) model and the quasiclassical trajectory (QCT) method have been combined to study the reaction of alkene methylation by methanol catalyzed by the zeolite H-MFI. The rate-limiting step of this reaction is the methylation of the alkene, and the apparent activation energy calculated at the ÏB97X-D/6-31G(d,p)//ÏB97X-D/6-311++G(3df,3pd) level of theory for this step agrees well with experiment and previous full QM studies. Following the ethene methylation transition state toward the products along the intrinsic reaction coordinate reveals the existence of a protonated cyclopropane (PCP+) carbocation intermediate. A similar protonated methylcyclopropane (mPCP+) carbocation intermediate is found for propene methylation. The intermediates produced during the alkene methylation reaction are metastable with a lifetime of O(1 ps) obtained from QCTs. Because of the short lifetime of these intermediates, the available energy in the carbocation is not in thermal equilibrium distribution with the zeolite lattice before subsequent reaction occurs. The qualitative difference between product distributions obtained by static and dynamic reaction pathways suggests the pathways of zeolite-catalyzed reactions proceed through high-temperature pathways that differ from the 0 K potential energy surface. The transformation of the m-PCP+ intermediate to the longer-lived secondary 2-butyl carbocation observed during QCTs suggests that more stable carbocations can properly thermalize and exist as reaction intermediates for longer than 1 ps.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
This chapter explains how fracture mechanics can be applied to subcritical crack growth, primarily by environmentally-assisted cracking, creep, and fatigue. It describes in each case the development of a crack-growth relationship characterizing the velocity of a crack, with respect to time or number of cycles, as a function of the relevant governing parameter, which is generally the stress intensity factor, K, for environmentally-assisted cracking, a series of characterizing parameters for creep-crack growth, such as C∗, C(t), and C t , depending on the mode of creep deformation, and the alternating stress intensity, ΔK, for fatigue crack growth. In addition to a brief discussion of mechanisms, for fatigue, we further derive how the form of the crack-growth law, which is known as the Paris law, can change for ductile (e.g., metallic) vs. brittle (e.g., ceramic) materials. Finally, we show how such crack-growth relationships can be utilized to predict the lifetime of components or structures using the damage-tolerant life-prediction methodology.
Peg-in-hole insertion is not only a longstanding problem in robotics but the most common automated mechanical assembly task. In this paper the authors present a high precision, self-calibrating peg-in-hole insertion strategy using several very simple, inexpensive, and accurate optical sensors. The self-calibrating feature allows the authors to achieve successful dead-reckoning insertions with tolerances of 25 microns without any accurate initial position information for the robot, pegs, or holes. The program the authors implemented works for any cylindrical peg, and the sensing steps do not depend on the peg diameter, which the program does not know. The key to the strategy is the use of a fixed sensor to localize both a mobile sensor and the peg, while the mobile sensor localizes the hole. The authors' strategy is extremely fast, localizing pegs as they are en route to their insertion location without pausing. The result is that insertion times are dominated by the transport time between pick and place operations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
We present optical spectra and photometry sampling the first 6 months after discovery of supernova (SN) 1999gi in NGC 3184. SN 1999gi is shown to be a Type II-plateau event with a photometric plateau lasting until about 100 days after discovery. Using the expanding photosphere method (EPM), we derive a distance to SN 1999gi of 11.1(-1.8)(+2.0) Mpc and an explosion date of 1999 December 5.8(-3.1)(+3.0), or 4.1(-3.1)(+3.0) days prior to discovery. This distance is consistent with a Tully-Fisher distance recently derived to NGC 3184 (Dapproximate to11.59 Mpc), but it is somewhat closer than the Cepheid distances recently derived to two galaxies that have generally been assumed to be associated with the group containing NGC 3184 (NGC 3319, D=13.30+/-0.55 Mpc, and NGC 3198, D=13.80+/-0.51 Mpc). From many lines of evidence, we conclude that SN 1999gi is only minimally reddened. A comparison between the color of SN 1999gi at early times and that of an infinitely hot blackbody restricts the reddening to E(B-V)<0.45 mag, while a comparison between the color evolution of SN 1999gi and the well-observed ( and extensively modeled) Type II-P SN 1999em implies an even more restrictive upper reddening limit of E (B-V)<0.3 mag. A variety of other, independent reddening estimates are consistent with these upper limits and yield a probable reddening of E (B-V)=0.21+/-0.09 mag. We reconsider the upper mass limit (9(-2)(+3) M-circle dot) recently placed on the progenitor star of SN 1999gi by Smartt et al. in light of these results. Following the same procedures, but using the new data presented here, we arrive at a less restrictive upper mass limit of 15(-3)(+5) M-circle dot for the progenitor. The increased upper limit results mainly from the larger distance derived through the EPM than was assumed by the Smartt et al. analyses, which relied on less precise (and less recent) distance measurements to NGC 3184. Finally, we confirm the existence of "complicated" P Cygni line profiles in early-time and later photospheric-phase spectra of SN 1999gi. These features, first identified by Baron et al. in spectra of SN 1999em as high-velocity absorptions, in addition to the "normal" lower velocity component, are here verified to be true P Cygni profiles consisting of both an absorption trough and an emission peak at early times. In the earliest spectrum, taken less than a day after discovery, the features extend out to nearly -30,000 km s(-1), indicating the existence of very high velocity material in the outer envelope of SN 1999gi.
Complexes [PhBP(Ph)3]RuH(η(3)-H2SiRR') (R,R' = Me,Ph, 1a; RR' = Ph2, 1b) react with XylNC (Xyl = 2,6-dimethylphenyl) to form Fischer carbene complexes [PhBP(Ph)3]Ru(H)═[C(H)(N(Xyl)(η(2)-H-SiRR'))] (2a,b) that feature a γ-agostic Si-H bond. The ruthenium isocyanide complexes [PhBP(Ph)3]Ru(H)(CNXyl)(η(2)-HSiHRR') (6a,b) are not intermediates as they do not convert to 2a,b. Experimental and theoretical investigations indicate that XylNC is activated by initial coordination to the silicon center in 1a,b, followed by 1,1-insertion into an Si-H bond of the coordinated silane and then rearrangement to 2a,b.
