Cyclic Ruthenium-Alkylidene Catalysts for Ring-Expansion Metathesis Polymerization

A series of cyclic Ru-alkylidene catalysts have been prepared and evaluated for their efficiency in ring-expansion metathesis polymerization (REMP). The catalyst structures feature chelating tethers extending from one N-atom of an N-heterocyclic carbene (NHC) ligand to the Ru metal center. The catalyst design is modular in nature, which provided access to Ru complexes having varying tether lengths, as well as electronically different NHC ligands. Structural impacts of the tether length were unveiled through 1H NMR spectroscopy as well as single-crystal X-ray analyses. Catalyst activities were evaluated via polymerization of cyclooctene, and key data are provided regarding propagation rates, intramolecular chain transfer, and catalyst stabilities, three areas necessary for the efficient synthesis of cyclic poly(olefin)s via REMP. From these studies, it was determined that while increasing the tether length of the catalyst leads to enhanced rates of polymerization, shorter tethers were found to facilitate intramolecular chain transfer and release of catalyst from the polymer. Electronic modification of the NHC via backbone saturation was found to enhance polymerization rates to a greater extent than did homologation of the tether. Overall, cyclic Ru complexes bearing 5- or 6-carbon tethers and saturated NHC ligands were found to be readily synthesized, bench-stable, and highly active catalysts for REMP

Ring-Expansion Metathesis Polymerization: Catalyst-Dependent Polymerization Profiles

Ring-expansion metathesis polymerization (REMP) mediated by recently developed cyclic Ru catalysts has been studied in detail with a focus on the polymer products obtained under varied reaction conditions and catalyst architectures. Depending upon the nature of the catalyst structure, two distinct molecular weight evolutions were observed. Polymerization conducted with catalysts bearing six-carbon tethers displayed rapid polymer molecular weight growth which reached a maximum value at ca. 70% monomer conversion, resembling a chain-growth polymerization mechanism. In contrast, five-carbon-tethered catalysts led to molecular weight growth that resembled a step-growth mechanism with a steep increase occurring only after 95% monomer conversion. The underlying reason for these mechanistic differences appeared to be ready release of five-carbon-tethered catalysts from growing polymer rings, which competed significantly with propagation. Owing to reversible chain transfer and the lack of end groups in REMP, the final molecular weights of cyclic polymers was controlled by thermodynamic equilibria. Large ring sizes in the range of 60−120 kDa were observed at equilibrium for polycyclooctene and polycyclododecatriene, which were found to be independent of catalyst structure and initial monomer/catalyst ratio. While six-carbon-tethered catalysts were slowly incorporated into the formed cyclic polymer, the incorporation of five-carbon-tethered catalysts was minimal, as revealed by ICP-MS. Further polymer analysis was conducted using melt-state magic-angle spinning ^(13)C NMR spectroscopy of both linear and cyclic polymers, which revealed little or no chain ends for the latter topology

A direct route to cyclic organic nanostructures via ring-expansion metathesis polymerization of a dendronized macromonomer

Cyclic organic nanostructures were prepared via ring-expansion metathesis polymerization of a dendronized norbornene macromonomer. The strategy provides a direct, efficient route to nanoscale rings in a single operation. AFM imaging confirmed toroidal features having diameters of ca. 35−40 nm

Synthesis and Direct Imaging of Ultrahigh Molecular Weight Cyclic Brush Polymers

Convenient route to cyclic polymers: Ultrahigh molecular weight cyclic brush polymers were synthesized through ring-expansion metathesis polymerization of various macromonomers. Atomic force microscopy was used to visualize toroidal shapes and large opening pores, along with linear chains, which may result from high sensitivity of brush polymers to mechanical degradation

Intrathecal Urokinase as a treatment for intraventricular hemorrhage in the preterm infant

Despite improvements in the care of preterm infants, intraventricular hemorrhage (IVH) and posthemorrhagic hydrocephalus (PHH) continue to be frequent occurrences in this patient population. Shunt procedures in these children are frequently complicated by obstruction and/or infection. As the hydrocephalus is usually caused by an obliterative arachnoiditis due to contact of the blood with the basilar meninges, it was postulated that infusion of urokinase into the ventricles of infants who have sustained an IVH would clear the blood, mitigate the arachnoiditis, and prevent the progression of PHH. Accordingly, 18 preterm infants who had sustained IVH and subsequently developed PHH were treated with intraventricular urokinase instilled via a surgically implanted subcutaneous reservoir. There were no complications associated with the urokinase. Infants were divided into two dosage groups: low dose (110,000–140,000 IU total) and high dose (280,000 IU total). One infant in the low-dose group died at 1 month of life of respiratory complications. In the low-dose group, 3 of 8 (37%) infants required shunt placement; in the high-dose group, all 9 required shunt placement. For the total group, the shunt rate was 71 %. This compares to a historical control group shunt rate of 92%. While the difference between the treatment group as a whole and control group approaches, but does not reach, statistical significance (p = 0.068), there was a significant reduction in the shunt rate when the low-dose group was considered separately (p \u3c 0.002). For those infants that required shunt placement, there were fewer shunt revisions performed in the treatment group than in the control group during the first 24 months following shunt placement: 0.67 versus 1.5 shunt revisions/shunted child. Initial experience with intraventricular urokinase following IVH and PHH in preterm infants suggests a beneficial effect in reducing the shunt revision rate in both high- and low-dose groups. Reduction in shunt placement rate is seen only in the low-dose group

Glyphosate Carryover in Seed Potato: Effects on Mother Crop and Daughter Tubers

Field studies were conducted in 2008 and 2009 in Aberdeen, ID, Ontario, OR, and Paterson, WA to determine the effect of simulated glyphosate drift on ‘Ranger Russet’ potato during the application year and the crop growing the next year from the daughter tubers. Glyphosate was applied at 8.5, 54, 107, 215, and 423 g ae ha⁻¹ which corresponds to 1/00, 1/16, 1/8, ¼, and 1/2 of the lowest recommended single-application rate for glyphosate-resistant corn and sugar beet of 846 g ha⁻¹. Glyphosate was applied when potato plants were at 10 to 15 cm tall (Early), or at stolon hooking (H), tuber initiation (TI), or during mid-bulking (MB). In general, the MB applications caused less visual foliar injury to the mother crop than earlier applications at ID or OR, and H applications at WA. Mother crop injury increased as glyphosate rate increased regardless of location, application timing, and rating date. U.S. No.1 and total tuber yields were usually related to the injury level resulting from glyphosate application timings and rates. Although injury to the mother crop from glyphosate applied at MB usually was the lowest compared to injury from other application timings, when daughter tubers from that timing were planted the following year, emergence, plant vigor, and yield was most detrimentally impacted compared with that of daughter tubers from other timing treatments. MB daughter tuber emergence was less than 30% of the nontreated control tuber emergence while emergence of daughter tubers from the other treatments was 60 to 95%. As rate of glyphosate applied to the mother crop increased, daughter tuber emergence decreased. When MB daughter tubers did emerge, plants were chlorotic and stunted as if the plants had been directly sprayed with glyphosate. Regardless of whether the daughter tubers had defects or not, results the following year were the same. Implications are that if amother seed crop encounters glyphosate during bulking, injury may not even be noticeable on the foliage or the tubers, however, emergence, vigor, and yield of the crop growing the following year from the daughter tubers could be greatly impacted.Keywords: Rate, Solanum tuberosum, Glyphosate, Mother crop, Daughter tuber, Application timin

Dependence of the kinetic energy absorption capacity of bistable mechanical metamaterials on impactor mass and velocity

Using an alternative mechanism to dissipation or scattering, bistable structures and mechanical metamaterials have shown promise for mitigating the detrimental effects of impact by reversibly locking energy into strained material. Herein, we extend prior works on impact absorption via bistable metamaterials to computationally explore the dependence of kinetic energy transmission on the velocity and mass of the impactor, with strain rates exceeding $10^2$ s$^{-1}$. We observe a large dependence on both impactor parameters, ranging from significantly better to worse performance than a comparative linear material. We then correlate the variability in performance to solitary wave formation in the system and give analytical estimates of idealized energy absorption capacity under dynamic loading. In addition, we find a significant dependence on damping accompanied by a qualitative difference in solitary wave propagation within the system. The complex dynamics revealed in this study offer potential future guidance for the application of bistable metamaterials to applications including human and engineered system shock and impact protection devices

Political Marketing Activity in Simultaneous Regional Elections 2015

Regional head election system was change in 2015. It has impact on political marketing strategy to all stake holders, such as political party and candidatures.The purposes of this research is to analyzeashifting ofpolitical marketing issueson regional election 2015. The research approach uses the mix method with the type of sequential explanatory. The subjects of this research are the candidates, election successful teams or supporting team, and young voters. Location of research based on cluster system district and sub district in Bandung, Cianjur, Magelang, Sleman, and Medan. The data are collected through techniques of questionnaires to young voters; interview to candidates, election successful teams and young voters, as well as the documentation of media and data on Regional General Elections Commission (KPUD). There are also triangular data techniqueinterviews with the General Elections Commission (KPU), the community and supporting team, and documentation and questionnaire form. The result shows that the system of political marketing has already started shifting from product, promotion, price, place, and people known as the 5Ps from mostly dominated by Political Partyinto the role of PEOPLE as candidature in influensing the voters. The Result also tells that shifting from using convetional media into almost using digital media was powerfull

Post-emergence selectivity of metribuzin to carrot.

The objective of this study was to evaluate the selectivity of the herbicide metribuzin to carrot plants as a function of genotype, dose, and plant growth stage at the time of application. Two experiments were carried out, one in a greenhouse and another in the field

Silver and Palladium Complexes of a Bis(benzimidazolin-2-ylidene)pyridine Pincer Ligand

Reaction of 2,6-bis(3-butylbenzimidazol-1-ium)pyridine dibromide with silVer oxide affords a dinuclear complex of the type [L2Ag2]2+ [L ) 2,6-bis(3-butylbenzimidazolin-2-ylidene)pyridine]. 1H NMR spectroscopic studies suggest that the dinuclear structure is also present in solution. Transmetalationof the silVer-NHC complex with PdCl2(CH3CN)2 yields a mononuclear palladium complex of the type [LPdCl]+, with a chelating C,N,C pincer ligand