Triphenylmethyl hexafluoroarsinate-initiated polymerization of 1,2-butylene oxide

The polymerization of 1,2-butylene oxide initiated with triphenylmethyl hexafluoroarsinate in the ?20 to +25°C temperature range with 1,2-dichloroethane as solvent is characterized by a rapid nonstationary initial stage. This is followed by a second slower stage, during which the disappearance of monomer is first-order with respect to its concentration. The conversion of monomer at the end of the first stage is related to the initial catalyst concentration but not to the initial monomer concentration. Invoking the hypothesis of an instantaneous initiation reaction, the experimental results lead to the conclusion of the existence of a unimolecular termination step. Propagation-to-termination rate constant ratios yield a propagation–termination activation energy difference of 5.9 kcal/mole. The termination step proposed is thought to involve the formation of stable macrocyclic oxonium ions. These, in turn, can reactivate the polymerization by an intramolecular reaction leading to the formation of new active centers. An energy of activation of 8.7 kcal/mole was calculated for this reactivation. GPC analyses of the reaction products recovered at the end of the first stage revealed the presence of large proportions of oligomers. Based on kinetic data, the formation of oligomers is explained by a backbiting process similar to the reactivation reaction suggested for the initiation of the second stage.     

Introducing regulation in the measurement of efficiency,with an application to the Canadian air carriers industry

This paper proposes a method to measure efficiency in highly regulated capital-intensive industries in the presence of state-owned enterprises. We generalize the data envelopment analysis method to include regulation in the model, as well as the quasi-fixed nature of capital and its links with the firms’ investment decisions. The framework is then applied to the Canadian air carriers industry to study the impact of regulation changes on the efficiency of the various carriers, between 1960 and 1999. Our results show that deregulation explains a large part of the measured inefficiency.     

Nickel(0)/NaHMDS adduct-mediated intramolecular alkylation of unactivated arenes via a homolytic aromatic substitution mechanism

A variety of polycycles can be synthesized via an intramolecular alkylation cyclization promoted by Ni(PPh(3))(4) and NaHMDS. Mechanistic investigations support the catalytic nature of Ni(0) in the course of TEMPO scavenging experiments and its association with the substrate and NaHMDS to form an adduct by DOSY NMR.     

LAD models,trees, and an analog of the fundamental theorem of arithmetic

Motivated by applications of Logical Analysis of Data (LAD) in medical contexts, original discrete optimization problems are proposed. When a patient arrives with a presumption of a disease, he is submitted to a sequence of tests. From one patient to another, the tests allowing to detect the disease may vary. A subset of tests whose results detect the disease in a given part of the population is called a pattern, which has its own prevalence in the population.If there is only a limited number of tests that can be done, which ones must be selected in order to maximize the number of spotted patients? Or, if each test has a cost, in which order the tests have to be done, in order to minimize the cost? It is the kind of questions that are investigated in this paper. For various special cases, polynomial algorithms are proposed, especially when the hypergraph whose vertices are the tests and whose edges are the patterns is a tree graph.One of these questions involves a criterion which is not a number but a sequence of numbers. The objective is then to find the best sequence for the lexicographic order. To solve this question, a new product on finite sequences is defined, namely the maximum shuffle product, which maps two sequences to their shuffle that is maximal for the lexicographic order. Surprisingly, this product leads to a theorem similar to the fundamental theorem of arithmetic: every sequence can be written uniquely as the product of prime sequences, with the suitable definition of prime sequences.     

A study of the glass transition temperature of asphalts and their viscosity

Summary The glass transition temperatures (T _g ) of asphalt samples of different origins and penetration grades were determined by differential scanning calorimetry (DSC-2). TheT _g values of samples originating from two sources decreased with increasing penetration whereas those of samples from a third source were identical at all values of penetration. Substituting theseT _g data and values of the universal as well as the optimized constantsC ₁ andC ₂ in the Williams-Landel-Ferry equation, viscosities were calculated for each of the samples and compared with the corresponding experimental results. The universal values forC ₁ andC ₂ yielded viscosities which were far removed from the experimental data while the optimized values produced much better results.

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Zusammenfassung Die GlasübergangstemperaturenT _g von Asphaltproben verschiedener Herkunft und Penetrationsgrade wurden mit einem Differentialkalorimeter (DSC-2) bestimmt. DieT _g -Werte von Proben aus zwei Quellen nahmen mit wachsendem Penetrationsgrad ab, wohingegen diese bei Proben aus einer dritten Quelle bei allen Penetrationsgraden gleich blieben. Durch Einsetzen dieserT _g -Daten in die Williams-Landel-Ferry-Gleichung wurden sowohl unter Verwendung von universellen als auch von optimierten Werten der KonstantenC ₁ undC ₂ die Viskositäten der verschiedenen Proben berechnet und mit den experimentell gefundenen Daten verglichen. Die universellen Werte ergaben Viskositäten, die große Unterschiede zu den gemessenen aufwiesen, während man bei Verwendung der optimierten Werte eine weitaus bessere Übereinstimmung erhielt.

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With 2 figures and 10 tables     

Ionic polymerization of 1,2-butylene oxide: GPC,NMR, and IR characterization of the reaction products

The triphenylmethyl hexafluoroarsenate-initiated cationic polymerization of 1,2-butylene oxide in dichloroethane between ?25 and +25°C and its sodium-initiated anionic polymerization in bulk at 20°C have been carried out. Gel permeation chromatography (GPC) molecular weight distribution curves of the reaction products are multinodal. Nuclear magnetic resonance (NMR) and infrared (IR) analyses show that the cationically prepared polymers are composed of cyclic oligomers and linear high-molecular-weight products, while the anionically prepared polymers contain only linear products some of which include double bonds. NMR analyses further reveal that the cationically prepared polymers consist of monomer repeat units, while the anionically prepared polymers are essentially made of side products originating from the reaction of 1,2-butylene oxide with the sodium mirror used as the anionic initiator.