Azoalkanes—novel flame retardants and their structure–property relationship

A number of symmetrical and unsymmetrical azoalkanes of the general formula R′?N = N?R and related azoxy, hydrazone as well as azine derivatives have been synthesized in order to assess their potential as novel flame retardants for polypropylene alone or in combination with commercially available flame retardants such as alumina trihydrate (ATH), decabromodiphenyl ether (DecaBDE) and tris(3‐bromo‐2,2‐bis(bromomethyl)‐propyl)phosphate (TBBPP). The experimental results show that in the series of different sized azocycloalkanes the flame retardant efficacy decreased in the following order: R = cyclohexyl > cyclopentyl > cyclobutyl > cyclooctanyl >> cyclododecanyl. Whereas in the series of aliphatic azoalkanes compounds the efficacy decreased in the following order: R = n‐alkyl > tert‐butyl > tert‐octyl. In addition, also some of the prepared azoxy, azine, and hydrazone derivatives provide flame retardancy to polypropylene films at already very low concentrations (0.25–1 wt%). Noteworthy is that in contrast to other halogen‐free radical generators, the azoalkanes are also very effective as flame retardants in polypropylene thick moldings. Interestingly, it was found that 4,4′‐bis(cyclohexylazocyclohexyl)‐methane) shows a strong synergistic effect with ATH. Thus, in the presence of 0.5 wt% of azoalkane the ATH loading could be reduced from 60 to 25 wt% and still UL94 V‐2 rating could be reached. Furthermore, the fire testing data reveal that azoalkanes show a synergistic effect with DecaBDE and when used in conjunction with very low loadings of TBBPP. Copyright © 2010 John Wiley & Sons, Ltd.     

Two-dimensional Quantum Random Walk

We analyze several families of two-dimensional quantum random walks. The feasible region (the region where probabilities do not decay exponentially with time) grows linearly with time, as is the case with one-dimensional QRW. The limiting shape of the feasible region is, however, quite different. The limit region turns out to be an algebraic set, which we characterize as the rational image of a compact algebraic variety. We also compute the probability profile within the limit region, which is essentially a negative power of the Gaussian curvature of the same algebraic variety. Our methods are based on analysis of the space-time generating function, following the methods of Pemantle and Wilson (J. Comb. Theory, Ser. A 97(1):129–161, 2002).     

A data-based stability-preserving model order reduction method for hyperbolic partial differential equations

Nonlinear Dynamics - This paper proposes a data-based approach for model order reduction that preserves incremental stability properties. Existing data-based approaches do typically not preserve...     

Immobilization of chiral ligands on polymer fibers by electron beam induced grafting and applications in enantioselective catalysis

[reaction: see text] Styrenic TADDOL and L-prolinol-derived monomers were immobilized on polyethylene fibers by electron beam induced preirradiation grafting using styrene as comonomer. The polymer-supported chiral ligands were utilized as catalysts in the asymmetric addition of diethylzinc to benzaldehyde. Fiber-bound titanium TADDOLate gave a quantitative conversion of benzaldehyde to 1-phenylpropan-1-ol in a 97:3 S/R enantiomeric ratio. The catalyst was successfully regenerated and employed in subsequent reactions with retention of high enantioselectivities.     

Viscoelastic-mapping of cellulose nanofibrils using low-total-force contact resonance force microscopy (LTF-CRFM)

Cellulose - Low-total-force contact resonance force microscopy (LTF-CRFM), an atomic force microscopy method, is introduced as a non-destructive means to quantify the local viscoelastic loss...     

Completeness of two systems of illative combinatory logic for first-order propositional and predicate calculus

Illative combinatory logic consists of the theory of combinators or lambda calculus extended by extra constants (and corresponding axioms and rules) intended to capture inference. The paper considers 4 systems of illative combinatory logic that are sound for first-order propositional and predicate calculus. The interpretation from ordinary logic into the illative systems can be done in two ways: following the propositions-as-types paradigm, in which derivations become combinators, or in a more direct way, in which derivations are not translated. Both translations are closely related in a canonical way. In a preceding paper, Barendregt, Bunder and Dekkers, 1993, we proved completeness of the two direct translations. In the present paper we prove completeness of the two indirect translations by showing that the corresponding illative systems are conservative over the two systems for the direct translations. In another version, DBB (1997), we shall give a more direct completeness proof. These papers fulfill the program of Church and Curry to base logic on a consistent system of -terms or combinators. Hitherto this program had failed because systems of ICL were either too weak (to provide a sound interpretation) or too strong (sometimes even inconsistent). Received: February 15, 1996     

In vivo sodium-23 magnetic resonance surface coil imaging: Observing experimental cerebral ischemia in the rat

Sodium-23 magnetic resonance imaging can be used to detect and assess experimental cerebral ischemia in the rat. An imaging technique utilizing a surface coil is described to produce sodium magnetic resonance images of good quality and resolution within 10 min. A novel method of hemispheric occlusion showed edema in the right brain of the rat head within 3 hr after injury. The edema was especially pronounced by 12 hr with effects in the right brain, eye and surrounding muscle evident.     

Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler‐Natta catalysts

The effect of type and concentration of external donor and hydrogen concentration on oligomer formation and chain end distribution were studied. Bulk polymerization of propylene was carried out with two different Ziegler‐Natta catalysts at 70 °C, one a novel self‐supported catalyst (A) and the other a conventional MgCl₂‐supported catalyst (B) with triethyl aluminum as cocatalyst. The external donors used were dicyclopentyl dimethoxy silane (DCP) and cyclohexylmethyl dimethoxy silane (CHM). The oligomer amount was shown to be strongly dependent on the molecular weight of the polymer. Catalyst A gave approximately 50 % lower oligomer content than catalyst B due to narrower molecular weight distribution in case of catalyst A. More n‐Bu‐terminated chain ends were found for catalyst A indicating more frequent 2,1 insertions. Catalyst A also gave more vinylidene‐terminated oligomers, suggesting that chain transfer to monomer, responsible for the vinylidene chain ends, was a more important chain termination mechanism for this catalyst, especially at low hydrogen concentration. Low site selectivity, due to low external donor concentration or use of a weak external donor (CHM), was also found to increase formation of vinylidene‐terminated oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 351–358, 2010