Unusual contributions of molecular architecture to rheology and flow birefringence in hyperbranched polystyrene melts

With the increase in sophisticated synthesis methods, it appears that polymer architecture may be a tunable property. Therefore, the role of architecture in rheological and processing properties has received renewed attention, mainly because of dendrimer synthesis and metallocene‐catalyst technology. Linear polymers and hyperbranched polymers represent two ends of branching complexity. Some previous studies have suggested that hyperbranched polymers may behave like unentangled polymers, whereas others have proposed that they exhibit the properties of soft colloids. In an effort to compare the responses of linear and hyperbranched polymers, we synthesized starlike hyperbranched polystyrenes (HBPSs) of various branch lengths and numbers of branches. The HBPSs used in this study were unentangled or weakly entangled, allowing us to study the effect of branch density more readily. Two linear polystyrene (L‐PS) melts and two HBPSs were studied. Using a custom‐built rheooptical apparatus, we characterized the rheology and flow birefringence of these materials. To our knowledge, these are the first flow birefringence measurements on highly branched polymer melts. Our results suggest that the flow behavior of HBPS is significantly different from that of L‐PS: (1) HBPS shows nonterminal behavior in the low‐frequency rheological response; (2) when the stress‐optical rule (SOR) holds, the stress‐optical coefficient of HBPS is much lower than those of analogous linear polymers; and (3) when the branch density is high and the branch length is sufficiently low, the SOR fails for these homopolymer melts. A significant increase in the birefringence for a given amount of stress in the low‐frequency region suggests that there may be a soft core in these materials due to the strong preferential radial orientation of chain segments near the center of a molecule versus those near the periphery. The predominantly elastic response of the soft structures may be responsible for the enhanced form birefringence. Our preliminary results indicate that these materials may exhibit both polymeric and soft‐colloid natures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2562–2571, 2001     

A facile one-pot synthesis of N-substituted tetrahydroquinolines

An uncatalyzed one-pot synthesis of N-substituted tetrahydroquinolines was achieved in good yields by the reaction of quinoline and alkyl/acyl halides with Hantzsch dihydropyridine ester under mild reaction conditions.     

Preparation of Vicinal Azidohydrins by Reaction of Oxiranes with Triethylaluminium/Hydrogen Azide

A novel, mild, and highly stereoselective transformation of epoxides to azidohydrins by treatment with Et₃Al/HN₃ in toluene is described. As an example for the versatility of the reaction, a polyfunctional compound, 14,15-epoxy-14,15-dihydromilbemycin D ( 1 ), was transformed to 14-azido-14,15-dihydro-15-hydroxymilbemycin D ( 2 ) in 61% yield.     

A new multi-objective genetic algorithm applied to hot-rolling process

A new genetic algorithms based multi-objective optimization algorithm (NMGA) has been developed during study. It works on a neighborhood concept in the functional space, utilizes the ideas on weak dominance and ranking and uses its own procedures for population sizing. The algorithm was successfully tested with some standard test functions, and when applied to a real-life data of the hot-rolling campaign of an integrated steel plant, it outperformed another recently developed multi-objective evolutionary algorithm.     

Colorimetric and fluorescence sensing of fluoride anions with potential salicylaldimine based schiff base receptors

Salicylaldimine based schiff base receptors with different substituents showing fluorescent enhancement in the presence of fluoride anion was visualized through naked eye as well as by change in spectral properties (UV–vis and fluorescent techniques). The reason for such fluorescence enhancement may be due to hydrogen bond interaction between receptor recognition site and fluoride anion. Such a hydrogen bond interaction creates a six-membered transition state, which avoids quenching processes. To support this, fluorescence enhancement factor (FEF) was calculated and it was found to be more (FEF = 652) for –NO₂ substituted receptor compared to other receptors.     

Asymptotically exact a posteriori error estimator for biquadratic elements

This paper addresses the finite element method with a posteriori error estimation for elements of degree p = 1 and p = 2. It gives the formulae for the error indicators and error estimators. Basic mathematical characterizations of the estimators are given and it is shown that the estimators for p = 1 and p = 2 have different structures. Numerical examples show the effectivity of the approach and the high quality of the estimator.     

Effect of pressure on luminescence properties of Sm3+ ions in potassium niobate tellurite glass

Emission spectra and decay properties of the ⁴G_5/2 level of Sm³⁺ ions in TeO₂+K₂O+Nb₂O₅ glass have been measured as a function of pressure upto 14.6 GPa at room temperature. A progressive red shift in the barycentres of ⁴G_5/2→⁶H_J (J=9/2, 7/2 and 5/2) emission bands and increase in splitting of these bands have been observed with increasing pressure. The luminescence decay profile of the ⁴G_5/2 level at ambient condition shows a nearly single exponential nature and with increase in pressure it becomes gradually non-exponential associated with a decrease in lifetime. The non-exponential decay curves are well-fitted to the Inokuti–Hirayama model for S=6, indicating that the interaction for cross-relaxation energy transfer between Sm³⁺ ions is of dipole–dipole type. The results obtained after release of pressure reveal that there is a small hysteresis.     

A rapid and highly efficient Michael addition of methoxybenzenes and indoles to α,β-unsaturated ketones using BF3·OEt2 as a catalyst

An efficient and general protocol is described for the Michael addition of α,β-unsaturated ketones with electron-rich arenes/indoles to give alkylated arenes/indoles under mild reaction condition at room temperature. Shorter reaction time, convenient and good isolated yields are the significant features of this protocol. Moreover, the procedure is environmentally benign in nature and applicable to variety of arenes/indoles as well as α,β-unsaturated ketones.