Stepwise Addition Of Monomers Research Articles

An Amphiphilic Mesoporous Polymer Comprising a “built‐in” Imidazolium Ionic Liquid via Nanocasting Method as a Novel Catalyst Support with Combined Prospects

AbstractAn imidazolium based ionic liquid bearing triethylene glycol (TEG) tag was employed as a functional monomer together with divinylbenzene to prepare a novel hydrophilic mesoporous polymer containing ionic liquid functionalities via nanocasting method using SBA‐15 as a hard template. The material was characterized using transmission electron microscopy (TEM), N2 sorption analysis, thermo‐gravimetric analysis (TGA), Fourier‐transform infrared spectroscopy (FT‐IR), elemental analysis (CHN), solid‐state NMR spectroscopy and contact angle measurement. It was found that the hydrophobic/hydrophilic properties of initial template, stepwise addition of monomers and initiator as well as amount of carrier solvent are of the important parameters in preparation of the polymer with uniform pore structure. Benefited from the combined properties such as incorporation of ionic liquid within the pore system of a flexible organic matrix together with its hydrophilic character, the material was found as an appropriate support to generate highly dispersed and very small size of Pd nanoparticles inside the pores. The prepared catalyst in this way, demonstrated outstanding activity, recyclability and high durability in the Suzuki cross‐coupling reaction of varied aryl halides with boronic acids in water as a green reaction medium. The beneficial role of imidazolium ionic liquid in the formation of small and highly active Pd nanoparticles was confirmed with comparative experiments.

Watching growth, step by step

Polymers Polymers can grow through the stepwise addition of monomers to an active end site. One might think that this would happen in a continuous linear process. With a focus on ring-opening metathesis polymerization of norbornene catalyzed by a Grubbs' catalyst, Liu et al. describe the growth of a single polymer chain. By attaching one end of a growing polymer to a bead exerting a constant force on it, they measured the extension occurring during the growth of the polymer. Oddly, the extension of the growing polymer did not increase continuously. Instead, it exhibited consecutive wait-and-jump steps, owing to conformational entanglements formed by newly incorporated monomers. Science , this issue p. [352][1] [1]: /lookup/doi/10.1126/science.aan6837

Aggregation of antiacetylcholine drugs in aqueous solution: monomer concentrations in non-micellar drug systems.

The self-association of the antiacetylcholine drugs, propantheline bromide, methantheline bromide and methixene hydrochloride in aqueous solution, has been examined by surface tension, light scattering and conductimetric methods. Surface tension graphs were similar to those of conventional surfactants, showing apparent critical micelle concentrations (cmc) at distinct inflection points. Surface tension measurements in the presence of increasing amounts of electrolyte indicated a decrease in the apparent cmc with increase in electrolyte concentration for propantheline bromide. Light scattering curves for propantheline bromide in electrolyte solution showed no significant discontinuity attributable to a cmc. A mode of self association involving aggregate growth by the stepwise addition of monomers was assumed and equilibrium constants for the initial stages of the association were evaluated. An increase in the magnitude of the stepwise association constants with increase in electrolyte concentration was noted. Integration of the light scattering data according to 1n x = oo [(M/Mapp) - 1] dln c (where M and M app are the monomer and apparent aggregate weights respectively and x is the weight fraction of monomers) showed an asymptotic increase in monomer concentration towards a limiting concentration, as the solution concentration, c was increased. Limiting monomer concentrations determined by this method were in reasonable agreement with the apparent cmcs from surface tension studies. It was not possible to detect a cmc for methantheline or propantheline bromide from conductivity measurements.

Association and Surface Properties of Amphiphilic Benzodiazepine and Benzothiazepine Drugs in Aqueous Solution

The mode of association in aqueous solution of three amphiphilic tranquillizing drugs, chlordiazepoxide hydrochloride, flurazepam hydrochloride, and diltiazem hydrochloride, which are benzodiazepine or benzothiazepine derivatives, has been examined by time-averaged light scattering and surface tension techniques. The association of chlordiazepoxide in water and electrolyte (concentration range 0.05-0.2 mol dm -3 NaCl) is described by a cooperative association model which assumes aggregate growth by the stepwise addition of monomers. Flurazepam and diltiazem form small micelles (aggregation number ⩽ 5) by a closed association pattern in water and 0.1 mol dm -3 NaCl. Inflections in the curves of surface tension vs log concentration for all drugs are shown to be consistent with the concentrations at which enhanced light scattering is first detectable. The differences in the modes of association of these drugs are related to structural features of the drug molecules.

A calorimetric study on the self-association of an amphiphilic phenothiazine drug in aqueous electrolyte solutions

The association characteristics of an amphiphilic phenothiazine drug, promethazine hydrochloride, in aqueous solutions containing high concentrations of electrolyte have been examined by heat conduction calorimetry. The application of deconvolution techniques has permitted the continuous determination of the concentration dependence of the apparent molar enthalpy extending to regions of high dilution. Theoretical treatments have been derived to describe thermogenesis in solutions of amphiphilic compounds exhibiting a range of association patterns. The calorimetric data for promethazine hydrochloride in the presence of 0.2-0.6 mol dm -3 sodium chloride could be satisfactorily described by an association scheme in which a primary unit of 3-4 monomers is formed below the critical micelle concentration by a continuous self-association process and grows with increasing concentration by the stepwise addition of monomers

Association models for an amphiphilic drug in aqueous solutions of high ionic strength from calorimetric studies

Theoretical treatments are presented to describe enthalpy changes in solutions of amphiphilic compounds in which primary micelles are formed by continuous association processes below the critical micelle concentration (c.m.c.) and subsequently grow with increase of concentration by the stepwise addition of monomers. The models have been applied to data obtained by heat conduction calorimetry for the association of the amphiphilic phenothiazine drug, promethazine hydrochloride, in the presence of 0.6 mol dm −3 NaCl. The most satisfactory simulation of data was obtained using association models in which a limited association was assumed below the c.m.c. leading to the formation of either trimers (by a cooperative association process) or tetramers (by stepwise association with equilibrium constants of equal magnitude). Subsequent growth of these primary aggregates with increase of concentration in the post-c.m.c. region was by the stepwise addition of monomers according to a cooperative association scheme. The models have permitted the evaluation of molar enthalpy changes and equilibrium constants for the formation and growth of the primary micelles.

Association characteristics of synthetic non-ionic surfactants in aqueous solution

The mode of association of three novel synthetic non-ionic surfactants CH3O[CH2]6CH(OCH3)CH(OCH3)[CH2]8[O.CH2CH2]xOH, (x= 6, 8, 18) has been determined in aqueous solution by total intensity light scattering, vapour-pressure osmometry and solubilisation techniques. The association of the hexaoxyethylene compound has been described using association models which assume micellar growth by the stepwise addition of monomers to primary micelles formed at the critical micelle concentration (c.m.c.). The scattering intensity from solutions of the other two surfactants increased non-linearly with concentration with no significant inflection attributable to a c.m.c. The association of the octadecyloxyethylene compound conformed to a stepwise process with successive equilibrium constants of equal magnitude, whilst that of the octaoxyethylene compound was most satisfactorily described using a cooperative association model.

Studies on transfer ribonucleic acids and related compounds. XLIII. Synthesis of oligoribonucleotides by using 5'-selective phosphorylation of 2'-O-tetrahydrofuranyl nucleosides.

2'-O-Tetrahydrofuranyl nucleosides have been synthesized from 2, 3-dihydrofuran via 3', 5'-bis-tert-butyldimethylsilylnucleosides. These nucleosides were used as intermediates for oligonucleotide syntheses by the phosphotriester method. Trimers C-C-A and C-C-U were synthesized by the stepwise addition of monomers. U-U-U-U-U-U, A-U-G-A-U-G and A-U-G-A-U-G-A-U-G were obtained by the block condensation of trimers in which the 5'-hydroxyl group had been selectively phosphorylated.

Self-association of phenothiazine drugs in aqueous solutions of high ionic strength

The association characteristics of several phenothiazine drugs in the presence of high concentrations of sodium chloride have been examined using light-scattering techniques. In solutions in which the electrolyte concentration exceeds ca. 0.2 mol dm–3 the micelles increase in size and polydispersity with increasing drug concentration. The association in these solutions may be satisfactorily described using association models which assume micellar growth by the stepwise addition of monomers to the primary micelles formed at the critical micelle concentration.