Regioselective rhodium-containing catalysts for ring-opening polymerizations and hydrosilylations

Organometallic rhodium complexes are described which are highly efficient initiators for the ring-opening polymerization of expoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon–hydrogen bonds must also be present. These same catalyst–cocatalyst mixtures are also highly active for hydrosilylation reactions. Other complexes bearing phosphine ligands have been discovered, which while active for hydrosilylation, are not catalysts for epoxide polymerizations. Polymer supported rhodium catalysts are also described which permit the synthesis of epoxy-functional silanes in high yields without competing ring-opening polymerization.     

Non-ionic amphiphilic block copolymers by RAFT-polymerization and their self-organization

Water-soluble, amphiphilic diblock copolymers were synthesized by reversible addition fragmentation chain transfer polymerization. They consist of poly(butyl acrylate) as hydrophobic block with a low glass transition temperature and three different nonionic water-soluble blocks, namely, the classical hydrophilic block poly(dimethylacrylamide), the strongly hydrophilic poly(acryloyloxyethyl methylsulfoxide), and the thermally sensitive poly(N-acryloylpyrrolidine). Aqueous micellar solutions of the block copolymers were prepared and characterized by static and dynamic light scattering analysis (DLS and SLS). No critical micelle concentration could be detected. The micellization was thermodynamically favored, although kinetically slow, exhibiting a marked dependence on the preparation conditions. The polymers formed micelles with a hydrodynamic diameter from 20 to 100 nm, which were stable upon dilution. The micellar size was correlated with the composition of the block copolymers and their overall molar mass. The micelles formed with the two most hydrophilic blocks were particularly stable upon temperature cycles, whereas the thermally sensitive poly(N-acryloylpyrrolidine) block showed a temperature-induced precipitation. According to combined SLS and DLS analysis, the micelles exhibited an elongated shape such as rods or worms. It should be noted that the block copolymers with the most hydrophilic poly(sulfoxide) block formed inverse micelles in certain organic solvents.     

Activation and stabilization of enzymes entrapped into reversed micelles

Observations of the activity of two hydrolyzing enzymes—protease and α-amylase—entrapped inside the reversed micelles formed by surfactants in hexane, benzene, and cyclohexane are reported. The surfactants chosen for this study are: Tween 80, a nonionic surfactant, Cetyl pyridinium chloride, a cationic surfactant, and two anionic surfactants, sodium lauryl sulfate and Aerosol OT. Tween 80 enhances the activity of both protease and α-amylase. Sodium lauryl sulfate and Aerosol OT, which are ionic surfactants, enhance the activity of protease, but inhibit the activity of α-amylase. Cetyl pyridinium chloride, however, enhances the activity of α-amylase, but inhibits the activity of protease. Enhanced activity is generally severalfold greater in comparison to the activity observed in the usual aqueous system in the absence of reversed micelles. It has also been observed that the enhanced activity of the enzymes entrapped inside the reversed micelles remains preserved for a much longer period of time in comparison to the activity in the usual aqueous systems. These observations, which support the view that with proper choice of surfactant and the organic solvent, reversed micelles act like a microreactor that provides a favorable aqueous microenvironment for enzyme activity, have biotechnological overtones.     

Solution viscosity behavior of polystyrene-based cationic ionomers. Effects of ion content and solvent

Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (ε_r) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low ε_r, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (A_N), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high A_N value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc.     

Novel pyridinium salts as cationic thermal and photoinitiators and their photosensitization properties

Novel pyridinium salts [N‐(α‐phenylbenzyl)‐, N‐(1‐naphthylmethyl)‐, or N‐cinnamyl p‐ or o‐cyanopyridinium hexafluoroantimonates] were synthesized by the reaction of p‐ or o‐cyanopyridine and the corresponding bromides followed by anion exchange with KSbF₆. These pyridinium salts polymerized epoxy monomers at lower temperatures than previously reported for N‐benzyl‐2‐cyanopyridinium hexafluoroantimonate. The o‐substituted pyridinium salts showed higher activity than the p‐substituted ones, and the crosslinked epoxy polymers cured with these initiators showed higher glass‐transition temperatures. These pyridinium salts photoinitiated radical polymerization as well as cationic polymerization. The photopolymerization was accelerated by the addition of aromatic ketones as photosensitizers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1037–1046, 2002     

Adsorptive Voltammetry of Polyelectrolyte Complex Between 11‐Ferrocenyltrimethylundecylammonium and Polyanions at Carbon Paste Electrode

For polyelectrolyte complex between cationic surfactant and polyanion, the adsorptive voltammetry at carbon paste electrode using an electroactive cationic surfactant was examined. The adsorption state of the cationic surfactant in the complexes at CPE was estimated from the half‐height width of the oxidation waves. The half‐height width for poly(styrene sulfonate) was independent of the molecular weight, and was same as that for poly(vinyl sulfate). The half‐height width for heparin was broad and different from that of the vinyl polyanions. According to the analysis by Frumkin isotherm, the interaction between cationic surfactants was attractive in heparin complex at CPE, however, in the vinyl polyanion complexes at CPE the interaction was non‐cooperative as that predicted with the Langmuir isotherm. In spite of the same adsorption state, the concentration dependency of the peak current for poly(styrene sulfonate) was quite different from that for poly(vinyl sulfate). The concentration dependence indicated the reactive property of each polyanion on the association with the cationic surfactant in aqueous solution.     

Micelle formation of N-decanoylglycine and N-decanoyl-L-alanine oligomer potassium-salts and the micellar structure. A small-angle neutron scattering study

 Potassium salts of N-decanoylglycine and N-decanoyl-L-alanine oligopeptides (monomer, dimer and trimer) were synthesized. For these oligomer salts in aqueous solutions, the microstructures of micelles have been investigated by small-angle neutron-scattering (SANS). In the calculation of SANS intensity data, the thickness of the hydrophilic layer was altered by changing the conformation of the oligomer moiety (helical and β-sheet structures). For micelles of the trimer salts, the helical structure models provide the best fit to the observed SANS intensity data. For micelles of the monomer-and dimer-salts, the β-sheet model provides the best fit to the observed data. For the monomer-and dimer-micelles, the aggregation number (n) is not dependent on the species of amino acid residue, imply-ing that the decanoyl group plays a critical role in micelle formation. However, for the trimer micelles, the n value is dependent on the species of amino acid residue. Received: 11 July 1996 Accepted: 11 September 1996     

Refractive index of water-AOT-n-heptane microemulsions

Refractive index measurements on water/AOT/n-heptane microemulsions as a function of the volume fraction of the dispersed phase (water plus AOT) and of the water/AOT molar ratio R have been performed at 25°C. The refractive index was found to vary monotonically with without any change in rate during the crossover of the percolation threshold. Such a behavior suggested that, well above the percolation threshold, the water-AOT-n-heptane microemulsions are still formed by water-containing AOT reversed micelles dispersed in the oil phase. The analysis of the experimental data allowed an evaluation the fraction of the water molecules bonded to the AOT head group as a function of R.     

Polymerization of cyclic imino ethers: From its discovery to the present state of the art

Topics concerning the cationic ring‐opening polymerization of cyclic imino ethers and functional material production based on the resulting polymers are reviewed. Cyclic imino ethers are readily subjected to isomerization polymerization via cationic initiators. Mechanistic studies have provided a new concept, electrophilic polymerization. Double isomerization polymerization and no‐catalyst alternating copolymerization are interesting examples that show characteristics of the ring opening of cyclic imino ethers. The living polymerization of these monomers affords precisely controlled polymeric materials. Through the use of the unique properties of the product polymers, various functional polymeric materials, such as polymeric nonionic surfactants, compatibilizers, hydrogels, stabilizers for dispersion polymerization, biocatalyst modifiers, and supramolecular assemblies, have been developed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 192–209, 2002     

Triblock copolymers based on cyclic ethers: Preparation and properties of tetrahydrofuran and 3,3-bis(azidomethyl) oxetane triblock copolymers

Novel energetic thermoplastic elastomers (TPEs) based on tetrahydrofuran (THF) and 3,3-bis (azidomethyl) oxetane (BAMO) were prepared in this present study by cationic living polymerization. A bifunctional catalyst, triflic anhydride [(CF₃SO₂)₂)O] was selected to be an initiator for the polymerization THF and BAMO. The resulting polymers were characterized by IR, NMR, and DSC, which demonstrated that triblock copolymers with A-B-A type were formed. The polymers were indicated from thermogravimetric analysis (TGA) to have decomposed at approximately 243°C. The decomposition enthalpies were determined by DSC. These enthalpies were varied with the poly-BAMO contents of the copolymers. The synthesized polymers exhibited relatively good mechanical properties and thermoplastic characteristics at room temperature. © 1994 John Wiley & Sons, Inc.