Water-soluble ionic liquids as novel stabilizers in suspension polymerization reactions: engineering polymer beads

Aqueous solutions of ionic liquids have been used as novel and environmentally friendly reaction media to synthesize and "control" the size of different cross-linked polymer beads by suspension polymerization reactions. It was found that the investigated ionic liquids can act as novel stabilizing agents of the suspensions as a result of their surface-active properties. The results have demonstrated that the average size of polymer beads can be varied from the macro- to the nanoscale and their surface area can also be "adjusted" by this synthetic approach. Furthermore, the use of a combination of ionic liquids and water for the synthesis of polymers, the simple isolation of the products formed in this polymerization procedure, as well as the recycling of the continuous medium for further reactions open up possibilities for the development of "new and green" polymerization processes.     

Designer dendrimers: branched oligosulfonimides with controllable molecular architectures

The synthesis of "designer" dendrimers and dendrons with sulfonimide units at every branching point is reported. The synthesis is based on a series of (regio)selective functionalization reactions of amines and sulfonamides allowing precise control of the dendrimers' shape, the number of branches in each generation, and their peripheral decoration with functional groups. In principle, structurally different branches can be incorporated at any position within the dendrimer structure at will. Structurally perfect symmetrical and two-faced "Janus"-type dendrimers, as well as dendrimers and dendrons with intended interstices were synthesized on a preparative scale and fully characterized. Oligosulfonimide dendrons of various generations bearing an aryl bromide functional group at their focal points were attached to a p-phenylene core with the aid of Suzuki cross-coupling reactions resulting in dendrimers with photoactive terphenyl cores. The structure and the high purity of all dendritic sulfonimides were confirmed by means of (1)H and (13)C NMR, electrospray ionization mass spectrometry (ESI-MS), and elemental analysis. The utility of MALDI-TOF mass spectrometry for the analytical characterization of these dendrimers was evaluated in comparison to electrospray ionization. Two model branched oligosulfonimides were characterized in the solid state by single-crystal X-ray analysis. Reaction selectivities and conformation of sulfonimide branching points were rationalized by DFT calculations.     

Effect of nuclear quadrupole interactions on the dynamics of two-level systems in glasses

The standard tunneling model describes quite satisfactorily the properties of amorphous solids at temperatures T < 1K in terms of an ensemble of two-level systems including the logarithmic temperature dependence of the dielectric constant. Yet, experiments have shown that at ultralow temperatures T< 5 mK such a temperature behavior breaks down and the dielectric constant becomes temperature independent (plateau effect). In this Letter we suggest an explanation of this behavior exploiting the effect of the nuclear quadrupole interaction on tunneling. We also predict that the application of a sufficiently large magnetic field B> 10T should restore the logarithmic dependence because of the suppression of the nuclear quadrupole interaction.     

Unexpected behaviour of tosylated and acetylated imidazolinium salts

Tosylated and acetylated imidazolinium salts revealed an unexpected reactivity when treated with methyl iodide or benzyl bromide. Moreover an unprecedented acid-catalysed rearrangement for an acetylated imidazolinium salt was observed during an anion metathesis.     

Interpolymer complexes of copolymers of vinyl ether of diethylene glycol with poly(acrylic acid)

 The complex formation reactions of poly(vinyl ether of diethylene glycol) as well as vinyl ether of diethylene glycol–vinyl butyl ether copolymers with poly(acrylic acid) have been studied in aqueous and alcohol solutions. The formation of interpolymer complexes which were stabilized by hydrogen bonds was shown. The effects of molecular weight of poly(acrylic acid) and the nature of the nonionic polymer on the composition and stability of interpolymer complexes were clarified. The critical pH values of complexation were determined for different systems with various molecular weights and hydrophobic–hydrophilic balances. The stability of the interpolymer complexes formed in aqueous and alcohol solutions with respect to dimethylformamide addition was evaluated. The role of hydrophobic interactions and the presence of active groups on stability of the interpolymer complexes is discussed. Received: 23 July 2001 Accepted: 27 September 2001     

Lattice model theory of chain stiffening and relaxation properties of macromolecules in the nematic LC state

The relaxation properties of polymer chains In the nematic LC-state or in the external quadrupole field may depend both on the variation of the conformation in the ordered state and on the activation barrier of the molecular (or external) field. This barrier should be surmounted during reorientation of chain elements. The lattice model theory of chain stiffening of macromolecules in the LC-state is proposed. The calculation and comparison of the longitudinal and transversal relaxation spectra for the continuous and discrete rotameric mechanism of the mobility are performed. For the simplest model of a heterogeneous polymer chain the possibility of the more complex relaxational behavior i.e. the existence of two longitudinal and two transversal relaxation spectra was shown.     

Collapse of Poly(methacrylic acid) Hydrogels in Response to Simultaneous Stimulation by an Electric Field and Complex Formation

Complex formation of poly(methacrylic acid) hydrogels with linear poly(ethylene glycol) has been studied at different pH values and in the presence of an electric field. The fastest contraction of the gel samples was observed under simultaneous action of electric field and complex formation.

Dependence of the volume ratio V/V₀ of PMAA sample on time: Sample in the absence of an electric field immersed in 0.1 M PEG solution at (1) pH 8.2, (2) at pH 5.1, and in the presence of an electric field (3) in water and (4) 0.1 M PEG solution at pH 5.1.     

Stability constants of ytterbium cyclohexaphosphate complexes

The compositions of complexes formed in solution are calculated by the iteration (in three approximations) complex method and using the earlier study of the solubility in the YbCl₃-Li₆P₆O₁₈-H₂O system, in which one poorly soluble compound Yb₂P₆O₁₈ · 16H₂O and soluble ytterbium cyclohexaphosphate complexes are formed. The composition are [Yb₆(P₆O₁₈)]¹²⁺, [Yb₂(P₆O₁₈)]⁰, [Yb₃(P₆O₁₈)₂]^3?, [Yb(P₆O₁₈)]^3?, and [Yb₂(P₆O₁₈)₃]¹². The stability constants of these complexes are determined: β₆₁ = 1.2 × 10¹², β₂₁ = 6 × 10⁴, β₃₂ = 9 × 10¹², β₁₁ = 29.6, and β₂₃ = 3.9 × 10¹² at an ionic strength of ～1. The solubility product of Yb₂P₆O₁₈ · 16H₂O is found to be 2 × 10^?10. The curves of residual concentrations of ytterbium and cyclohexaphosphate plotted with reference to the stability constants of the complexes and the solubility product of Yb₂P₆O₁₈ · 16H₂O agree with experimental data.