Miroslav Janata

Multifunctional ATRP macroinitiators for the synthesis of graft copolymers

Abstract Multifunctional ATRP macroinitiators, polystyrene with 1-(2-bromopropionyloxy)ethyl or 1-(2-bromoisobutyryloxy)ethyl groups in the benzene rings and poly[4-methylstyrene- co -4-(bromomethyl)styrene], were synthesized. All the functionalized polymers were characterized by IR, 1 H and 13 C NMR spectroscopy and by size exclusion chromatography.

50 years of superbases made from organolithium compounds and heavier alkali metal alkoxides

AbstractA review of reactions of organolithium compounds (RLi) with alkali metal alkoxides is presented. On the one hand, simple lithium alkoxides form adducts with RLi the reactivity of which differs only slightly from that of RLi. On the other hand, after mixing heavier alkali metal alkoxides (R’OM, M = Na, K, Rb, Cs) with RLi, a new system is formed, which has reactivity that dramatically exceeds that of the parent RLi. A metal interchange, according to the equation RLi + R’OM = RM + R’OLi, occurs in this system, giving rise to a superbase. This reaction is frequently used for the preparation of heavier alkali metal organometallic compounds. Similar metal interchange takes place between R’OM and compounds such as lithium amides and lithium enolates of ketones or esters, thus demonstrating the general nature of this procedure. Superbases react easily with many types of organic compounds (substrates), resulting in the formation of a heavier alkali metal derivative of the substrate (metalation). The metalated substrate can react in situ with an electrophile to yield the substituted substrate, a procedure that is frequently used in synthetic and polymer chemistry. An improved mechanism of metal interchange and reaction of superbases with substrates is proposed.

Tailoring of polymers by combination of ionic and radical controlled polymerizations

Poly(methyl methacrylate)s with terminal bromine atom, prepared by bromination of anionically polymerized MMA, were used as ATRP macroinitiators giving di- and triblock copolymers with MMA, styrene and butyl acrylate blocks. Multifunctional ATRP macroinitiators were synthesized by introducing bromomethyl or 2-bromoacyloxy groups onto the main chain of polystyrene or poly(4-methyl styrene) and used for ATRP grafting of tert-butyl acrylate leading to densely grafted copolymers with more or less uniform grafts.

Chromatographic study of the conformational behavior of graft copolymers with a broad distribution of grafting densities in dilute solutions in selective solvents for grafts

ABSTRACT A graft copolymer of poly(4-methylstyrene-graft-2-vinylpyridine) was prepared by the living “grafting onto” method. Its molecular weight and composition was analyzed by size-exclusion chromatography, liquid chromatography under limiting conditions of desorption, 1H NMR, and light scattering. The results indicated a non-negligibly broad distribution of grafting density. Its conformational behavior was studied by reversed phase liquid chromatography with gradient elution. Targeted studies provided two discrete base-line separated fractions. Their compositions were estimated by pyrolysis gas chromatography. The results suggest that distinct chain conformations (differing in grafting density and interacting differently with stationary phase) exist in studied solutions and can be separated by well-tuned chromatographic techniques. Experimental data were analyzed and interpreted on the basis of theoretical and computer studies of the conformational behavior of graft copolymers in selective solvents. GRAPHICAL ABSTRACT

Micellization of a Novel Type of Hydrophilic/Hydrophobic Block Copolymers

Abstract Hydrophilic/hydrophobic block copolymers, which consist of hydrophilic blocks containing carboxylated polystyrene or poly(4-methylstyrene) chains, resist micellization by routine procedures. Micellization may be achieved in the presence of tris (2-hydroxyethyl)amine (THEA). Apparently, in a THF/water mixture. THEA with carboxyls forms tight ionic pairs that are quite hydrophilic and keep the micelles in solution. The resulting micelles could be transferred into water, aqueous LiCl, and THEA buffer solutions. They were characterized by static and dynamic light scattering and their properties were shown to conform to a typical behavior expected for micellar solutions.

Improvement of performance of a ductile/brittle polymer system by graphite nanoplatelets: effect of component coupling

Addition of a high-modulus polymer to a pseudo-ductile matrix may lead to increased strength, stiffness and toughness. This can be achieved by plastic deformation of a well-dispersed phase with higher modulus and lower Poissons ratio compared with the matrix. Recently, this system has also been successfully modified by organophilized montmorillonite. In this work, a reactively compatibilized PA6/PS system is upgraded using modified graphite nanoplatelets (GNP) in combination with their simultaneous coupling to polymer components. The best balanced mechanical properties have been obtained in the case of the combination of amine-modified GNP with a styrene maleic-anhydride copolymer. Here, coupling of both polymer phases with GNP could take place. Structure of the in situ formed adduct can be controlled by component ratio and mixing protocols. The complex effect of such modified GNP on the system behaviour, including favourable change of components parameters and modification of the interface, is discussed.

Decomposition of size-exclusion chromatography elution curves of complex branched polymers.

A new method for the decomposition of non-baseline-resolved multimodal elution curves of SEC with the concentration, light scattering and viscosity detection is presented. The method makes possible the characterization of the polymer-sample components, represented by the peaks forming multimodal elution curves, individually and reduces also the error in the calculation of molecular-weight averages. The procedure is demonstrated on narrow molecular-weight distribution polystyrene standards and their mixture as well as on a grafted polymer sample.

Synthesis of highly sulfonated polystyrene-based block copolymers soluble in tetrahydrofuran

Abstract Polystyrene-block-polyisoprene with hydrogenated polyisoprene block (Shellvis 50) was sulfonated to a high degree (up to 42 mol% of styrene units) using acetyl sulfate as sulfonation agent in various chlorinated solvents. Membranes were prepared from the tetrahydrofuran solution of the sulfonated copolymer by casting. The membranes were characterized by conductivity and SAXS measurements.

MALDI-TOF MS analysis of the self-termination products in the anionic methyl methacrylate/tert-butyl acrylate block copolymerization

The p(MMA-b-t-BuA) copolymer was prepared using the initiation system methyl 2-lithioisobutyrate/lithium/tert-butoxide (MIB-Li/t-BuOLi). A low-molecular-weight fraction was isolated and analyzed by MALDI-TOF mass spectrometry with the aim to find out structures of products of self-termination, which proceeds mainly after the addition of t-BuA into the living PMMA. The main self-termination products are formed after addition of one or two t-BuA units onto living PMMA-Li by backbiting reaction of t-BuA-Li chain-ends and carbonyl group of the antepenultimate MMA units of the same chain. The oxoesters generated in this way contain hydroxygroup, and its hydrogen can protonize any of the living chains, regardless of the type of its terminal unit. Signals of the chains, terminated by this protonization, have also been found in the spectra. Thus, the first direct evidences for the structures of the self-termination products in the anionic methacrylate/acrylate block copolymerization were obtained in this way.