Anton L. German

Controlled radical copolymerization of styrene and maleic anhydride and the synthesis of novel polyolefin-based block copolymers by reversible addition-fragmentation chain-transfer (RAFT) polymerization

Reversible addition–fragmentation chain transfer (RAFT) was applied to the copolymerization of styrene and maleic anhydride. The product had a low polydispersity and a predetermined molar mass. Novel, well-defined polyolefin-based block copolymers were prepared with a macromolecular RAFT agent prepared from a commercially available polyolefin (Kraton L-1203). The second block consisted of either polystyrene or poly(styrene-co-maleic anhydride). Furthermore, the colored, labile dithioester moiety in the product of the RAFT polymerizations could be removed from the polymer chain by UV irradiation.

Vesicle‐Directed Growth of Silica

Silica-coated vesicles have been produced by the deposition of silica onto unilamellar vesicles from aqueous solution for the first time. The quaternary ammonium surface of the surfactant vesicles is receptive to silica and facilitates deposition of up to 5-10 nm of it. The petrified vesicles are stable to dehydration and can be visualized by conventional TEM (see Figure) without additional staining agents.

Alkyd-acrylic hybrid systems for use as binders in waterborne paints

Alkyd-acrylic hybrids were prepared by polymerizing acrylic monomers in the presence of colloidal alkyd droplets. Polymerization in the presence of alkyd caused a retardation of the polymerization through radical delocalization following radical transfer to the unsaturated groups of the fatty acids in the alkyd. The conversion could be raised to nearly 100% by adjusting the reaction conditions. The application properties of hybrids prepared according to this method could be varied over a broad range by changing either the acrylic part, the alkyd part or their ratio. The homogeneity of the hybrids differed from blends of acrylic dispersions and alkyd emulsions, as was shown by the minimum film formation temperature (MFFT). A good film formation was found without the use of co-solvents. Mixing of alkyd and polyacrylate on microscale, however, could not be determined. In some cases a true synergistic behaviour was observed, where the hybrid had properties superior to those of the acrylic polymer and the alkyd.

Autoxidation of mercaptans promoted by a bifunctional catalyst

A new bifunctional catalyst of cobalt—phthalocyanine (CoPc) has been developed in which an efficient cooperation between oxidation catalyst and basic sites has been attained. Investigation of this bifunctional catalyst has led to the following interesting observations. (1). A significant enhancement in specific activity is observed for the bifunctional system compared with the corresponding NaOH/CoPc system (factor 50); the polymeric character of the base appears to be essential. (2). The amount of basic groups incorporated in the polymer, necessary to get this high activity, is less than the amount of NaOH used in the corresponding NaOH/CoPc system by about a factor of 100 – 1 000. From the reaction products, being disulfide and H2O2, the accumulated H2O2 is probably responsible for the formation of traces of sulfur acids, which may occupy and thus deactivate the basic sites of the polymer in subsequent runs. The high activity of the bifunctional catalyst may be ascribed to a fundamental change in the mechanism of oxidation, which also can be inferred from the notably reduced value of the apparent activation energy observed for the bifunctional catalyst compared with its NaOH/CoPc counterpart (8 and 12.7 kcal/mole), respectively.

Critical retention behaviour of polymers a study on the influence of some practical parameters

Liquid chromatography under critical conditions is an important tool for the microstructural characterization of telechelic polymers and block copolymers. Until now, only little information on the practical aspects of this technique is available. The influence of some important practical parameters was investigated, using polystyrene. Critical conditions depend strongly on the type of column packing. The solubility of polymers under critical conditions for different solvent-non-solvent combinations differs to a great extent. For different solvent-non-solvent pairs on reversed-phase systems, a roughly constant eluent strength in terms of the Hildebrand solubility parameter, under critical conditions is found. Temperature can be a useful tool for fine-tuning critical conditions. On normal-phase systems, however, the retention of polystyrene changes non-monotonously with temperature, which limits the use of temperature variations. It is not possible to obtain exact molecular mass independence on any of the investigated systems, which can not be ascribed to chemical differences. This makes the validity of the current theories on critical conditions questionable. Especially for the higher-molecular-mass polystyrenes, peak broadening increases significantly when going from size exclusion conditions to critical conditions. This phenomenon can limit the application of liquid chromatography under critical conditions to a certain molecular mass range. The composition of the solvent in which polystyrenes are dissolved prior to injection, has to be exactly the critical solvent composition, in order to suppress zone splitting as much as possible. For higher-molecular-mass polystyrenes this effect cannot be completely prevented.

Oil-Acrylic hybrid latexes as binders for waterborne coatings

The combination of the characteristics of oil, or alkyd, emulsions and acrylic latexes in a waterborne binder has been the object of various studies in the past. Strategies for combining the positive properties of alkyds, e.g. autoxidative curing, gloss and penetration in wood, with the fast drying and gloss and color retention properties of acrylic latexes have mainly been directed towards the modification of the alkyd with an acrylate during alkyd synthesis followed by emulsification. This paper describes the preparation and application of oil-acrylic hybrid latexes as binders for waterborne coatings. The hybrid latexes were prepared using hydroperoxidized triglycerides as initiators for the mini-emulsion polymerization of acrylates in an Fe(II)/EDTA/SFS redox system. The particle morphology of hybrids initiated by fatty-acid hydroperoxides was compared with tert-butyl hydroperoxide-initiated systems. Cryo-TEM analysis indicated that, whereas tert-butyl hydroperoxide initiation resulted in the formation of heterogeneous particles, fatty-acid hydroperoxide-initiated hybrid particles showed no intra-particle heterogeneity. An AFM study of the film formation process of the oil/alkyd-acrylic hybrid latexes showed that phase separation occurred between the oil and the acrylic phases upon drying, resulting in films that consist of deformed acrylic particles embedded in a continuous matrix of oil. This results in a very smooth surface of the film.

Critical Retention Behavior of Homopolymers

Abstract The isocratic retention behaviour of a homopolymer at a specific temperature and varying solvent compositions can be divided into three modes: exclusion mode, transition mode (critical conditions) and adsorption mode. Under critical conditions (a specific non-solvent/solvent composition at a specific temperature) the retention of a homopolymer is independent of the molar mass. The critical conditions depend upon the temperature, the type of polymer and the type of non-solvent/solvent mixture. A difference in the critical conditions between polystyrene standards and polybutadiene standards was found. No significant influence of different types of column packing on the critical solvent composition was noticed. The exact mechanism of the retention of a polymer under critical condition is not clear yet. In order to determine the critical conditions, a new method has been developed. The method can be easily performed on existing equipment. The method contains a different setup of the data acquired by ...

BIMOLECULAR FREE-RADICAL TERMINATION AT LOW CONVERSION

A review on free-radical polymn. termination kinetics covering aspects of diffusion control of bimol. termination such as viscosity dependence and the effects of excluded vol. and coil size, chain-length dependence and theor. models. [on SciFinder (R)]

Determination of the chemical composition distribution of copolymers of styrene and butadiene by gradient polymer elution chromatography

Abstract In order to determine the chemical composition distribution (CCD) of styrene-butadiene copolymers, gradient polymer elution chromatography has been performed. The separation is mainly based on differences in solubility among the copolymer molecules with different chemical composition. The solubility of a copolymer is dependent on the following parameters: temperature, type of solvent/non-solvent mixture, molecular mass of the polymer and the chemical composition of the polymer. The resolution of the gradient polymer elution chromatographic separation and the molecular mass dependency are influenced by the solvent/non-solvent combination. In order to obtian a reliable separation according to chemical composition, the differences in solubility must be sufficientyl high and the molecular mass dependence must be negligible. In order to separate styrene-butadiene copolymers, synthesized by emulsion polymerization, a tetrahydrofuran-acetonitrile gradient was used. After calibration of the chromatographic system with styren-butadiene copolymer standards, the CCD of styrene-butadiene copolymers could be calculated.

Current understanding of the deformation of latex particles during film formation

This article reviews models of polymer particle deformation in film formation. Dillon et al. modelled polymer particles as viscous bodies whose surface tension provides the main driving force for particle deformation. In Browns alternative model, deformation is driven by capillary pressure due to water evaporation and opposed by the elastic force of the polymer itself. Brown, however, assumes the area on which capillary and deformation pressures act to be equal and the particles to be elastic rather than visco-elastic. The first assumption is addressed by Mason and the second by Lamprecht. Brown, Mason and Lamprecht modelled the polymer particles response as the response of two non-attracting spheres pressed together. Kendall and Padget followed an alternative approach using the JKR theory thus incorporating the van der Waals attraction. The existence of a sharp transition in the film forming qualities near Tg is predicted by these theories through a sharp change in the elastic modulus. The predicted inverse proportionality for the particle radius is not observed experimentally. Experiments performed by Sperry et al. cast further doubt on the applicability of these theories. Keddie et al. propose a new approach to particle deformation. According to them transparent films can either be obtained along an ‘easy’ route, by particle deformation due to capillary forces, or along a “hard” route, by particle deformation due to other surface forces; e.g. the polymer/water interfacial tension, the polymer/air surface tension or the forces due to residual water left between the particles.