A Kinetic Method for Investigating the Structure of Adsorbed Polymer Layers

A kinetic method for investigating the adsorbed layer structure of a polymer (the copolymer of styrene and maleic anhydride) on a ZnO powder surface was developed, the method is based on the model of the heterogeneously inhibited polymerization of styrene ‘filled’ with ZnO powder. The polymerization is preceded by an induction period. The length of this period depends on the concentration of inhibiting sites (n) on the surface of ZnO. The adsorbed polymer blocks such inhibiting sites and the induction period decreases. This model was used to estimate n. A peak was observed in the experimental relationship connecting n with the amount adsorbed. This peak was interpreted as the critical concentration for conformation transition brought about by the interaction of the polymer chains at the surface. Below this concentration adsorbed macromolecules are considered as isolated chains at the surface. This state is characterized by the poor mobility of segments.

Modification of the Interface by Polymeric Peroxides — A New Approach to the Creation of Composites

The peroxidic modification of the surface of a dispersed phase by heterofunctional polymeric peroxides (HFPPs) is discussed. HFPPs are carbochain polymers which have statistically located peroxidic (–OO–) and high-polar functional (carboxylic) groups along the main chain.

Sharp differences in the polarity of these groups endowes HFPP macromolecules with the capability of interfacial adsorption in various polymeric colloidal systems. The reactions of the functional groups provide chemical bonding of the macromolecules to the interfacial surface. As a consequence of such physical adsorption or chemisorption of HFPP, peroxidation of filler surfaces and the localization of active –OO– groups on the interface may be effected.

In addition, such –OO– groups can facilitate the grafting of matrix polymer macromolecules to the surface of the dispersed phase. Such grafting reactions can be carried out during polymer filling, the curing processes of composites or the vulcanization of a rubber mixture. It has been shown that an improvement in the physical and mechanical properties of polymers and an increase in the electroconductivity and heat conductivity of filled compositions is achieved on modification by HFPP.

Synthesis of a Polymer Covering on Al(OH)3 and BaSO4 Surfaces by Means of Radical Polymerization in Water Medium

The graft polymerization of butyl methacrylate on to the surface of Al(OH)3 and BaSO4 fillers initiated by an adsorbed peroxidic macroinitiator was studied in water medium relative to the corresponding polymerization in toluene. It was established that, in water medium, the nature of the solid surface as well as the monomer concentration has only a very slight influence on the rate of grafting and the amount of polymer grafted, both of which depend on the specific surface area of the filler and the temperature. To explain these features, a microreactor polymerization model is proposed in which the filler particles or aggregates of the particles together with the immobilized macroinitiator and adsorbed monomer are considered as microreactors. As a result of graft polymerization, compatibilizing polymer shells were formed on the Al(OH)3 and BaSO4 particles. Due to solvation, such shells enhance the organophilicity of the filler surface sufficiently and provide a high steric stabilization of the filler dispersions in organic media. When both the adsorption of the macroinitiator and the graft polymerization of the monomer proceed in water medium, the efficiency of the process and its ecological cleanliness are increased greatly.

Design of a new invertible polymer coating on a solid surface and its effect on dispersion colloidal stability

This article presents a new approach to building up self-adjustable invertible polymer coatings at solid surfaces. The approach is based on a two-step process. In the first step, the surface of dispersed TiO2 or silicon wafers was functionalized with the aid of a reactive copolymer, viz., poly(styrene-alt-maleic anhydride) (PSM), to which, in the second step, the chains of amphiphilic oligoester have been tethered. The latter contains both hydrophilic poly(ethylene glycol) and hydrophobic aliphatic dibasic acid moieties being alternately distributed along the oligomer chains. It is shown that the titania modified in this way can form stable suspensions in both polar (water) and nonpolar (toluene) media. Moreover, multiple drying/redispersion cycles demonstrate the ability of the modified titania particles, after their removal from one type of dispersion and consequent drying, to be redispersed in dispersing media strongly differing by polarity from that of the previous medium. An environmentally induced switching of the surface properties has been observed via the measurement of the wetting contact angles and scanning force microscopy (SFM) of silicon wafers covered by PSM with tethered oligoester chains. These experiments give strong support for the predicted capability of such polymer coatings to switch their environmental appearance (i.e., to behave as a self-adjustable invertible interface because of the ability of the tethered amphiphilic oligoester chains to change their conformations in response to environmental changes in such a manner so as to adapt and enhance their compatibility with the surrounding media).

Glycosylation of bovine pulmonary angiotensin-converting enzyme modulates its catalytic properties

To study the role of the oligosaccharide moiety in the catalytic properties of angiotensin-converting enzyme (ACE), we obtained asialo- and partially deglycosylated ACE by enzymatic treatment of two-domain somatic enzyme from bovine lung. Treated enzymes demonstrated appreciable, but different changes of catalytic properties in the reaction of the hydrolysis of N-substituted tripeptides, C-terminal analogs of angiotensin I and bradykinin among them, compared to those for native enzyme. Deglycosylation also altered the catalytic properties of a single N domain of bovine ACE. So, various patterns of glycosylation modulate substrate specificity of somatic ACE and may be the reason for functional heterogeneity of the enzyme.

Selective zoning of high harmonic emission using counter-propagating light

High harmonic production can be dramatically increased by utilizing an interaction region much longer than a coherence length. Counter-propagating light pulses can be used to disrupt the out-of-phase harmonic emission from selected zones in the focus so that the remaining emission builds constructively. Counter-propagating light creates a standing field modulation repeating over a half laser wavelength in which phase cancellations for harmonic emission occur. A simple power-law model is used to demonstrate how such pulses can be designed to counteract geometrical phase mismatches and improve emission for individual harmonics by more than two orders of magnitude.