The kinetics of swelling were studied for polyacrylamide gels used in medicine. The gels contained varying concentrations of N,N'-methylene bisacrylamide crosslinking agent and a small amount of poviargolum, a dispersion of colloidal silver stabilised with polyvinyl pyrrolidone. The kinetics of swelling were described by considering this process as a relaxation process with the diffusion coefficient changing over time. The average molec.wt. of interjunction chains was estimated and the network was found to be rather imperfect. As the proportion of the crosslinking agent increased from 1 to 2 wt %, the molec.wt. of linear chains between the network junctions increased to remain approximately constant with the further increase in the amount of crosslinking agent from 2 to 5 wt %. In the range of high crosslinking agent concentrations, only the swelling rate varied, the amounts of free and bound water in the gel remaining virtually unchanged. A histological examination of the hydrogels showed that they were suitable for medical applications. The required crosslink density of these gels was achieved by selecting a suitable concentration of the crosslinking agent and sterilisation was achieved by the introduction of poviargolum. 43 refs. (Full translation of Vys.Soed.A, 47, No.7, 2005, p.1187-95)

The phenomenon of significantly enhanced mechanical strength that occurs when hydrogenated acrylonitrile-butadiene rubbers(HNBR) are correctly blended with methacrylate additives is investigated. The way in which this technology can be applied to HNBR elastomers to improve low temperature performance is examined. The basic reinforcement mechanism that occurs within a HNBR/zinc dimethacrylate blend is considered, typical laboratory test data are presented and the way in which this technology can be translated into practical applications for these HNBR-based materials is examined. 2 refs.

The influence of non-covalent, specific crosslinks on the properties of chlorosulphonated PE cured using organosilicone compounds containing amino groups was studied. These chemicals were suitable for creating network bonds with C-Cl groups of the elastomer, without adding catalysts or stabilisers, either at the crosslinking temperature or at room temperature. The ionic bonds formed this way had an effect on the mechanical properties of the vulcanisates, in particular they increased the ability to dissipate critical stresses and improved the adhesion of chlorosulphonated PE to steel. The contribution of hydrogen bonds to adhesion energy was examined. 19 refs.

An experimental investigation was conducted of the changes in some mechanical properties of binary blends of PEs (HDPE and LDPE) with an elastomer (ethylene-propylene-dicyclopentadiene terpolymer) in the course of gamma-radiation and chemical crosslinking. A wide range of component ratios was used. Data were obtained on changes in the TS and total, residual and reversible strains at break and on the microhardness and other characteristics. The effect of component ratio and crosslinking on these properties was examined. 13 refs.

The general chemistry involved in the crosslinking of synthetic latices based on ethylene-propylene copolymers(EPM) and/or EPDM, which is a prerequisite for the formation of a PMMA shell, was studied. Particular attention was paid to the influence of the initiation method, i.e. use of a peroxide or a pulsed electron beam, on the crosslinking efficiency. The efficiency of various peroxides was also examined. The incorporation of a coagent, e.g. divinylbenzene, into the EP(D)M phase was studied at a microscopic level by solid-state carbon-13 NMR and PMR. The efficiency of crosslinking initiated by a pulsed electron beam was improved to a significant extent by the presence, in the aqueous phase, of potassium nitrosodisulphonate (Fremy salt). MALDI-TOF mass spectroscopy was used to determine the influence of electron beam irradiation on the chemical stability of surfactants. 48 refs.

Effects of temperature, degree of crosslinking, carbon black filler level and whether crosslinking was of a carbon to carbon type from peroxides, or sulphur crosslinkages were examined by measurement of tear strength of natural rubber vulcanisates and by examination of ruptures surfaces using scanning electron microscopy. Different torn surface structures indicating different routes of crack propagation in the different samples were observed and described. Tear strength reduces with temperature, and optimum crosslink density is required for maximum tear strength. 26 ref.

Preparation of biodegradable polyurethanes by copolymerisation of polycaprolactone (PCL) or polyethylene glycol (PEG) with glycidol, using thermal polymerisation, is described. Hexamethylene diamine was used as a crosslinking agent. Elastomeric polymers were characterised using Fourier transform infrared and nuclear magnetic resonance spectroscopies, thermogravimetric analysis, dynamic mechanical thermal analysis, hardness, contact angle measurement, saline solution degradability and tensile properties. Mechanical properties of the PCL based polyurethane were better than those of the PEG based polymer, but degradation rates were inferior. 39 refs.

The opportunities for designing polymers and developing polymerisation processes that are safe, prevent pollution and are more efficient in the use of materials and energy are enormous, judging by the breadth of topics discussed several weeks ago at a symposium on green polymer chemistry. Iowa State University described how novel rubbers can be prepared from a renewable feedstock, soybean oil. The approach relies on the catalyst boron trifluoride diethyl etherate to initiate the cationic polymerisation of the oil. Work at Eindhoven University of Technology has shown that microwave irradiation provides a green alternative to conventional heating for the cationic ring-opening polymerisation of 2-oxazoline monomers from soybean oils. The Colorado School of Mines, Golden, presented a paper on a new class of green materials referred to as ecobionanocomposites. The composites consist of polylactic acid, derived from cornstarch, grafted onto cellulosic nanowhisker fillers produced by acid hydrolysis of cellulose.

Lithium acrylate (LiAA) was in situ prepared in nitrile rubber (NBR) through neutralisation of lithium hydroxide (LiOH) and acrylic acid (AA) during mixing. The NBR/LiAA compounds were vulcanised with dicumyl peroxide (DCP). The in-situ preparation and polymerisation of LiAA were characterised using FTIR spectrometry. The micrographs of the compounds and vulcanisates were explored using SEM. The effects of DCP and LiAA contents on the water-swelling and mechanical properties of the vulcanisates were studied, and the relationship between the LiOH/AA molar ratio and the properties of the vulcanisates was investigated. Results showed that the in situ formed LiAA could improve the mechanical and water-swelling properties of the NBR/LiAA vulcanisates. Properly compounded vulcanisates were found to have high water-swelling ratios over 800%, and tensile strength of ore than 12MPa. DSC measurements indicated that he water absorbed in the vulcanisate existed in PLiAA and NBR networks in three different physical states, namely: free water, freezable bound water and non-freezable bound water. 36 refs.

In order to control the service properties of polyurethanes, it is possible to vary the nature of the initial feedstock, and by the selection of appropriate modifiers, to change their physicomechanical properties. The molecules of heat-resistant polymers are known to contain nitrogen-containing heterocycles. Aminosuccinimides (AMSs) containing hydroxyl groups were produced in this work, and a study was made of their effect on the properties of polyurethane elastomers (PUEs). AMSs were used as curing agents for oligoester urethane diisocyanates (OUDs). The PUEs obtained comprised elastic transparent polymers of a yellow colour, the physicomechanical and dielectric properties of which were investigated. The influence of the amount of AMSs added to the OUD was investigated in terms of the strength and structural characteristics of the PUE. It was determined that the use of AMSs with aromatic rings as modifying additives improved the physicomechanical properties of the polyurethanes by increasing the number of rigid segments in the polymer chains. High values of the gel fraction content also indicate a high degree of crosslinking of the PUE, leading to a reduction in the mobility of the macromolecular segments. The latter was manifested by a reduction in the values of the tangent of dielectric losses and an increase in value resistivity. Thus, polyurethane elastomers based on tetrahydroxybis(aminosuccinimides), 1,4-butanediol, and OUDs were found to be characterised by high physicomechanical properties and heat resistance. 7 refs. (Article translated from Kauchuk i Rezina, No.4, 2004, p.6-9).