Polymerisation radiochimique de l'acide acrylique en solution dans l'alcool isopropylique et le dimethylformamide

The radiation-induced polymerization of acrylic acid in isopropyl alcohol and dimethylformamide solutions was investigated between?196°and40°. Mixtures which form glasses at low temperatures exhibit a maximum in the rate of polymerization at 30° and 50° above the glass transition temperature (T_g). The difference between the most favourable temperature for polymerization and T_g is larger than in systems studied previously. This fact could be due to the presence of H-bonded aggregates.The study of the polymerization of acrylic acid in dimethylformamide solution at 20° led to a correlation between this reaction and the presence of plurimolecular aggregates. The very high polymerization rate and the syndiotacticity of the resulting poly(acrylic acid) confirm the earlier assumption of a favourable orientation for propagation of the molecules of acrylic acid in these aggregates.     

Effets des solvants sur le greffage radiochimique de la vinyl-4-pyridine dans des films de polytetrafluoroethylene

Grafting of 4-vinylpyridine into the depth of PTFE films was studied using the direct radiation chemical method and solutions of monomer in either methanol or pyridine. In methanol solutions, the grafting rate is maximum for monomer concentrations of 60–85 per cent. In pyridine solutions, the rate of grafting steadily increases with monomer content. The extent of swelling of the grafted films in water is greater the longer the grafted branches. These various results are discussed.     

Polymerisation purement thermique de l'acide acrylique en masse et en solution

The thermal polymerization of acrylic acid in bulk is faster than that of styrene. The conversion curves exhibit auto-acceleration and the product contains a significant fraction of syndiotactic polymer. The overall activation energy is 14 kcal/mol. The rate of the thermal polymerization decreases sharply when the monomer is diluted with toluene. In 50% monomer solutions, the conversion curves are linear and the overall activation energy is 29.8 kcal/mol. With 75 and 90% monomer solutions, the Arrhenius diagrams showed breaks caused by a change in the type of auto-association of the monomer. A comparison of these results with earlier findings obtained in the radiation polymerization of acrylic acid makes it possible to estimate the activation energies of the thermal initiation. It is found that E_i is 14.1 kcal/mol in systems where the monomer forms linear oligomeric association complexes and 34.4 kcal/mol if only cyclic dimers are present in the system.     

Greffage de l'acrylonitrile sur le polyethylene et les copolymeres ethylene-propylene peroxydes par voie radiochimique

The radiation-induced peroxidation of polyethylene and ethylene-propylene copolymers was investigated under different irradiation conditions (temperature, dose and dose-rate). The buildup of peroxides was derived from the kinetics of the graft copolymerization of acrylonitrile on the irradiated polymers. The results show that the mechanism of peroxidation of polyethylene depends on irradiation temperature. A chain hydroperoxidation is observed at a certain temperature, largely above T_g of the polymer, whereas a single step peroxidation leading to a mixture of biperoxides and hydroperoxides occurs at lower temperatures. The critical temperature above which chain hydroperoxidation sets in increases the higher the dose-rate. For the poly(ethylene-co-propylene), special precautions were taken to remove the anti-oxidant of the polymer. A chain hydroperoxidation process was observed at all temperatures above T_g. These various results are discussed.     

Sur les causes de l'auto-accélération dans la polymérisation de l'acrylonitrile en masse et en solution

A study of the polymerization of acrylonitrile in bulk and in DMSO solutions has shown that the auto-acceleration in these systems cannot be explained by non-steady-state conditions as usually assumed. It is suggested that the polyacrylonitrile formed in the initial stages of the reaction acts as a matrix onto which the monomer associates to form an oriented molecular complex in which chain propagation is favoured. This assumption conforms with the various results of this investigation.     

Membranes hydrophiles non-ionisables obtenues par le greffage radiochimique de la n-vinylpyrrolidone dans des films de polytetrafluoroethylene

Non-ionizable, hydrophilic membranes were prepared by radiation grafting of vinylpyrrolidone into polytetrafluoroethylene films. The conditions under which grafting proceeds into the depth of the films were determined. It was found necessary to use aromatic solvents such as pyridine or benzene. The kinetics of the reaction were examined considering the following parameters: temperature, dose, dose-rate and concentration of monomer. The rate of grafting was found highest for monomer concentrations of 60–70 per cent. The results show that the grafting process is complicated by the high viscosity of the reaction medium and by the fact that the rate of diffusion of monomer into the films may become the controlling factor. The rate of homopolymerization of vinylpyrrolidone was also determined. The swelling of the resulting membranes was studied in various solvents. It was found that the limiting swelling ratio depended on the composition of the film but for given composition the swelling ration in water also depends on the grafting conditions. These various results are discussed.     

Copolymerization of acrylic and methacrylic acids with N-vinylpyrrolidone

The copolymerization of an acidic monomer (acrylic or methacrylic acid) and a basic monomer (N-vinylpyrrolidone) (NVP) is investigated. Various physical measurements revealed a strong molecular interaction between the two monomers. However, the resulting association complex does not seem to control the copolymerization. A slight solvent effect is observed with dimethylformamide for the acrylic acid-NVP system. Methacrylic acid appears to be much more reactive than acrylic acid in its copolymerization with NVP. The results obtained with methacrylic acid-NVP system conflict with earlier published results.