Radiation polymerization comparison

Because of acid-catalyzed hydrolysis of N-vinylpyrrolidone in water, polymerization was carried out in organic solvent - DMF. Three types of samples of poly(methacrylic acid) were used syndiotactic - obtained by radiation polymerization, atactic - obtained by radical polymerization, and isotactic - obtained by hydrolysis of isotactic poly(methyl methacrylate). It was found that in all cases the rate enhancement appeared in comparison with the blank polymerization (without template). The rate enhancement became more pronounced with increasing chain length and syndiotacticity of the template. According to the authors, the rate enhancement is connected with the stronger complex formation between poly(vinyl pyrrolidone) and syndiotactic poly(methacrylic acid) then with isotactic template. This conclusion was supported by turbimetric titration in DMF/DMSO system and by model considerations. It is worth noting, however, that... 

In parylene polymerization, the thermal cracking of the dimer (starting material) creates monomeric diradicals. All starting materials are converted to the reactive species, i.e., diradicals. No specific initiator for the chemical structure of starting material is formed. The situation is close to that of plasma polymerization. The comparison of plasma polymerization and radiation polymerization, and the comparison of the two vacuum deposition polymerizations (parylene polymerization and plasma polymerization) enable us to construct an overall view of material formation in the luminous gas phase. 

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

The role of low heat conductivity was found to be out of significance by the comparison of data obtained at various thicknesses of monomer layers in our calorimeters, at various dose rates, by the comparison of irradiation of monomer (both radiation and polymerization can heat the system) and polymer (only external radiation is the source of heat). 

The monomer 1 was polymerized by heating the crystals in a vacuum vessel below the melting point or by y-ray or UV irradiation of the crystals at room temperature. 60Co y-ray irradiation with a dose rate of 0.1 Mrad h 1 or a high-pressure mercury lamp (200 W) without filter was used as the radiation sources for the polymerization the conversion ratio was determined by extraction of residual monomer with ethanol. A comparison of the polymerization rates indicates that 60C y-ray irradiation is much more efficient than UV irradiation in inducing polymerization. 

Sub-crystal fractions in PTOX from both radiation and plasma initiated polymerizations were determined from the (100) reflections and summarized in Table 2. Their values are somewhat, but not substantially, lower for the plasma samples than for the radiation samples. However, since the amount of subcrystal fraction depends on both the temperature and the yield, meaningful comparisons between these two types of samples are difficult on the basis of these rather limited data. 

In comparison with the catalytic cationic polymerization of these monomers (14), It Is remarkable that the radiation-induced polymerization gives high conversions at room temperature to a preclpltatable polymer. Although the catalytic polymerizations (14) were carried out in solution between -78 and -130°C under conditions which should minimize the formation of dimer oils and monomer rearrangement products, the highest reported conversion of a-pinene oxide to polymer was only 28%, and In this case the material was described as a viscous oil. Conversions to polymer In the form of a white powder varied from 1 to 20% although 76-100% of the o-pinene oxide... 

The kinetics of ultrafast polymerization of acrylic monomers exposed to UV radiation or laser beams has been investigated by IR spectroscopy. An 8 fold increase of the cure speed was observed by using diphenoxybenzophenone as photoinitiator instead of benzophenone. llie reactivity of polyurethane-acrylate or epoxyacrylate systems was markedly improved by adding acrylic monomers that contain carbamate or oxazolidone groups and which impart both hardness and flexibility to the cured polymer. Time-resolved infirared spectroscopy was used to directly record the actual polymerization profile for reactions taking place within a fraction of a second upon UV or laser exposure. Comparison with other techniques of real-time analysis show the distinct advantages of this method for an accurate evaluation of the important kinetic parameters and of the dark polymerization which develops just after the irradiation. 

As all polyolefins, polyethylene is sensitive to UV radiation, although less than polypropylene. For outdoor use polyethylene needs special stabilization against UV light. The light stabilizers for polyethylene are in principle the same as for polypropylene. On accelerated weathering, HALS show much better performance in HDPE tapes than UV absorbers, despite the latter being used in much higher concentrations. The comparison between HALS is, however, in favor of the polymeric HALS-III, which has the same performance when added at a concentration of 0.05% as HALS-I and HALS-II at 0.1%. 

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