Polymerization - curves radiation

Figure 11. Solutions of the Smith-Ewart recursion equation for the case of no aqueom propagation or termination. Dotted line m = 0 (Smith-Ewart Case II). Curve 1 (m = 10 ) depicts typical styrene-like polymerization. Curve 2(m = 0.01) depicts radiation initiated emulsion polymerization of vinyl chloride. Curve 3 (m > 1.0) depicts chemically initiated emulsion polymerization of vinyl chloride.

When this resin was exposed as a thin film to the UV radiation of a medium pressure mercury lamp (80 W aiH), the crosslinking polymerization was found to develop extensively within a fraction of a second (18). The kinetics of this ultra-fast reaction can be followed quantitatively by monitoring the decrease of the IR absorption at 810 an-1 of the acrylic double bond (CHCH twisting). Figure 8 shows a typical kinetic curve obtained for a 20 pm thick film coated onto a NaCl disk and exposed in the presence of air to the UV radiation at a fluence rate of 1.5 x 10 6 einstein s-1 cm 2. 

Smirnova and coworkers studied the influence of various types of ionizing radiations on the physiomechanical characteristics of a statistical polymer of butadiene and acrylonitrile137. Although the polymer is a statistical polymer, the nature of its thermo-mechanical curve indicates a block nature of the polymeric basis of the rubber there is a... 

It is necessary now to find out whether my theoretical conclusion is supported by experimental evidence in fact, there are many results for bulk polymerizations that indicate a first-order growth reaction. The experimental support that I seek would be found in the shape of the curves relating the conversion, Y, to the total received dose of radiation or to the time at a constant dose-rate. If the polymerizations are of zero order with respect to m, the conversion curves will be rectilinear instead of concave to the dose (or time) axis. Rectilinear conversion curves are actually much more common than first-order type curves, and some instances of this behaviour are listed in Table 1. In example 8 of Table 1 the experimental points are actually on a straight line, but a curve has been drawn past them. 

In order to get further insight into the reaction mechanism for the degradation of PMMA, we have studied the nature and behavior of radical entities in irradiated PMMA by using the ESR and ESE techniques complementarily [37]. Two PMMA samples, a commerical PMMA and an initiator-free PMMA prepared by the radiation-polymerization of bulk monomer, were used, but no difference was found in the results. Residual monomer was carefully removed from the PMMA samples, because the monomer molecule readily modifies the radicals derived from the polymer. The samples were irradiated in vaccum. Figure 9 demonstrates the dose-yield curve we obtained by irradiating PMMA in vacuum at 273 K. The G value for the radical formation is determined to be 3.0 from the slope of the linear portion below 12 kGy. 

Fig. 22. IRES spectra collected in situ during the first stages of the ethene polymerization reaction on a Cr(II)/Si02 catalyst, by using the catalyst as the radiation source. The four set of data show the spectral evolution as a function of the contact time from bottom to top at 10, 20, 30, and 40 s, respectively. Experimental data (dotted curves) are compared with the best fit (full curves) (unpublished).

The dosage conversion curve for the polymerization of PTS-12 by Co radiation is plotted in Fig. 13 for two temperatures. It is characterized by an induction period followed by a rapid reaction leading to complete conversion which is reached at about 15 Mrad. The onset of the rapid reaction is connected with a phase transition which will be discussed later. 

Acres and Dalton (1963a) also studied the emulsion polymerization of methyl methacrylate initiated by Co y radiation using a recording dilatometer. Only the conversion-time curves were measured with constant dose rate, varying monomer concentration, and with constant monomer concentration at different dose rates. Except at the lowest monomer concentration a clear gel effect was observed, with linear rates up to that point. The linenr rates increased with increasing monomer concentration up to about 0.4 mol/liter and then leveled oif. The dependence of the rate, before the gel effect, on the dose rate was 0.4 and, unlike their findings with styrene, not dependent on the monomer concentration. Their results were consistent with those of Hummel ei al. that methyl methacrylate follows, with y radiation, the generally accepted Smith-Ewart Case 2 kinetics except for the marked gd effect. 

Panajkar and Rao (1979) have reported a ratber extensive study of the y radiation-initiated polymerization of vinylidene chloride in emulsion. With sodium lauryl sulfate as the emulsifier smooth polymerization-time curves at high rates were obtained, up to more than 9 conversion. Between 45 and 60% conversion, the linear region, the rate was 0.3 order with respect to tbe emulsifier concentration. The molecular weights were found to increase with conversion and values up to 79,000 were obtained. Some reasons for the departure from Smith Ewart behavior were suggested. Earlier. Hummel el al. (1967) had presented some interesting data on a closely related system, a similar rate-time behavior was observed and a tentative explanation proposed. Both discussions were based on tbe insolubility of the polymer in its own monomer. 

Figure 3. Temperature dependence in Arrhenius coordinates) of polymer chain growth time T (curve 1) and mean time of one unit attachment to this chain Tq (curve 2) under radiation-induced polymerization of formaldehyde.

MM A. Figure 6 shows the over-all reaction rate plotted logarithmically vs. time in case of the y-emulsion polymerization of MM A. After the sharp rise of Ufir, a period of zero order of Ubf seems to follow. But then Ubf increases further and reaches a maximum at about 50% conversion. Soon afterwards, the curve drops sharply, and Ubf decreases almost as fast as if the radiation source were removed at this point. This decrease does not follow, or follows for only a short time, a first-order law with respect to monomer concentration. There also is no reaction of the second order with respect to [M]. 

Termination rate coefficients can be measured using the y-radiolysis relaxation method. This involves initiation using y-radiation, followed by removal of the reaction vessel from the y-source. Conversion during the relaxation period is monitored by dilatometry, and the decay in polymerization rate over time is related to the rate of radical loss. When large particles are used, radical loss is dominated by intraparticle termination, rather than exit into the aqueous phase, and the rate coefficient for termination can be determined from the decay curve. By using multiple insertions and removals, the termination rate coefficient is determined over a wide range of polymer mass fraction (wp). 

In their recent publication, Odajima and his coworkers (11) have shown that the rather broad and asymmetric (009) and (0018) WAXS profiles of PTEOX polymerized above 80 C by radiation initiation may be resolved into two curves. One can be attributed to the extended chain crystals (the only kind present in sample PTEOX-12), and the other is the lamellar type crystals with thicknesses of about 100 X. Figure 7 shows that the line shape of the (009) profile of the plasma sample PTEOX-5P is rather sharp and similar to that of the radiation sample PTEOX-25. The half width (A20)1 = 1.72° or 0.012 X ) of the (0018) profile is narrower than those of PTEOX-25 (2.50° or 0.017 A ) and PTEOX-80 (2.25° or... 

Figure 5.6 shows the DSC curves for a methacrylic acid sample radiated for 30, 60 and 90 s. It can be seen from the curves that an exothermic reaction occurs during irradiation and then the reaction slows gradually when the radiation stops, resulting in an exothermic curve due to the after-polymerization. 

The microwave and thermal cure processes for the epoxy-amine systems (epoxy resin diglycidyl ether of bisphenol A, DGEBA) with 4,4 -diaminodiphenyl sulfone (DDS) and 4,4 -diaminodiphenyl methane (DDM) were investigated for 1 1 stoichiometries by using fiber-optic FT-NIR spectroscopy. The kinetic rate parameters for the consumption of amines were determined by a least squares curve fit to a model for epoxy/amine cure. The activation energies for the polymerization of the DGEB A/DDS system were determined for both cure processes and found to be 66 and 69 kJ/mol for the microwave and thermal cure processes, respectively. No evidence was found for any specific effect of the microwave radiation on the rate parameters, and the systems were both found to be characterized by a negative substitution effect [99]. 

MGr (for polyethylene, for example) a slight increase of dielectric permeation at frequencies from 10 kHz to 60 MHz is observed s = 121 for non-radiated and s = 2.29 for polymer radiated by 640 kGr dose [163], This indicates the predominant influence of the anomalous dispersion curve run on the refractive index change n =/(/ ) and the possibility of at least one more part of increment and saturation tSn at high radiation doses of polymeric materials, isotactic PP, in particular, compared with doses indicated in this paragraph. 

---