Apparently the shielding layer of anhydride is not formed in this case. Use of the calibration curve permitted rapid evaluation of the thickness of films whose thickness was on the order of 10O3 cm. Infrared Spectrum of Resin A. Measurement of Molar Absorptivities Molar absorptivities of phthalic acid, phthalic anhydride, and Resin A were measured at 5. Infrared Spectrum of Phthalic Anhydride. To eliminate this source of error and to save time and effort, a new holder was designed which could hold three disks in the irradiation cell and was also fitted with an adapter which fit the instrument directly and allowed the holder to be rotated, positioning first one, then another of the samples in the beam for scanning.
The wave lengths and relative intensities of these bands at 5. In all four of these cases the results were the same. A peroxide group adjacent to the carbonyl produces a marked shift to shorter wave lengths. This is not to say that subsequent reactions in the overall degradation process are not of the thermal type. The sodium chloride cells used in infrared analysis were calibrated by two independent methods.
As might be expected the rate is much faster in an oxygen atmosphere than with nitrogen, Some inferences about the role of water vapor in this reaction may be made by examination of the results of this irradiation in wet nitrogen. Due to the relative insolubility of phthalic anhydride and phth a lic acid in solvents which do not themselves absorb infrared radiation in the region from PAGE thesiz 17 5 to 7 microns, it was found necessary to use mixed solvent systems.
Since it was desired to correlate these infrared data, if possible, with data published on evolution of gases from the films, Experiment I was repeated at a higher temperature, 75 2C. This method was checked by weighing a film of known area and calcu lating thickness from the weight, area, and density. The method described above may only be employed when the film is thin enough to allow measurement of the absorbance of the 5. The thicknesses were calculated from the equations: The con clu s ion to which the author is forced, in the light of this result, is that the degradation process consists of an initial photolytic tbesis of the polymer at the site of the ester linkage.
This is not to say that subsequent reactions in the overall degradation process are not of the thermal type. Glyceryl phthalate alkyds have been popular in the field of surface coating because of their gloss retention and general pleasing appearance throughout a relatively long protective life. The ether served to dissolve the solute and the chloroform merely diluted the solution to a useable concentration without introducing any additional solvent absorption in the region of interest.
A study of some factors affecting the degradation of alkyd resins
Patent 1,Jan. It was reasoned that chain rexin at this point would result in formation of small fragments which could be removed from the film either as gases or as water soluble compounds leaving behind phthalic acid or related free radicals which might further decompose with evolution of carbon dioxide. One would predict qualitatively that the rates of degradation of Resins A and B should be approxi mately equal and the rate for Resin C should be somewhat greater due to att a ck at the sites of u.
The sodium chloride cells used in infrared an a lysis were calibrated by two independent methods. Gropp for continuing advice, assistance, and ins p iration.
This dissertation was prepared under the direction of the chairman of the candidate’s supervisory committee and has been approved by all members of that committee. The curve was obtained by casting films in metal spacers of known thickness and pressing between two sodium chloride plates. With care, it is a highly reproducible method and the versatility of modern spectrophotometers allows accuracy which may be easily refined to 1 per cent even for such ill-defined molecules as the polymers studied in this case.
After 48 hours the unknown band had a transmittance of about 40 per cent as compared to a background of 80 per cent.
The results of the irradiation are shown in graphical form in Figure On the assumption that much of this scattering was the result of non-reproducible positioning of the samples on the spectrophotometer, a new sample holder was constructed which largely eliminated this source of error.
Others have suggested that the hydroperoxides formed oxidize titanium IV oxide to pertitanic acid which in turn oxidizes the film to produce chalking.
As might be expected the rate is much faster in an oxygen atmosphere than with nitrogen o Some inferences about the role of water vapor in this reaction may be made by examination of the results of this irradiation in wet nitrogen. Past research into the chalking process has centered around two mechanisms. The films were allowed to dry in air for fifteen minutes and then were dried in an oven at C. In this section, however, chronology has been i g nored in favor of clarity and continuity in discussing results.
Thus the reaction after 50 hours is still first order in ultraviolet intensity or actually pseudo first order since there is a large excess of ester present.
The wave lengths and relative intensities of these bands at 5. Appreciation is also expressed to the General Motors Corporation for the Fellowship w hi c h made this work possible and to the Renshed-Mason Company for formation of the resins used in this stu d y. The first appearance of a band in the spectrum, of the resin which might be associated with the products of the degradation occurred while irradiating a sample of Resin A in an atmosphere of oxygen saturated alkgd water vapor tuesis a temperature of C.
This data in addition to the known ability of alkyds, modified only with pigments, to chalk rapidly seemed to indicate some degradation of the C-C-C ester linkage in addition to other effects studied in the modified alkyds. Among these products were the various modified glyceryl phthalate resins which made great strides both as surface coatings and rewin binders for molded products and by the actual commercial pro d uction of these alkyds was in excess of 34 million pounds yearly.
A study of some factors affecting the degradation of alkyd resins
Between 40 and 50 hours a break in the line occurs and the data between 50 and hours follows the equation: Peter Edward Morrisett is married to the former Suzanne Hamrick and is the father of two daughters. On the assumption that much of this scattering was the result of non-reproducible positioning of the samples on the spectrophotometer, a new sample holder was con structed which largely eliminated this source of error.
The principal degradation product was identified as phthalic anhydride.
All subsequent irradiation experiments employed this holder.