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The photochemistry of poly(n-butyl acrylate) (PnBA) has been studied at 77 and 298 K. The principal photoproducts of Norrish type I and II processes have been identified and their quantum yields have been measured. The chemistry of photogenerated radicals has been monitored via ESR spectroscopy. Both Norrish type I and II products are observed at room temperature on excitation at 253.7 nm. Hydrogen abstraction takes place from backbone methylene groups in samples excited at 77 K, while tertiary hydrogen abstraction from the main chain becomes the dominant radical termination process at or above 210 K, which is the glass transition temperature of PnBA. Excitation at 313 nm in the presence of air causes photooxidation but little or no photolytic bond cleavage.

The curing reaction of tetraglycidyl diaminodiphenyl methane (TGDDM) with diaminodiphenyl sulfone (DDS) has been investigated using differential scanning calorimetry, Fourier transform IR spectroscopy, and ESR spin trapping techniques. A mechanism has been proposed, and the cure kinetics has been obtained at 177°C. The major conclusion is that cure proceeds mainly through chain extension, while crosslinking occurs through the reaction of hydroxyl groups with epoxides, resulting in formation of ether linkages.

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IntroductionT HE concerted synergistic interaction between high-velocity oxygen atoms and vacuum ultraviolet (VUV) radiation has been found to contribute significantly to materials degradation in low-Earth-orbiting spacecraft. In particular, organic polymers used as electrical insulation materials and as thermal control blankets show the most significant degradation due to these environmental effects.The existence of this synergistic effect has been proven under laboratory conditions 1>2 and inferred from the degradation observed in samples of silverized FEP (fluorinated ethylene propylene) Teflon (®E.I. Du Pont de Nemours Inc.) thermal blanketing materials recovered from the Solar Maximum Mission satellite and, 3 ' 4 more recently, from the Long Duration Exposure Facility (LDEF) satellite. To date, the detailed chemical origin of this synergistic effect has not yet been fully elucidated.We report here preliminary results of a micrographic investigation of FEP thermal blanket samples recovered from the LDEF satellite. From this investigation and from laboratory experiments, we are able to propose a possible mechanism for the synergistic effect by identifying the role VUV radiation plays in enhancing the atomic oxygen reactivity of FEP. ExperimentalSamples of silverized FEP (Teflon) thermal blankets recovered from two specific areas of the LDEF satellite were analyzed. A sample was taken from row 2 on the trailing edge (P0004) of the spacecraft, which received predominantly VUV exposure (9346 equivalent solar hours) with very little atomic oxygen fluence (4.7 x 10 9 atoms/cm 2 ), and a sample was taken from row 8 (a position -40 deg off ram), which received both

Kinetics of the reactions of the principal radical species, the tertiary alkyl and peroxy radicals, generated on photooxidation of poly(n-butyl acrylate) (PnBA) were studied at room temperature under different oxygen pressures. A simplified mechanism of photooxidation, similar to that proposed earlier (Liang, R. H.; Tsay, F.-D.; Gupta, A. Macromolecules 1982,15,974), was used to interpret the data. The kinetic rate parameters as well as the radical concentrations developed under steady-state illumination conditions were estimated by a least-squares fit to the observed data by using kinetic equations based on such a mechanism. It was found that at least two different types of tertiary alkyl radicals (i.e., radicals of different reactivities) were being formed during photooxidation of PnBA.

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