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RECEIVED DATERunning title: "MQ-NMR of Radiation damage in filled siloxanes" CORRESPONDING AUTHOR FOOTNOTE: Mail code: L-231, (925) 423-4991, (925) 422-3750, maxwell7@llnl.gov ABSTRACT: DC745 is a commercially available silicone elastomer consisting of dimethyl, methylphenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is generally considered to age gracefully and to be resistant to chemical and thermally harsh Maxwell, et al. MQ-NMR of radiation damage in filled silicones p.2 environments. However, little data exists on the radiation resistance of this commonly used silicone elastomer. We report static 1 H NMR studies of residual dipolar couplings in DC745 solid elastomers subject to exposure to ionizing gamma radiation. 1 H spin-echo NMR data shows that with increasing dose, the segmental dynamics decrease is consistent with radiatively induced crosslinking. 1 H multiple quantum NMR was used to assess changes in the network structure and observed the presence of a bimodal distribution of residual dipolar couplings, <Ω d >, that were dose dependent. The domain with the lower <Ω d > has been assigned to the polymer network while the domain with the higher <Ω d > has been assigned to polymer chains interacting with the inorganic filler surfaces. In samples exposed to radiation, the residual dipolar couplings in both reservoirs were observed to increase and the populations were observed to be dose dependent. The NMR results are compared to Differential Scanning Calorimetry (DSC) and a two-step solvent swelling technique. The solvent swelling data lend support to the interpretation of the NMR results and the DSC data show both a decrease in the melt temperature and the heat of fusion with cumulative dose, consistent with radiative crosslinking. In addition, DSC thermograms obtained following a 3 hr isothermal soak at -40 ºC showed the presence of a second melt feature at T m ~ -70 ºC consistent with a network domain with significantly reduced segmental motion.

Recent advances in membrane introduction mass spectrometry (MIMS) have demonstrated the utility of MIMS in the trace level analysis of volatile organic compounds in water. The present study details the performance of an ion trap mass spectrometer fitted with a capillaiy membrane probe in the direct analysis of volatile organic compounds in water using flow injection techniques. Detection limits for 59 volatile organic compounds listed in EPA method 524.2 were determined to be in the mid to low parts per trillion (pptr) range using MIMS. Analyses of these compounds in untreated river water, sea water, and matrices containing strong adds and bases are demonstrated. The matrix studies show that there are no adverse effects on compound identification or detection limits resulting from matrix interferences in MIMS. Further experiments demonstrate the utility of MIMS as a direct analysis technique for on-line monitoring of trihalomethane formation in water treatment facilities. Detection limits of 100 pptr were obtained for the four trihalomethanes, with repetitive sample times averaging 6 min/sample. Quantitation of the total trihalomethane content was performed in one step, demonstrating further increases in analytical speed over traditional analysis methods.As we approach the year 2000, a move is underway by the Environmental Protection Agency (EPA) to a policy of point source environmental compliance. Any industry that discharges anything into the environment will have to demonstrate, on site, that their emissions are within the allowable limits. This will create an entirely new market for on-site monitoring instrumentation designed to allow individual industries to inexpensively record compliance with environmental waste stream and smoke stack emission limit policies. The challenge faced by analytical instrumentation manufacturers and government regulators is to move away from slow and inefficient established analytical methodology and create a new breed of instrumentation designed to meet the requirements of the new regulations.Membrane introduction mass spectrometry (MIMS) is emerging as a prime candidate to fill these requirements for the direct analysis of volatile organics in water and air. At the present time,

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