The lower critical solution temperatures (LCSTs) for mass fractionated samples of poly(N-isopropylacrylamide) (PNIPAM) were studied to determine the effect of polymer molecular weight on the LCST using a high throughput temperature gradient apparatus. PNIPAM fractions prepared by a conventional radical polymerization using azoisobutyronitrile (AIBN) as the initiator had LCSTs that were largely invariant with molecular weight or dispersity. Only slight deviations were noted with lower molecular weight samples. An 18-kDa sample had a 0.6 8C higher LCST. A 56-kDa sample had a 0.2 8C higher LCST. PNIPAM derivatives prepared with a triphenylmethyl (trityl) functionalized azo initiator were also prepared and mass fractionated. These samples' LCSTs were identical to those of PNIPAM samples prepared using AIBN initiation when higher molecular weight samples were compared. The trityl-containing PNIPAM fractions' LCSTs varied when the molecular weight decreased below 100 kDa. Acidolysis of the trityl end groups provided a third set of PNIPAM derivatives whose LCST differed only with samples with M w values < 60 kDa. These results show there is no effect of molecular weight on LCST until the degree of polymerization is such that end group structure becomes significant.

The radiation oxidative degradation of a commonly used silica-filled silicone elastomer DC745 was investigated by a series of experimental techniques. This elastomer is known to be chemically and thermally stable, but insufficient data exist on its radiation resistance. In the present work, gamma doses up to 200 kGy were applied under air at room temperature and 1 Gy/s. Chemical changes due to radiation were investigated by NMR, FT-IR, resonance Raman, and mass spectroscopy. DSC and TGA experiments probed thermal transitions and thermal stability changes with exposure dose. SEM probed variations on the surface of the elastomer, and changes in the polymer network were investigated using solvent swelling methods. Electron paramagnetic resonance (EPR) was employed to detect and identify free radicals. Uniaxial compression load tests at variable temperatures were performed to assess changes in the material"s mechanical response as a function of radiation dose. Results demonstrate that, with increasing exposure, DC745 undergoes changes in chemistry that lead to an increase in thermal stability and cross-link density, formation of free radical species, decrease in heat of fusion and increase in stiffness at low temperatures. Taken together, these results indicate that oxidative crosslinking is the dominant radiolysis mechanism that occurs when this material is exposed to gamma irradiation in air.

Organic getters are used to reduce the amount of reactive hydrogen in applications such as nuclear plants and transuranic waste. The present study examines the performance of getter loaded silicone elastomers in reducing reactive hydrogen gas from the gas phase and their capability of being This article is protected by copyright. All rights reserved. 23D printed using Direct Ink Writing techniques. The samples are placed in closed vessels and exposed to hydrogen atmosphere at pressures of 580 torr and 750 mtorr and at a temperature of 25 ºC.The hydrogen consumption is measured as a function of time and normalized to getter concentration in the polymer. The performance of the getter-loaded silicone elastomer containing DEB as the organic getter and Pd/C catalyst (ratio of 3:1 DEB to catalyst) decreases with increasing the resin's curing temperature. Chemical analysis suggests that DEB reacts with the silicone resin at high temperatures. In addition, it is demonstrated that the increased surface area of 3D printed composites results in improved getter performance.

Goal Develop new characterization techniques, especially those that can be integrated into production scenarios, to quantify and characterize the cure inhibition of silicone elastomers. Background Silicone elastomers are among the most versatile polymer materials due to their desirable properties, including good thermal and chemical stability, low electrical conductivity, biocompatibility, and good aging characteristics. The properties of silicone elastomers can be tuned giving rise to materials for a variety of applications, such as encapsulants, coatings, medical devices, microfluidic devices, and lithography. Sylgard® is a two-part, liquid silicone-based polymer manufactured by Dow Corning®.[1] Sylgard® can be modified by added cure accelerator and/or filler.[2-5] Modified formulations of Sylgard® are currently used potting materials at LANL and Pantex. One composition of Accelerated Sylgard® 184 that is used is as follow: Resin (100 PBW total) Sylgard® 184 elastomer ("base") 90 PBW Resin Accelerator 3-6559 10 PBW Curing Agent (10 PBW total) Sylgard® 184 curing agent 10 PBW

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