No description available.

No description available.

No description available.

Polysiloxane networks have excellent oxidative and good UV environmental stability, flexibility at low temperatures, and thermal stability at higher temperatures. This wide service temperature range makes these materials a candidate class of materials for high performance adhesives and sealants, and in particular for applications on high speed aircraft. Polar polysiloxane networks were prepared with cyanopropyl substituents to lower any propensity for the materials to swell in hydrocarbon fuels and to improve adhesion to metal substrates. 1,3,5,7-tetramethyl,1,3,5,7-tetrahydrocyclotetrasiloxane (D4H) was hydrosilated with allyl cyanide to yield the corresponding 3-cyanopropylmethylcyclotetrasiloxane monomer (D4CN). Controlled molecular weight oligomers with vinyl termination were prepared in equilibrium reactions using a basic catalyst. These oligomers were then crosslinked with various hydride functional crosslinking reagents to yield model networks for mechanical and adhesion studies. The network properties of nonpolar polydimethylsiloxane (PDMS), polar poly[methyl(3,3,3-trifluoropropyl)siloxane] (PMTFPS), and the novel polar poly(3-cyanopropylmethyl-siloxane) (PCPMS) were investigated as a function of sidechain chemical structures. Effects of increasing crosslink density were investigated for the PDMS networks by adding a difunctional siloxane dimer with vinyl groups. Moduli and tensile strengths increased while percent elongation decreased as the crosslink density was increased. All networks were thermally stable above 300 °C in both air and N2 (when heated at a rate of 10 °C/min.) and exhibited Tgs lower than -55 °C. The polar networks swelled to a much lesser extent (at least one order of magnitude) than the nonpolar networks in hydrocarbons and Jet fuel. Cohesive failure was observed for the polar networks via metal to metal (Al foil substrate to Al and Ti adherends) 180° peel test. The PCPMS elastomers had average load values twice those of the PDMS networks independent of crosslink density. / Master of Science

Pavement concrete joints are the weakest locations in concrete pavement systems. They are man-made cracks to accommodate concrete slab expansion and contraction due to temperature fluctuations. Sealant is usually used in pavement joints to prevent roadway debris, deicing chemicals, and moisture from entering the joint. When sealant fails, the pavement deteriorates rapidly; and when joint sealant performs adequately, the pavement preserves its intended performance. In the field, joint sealant undergoes two types of mechanical loading simultaneously. The sealant is experiencing tension or compression as slabs contract (low temperature) or expand (high temperature), respectively. Sealants also experience shear as heavy trucks travel over the joint and deflect the ends of the pavement slabs. In addition, sealants may also be exposed to a variety of environmental conditions, such as moisture, ultraviolet light, and jet fuel, which in some cases could be detrimental to their performance. In this study, the effects of vehicular and environmental loading on joint sealant performance were evaluated. To simulate the sealed joint performance, specimens were constructed by sandwiching a sealant between two 50.8 mm Portland cement concrete (PCC) cubes. Prior to mechanical loading, specimens were subjected to partial immersion in distilled water, partial immersion in jet fuel, and/or exposure to UV-A light. The specimens were then subjected to static horizontal tension, simulating slab contraction, and cyclic deflection-controlled shear, simulating heavy trucks travelling over the joint. The cycle consists of one 0.2 second period of sinusoidal loading (total 6.4 mm deflection) followed by a 0.4 second relaxation. The mechanical loading was applied using a special fixture developed at Virginia Tech, which is connected to a closed-loop servo-hydraulic loading machine. Two types of sealants (preformed neoprene and field-molded silicone with a primer) were tested using PCC mixes with two different aggregate types. In, addition, two different joint widths were evaluated for each sealant type. From the results of the cyclic testing and environmental conditioning, it was shown that the use of a primer greatly enhances the performance of the silicone sealant used with concrete containing limestone aggregate. In addition, severe swelling occurs when silicone sealant is exposed to jet fuel, and the failure of the field-molded silicone initiated at the bottom of the sealant and propagated upward. The preformed neoprene sealants proved very durable despite any combination of environmental conditioning, provided that the sealant remained in compression. / Master of Science

Thesis (M.S.)--University of Michigan, 1973.

Thesis (M.S.)--University of Michigan, 1972.

Thesis (M.S.)--University of Michigan, 2003. / Includes bibliographical references.

Thesis (M.S.)--University of Michigan, 1972.

Thesis (M.S.)--University of Michigan, 1973.