Edward N. Peters

Poly (dodecacarborane-siloxanes)

Abstract The need for elastomeric polymers which will maintain their elastic properties at high temperatures has led to a wide interest in inorganic-based polymers [l]. The development of carborane-siloxane polymers in the early 1960s was a breakthrough in the search for a high-temperature elastomer. Incorporation of a carborane moiety into the siloxane backbone significantly enhanced the overall thermal stability [2].

D2-m-Carborane-Siloxanes. VI. Oxidative Stabilization of Vulcanizates with Ferric Oxide

Ferric oxide produced from iron pentacarbonyl was evaluated as an oxidative stabilizer in D2-m-carborane-siloxane and polydimethylsiloxane vulcanizates. The results indicate a significant improvement in efficiency compared to powdered ferric oxide. Thus a carborane-siloxane vulcanizate retained elastomeric properties after 1000 hours in air at 315°C. The practical upper use temperature for carborane-siloxane vulcanizates were evaluated by heat aging samples at 340° and 370°C.

D2-meta-Carborane-Siloxanes. II. Factors Affecting High Performance Properties Of Vulcanizates

D,-rneta-carborane-siloxane polymers have been developed for ultrahigh temperature elastomer applications. In particular, these materials have outstanding thermal stability in addition to fire and chemical resistance. Basic studies relating to resin-filler interactions, polymer structure, peroxide and extending fillers on thermal stability have been carried out. The optimization studies have afforded valuable information leading to both improvements in long term aging stability and fabrication characteristics. The use of a hydrophobic silica as a reinforcing agent instead of a fumed silica resutted in substantial improvements in retention of properties after aging. Furthermore, the use of high molecular weight stock and lower peroxide levels for curing has led to a system with outstanding retem tion of properties after heat aging in air a t 315C. These unique high performance capabilities are being confirmed in sealant, gasket, O-ring, and coating applications. INTRODUCTION CARSI L D,-META-CARBORANESILOXANE polymer has been developed for ulU trahigh temperature elastomer applications. It offers a unique combination of properties unavailable with fluorocarbon, silicone, o r polyphosphazine based high performance elastomer. In particular, these elastomers have superior thermal stability (over 300 hours in air a t 315°C) in addition to fire and chemical resistance, and good processing characteristics [ l ] . Such polymers are represented by the following structure: Presented in part a t the 10th Middle Atlantic Meeting, American Chemical Society, Philadelpbia, Pennsylvania, February 24, 1976. J. Elastomers and Plastics, Val. 9 (April 19771, P177 E. hr. Peters, et al. where R = R = CH3 with 33 mole percent diphenyl (R = R = c6 H5 ) or 33 mole percent methylphenyl ( R = CH,; R = C6H5) modification. The incorporationof 4 mole % methylvinyl (R = CH,; R = vinyl) facilitated in the vulcanization by conventional peroxide cures. Basic studies relating to resin-filler interactions, polymer structure, peroxide, and extending fillers on thermal stability have been carried out. Utilizing data from these optimizations studies, marked improvements in performance have been achieved over earlier data reported for carborane-siloxane elastomers [ l , 21.

Neighbouring group participation and the tool of increasing electron demand : A review

Solvolytic reactions could be greatly influenced by the presence of neighbouring groups. The tool of increasing electron demand has been successfully used to detect such participation. For example, the tool has detected the presence of major π-participation inanti-7-norbornenyl and π-conjugation in cyclohexen-2-yl derivatives. The changes observed in the absolute values ofp+ with ring size in cyclic systems could be adequately explained by the I-strain concept. The tool has established major πδ-conjugation in cyclopropylcarbinyl and nortricyclyl derivatives. πδ-participation in the Coates’ cation has been unambiguously established. However, this sensitive probe has failed to provide evidence for δ-participation in the solvolysis of 2-norbornyl system. It, is concluded that the tool of increasing electron demand is quite sensitive to detect the presence or absence or neighbouring group participation.

Correlation of carbonyl frequencies of aromatic derivatives with their nonaromatic analogues

Abstract A linear free energy relationship, ν = ν0 + ϱγ+, with group constants, γ+, was defined. The group constants are characteristic of the inductive and resonance effects of aryl and hydrogen groups. The use of group constants allows the direct correlation of carbonyl stretching frequencies of aromatic derivatives with their corresponding nonaromatic analogues in which the aryl group has been replaced by a hydrogen group.