Showing papers by "3M published in 1960"

Polymer NSR spectroscopy. II. The high resolution spectra of methyl methacrylate polymers prepared with free radical and anionic initiators

Abstract: Spectra of methyl methacrylate polymers in chlorofornm solution at 90° show three α-methyl proton peaks. Measurements of their areas in spectra of polymers prepared with free radical and anionic initiators indicate that these may be attributed to (1) iso- tactic sequences (ddd or lll), (2) syndiotactic sequences (ldl or dld), and (3) heterotactic sequences (ldd, dll, ddl, or lld). The conformation and stereochemical configuration of the chains may thus be examined with considerable discrimination; degrees of regularity. block sizes, etc. appear to be determinable. Free radical polymers of methyl methacrylate are found to be predominantly syndiotactic, whereas those produced with anionic initiators. such as n-butyllithium, are shown to be predominantly isotactic, in agreement with the findings of others. The backbone methylene resonance also shows striking changes with chain stereochemical configuration, such as to provide absolute, independent confirmation of the assigned structures.

Fluorine N.S.R. Spectroscopy, II. A “Distant” Carbon-13 Isotope Effect

Abstract: A nuclear spin resonance "isotope effect" upon shielding values for fluorine atoms attached to C/sup 13/was investigated. The small excess shielding produced by "distant" C/sup 13/ is shown to vary by a statistically significant factor of two among the compounds studied in the F--C/sup 12/--C/sup 13/ system. No correlation is observed between this strongly varying quantity and other closely related measurements, nor to the fluorine shielding values listed for the compounds. The magmtude of the C/sup 13/ effect increases with the number of trigonal carbons in the F--C--C/sup 13/ system; this "correlation" may perhaps extend to the smaller F--C/sup 13/ system, with the opposite sign. Experiments are underway to determine the relative sign of the two C/sup 13/ coupling constants. (B.O.G.)

Radiolysis of polymethyl isopropenyl ketone

Abstract: Polymethyl isopropenyl ketone (PMIPK) undergoes random chain scission when irradiated at 23°C. with gamma rays or with ultraviolet light. Total energy absorption per chain scission, Ed, is 94 e.v./scission for PMIPK powders irradiated in vacuo with spent reactor fuel element gamma rays (0.42 Mrad/hr.). Ed is 84 e.v./scission for a PMIPK powder irradiated in vacuo with Co60 gamma rays (0.109 Mrad/hr.). The presence of air lowers the value of Ed to 41 e.v./scission under the former conditions. A film of PMIPK irradiated in air with 2537-A. wavelength light exhibits Ed = 22 e.v./scission or a quantum yield ϕd = 0.22 chain scissions/absorbed photon. The viscosity-average molecular weights of this film vary with light exposure in accordance with theoretical predictions.

Design parameters for optimizing the efficiency of thermoelectric generators utilizing p-type and n-type lead telluride

Abstract: Thermoelectric generators are presently being developed for many uses which range from small flame-operated power supplies for automatic control systems to several kilowatt-size thermopiles for prototype evaluation of marine propulsion systems.1 This renewal of interest in thermoelectric power generation and thermoelectric heat pumping is based on recent advances in the development of special semiconducting materials which exhibit properties intermediate to metals and semiconductors of the type used in P-N junction transistor devices. Often called ?semimetals,? these thermoelectric materials are prepared from semiconducting crystals which are more heavily doped than transistor devices to provide higher electrical conductivity. Such materials exhibit much lower thermal conductivity than do metals and substantially higher thermal emf (electromotive force).

Observations on Boron and Some Borides

Abstract: Single crystals of beta-rhombohedral boron have been grown in both needle and plate habit from the vapor phase. Maximum size of needle crystals was approximately 5 mm × 0.1 mm × 0.1 mm. Penetration twinning and growth steps at one end of a crystal were detected in some cases. These boron needles were characterized by smooth lateral faces of high reflectivity. Thin lathlike red crystals of AlB12 were prepared from the elements at reduced pressure.

Effects of corona on vinyl tapes

Abstract: Pressure sensitive vinyl tapes are extensively used as an outer wrap for cable splices and terminations, and for bus bar insulation and other high voltage applications For such service, resistance to corona is an important factor However, most published information on corona resistance is concerned with polyethylene and insulations other than vinyl (1–8)