Glass and melting transitions of copolymers of tetrafluoroethylene with propylene and isobutylene

Copolymers of tetrafluoroethylene and propylene were prepared that contained 30–65 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and propylene-ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures, T_g, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot of T_g versus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30–56 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and isobutylene-ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained when T_g is plotted versus composition. Isobutylene-containing copolymers having 45–54 mole-% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in the polymer having two T_g.     

Disorder variables for a non-abelian symmetry group

This paper is concerned with the construction of local disorder operators for two-dimensional statistical mechanical systems, and with the representation of these operators in transfer matrix language. Each internal global symmetry operation leads to a separate disorder variable. This idea is illustrated in the example of the Ashkin-Teller model, in which the symmetry operations form a non-abelian group. There are seven non-trivial disorder operators. Five of these are shown to be simply duals of various kinds of spin operators. Series analysis is used to describe the critical behavior of one of the remaining two operators. No essentially new scaling behavior is observed.     

Structures and thermodynamic stabilities of the C2H4O isomers: Acetaldehyde,vinyl alcohol and ethylene oxide

Ab initio molecular orbital theory with a sequence of basis sets ranging from minimal to triple zeta plus polarization and with electron correlation incorporated using Möller-Plesset perturbation theory terminated at third order (MP3) is used to examine the structures and relative energies of the C₂H₄O isomers, acetaldehyde, vinyl alcohol and ethylene oxide. Acetaldehyde is indicated to be the most stable isomer with vinyl alcohol lying 45 kJ mol^–1 and ethylene oxide 114 kJ mol^–1 higher in energy. The theoretical structures and energies are in reasonable agreement with the best available experimental data.     

Measurement of the spin correlation parameter A00nn and the polarization A00n0 in elastic p-p scattering between 400 and 600 MeV

We have measured the spin correlation parameter A_00nn and the polarization A_00n0 for p-p elastic scattering in the c.m. angular range between 30° and 90° at seven energies between 400 and 600 MeV. The experiment was performed at SIN using a polarized beam and target and a fast on-line event reconstruction method. The results are compared with phase-shift predictions.     

Diastereoselektive Synthese von β-Methyl-homoallylalkoholen durch lk-Addition von (2-Butenyl)triphenoxytitan an Aldehyde

Diastereoselective Synthesis of β-Methyl-homoallylic Alcohols by lk-Addition of (2-Butenyl)triphenoxytitanium to Aldehydes (2-Butenyl)triphenoxytitanium, prepared in situ from (2-butenyl)magnesium halogenide and chlorotriphenoxytitanium in tetrahydrofuran solution, adds to aldehydes with like (Re,Re/Si,Si?Re*,Re*) relative topicity in diastereoselectivities of 80–99%.