TÉLOMÉRISATION ENÉMULSION DU STYRÈNE AVEC LES MERCAPTANS
Abstract The telomerization in emulsion of styrene is studied with two transfer agens: thioglycolic acid and 1,1,2,2-tetrahydro perfluorooctane thiol. The influence of the telogen-amount vs the degree of telomerization, that of the surfactant concentration and that of the nature of the initiator are investigated. The telomerization of this monomer with these aliphatic mercaptans is possible in aqueous medium whatever the solubility of the thiols in water. Transfer constants of both these mercaptans were determined as 1.60 and 1.16 for thioglycolic acid and the fluoronated thiol, respectively. © 1997 Elsevier Science Ltd. All rights reserved
We study in perturbative QCD the helicity amplitudes of the process ${\ensuremath{\gamma}}^{*}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rho}p$ at large virtualities Q of the photon ${\ensuremath{\gamma}}^{*}.$ We estimate all spin-flip amplitudes taking into account an important effect of the scale behavior of the gluon density. The transition of a transverse virtual photon to a longitudinal vector meson is not small at typical conditions at the DESY ep collider HERA. This helicity nonconserving amplitude leads by interference to a measurable effect in the distribution of the angle between the electron scattering and the meson production planes.