Primary Reactions during the Free Anionic Polymerization of β Nitrostyrene

Abstract

Abstract β-Nitrostyrene (βNS) was irradiated at r. t. in solutions of hexamethylphosph. triamide (HMPT) with 50 ns pulses of 15 MeV electrons. It was found that βNS reacts with solvated electrons almost encounter controlled (k(e- solv + βNS) = (9 ± 3) · 109 l/mol s) forming the radical anion · βNS-. The optical absorption spectrum of the latter was recorded in dilute solutions ([βNS] < 5 × 10-3 mol/l). At higher βNS concentrations the formation of an additional optical absorption after the pulse in the wavelength range between 460 nm and 570 nm was detected, which is attributed to the reaction of βNS with · βNS- yielding the dimeric radical anion (· βNS-βNS-). The rate constant for this process is 4 × 107 l/mol s. At low βNS concentrations ( < 5 × 10-3 mol/l) the transient spectrum decayed by a second order process (k2 - (2.2 ± 0.5) · 109 l/mol s). This process is correlated to the neutralization of radical anions by cations formed initially. At [βNS] > 5 × 10-3 mol/l only the band at 630 nm decays according to second order kinetics. This band is correlated to the part of the anions with the highest electron density, the nitro groups. At wavelengths below 570 nm the absorptions of various species overlap. These species decay by different rate laws.