No abstract

ZUSAMMENFASSUNG:Versuche mit feinkornigen Pulvern, bestehend aus Kieselgel, Kaolinitverbindungen und Calciumcarbonat, wurden durchgefuhrt, um zu prufen, o b mit Hilfe der 60Co-y-Vorbestrahlungsmethode die Oberflachenpfropfung rnit Methylmethacrylat (MMA) und Styrol gelingt. Es zeigte sich, daD nennenswerte Mengen Polymeres aufgepropft werden konnen. Der Pfropfungsgrad (PG) steigt mit zunehmender absorbierter Dosis an und strebt bei hoheren Dosen einem Sattigungswert (PG"' "") zu. Die gemessenen Werte von PGYx (in g Polymeres/m2 Pulveroberflache) sind fur alle Substanzen groDenordnungsmaDig gleich. Daraus wird geschlossen, daB die Polymerisation durch aktive Zentren ausgelost wird, die sich an der Oberflache der Pulverpartikeln befinden, und daD die an der Oberflache maximal erreichbare Konzentration an aktiven Zentren ungefahr gleich groD ist. Unterschiede in den PG$""-Werten der einzelnen Substanzen sind vermutlich darauf zuruckzufiihren, da13 die verschiedenen gepfropften Pulver einen unterschiedlich groRen Anteil an nicht kovalent gebundenen und trotzdem nicht extrahierbaren Polymeren enthalten, der sich in engen Poren befindet. Hinweise dafur ergab die durch AIBN thermisch ausgeloste Polymerisation von .MMA in Gegenwart von porenreichem Kieselgel, die zu P G F =~ x 10-4g Polymeres/m2 fiihrte. Mit der Vorbestrahlungsmethode wurde PGY" = 8 x 10-4g Polymeres/m2 erhalten. Es wird vermutet, daD das nach der Vorbestrahlungsmethode aufgepfropfte Polymere zumindest zum Teil nicht kovalent gebunden ist. Der Anteil des nicht kovalent gebundenen und nicht extrahierbaren Polymeren sollte eine Funktion der Anzahl und der GroBe der Poren und infolgedessen substanzabhangig sein. SUMMARY:Experiments with fine grained powders of silica gel, kaolinite and calciumcarbonate have been carried out, in order to prove whether the h°Co-y-preirradiation method is applicable for grafting methylmethacrylate (MMA) and styrene onto the surface of these powders. It is demonstrated that significant amounts of polymer may be grafted by this method. The degree of grafting (PG) increases with increasing absorbed dose and approaches a limiting value (PGmaX) at high doses. Measured values of PGY" (expressed in units of g polymer per m2 surface of powder) are the same within an order of magnitude for all substances. Therefore, it is concluded, that the polymerization is 23 B. Dinh-Ngoc, J. G. Rabe und W. Schnabel started by activecentersgenerated previously at the powder surface and that the maximum concentration of active centers attainable at the particle surface is about the same for all powders. Differences of PGt""-values obtained with the various substances are presumably due to the fact that the grafted powders contain a fraction of not covalently bonded and in spite of this not extractable polymer in narrow pores. Evidence for this was obtained by initiating the polymerization of MMA with AIBN at 50°C in the presence of a highly porous sample of silica gel. In this case P G F =~ x 10-4g polymer/m2 was obtained which compares with PGIa"=8 ...

r-1, c-2, t-3, t-4-tetraphenvlcyclobutane (TPCB) was irradiated in dilute solutions of hexamethylphosphoric triamide (HMPT) with 20 ns pulses of 16 MeV electrons. Solvated electrons (e-solv) produced during the radiolysis of HMPT react with TPCB with k = (6 ± 1) · 109 l/mol s. Simultaneously with the decay of the optical absorption of the solvated electrons, the formation of the absorption of t-stilbene (at 300 nm) and that of stilbene radical anions (at 500 nm) was observed. Thus, it is concluded th at TPCB is undergoing a dissociative electron attachment process e-solv + TPCB→t-St + t-St·̄̅. The lifetime of a possible intermediate (TPCB·̄̅) was estimated as being smaller than 10-9 s. The 100 eV yield of t-stilbene was determined as G(t-St) = 3.4.

/J-Nitrostyrene (/5NS) was irradiated at r. t. in solutions of hexamethylphosph. triamide (HMPT) with 50 ns pulses of 15 MeV electrons. It was found that /3NS reacts with solvated electrons almost encounter controlled (&(e^,iv + /?NS) = (9 3) • 10 9 1/mol s) forming the radical anion • /JNS -. The optical absorption spectrum of the latter was recorded in dilute solutions ([/SNS] < 5 X 10 -3 mol/1). At higher /SNS 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 /?NS with -/SNS -yielding the dimeric radical anion (-/SNS-/SNS -). The rate constant for this process is 4 X 10 7 1/mol s. At low /?NS concentrations (< 5 X 10~3 mol/1) the transient spectrum decayed by a second order process (k2 -(2.2 ± 0.5) • 10 9 1/mol s). This process is correlated to the neutralization of radical anions by cations formed initially. At [/SNS] > 5 X 10~3 mol/1 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.

A B S T R A C T 0-Nitrostyrene (PNS) was polymerized in aprotic solvents. The rate of polymerization increased in the series dimethyl sulf oxide = dimethylf ormamide < N-methylpyr rolidone < hexamethylphosphoric triamide (HMPT). From copolymerization experiments with a-methylstyrene and methacrylonitrile, evidence for an ionic mechanism was obtained. Electron scavengers inhibited the polymerization. Thus it was concluded that in dilute solution the initiation comprises the thermalization of electrons which become solvated and react with PNS to form the radical anion .PNS-. Pulse radiolysis experiments were carried out in HMPT. The spectrum of an intermediate (presumably .PNS-) was recorded. By measuring the rates of the formation of *PNS-and of the decay of solvated electrons the rate constant ke-(solv + ONS) = (9 * 3) x 10' liter/mole-sec was determined. At higher monomer concentrations the polymerization was autoinhibited which is probable due to the fact that direct absorption of radiation by the monomer becomes important. 1637