No abstract

The oil-in-water-type (o/w) microemulsion polymerizations of butyl acrylate initiated by a water-(ammonium peroxodisulfate, AP) -and oil-soluble (dibenzoyl peroxide, DBP, and 2,2'-azoisobutyronitrile, AIBN) radical initiators were investigated. Polymerizations with AP were faster than those with DBP or AIBN. The rate of polymerization shows initiation and termination intervals, but no constant interval. The rate of polymerization is found to be proportional to the 0.46th, 0.53rd and 0.24th power of the AP, AIBN and DBP concentration. The rate per particle is found to be proportional to the 0.29th, 0.32nd and 0.37th power of the AP, AIBN and DBP concentration. The number of radicals per particle was found to increase with increasing the initiator concentration. The most pronounced increase in the number of particles with increasing the initiator concentration was observed with AP, much less with AIBN and the slight decrease with DBP. The molecular weights of polymers were found to vary only slightly with increasing the initiator concentration. The formation of radicals proceeds in the aqueous phase (AP and a water-soluble fraction of AIBN or DBP) and the monomer-swollen micelles (AIBN or DBP) as well. The polymer particles grow by recruiting monomer and emulsifier from the free monomer-swollen emulsifier micelles. ZUSAMMENFASSUNG: Die 01-in-Wasser-Mikroemulsionspolymerisation von Butylacrylat mit einem wasserloslichen (Ammoniumperoxodisulfat, AP) bzw. zwei wasserunloslichen radikalischen Initiatoren (Dibenzoylperoxid, DBP, und Azoisobutyronitril, AIBN) wurde untersucht. Die Polymerisation verlauft mit AP schneller als mit DBP oder AIBN. Die Polymerisationsgeschwindigkeit 1mt sich in ein Start-und ein Abbruchintervall gliedern. Die Reaktionsordnungen betragen 0,46 fur AP, 0,53 fur AIBN und 0,24 fur DBP. Die Reaktionsgeschwindigkeit pro Polymermizelle ist proportional zur 0,29. (AP), 0,32. (AIBN) bzw. 0,37. (DBP) Potenz der Initiatorkonzentration. Die Zahl der pro Latexteilchen gebildeten Radikale nimmtim Fall von AP deutlich, mit AIBN weni-0 1994 Hiithig & Wepf Verlag, Zug CCC OOO3-3146/95/$07.00P. Potisk, I. Capek ger deutlichmit steigender Initiatorkonzentration zu; bei DBP nimmt sie sogar etwas ab. Die Molekulargewichte der hergestellten Polymeren zeigten nur eine geringe Abhangigkeit von der Initiatorkonzentration. Die Radikale werden sowohl in der wanrigen Phase (AP sowie einer wasserldslichen Fraktion von AIBN oder DBP) als auch in den mit Monomeren gequollenen Mizellen (AIBN oder DBP) gebildet. Die Polymerteilchen wachsen durch Anlagerung von Monomerem und Emulgator aus den freien, mit Monomerem gequollenen Emulgatormizellen.

The oil/water microemulsion polymerizations of butyl acrylate initiated by a water (ammonium peroxodisulfate, APS) or oil (dibenzoyl peroxide, DBP) soluble radical initiator at different emulsifier concentrations were investigated. The rate of polymerization vs. conversion curve shows two intervals. The rate of polymerization is found to decrease with the emulsifier concentration. This finding was discussed in terms of the decrease of both radical and monomer concentration, the chain transfer to emulsifier, desorption of chaintransferred radicals, and the contribution of solution polymerization. The polymerization is faster with APS. In the APS system the rate per particle or the number of radicals per particle increases exponentially with increasing particle size. The particle size and number increase during the whole polymerization. This behavior was discussed in terms of the nucleation of monomer‐containing micelles and agglomeration of primary particles during the whole polymerization. © 1995 John Wiley & Sons, Inc.