Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate

Abstract

The factors affecting the induction period and polymerization rate in ultrasonically initiated emulsion polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymerization of BA without any added initiator by enhancing the N2 flow rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced polymerization rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymerization rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical polymerization mechanism for ultrasonically initiated emulsion polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of polymerization and the polymerization process. Compared with conventional emulsion polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster polymerization rate, and higher molecular weight of the polymer prepared.

Early Activation of STAT3 Regulates Reactive Astrogliosis Induced by Diverse Forms of Neurotoxicity

“…In aggregate, our data for neurotoxic exposures add to the mounting evidence from other injury models showing that STAT3 signaling plays a dominant role in reactive gliosis [12], [72]–[74]. While brain damage also initiates neuroinflammation, as noted above, this latter response does not initiate astrogliosis.…”

Ultrasound and Sonochemistry for Radical Polymerization: Sound Synthesis

“…[61] In others tudies, under low frequency ultrasound, it has often been observed that the addition of ar adical initiator is essential for polymerization, [19,[62][63][64] indicating that the chemical effects of cavitation are minimal under these conditions. However,s onochemical polymerizations of monomer-in-watere mulsions have been conducted by Biggs [65][66][67] and colleagues in the absence of an added initiator,r esulting in the formationo fu niform latex particles with conversion values dependent on the irradiating intensity.O thers have investigated the (mini)emulsion polymerization of methyl methacrylate (MMA), [68,69] n-butyla crylate (nBA), [58] n-butyl methacrylate (nBMA), [70,71] ethyl methacrylate (EMA), [72] glycidyl methacrylate( GMA), [73] 2-ethylhexyl methacrylate (EHMA), [74] and acrylonitrile (AN), [75 ] among others. [76] The emulsion polymerization of nBA in water was investigated by Xia et al,w here it was observed that in the absence of an added surfactant( e.g.,s odium dodecylsulfate (SDS)), the polymerization wase xtremely sluggish (2.4 %c onversion after 20 min vs.9 1.9 %c onversion in the presence of SDS).…”

“…This indicated that surfactant-derived radicals may play ap rimary role as initiating speciesf or the emulsion polymerization. [58] This conclusion was challenged by Grieser et al,w ho reasoned that kinetic and nucleation arguments indicate that the contribution of surfactant-derived radicals in such oil-in-water emulsions would be unlikely under ultrasonic conditions. [68] Moreover,t heir data indicate that ultrasound has almostn oi nfluence on the propagation phase of the radical polymerization, only on the initiation.…”

“…Relatedly,i nt he study by Xia, the polymerization of bulk nBA produced 28.0 %c onversion after 20 min, indicating that monomer-derived radicals could also be formed. [58] In almosta ll cases, it was reported that compared with traditional emulsion polymerizations conducted in the presenceo fa na dded initiator,h igher polymer molecular weights and smaller,m ore narrowlyd ispersed latexes could be formed in shorter reactiont imes by ultrasonic initiation. The mechanism for ag eneral ultrasonic emulsion polymerization is shown schematically in Figure 10.…”

Two-stage mathematical model of ultrasonically initiated emulsion polymerization part one, stage I

“…According to previous work [15,[19][20][21], Xia and Wang [22] summarized that there were mainly four kinds of free radicals: (1) H % and OH % coming from water, (2) coming from the decomposition of the monomer, (3) coming from the decomposition of the emulsifier, and (4) coming from the degradation of macromolecules. They [22] considered that the free radicals coming from water and monomers could be neglected in the ultrasonically initiated emulsion polymerization. In our previous paper [23], we proposed a new theory, which detailedly discussed the particles nucleation mechanism of the ultrasonically initiated emulsion polymerization according to Poehlein's [24] comprehensive picture of mechanisms for particle nucleation of the emulsion polymerization.…”