Kinetics and mechanism of emulsifier‐free emulsion polymerization. III. Styrene/nonionic comonomer (2‐hydroxyethyl methacrylate) system

Abstract

SynopsisThe emulsifier-free emulsion polymerizations of styrene in the presence of about 0.33-2.7% (relative to styrene) of the water soluble comonomer, 2-hydroxyethyl methacrylate ( HEMA), and of the initiator, potassium persulfate ( K P S ) , were carried out. It was found that KPS plays a predominant role in the particle nucleation process, since the number density of polymer particles (N,) was dependent on the 0.97-power of [ KPS] . The nucleation ability of HEMA was weak, since N p was dependent only on the 0.17-power of [ HEMA]. The particle nucleation stage ceased quite early before 1% conversion, leading to nearly monodispersed polymer particles. The nucleation is suggested to be via the homogeneous nucleation mechanism. The particles grow via the core-shell structure mechanism (shell region polymerization), since the particle size is rather large-from 1500 to 6000 A. The amount of HEMA can affect the shell thickness and physical properties of the shell, such as the monomer swelling capacity and monomer diffusion rate.

Effects of ethyl acetate on the soap‐free emulsion polymerization of 4‐vinylpyridine and styrene. II. Aspects of the mechanism

“…4(c,d)]. This incorporation is probably the main reason for postulation of the core-shell particle growth mechanism by Chen et al 10 Similar morphology development was also found in the presence of 8 wt % EA, as shown in Figure 5. However, gray particles existed for a longer time in the polymerization system because of the lower transfer rate of 4VP to the aqueous phase, and apparently a core could be found in the gray particles [ Fig.…”

“…8,10 However, this explanation is inadequate for the explanation of the phase separation because a core-shell structure should be formed, rather than the anomalous shape, in view of the variation of interfacial tensions, particularly in the copolymerization of a hydrophilic monomer and a hydrophobic one, as discussed in this work. Furthermore, the anomalous morphologies were also found in the soapfree emulsion homopolymerization of St.…”

“…Similar results were also observed in the soap-free emulsion copolymerization of St and acrylamide (AA)/St. 4,5 Chen et al 10 reported an anomalously low content of hydrophilic monomer units in the initial (co)polymer, in which St and a nonionic hydrophilic monomer, 2-hydroxyethyl methacrylate, were employed with the anionic initiator KPS. However, this anomalous phenomenon was not observed in the soap-free emulsion copolymerization system of St and AA derivatives reported by Pichot et al, [7][8][9] who used the cationic initiator 2,2Ј-azobis(2-amidino-propane) dihydrochloride (V50).…”

“…[1][2][3][4][5][6][7][8][9][10] All these studies are focused on factors, such as the pH of the aqueous medium and the employment of ionic or nonionic monomers, that affect the overall hydrophilicity of the comonomer and (co-)polymer initially formed. This is possibly because the hydrophilicity of the monomer or (co)polymer is very important for nucleation according to the prevalent Fitch-Tsai theory, 11,12 well known as homogeneous nucleation.…”

Effects of Acrylic Acid on Number Density of Polymer Particles in Emulsifier-Free Emulsion Copolymerization of Styrene and Acrylic Acid

“…According to the Smith-Ewart theory in which the number density of polymer particles is proportional to the 0.6-power of emulsifier concentration in conventional emulsion polymerization of styrene, they suggest that In N is proportional to the logarithmic value of the comonomer concentration. From data fitting, this number density is proportional to [NaUI], [NaSEM] 2 , [HEMAJ 0 · 17 , and [AAmJ 0 · 19 in the systems of different comonomers, undecylenic isethionate sodium salt (NaUI), 9 sodium salt of 2-sulfoethyl methacrylate (NaSEM), 9 2-hydroxyethyl methacrylate (HEMA), 10 and acrylamide (AAm), 11 respectively. They explained the different power order of the various comonomer by the contribution of the comonomer on the particle nucleation.…”