Emulsifier-free polymerization

Acrolein-containing latex particles were used for immobilization of proteins. The latex particles were prepared by emulsifier-free polymerization of acrolein and styrene (Table I). Fluorescent latex particles were prepared by mixing fluorescent dyes such as Hostalux KCB (Hoechst) or coumarin-6 into styrene before the emulsion polymerization (Table I). To increase the immunological sensitivity of the protein-conjugated latex particles, a hexyl group was introduced between the latex particle and the protein (Protein-spacer-latex). Proteins such as human serum albumin (HSA), anti-human serum albumin (anti-HSA-IgG), and a fragmented antibody (anti-HSA-... 

The equations for dN/dt and dRj/dt, as well as for dV dt [Eq. (39)] are solved by numerical integration for the polymerization stem MMA-K2S20e water, with rate constants obtained from the literature. The initiator efficiency was set equal to unity. Particle numbers between 10 and 10 were drained for initiator concentrations of 10 -10 mol/dm. The calculations showed that N should be almost independent of the chosen value offor values between 5 and 70 (in strong contrast to our calculations). The reason for this is probably that aqueous-phase termination with subsequent precipitation is the dominant particle-formation mechanism in Aral s model, even more so with increasing initiator concentration. The theoretical particle-formation time was on the order of 2 sec, a veiy low value compared to the experimental results of Fitch and Tsai. Aral et at. found that their calculated particle numbers were approximately in accordance with the experimental results of Yamazaki et al. (1968) for emulsifier-free polymerizations. Aral s model does not inclnde any coagulation mechanisms. It will therefore have the same shortcomings as most other models, namely that the strongly increased particle number in... 

In all such cases the process initiated by persulfate begins in the aqueous phase with the formation of water-soluble, surface-active polymeric radicals which, after growing to a certain critical size, precipitate to form particles subsequent polymerization proceeds mainly within these particles. The higher the solubility of the monomer in water, the more surface-active radicals and therefore primary particles are formed and the higher the stability and the concentration of the latex, A kinetic curve of the emulsifier-free polymerization of ethyl acrylate confirming this scheme is shown by Curve 1 in Fig. 3 (Yeliseyeva and Petrova, 1970). The process... 

This paper focuses on heterophase free radical polymerizations. It is limited to processes where multiple phases, distinguished by the insolubility of reagents, exists at the onset of the reaction. It therefore does not consider precipitation polymerization [1], which occurs when the polymer is insoluble in the monomer and precipitates out from an initially homogeneous solution. It also does not address emulsifier-free polymerization or dispersion polymerization. This rather general nomenclature is now accepted as applying to specific systems where the heterophase nature is produced at the onset of the reaction by homogeneous nucleation of oligomers or polymer chains which have exceeded their solubility limit [2]. 

Kinetic studies on the radiation-induced polymerization and post-polymerization of TFE were carried out using chlorofluorohydrocarbons as solvents. The remarkable postpolymerization is again explained by the unusually slow rate of the bimolecular chain termination. A chain transfer reaction was also discussed by Hisasue et al. [721]. Suwa et al. [679] discussed the emulsion polymerization of TFE by radiation with ammonium perfluorooctanoate (FC-143) as the emulsifier. The polymerization rate is proportional to the 0.8 power of the dose rate and is almost independent of the emulsifier concentration (up to 2wt% in water). Molecular weights between 10 and 10 were observed, which increases with reaction time but decreases with the emulsifier concentration. In general, the molecular weight of PTFE prepared by radiation-induced polymerization in solution and in emulsion is relatively low compared with commercial PTFE. However, it is also possible to produce molecular weight of up to 3 x 10 if an emulsifier-free polymerization are carried out [677,678,723]. 

An interesting discovery is that PTFE as a hydrophobic polymer forms a stable latex in the absence of emulsifier. Under certain conditions PTFE latex coagulates during polymerization and the polymerization rate decreases. Probably because polymerization proceeds mainly on the polymer particle surface. The observed rate acceleration and successive increase in polymer molecular mass may be due to a slow termination of propagating radicals in the rigid PTFE particles [723]. The size, distribution, and number of PTFE particles formed by radiation-induced emulsifier-free polymerization were... 

Polymerizations of Methyl /r-Styrenesulfonate (MSS, 3). A batch emulsifier-free polymerization of MSS, VBC and styrene (25 25 50 wt %) gave a viscous dispersion that would not pass through a cotton plug. Reaction with trimethylamine did not reduce the viscosity, which was probably due to water-soluble polymer. 

The basic constituents of all commercial emulsion polymerization recipes are monomers, emulsifiers, and polymerization initiators. Other common components are modifiers, inorganic salts and free alkaH, and shortstops. The function of these different components and the mechanism of emulsion polymerization have been described (43,44). 

When the emulsion polymerization is conducted in the absence of an emulsifier, this process is termed emulsifier free or soapless emulsion polymerization [68-73]. In this case, the particle formation occurs by the precipitation of growing macroradicals within the continuous... 

Recently, Smigol et al. [75] extensively studied emulsifier-free emulsion polymerization of different monomers including styrene, methyl methacrylate, and glycidyl methacrylate in an aqueous medium by using potassium peroxydisulfate as the initiator. In this study. 

PS/PHEM A particles in micron-size range were also obtained by applying the single-stage soapless emulsion copolymerization method [124]. But, this method provided copolymer particles with an anomalous shape with an uneven surface. PS or PHEMA particles prepared by emulsifier-free emulsion polymerization were also used as seed particles with the respective comonomer to achieve uniform PS/PHEMA or PHEMA/PS composite particles. PS/PHEMA and PHEMA/PS particles in the form of excellent spheres were successfully produced 1 iLitm in size in the same study. 

Preparation of uniform seed particles Soapless emulsion polymerization is usually preferred for the preparation of uniform seed particles since this technique provides emulsifier-free, larger, and highly uniform micropheres relative to those that can be obtained by the conventional emulsion recipes including emulsifiers and various additives. The size of uniform seed particles with the soapless emulsion procedure is in the range of 0.6-1.2 tm depending on the polymerization conditions [75,108]. 

For the characterization of Langmuir films, Fulda and coworkers [75-77] used anionic and cationic core-shell particles prepared by emulsifier-free emulsion polymerization. These particles have several advantages over those used in early publications First, the particles do not contain any stabihzer or emulsifier, which is eventually desorbed upon spreading and disturbs the formation of a particle monolayer at the air-water interface. Second, the preparation is a one-step process leading directly to monodisperse particles 0.2-0.5 jim in diameter. Third, the nature of the shell can be easily varied by using different hydrophilic comonomers. In Table 1, the particles and their characteristic properties are hsted. Most of the studies were carried out using anionic particles with polystyrene as core material and polyacrylic acid in the shell. 

Figure 13. Gel permeation chromatogram of polystyrene latex, (PL), prepared by emulsifier-free emulsion polymerization at 1 5 °C(in the absence of silica particles).

Materials. The polystyrene latex, with a mean diameter of 0.42 fim, was synthesized by emulsifier-free emulsion polymerization. Potassium persulfate was used as initiator and the surface charge that stabilizes the latex particles thus originates from sulfate radicals. The synthesis was carried out at the Department of Polymer Technology at Abo Akademi, Finland. 

In the case of more water-soluble monomers and (amphiphilic) macromonomers, the Smith-Ewart [16] expression does not satisfactorily describe the particle nucleation. The HUFT [9,10] theory, however, satisfactorily describes the polymerization behavior or the particle nucleation of such unsaturated hydrophilic and amphiphilic monomers. The HUFT approach implies that primary particles are formed in the aqueous phase by precipitation of oligomer radicals above a critical chain length. The basic principals of the HUFT theory is that formation of primary particles will take place up to a point where the rate of formation of radicals in the aqueous phase is equal to the rate of disappearance of radicals by capture of radicals by particles already formed. Stabilization of primary particles in emulsifier-free emulsion polymerization may be achieved if the monomer (or macromonomer) contains surface active groups. Besides, the charged radical fragments of initiator increases the colloidal stability of the polymer particles. 

Thus in the emulsifier-free emulsion copolymerization the emulsifier (graft copolymer, etc.) is formed by copolymerization of hydrophobic with hydrophilic monomers in the aqueous phase. The ffee-emulsifier emulsion polymerization and copolymerization of hydrophilic (amphiphilic) macromonomer and hydro-phobic comonomer (such as styrene) proceeds by the homogeneous nucleation mechanism (see Scheme 1). Here the primary particles are formed by precipitation of oligomer radicals above a certain critical chain length. Such primary particles are colloidally unstable, undergoing coagulation with other primary polymer particles or, later, with premature polymer particles and polymerize very slowly. 

Poly(ethylene oxide) (PEO) macromonomers constitute a new class of surface active monomers which give, by emulsifier-free emulsion polymerization or copolymerization, stable polymer dispersions and comb-like materials with very interesting properties due to the exceptional properties of ethylene oxide (EO) side chains. They are a basis for a number of various applications which take advantage of the binding properties of PEO [39], its hydrophilic and amphipathic behavior [40], as well as its bio compatibility and non-absorbing character towards proteins [41]. Various types of PEO macromonomers have been proposed and among them the most popular are the acrylates and methacrylates [42]. 

Fig. 4. Dependence of monomer conversion (open symbols) and the rate of polymerization (closed symbols) in the emulsifier-free emulsion polymerization of PEO-VB macromonomers on reaction time and the PEO-VB type [85]. Recipe [PEO-VB] =0.045 mol dm-3, [AVA]=0.45xl0-3 mol dm"3,60 °C. In water Cr(EO)38-C7-VB (O, ), Cr-(EO)25-VB (A,A)...

The emulsifier-free emulsion terpolymerization of PEO-MA macromonomer, BA, and acrylic acid (AA) led to the formation of graft copolymers and stable latexes [101]. At the beginning of terpolymerization, the PEO-MA macromonomer polymerized more quickly than BA or AA. Conversion of the macromonomer increased with increasing initiator concentration and with decreasing mo-... 

In the emulsifier free-emulsion polymerization the reaction loci are formed by nucleation of amphiphilic macromomer micelles (micellar mechanism) or by... 

N-(hydroxymethyl)acrylamide, N,N-dimethylacrylamide, and methacrylamide) were carried out in emulsifier-free aqueous media. When either of the former three acrylamides were used, the copolymerization course was divided into three srages on the basis of the main reaction locus. At first acrylamides polymerized preferentially in the aqueous phase. After the particle formation styrene... 

---