Polarity monomers

In interpreting the influence of the medium on chain configuration of the polymers, the medium must be specified as a three-component system polar monomer, polar solvent, nonpolar solvent. 

The electron transfer induced reaction of this diene system results in rapid [4 + 2]dimerization conversely, the dimer rapidly undergoes cycloreversion upon electron transfer. Both reactions result in strong CIDNP effects. The monomer polarization supports a radical cation with a spin density distribution like those of the butadiene or fulvene radical cations. The dimer polarization identifies a dimer radical cation with appreciable spin density only on two carbons of the dienophile fragment this species can only be the doubly linked radical cation D [135, 136], Significantly, a second dimer radical cation is implicated in a pulsed... 

However, it was shown long ago, that the surface activity, i.e. the substance capability to adsorption on the interface is the lower the smaller is the difference between polarities of the phases (, that is in the case of emulsion polymerization the higher Is the monomer polarity. 

Formally the monomer polarity is not nearly sufficient to explain the differences in the adsorption energies of a given emulsifier on the water-alkylacry-lates interfaces (5) according to (21) the dipole moments of lower alkylacrylates have practically identical values. It appears possible that polcu ity of the interface itself is significant here this polarity increases as the monomer solubility in water increases from BA to HA the decrease of the free energy of the Interface, caused by it, results in its turn in decreased adsorption energy of emulsifier. 

Zuikov and Soloviev (1979) studied the effect of monomer polarity on both the size and the size distribution of particles in the forming latexes. As a criterion of polarity they took the solubility of the monomer in water, which in this case has an independent significance as well. Polymerizations of styrene, methyl methacrylate, butyl methacrylate, and methyl acrylate... 

Summarizing the described results, it may be concluded that when using the emulsifiers described above, the colloidal behavior of polymerization systems is mainly determined by monomer polarity. Latexes of polar... 

It was established by Yeliseyeva and Bakaeva (1968) that in the polymerization of polar monomers (MA) the decrease of emulsifier adsorption depends on tbe structure of the latter and for some types of emulsifiers may reach limiting values. This was observed in tbe polymerization ofMA in the presence of a mixed type of emulsifier, partially sulfurated with sulfuric acid oxyethylated alkylphenol (emulsifier C-I0 ). Its adsorption on the particle surface increases with the initial concentration and reaches > 100% filling of the adsorption layer, conditionally corresponding to 0.3S nm per molecule. Stable, concentrated latexes with small particles are formed. Therefore, emulsifier adsorption and the mechanism ctf particle formation associated with it depends not only on monomer polarity but also on the chemical structure of the emulsifier. 

Under dynamic conditions of emulsion polymerization the process of formation and aggregation of primary particles is accompanied by estab-Hshment of an equilibrium adsorption of the emulsifier on the polar surface of particles. As a result of competition of these processes, secondary" panicles of complex structure are formed (Figs. 11 and 14). The rate of attainment of equilibrium adsorption, depending on monomer polarity and the nature of the emulsifier, determines the degree of limited flocculation of primary particles at which aggregate stability of the secondaiy" latex particles is reached. The formation of nuclei from micelles during the... 

In the study of emulsion polymerization kinetics which depend on monomer polarity, the homologous scries of alkyl acrylates and alky] methacrylates are usually used because of thcir wide ranges of solubility in... 

Slvrenie monomers Hydrocarbon monomers Hallogenated monomers Polar monomers... 

In another set of carboxylated emulsions prepared with similar Tg, styrene-ethyl acrylate (S-EA) copolymers showed no expansion, but MMA-EA copolymers did. This finding strongly suggested that monomer polarity is also an important factor. The more polar MM A copolymer apparently was able to interact with the highly polar aqueous phase and was thereby plasticized. 

Fig. 2.4 I mpact of monomer polarity on the solubility of various poly(acrylates). The arrow indicates increasing polarity of the acrylate group. Filled circles poly(ethyl ac late) (PEA), open triangles poly(butyl ac7late) (PBA), filled diamonds poly(ethyl hexyl ac7late) (PEHA), open squares poly(octadecyl ac7late)(PODA). Experimental data from [5].

Oils Fryii at 195"C Cyclic monomers Polar compounds Non-eluted material... 

Sutterlin [46] studied the effect of the polarity of various monomers (styrene, acrylate ester monomers, and methacrylate ester monomers see Table 3.1) on the particle nucleation mechanisms involved in emulsion polymerization. When the surfactant concentration is above its CMC, the emulsion polymerization of styrene follows the Smith-Ewart theory (Npj 5o ) except those experiments with relatively low levels of surfactant. The exponent x in the relationship Npj So decreases with increasing monomer polarity when the surfactant concentration is above its CMC. This trend is attributed to the increased tendency of agglomeration of particle nuclei with monomer polarity. The emulsion polymerizations of less polar monomers deviate significantly from the Smith-Ewart theory (x 0.6) if the surfactant concentration is reduced to a level just below its CMC. This implies that some mechanisms other than micellar nucleation (homogeneous nucleation or coagulative nucleation) must operate in these emulsion polymerization systems. 

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