Poly initiator concentration effects

The molecular weight of a polymer can be controlled through the use of a chain-transfer agent, as well as by initiator concentration and type, monomer concentration, and solvent type and temperature. Chlorinated aUphatic compounds and thiols are particularly effective chain-transfer agents used for regulating the molecular weight of acryUc polymers (94). Chain-transfer constants (C at 60°C) for some typical agents for poly(methyl acrylate) are as follows (87) ... 

Abstract Recently, the interest on bioniaterials and especially in tannins was growing and some attractive results were obtained in the adsorption of some metals by taimin adsorbents. Tannins are widely distributed in nature and have multiple adjacent poly-hydroxyphenyl groups in their chemical stmctnre which have extremely high affinity for heavy metal ions. This study will describe how tannin can be used as an effective zinc and lead sorbent by the use of tannin resins. Batch method was used in the experiments in which pH profile, adsorption time, adsorbent/hquid ratios, initial concentration of metal ions, adsorbent amormt and temperatrrre were investigated to determine binding properties of adsorbent for the Zn(ll) and Pb(II) iorrs. 

The lower the initiator concentration the higher the molecular weight of polymer formed. Moreover, the effect of the ratio template/monomer concentration is more pronounced for low initiator concentration. In addition, it was found that tacticity of the template does not influence the suppression of degradative addition nor the tacticity of the poly(vinyl imidazole) obtained by the template process. 

The photo-oxidation of poly(p-methylstyrene) has been studied initiated by azo-bis-isobutyronitrile. The effects of polymer concentration, light intensity, initiator concentration, and oxygen pressure were related by the following expression ... 

As in the Eq. (64) X value has no effect on the distribution P (N), then the indicated relationship supposes three basic parameters influencing on distribution P (N) d, b and ty. Each of the indicated parameters characterizes a certain feature of the poly condensation process. The exponent d is thus essentially defined by the macromolecular coil stmcture, that directly follows from the Eq. (63). The value b characterizes the type and intensity of the destructive processes. Parameter is determined by the stochastic contribution to a polycondensation process and it is possible to assume dependence on comonomers initial concentration c the greater C(, the higher the probability of random collisions. This postulate is particularly important for the mode of interfacial polycondensation, where synthesis proceeds not in all reactive vessel volume, but only in the interfacial layer, for which enhanced in comparison with average value the magnitude c is expected. All experimental MWD curves have the unimodal shape that supposes low mobility for coils in solution or < 2/3 [101]. 

Under such conditions, the rate of polymerization is indqiendent of the polymer particles. The number of particles is independent of or varies very slightly with the initiator concentration. The molecular weights of poly(vinyl chloride) were very small and nearly independent of initiator concentration. Thus, the degradative chain-transfer to VC or unsaturated PVC depresses the effects of initiator and particle concentrations on polymerization behavior. 

Kizakkedathu, J.N. and Brooks, D.E. 2003. Synthesis of poly(AJ,AJ-dimethylacrylamide) brushes from charged polymeric surfaces by aqueous ATRP Effect of surface initiator concentration. Macromolecules 36 591-8. 

We have studied the effect of monomer concentration in the dispersion polymerization of styrene carried out in alcohol-water mixtures as the dispersion media. We used AIBN and poly(acrylic acid) as the initiator and the stabilizer, respectively, and we tried isopropanol, 1-butanol, and 2-butanol as the alcohols [89]. The largest average particle size values were obtained with the highest monomer-dispersion medium volumetric ratios in 1-butanol-water medium having the alcohol-water volumetric ratio of 90 10. The SEM micrographs of these particles are given in Fig. 15. As seen here, a certain size distribution by the formation of small particles, possibly with a secondary nucleation, was observed in the poly-... 

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