Graft copolymerization concentration

Fig. 2 A Oscillator frequency changes with graft copolymerization of styrene (ST) on the dithiocarbamated copolymer-coated quartz crystal microbalance (QCM) in methano-lic solution with UV irradiation (light intensity 5mWcm ). Concentration of ST a 0, h 0.26, c 0.5, d 0.76 mol dm . B Relationship of oscillator frequency change calculated from A with concentration of ST...

For low radiation doses, peroxides accumulate almost linearly with dose. However, after a certain dose has been reached, their concentration tends to level off. This conclusion can be derived from the observed change in the rate of graft copolymerization initiated by polymers subjected to increasing doses of preirradiation in air. Figure 2 illustrates this effect in the case of grafting acrylonitrile onto polyethylene (2). The drop in the yield of peroxide production presumably results from the efficient radiation-induced decomposition of these peroxides. Peroxides are known to decompose under free radical attack, and selective destruction of peroxides under irradiation has been established experimentally (8). This decomposition can become autocatalytic, and sometimes the concentration of peroxides may reach a maximum at a certain dose and decrease on further irradiation. Such an effect was observed in the case of poly (vinyl chloride). Figure 3 shows the influence of preirradiation dose on the grafting ratio obtained with poly (vinyl chlo-... 

Homopolymerization can also be reduced by working in the presence of large polymer concentrations, e.g. with polymers swollen in the monomer. In this case, even when the monomer B is sensitive to radiolysis the quantitity of homopolymer Bn remains unimportant. For example, Sebban-Danon(202) studied the effect of y-radiation on solutions of polyisobutylene in styrene. The much higher G-value of the polymer compared to that of styrene enhances the graft copolymerization with respect to the homopolymerization. 

The results of the graft copolymerization on cellulose in various conditions are shown as a function of the irradiation time, initiator concentration, monomer concentration, presence of additive. 

Figure 7. Effect of ceric ammonium nitrate concentration on the graft copolymerization of methyl methacrylate onto cellulose nitrate. (Reprinted, with permission, from Ref. 19. Copyright 1979, Wiley.)...

The effect of ceric ion concentration on the graft copolymerization of acrylonitrile onto bamboo is shown in Figure 3 As can be seen the grafting percentage increases to a maximum and then decreases with further increase in the concentration of the initiator. The optimum concentration of the initiator was found at around 0.15 M. 

Figure 6. Effect of ceric ion concentration on the graft copolymerization of acrylonitrile onto holocellulose. Key A, using gravimetric method O, using spectroscopic method.

This technique has been extended to polar media, especially alcohols and their mixtures with water as a continuous phase.Kobayashi and Uyama et al. [121-124] reported that poly(2-oxazoline) macromonomers such as 5 and 6 are very effective for dispersion copolymerization with styrene, MMA, and JV-vinyl-formamide in methanol, ethanol, and mixtures of these alcohols with water. They reported that the particle size decreased with increasing initial macromonomer concentration and that graft-copolymerized poly(2-oxazoline) chains are concentrated on the particle surface to act as steric stabilizers. 

Aluminoxanes suppressed side reactions involving hydrogen transfer. They also formed cyclic structures with starch, giving copolymers that were coated with crystalline polyethylene. A catalyst composed of dicyclopentadienylzirconium dichloride and trimethylaluminium permitted polymerization of ethylene on starch in a toluene suspension at 60 °C for 2h.2806 Graft copolymerization of methyl methacrylate onto starch was also performed with an acetylacetone-copper(II) complex in trichloroacetic acid.2807 The grafting yield and efficiency were proportional to the initiator concentration up to 7.0 x 10-3 mole/L. 

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