Grafting reactions 250 INDEX

Diene substrate latices were prepared by seeding techniques following the scheme shown in Figure 1. Persulfate anion was the initiator, and an alkyl aryl sulfonate was the emulsifier. Reaction time varied between 13 and 33 hours. Since all the substrates were prepared by similar techniques, the volumetric swell index and gel gravimetric data (toluene) varied little with particle size. Small differences in swell and gel characteristics should not be a variable in this study because of the polarity of the grafting monomer mixture and rapidity of the graft reactions. 

The various data obtained for the kinetics of graft copolymerization onto PTFE films demonstrate that this reaction is complicated by the fact that the rate of diffusion of the monomer may become the controlling factor. It seems interesting at this point to compare and discuss together the results obtained with the different monomers. Table I summarizes the data obtained for autoacceleration indexes (/ ), dose-rate exponents (a), and over-all activation energies E, with styrene, acrylic acid, and vinylpyridine. Several conclusions can be derived from an examination of these data. 

With acrylic acid the situation is very different. For 0.1-mm. thick films /3 is independent of temperature, whereas for 0.05-mm. thick films /3 rises above 40°C. At low temperatures ft is unusually small. This effect may be ascribed to the use of a selective inhibitor to prevent homopolymerization. It was shown above that in grafting vinylpyridine the autoaccelerated character of the reaction at 20°C. vanishes in the presence of inhibitors. Moreover, with acrylic acid the autoacceleration index is lower if a more efficient inhibitor (CuCl2) is used, and f decreases as the amount of inhibitor increases (Figure 8). 

Fig. 2. Dry thickness h0 f various PDMS layers end grafted on the modified silica surface of a silicon wafer, as a function of the scaling variable Nm 0718, with N the polymerisation index of the grafted chains and < )0 he polymer volume fraction in the reaction bath. The range of molecular weights used for the grafted chains is 5 kg mol 1

Most of the sesqueterpene alkaloids showed depressant effects on humoral immunity using the hemolysin reaction as an index. Wilfortrine 55 (160 mg/kg mg/kg/d x 9d, i.p.) suppressed the graft-vs.-host reaction (GVHR). 53 (80 mg/kg/d x lOd, i.p.) showed marked inhibitory effects on the DNCB-induced DTH reaction on mouse skin. Both alkaloids (80 mg/kg/d x 4d, i.p.) significantly decreased the clearance rate of charcoal particles and the weights of spleen and thymus [103]. However, the potency of the suppressive activities was not comparable with that of triptolide diterpenoids... 

Figure 5.10 The first-order time-conversion plot (a), and apparent number-average molecular weight (Mn) and polydispersity index (PDI) of the free polymer as a function of monomer conversion (b). TGA weight loss curves for the pristine MWCNTs, MWCNT-Br, and linear glycopoly-mer (PMAIG)-grafted MWCNTs obtained at different reaction times (c), and the content and average molecular weight of the polymer grafted on to MWCNTs, calculated from corresponding TGA data, as a function of monomer conversion (d). Reprinted with permission from Gao et al ...

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