Graft ratios

PA6 (wt%) Recipe SEES (wt%) MA-g-SEBS (wt%) MA graft ratio (gMA/gSEBS) Impact strength (J/m)... 

The Protein Profiling Biochip is composed of six chips assembled in a flow cell cassette device. Each chip provides 200 data points (200 pillars per chip) for a total of 1200 data points per cassette. Pillars are 50 p in diameter. The mesa on each pillar is covered with a self-assembled monolayer (20 to 25 A thickness) of biotin-derivatized PLL-g-PEG groups. A constant grafting ratio of 3.5 parts Lys to 1 part PEG is maintained with variable biotin-PEG content. sAV antibody is immobilized at 0.5 to 2 pmole/cm and Fab fragments at 4 pmole/cm. ... 

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-... 

In solution or in bulk it is often difficult or impossible, because of solubility or viscosity problems, to achieve the desired backbone/graft ratio especially if a small amount of monomer is to be grafted from a large excess of backbone. 

Dichloroethane can act as chain transfer agent the grafting ratio must be reduced. Experimentally, the grafting ratio is roughly constant whatever the dichloroethane ratio, but dichloroethane can act also as diluent for the monomers, reducing reactions of crosslinking but not the grafting ratio. 

Consequently, all experimental results can be explained. Polymers prepared without any additive are graft copolymers (containing perhaps separate BD-AN copolymer) whose grafted chains are crosslinked. Decrease of crosslinking ratio linked possibly with a decrease of grafting ratio leads to a more soluble polymer and conversely, increasing of cross-linking leads to a less soluble polymer. 

Similar experiments were performed with 0.05-mm. thick films. The log-log plot of the conversion curves is shown in Figure 4. Here the autoacceleration index is / = 1.15. The break on the curves occurs at lower grafting ratios than for the 0.1-mm. films. The dose-rate exponent for the instantaneous rate at 10% weight increase is a = 0.45 as shown in Figure 3. 

From experiments conducted at the two dose rates investigated the dose-rate exponent is estimated to be a = 0.47. At the higher dose rate the reaction was diffusion controlled, heterogeneous films being obtained at elevated grafting ratios. 

Another peculiar feature of the grafting of acrylic acid is the break observed in the conversion curves particularly at low dose rates. The interpretation of this effect proposed above does not account for the fact that no break is observed with other monomers except at much higher grafting ratios (2, 4). These striking differences in kinetics for systems which in principle should exhibit comparable behavior are presumably related to differences in diffusion rates and polymer-polymer and polymer-monomer compatibilities. Little is known at present on the factors which govern these effects and on their influence on the kinetics. 

With styrene, the autoacceleration index gradually changes with temperature which makes it impossible to define an activation energy since its apparent value depends strongly on the grafting ratio at which the rates are measured. 

The main drawback of this method is that aminopolysiloxanes are not easily available in aU desired grafting ratios and molecular weights. Only a little range of MW (up to 8000) and grafting ratios (1-7%) are available commercially. This is due to limitations when polycondensation reactions are carried out with aminopropylsi-loxane units. Methods for obtaining aminopolysiloxanes by hydrosilylation, in their NH form suitable for nucleophilic reactions, are not available either. 

Figure 3 Relationships between the weight percent gains due to allylation and the grafting ratios of styrene on wood meal. Note copolymerized at lOO C for 2 h using BPO 0.041 mol/L as an initiator. (From Ref. 13.)...

Entry Butene Content (mol%) Reaction Time (h) AIBN (mg) Graft Ratio of PEG (mol%)... 

Grafting ratios were calculated either from weight loss of grated silicas when heat treated in air at 750°C or from elemental analysis of the modified silica. The two methods give concordant results. 

This study shows that small and well defined molecules behave in a complex manner when chemically linked to the surface of a solid. Their behaviour is strongly dependent on the characteristics of the graft and the surface, and on geometrical factors like the fractality of the surface. Obviously, the grafting ratio, which determines the intensity of interactions that adjacent grafted molecules experience is also important. 

To establish a purely ionic reaction, experiments were conducted with isobutylene, a monomer known to react exclusively with cationic initiators. Chloroform was added to the systems to ensure better polymer swelling. Under these conditions polymerization occurred, the monomer being grafted onto the PVC films. Conversion curves are shown in Figure 7. A limiting conversion is reached after a dose of ca. 8 Mrad, corresponding to a grafting ratio of 22%. 

Figure 7. Grafting ratios of PVC films swollen at 25°C. in a 25% solution of isobutylene in chloroform and subjected to cobalt-60 gamma-rays or 7 Mev. electrons at — 78°C. Broken curve corresponds to intermittent irradiation...

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