Cross-linking ratio

Being a tri functional group molecule, triisocyanate is used as a cross-linking agent. The degree of cross-linking affects the stiffness of the MIP. It seems that the best compromise between activity and selectivity is obtained with a cross-linking ratio of 50/50 [8]. We then obtain an enantiomeric excess of 70%. 

We have then reduced substrates with structure similar of that of the acetophenone (Table I). Conditions were 60°C temperature, one hour pre-expansion, cross-linking ratio 50/50, [tBuOK]/[Rh] = 6 (Table I). 

Fig. 39 Effect of the cross-linking density on the temperature-dependent relative swelling degree of PNIPA beads. The cross-linking ratio is indicated on the figure. The initial diameter of the NIPA gel beads was 1 mm...

Ye et al. [33] also showed that microspheres imprinted with theophylline or 17-p-estradiol but using low cross-linking ratios (MAAiEDMA ratio 2.3 1) could be employed in MIAs for each of these analytes and worked as well as MIPs with more conventional higher cross-linking ratios. A benefit of this was that further monomers could be incorporated it was shown that the latent monomer nitro-phenylacrylate in the theophylline MIP was not detrimental to its affinity for H-theophylline, although it was not shown whether cross-reactivity of interferents was affected and it is unclear what benefit the additional monomer would bring to an MIA. 

Particular attention has also been paid to aerogels synthesized with a high cross-linking ratio (i.e., a T/C ratio greater than the theoretical stoichiometric value or, in other words, CH < 2.8). Contrary to other samples, those aerogels present rather constant textural properties whatever the sol-gel parameters may be (cellulose acetate concentration, DP , etc.). They are dense (>0.7 g/cm ) and possess a narrow (meso)pore size distribution... 

Figure 10.27. N2 srapti isotherms of cellulose acetate-based aerogels coming from supercritical CO2 drying of gels synthesized in extra-dry acetone by cross-linking of cellulose acetate (with a DP of 190) with P-MDI under dibutyltin dilaurate catalysis (at 8 g/1)- Cellulose acetate concentration in solution is maintained constant ( 80 g/1) while the cross-linking ratio (C/T) is varied [22].

Figure 10.28. Influence of the cross-linking ratio CjT on pore size distribution of cellulose acetate-based aerogels determined by nonintrusive mercury porosimetry (using a bucking constant kf equal to 28 nm MPa " [41]). Characteristics of the aerogels are summarized in Table 10.1 (mercury porosimetry conducted by R. Pirard, LGC, Univervity of Liege, Belgium) [22].

By studying chemical cross-link density, stress-relaxation behaviour, and the nature of peroxide reaction products attempts have been made to obtain data on the initiator efficiency and on the scission-cross-link ratio. Widely different results have however been quoted and there is disagreement on the methods of interpreting the data available (see Baldwin and VerStrate, 1972). It would appear that one cause of the disparity is due to physical entanglements. Typical figures for the scission cross-link ratio are of the order 0 5-0 7. 

Blank, R.D. et al (2003) Spectroscopically determined collagen Pyr/deH-DHLNL cross-link ratio and crystallinity indices differ markedly in recombinant congenic mice with divergent calculated bone tissue strength. Connect Tissue Res., 44 (3-4), 134-142. 

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