Cross-linked polymeric networks

For the polymer-based peptide synthesis it is neccessary that the reaction of the polymer-bound functional groups with an excess of the reagents in the solution phase should go to completion. In this connection, it is important to know whether the functional groups attached to a cross-linked polymeric network are kinetically equivalent. 

Precipitation reactions are similar in principle to agglutination reactions, the difference being that the antigen is a soluble, molecular species rather than a suspended particle such as a bacterium or erythrocyte. At a certain Ab/Ag ratio, the cross-linked polymeric network of antibody and antigen loses its solubility and precipitates. This is called the precipitin reaction.11 Figure 5.6 shows how the quantity of precipitin produced varies with the quantity of antigen added, for a fixed total antibody concentration. 

Entrapment of enzymes or whole cells in a cross-linked polymeric network can be achieved by a number of methods. The most common methods of gelation of a polymer or pre-polymer include ... 

Studied. A cross-linked polymeric network was prepared in the presence of a given amount of diluent. When the gelation reaction was complete, the gel sample was transferred to a cell containing an excess of solvent. The cell was placed onto the stage of a profile projector. As the gel swelled to its equilibrium concentration, its size was recorded photographically. This method allowed an accurate measurement of the time evolution of the gel size during the swelling process. 

As mentioned earlier, the discrete microgels are colloidal stable cross-linked polymeric networks on the nanometre to micrometre size scale. The de-swelling process of microgels is controlled by diffusion, where the rate of the collapsing of the macromolecule is correlated to the dimensions of the pores in the polymeric matrix. 

Kessler and co-workers synthesized norbornene-functionalized MWCNT (f-MWCNTs) (Scheme 5.9), and prepared bulk composites of f-MWCNTs/poly(dicyclopentadiene) (DCPD) by in situ ROMP of f-MWCNTs in the presence of DCPD and Grubbs catalyst for 2 h at 70 °C followed by 90 min at 170 °C. A cross-linked polymeric network was instantaneously formed, and the mechanical properties with low loadings (<0.5 wt%) of f-MWCNTs were studied. A remarkable increase in tensile toughness (925% increase over the neat polyDCPD) with only 0.4 wt% f-MWCNTs was found, and the corresponding elongation at break significantly increased from 5.75 to 51.8%. The DSC results demonstrated an increase in with the addition of f-MWCNTs.Using the same method, they subsequently... 

Free-radical photopolymerizations (see Chap. 10) of multifunctional acrylic monomers result in cross-linked polymeric networks. The kinetic picture of such polymerizations varies from ordinary linear polymerization because the diffusion of free radicals and functional groups becomes severely restricted. This causes growing polymer chains to rapidly cyclize and cross-link into clusters (microgels). The clusters become linked up into networks. Many free radicals become trapped, but terminations take place by combinations and by chain transferring. The cumulative chain length in such polymerizations can be calculated from the following equation [125] ... 

Hydrogels are cross-linked polymeric networks that have the ability to hold water within the cross-linked polymeric chains. They have been used extensively in biomedical applications such as drug... 

Hydrogels are cross-linked polymeric networks swollen in biological fluid. They are widely used in dmg delivery and tissue/organ repairs. Two types of hydrogels are usually available sheet and amorphous. 

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