Resin swelling

The sulfonated resin is a close analogue of -toluenesulfonic acid in terms of stmcture and catalyst performance. In the presence of excess water, the SO H groups are dissociated, and specific acid catalysis takes place in the swelled resin just as it takes place in an aqueous solution. When the catalyst is used with weakly polar reactants or with concentrations of polar reactants that are too low to cause dissociation of the acid groups, general acid catalysis prevails and water is a strong reaction inhibitor (63). 

A. Meissner, P. Bloch, E. Humpfer, M. Spraul and O. W. Sorensen, Reduction of inhomogeneous line broadening in two-dimensional high-resolution MAS NMR spectra of molecules attached to swelled resins in solid-phase synthesis, J. Am. Chem. Soc., 1997, 119, 1787-1788. 

Although swelled resins could allow the diffusion of large molecules and their approach to the reactive sites, the bead form of the resins may induce some kinetic limitations. The use of fibers or membranes might help solve this issue. 

Sonicate the swelled resin briefly to disperse the beads thoroughly. 

Hydrate the dry resin (Sigma G 4510) in freshly made PBT by rocking at 4"C for at least 3 hours. Centrifuge in a clinical centrifuge at 1000 rpm for 15 seconds to pellet the resin. Rinse three times in ice-cold PBT. For the final resuspension, add an equal volume of ice-cold PBT to make a 50% slurry of the resin. Swelled resin can be kept at 4"C almost indefinitely. For long-term storage, add sodium azide to 0.02%. 

Swell resin for 15 min in twice the resin bed volume NMP (see Note 5). 

To illustrate the specific operations involved, the scheme below shows the first steps and the final detachment reaction of a peptide synthesis starting from the carboxyl terminal. N-Boc-glycine is attached to chloromethylated styrene-divinylbenzene copolymer resin. This polymer swells in organic solvents but is completely insoluble. ) Treatment with HCl in acetic acid removes the fert-butoxycarbonyl (Boc) group as isobutene and carbon dioxide. The resulting amine hydrochloride is neutralized with triethylamine in DMF. 

Microreticular Resins. Microreticular resins, by contrast, are elastic gels that, in the dry state, avidly absorb water and other polar solvents in which they are immersed. While taking up solvent, the gel structure expands until the retractile stresses of the distended polymer network balance the osmotic effect. In nonpolar solvents, little or no swelling occurs and diffusion is impaired. 

SAN resins show considerable resistance to solvents and are insoluble in carbon tetrachloride, ethyl alcohol, gasoline, and hydrocarbon solvents. They are swelled by solvents such as ben2ene, ether, and toluene. Polar solvents such as acetone, chloroform, dioxane, methyl ethyl ketone, and pyridine will dissolve SAN (14). The interactions of various solvents and SAN copolymers containing up to 52% acrylonitrile have been studied along with their thermodynamic parameters, ie, the second virial coefficient, free-energy parameter, expansion factor, and intrinsic viscosity (15). 

The degree of swelling and shrinking is important for design of ion-exchange columns, especiaUy for the location of the distributors used to disperse incoming fluids, and coUect outgoing ones, evenly over the cross-sectional area of the resin bed. Once placed, these distributors are not adjustable. The upper distributor should be above (the lower one below) the resin bed, even in the bed s swoUen form. 

As the parison is extmded, the melt is free to swell and sag. The process requires a viscous resin with consistent swell and sag melt properties. For a large container the machine is usually equipped with a cylinder and a piston called an accumulator. The accumulator is filled with melt from the extmder and emptied at a much faster rate to form a large parison this minimises the sag of the molten tube. 

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