Crosslinking swelling

Degree of hydrolysis, % Molar ratio NCO/NH (at crosslinking) Swelling, g g"1 l... 

Three common methods of measuring crosslinking (swelling, elastic modulus, and gel point measurements) have recently been critically appraised by Dole (14). A fourth method using a plot of sol + sol against the reciprocal dose has also been used extensively. However, Lyons (23) has pointed out that this relation, even for polyethylenes of closely random distribution, does not have the rectilinear form required by the statistical theory of crosslinking. Flory (19) pointed out many years ago that the extensibility of a crosslinked elastomer should vary as the square root of the distance between crosslinks. More recently Case (4, 5) has calculated that the extensibility of an elastomer is given by ... 

Yin Y, Yang YJ, Xu H. Hydrophobically modified hydrogels containing azoaromatic crosslinks swelling properties, degradation in vivo and application in drag delivery. Eur Polym J 2002 38 2305-2311. 

The properties of the ion-exchange/coordination resin, such as degree of crosslinking, swelling, and the nature and structure of the ligands present in the stmcture of the resin. ... 

Ion-exchange resins swell in water to an extent which depends on the amount of crosslinking in the polymer, so that columns should be prepared from the wet material by adding it as a suspension in water to a tube already partially filled with water. (This also avoids trapping air bubbles.) The exchange capacity of a resin is commonly expressed as mg equiv./mL of wet resin. This quantity is pH-dependent for weak-acid or weak-base resins but is constant at about 0.6-2 for most strong-acid or strong-base types. 

Lightly crosslinked resins are less robust but have greater ability to swell in appropriate solvents. Typically a 1-2% crosslinked divinyl benzene polystyrene resin is employed in organic synthesis. 

Fig. 1. Solvent swelling experiments with ECA polymers crosslinked with 7.

Solvent swelling experiments, with CH2CI2 and ECA polymer crosslinked with 7, demonstrate that the addition of a difunctional cyanoacrylate monomer does improve solvent resistance [6], shown in Fig. 1. 

Figure 4 (a) Polymerization time versus degree of swelling (in toluene) curves for styrene-PEG crosslinked copolymers initiated by macroinimers ( ) MAIM-200, ( ) MAIM-400, (O) MAIM-600, (A) MAIM-1000, and ( ) MAIM-1500. (b) Polymerization time versus degree of swelling (in water) curves for styrene-PEG crosslinked copolymers initiated by ( ) MAIM-1500 and ( ) MAIM-400. Source Ref. 50. 

Fig. I. Steady structure of crosslinked MA-EDMA copolymers obtained in solutions of acetic add of different concentrations. K — relative swelling coefficient, Ks — swelling coefficient (by a = 0 and a = 0.5, respectively)...

Fig. 3. Change in relative swelling coefficient Kw during ionization of macroreticular MA-EDMA copolymers obtained in 30% Ac A solution (1-4) and heteroreticular MA-EDMA copolymers obtained in 5% Ac A solution (5,6) with different amounts of the crosslinking agent — EDMA (mol%) /) 1.0 2) 1.5 3) 2.5 4) and 5) 4.0 6) 10.0...

Fig. 4. Swelling coefficients of crosslinked MA-DMEG copolymers as a function of the content of the crosslinking agent 1) pH 2.8 2) pH 12.5...

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