Solvent swelling, crosslinked polymers

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. 

As we have seen previously not all polymers are capable of being dissolved. In principle the capacity to dissolve is restricted to linear polymers only crosslinked polymers, while they may swell in appropriate solvents, are not soluble in the fullest sense of the word. While individual segments of such polymers may become solvated the crosslinks prevent solvent molecules from establishing adequate interactions with the whole polymer, thus preventing the molecules being carried off into solution. 

We immerse a weighed sample of a crosslinked polymer in a suitable solvent and allow it to swell for up to 24 hours. We calculate the molecular weight of effective chains from Eq. 5.7. 

Polymer-based, synthetic ion-exchangers known as resins are available commercially in gel type or truly porous forms. Gel-type resins are not porous in the usual sense of the word, since their structure depends upon swelling in the solvent in which they are immersed. Removal of the solvent usually results in a collapse of the three-dimensional structure, and no significant surface area or pore diameter can be defined by the ordinary techniques available for truly porous materials. In their swollen state, gel-type resins approximate a true molecular-scale solution. Thus, we can identify an internal porosity ep only in terms of the equilibrium uptake of water or other liquid. When crosslinked polymers are used as the support matrix, the internal porosity so defined varies in inverse proportion to the degree of crosslinking, with swelling and therefore... 

Coals are considered macromolecular solids.(l) Although they are not polymers in the sense that they possess a repeating unit, they do possess several fundamental properties typical of synthetic crosslinked polymers.(2) One of these properties is the ability of coals to swell in organic solvents without dissolving. 

Manatt SL, Horowitz D, Horowitz R, Pimnell RP, Solvent swelling for enhancement of carbon-13 nuclear magnetic resonance spectral information from insoluble polymers chloromethylation levels in crosslinked, Anal. Chem., 52 1529-1532, 1980. 

Absorption of solvent causes the polymer to swell. Within a swollen polymer, the pressure acting on the solvent is greater than the atmospheric pressure, Pq. The excess pressure ir caused by the elastic forces of a cross inked polymer (crystalline domains act as effective crosslinks) raises the chemical potential of the solvent Ms within the polymer phase. The condition of equilibrium is... 

As can be seen from the derivation of Eq. (20), the swelling pressure ir is equivalent to the osmotic pressure developed by a non-crosslinked polymer solution of the same concentration In the absence of significant swelling, this pressure will be relatively small and to a good approximation the right hand side of Eq. (20) can be set equal to zero. Thus, a measurement of the equilibrium absorption of solvent (cfrj) yields an approximate experimental value of x p-... 

Swellable polymers Crosslinked polymers are 3-dimensional networks and can easily be separated by. sedimentation or filtration. Slightly crosshnked polymers such as, e.g., polystyrene crosslinked with 0.5—3% 1,4-divinylben-zene have to be used in solvents in which they swell, otherwise mass transport may be completely stopped. 

A mixture of a good solvent (toluene) with a bad one in such a ratio as to cause a sufficiently fast dissolution of the non-irradiated polymer with the minimum swelling of the crosslinked polymer taking place proved to be the optimum one. 

The swelling of negative resist patterns can be minimized, but cannot be totally eliminated. This is because the solvent which can dissolve the unexposed polymer has a natural tendency to diffuse and penetrate into the exposed crosslinked polymer area. The poor edge acuity and low resolution of the conventional negative polymer resist is a well known problem. 

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