Polymer Solution
Solution Process
Disolving a polymer is a slow process that occurs in two stages. First, solvent molecules slowly diffuse into the polymer to produce a swollen gel. This may be all that happen if for example, the polymer-polymer intermolecular forces are high because of crosslinking, crystalinity, or strong hydrogen bonding. But if these forces can be overcome by the introduction of strong polymer-solvent interaction, the second stage of solution can take place. Here the gel gradually disintegrates into a true solution. Only this stage can be materially speeded by agitation. Even so, the solution process can be quite slow (days or weeks) for materials of very high molecular weight.
Polymer Texture and Solubility
Solubility relations in polymer system are more complex than those among low molecular weight compounds, because of the size differences between polymer and solvent molecules, the viscosity of the system, and the effects of the texture and molecular weight of the polymer. In turn, the presence or absence of solubility as conditions (such as the nature of the solvent, or the temperature) are varied can give much information about the topic.
From what has already been said, it is clear that the topology of the polymer is highly important in determining its solubility. Crosslinked polymers do not dissolve, but only swell if indeed they interact with the solvent at all. In part, at least, the degree of this interaction is determined by the extent of crosslinking. Lightly cross linked rubbers swell extensively in solvents in which the unvulcanized material would dissolve, but hard rubbers, like many thermosetting resin, may not swell appreciably in contact with any solvent.
The absence of solubility does not imply crosslinking, however. Other feature may give rise to sufficiently high intermolecular forces to prevent solubility. The presence of crystallinity is the common example. Many crystalline polymer, particularly nonpolar ones, does not dissolve except at temperatures near their crystalline melting points. Because crystallinity decrease as the melting point is approached and the melting point is itself depressed of the solvent, solubility can often be achieved temperature significantly below the melting point. Thus linear polyethylene, with crystalline melting point Tm = 135 oC, is soluble in many liquids at temperatures above 100 oC, while even polytetraflouromethylene Tm = 325 oC, is soluble in more of the few liquids that exist above 300 oC. More polar crystalline polymers, such as 66-nylon Tm = 265 oC, can dissolve at room temperature in solvent that interact strongly with them (for example, to form hydrogen bonds).
Other polymers:
Disolving a polymer is a slow process that occurs in two stages. First, solvent molecules slowly diffuse into the polymer to produce a swollen gel. This may be all that happen if for example, the polymer-polymer intermolecular forces are high because of crosslinking, crystalinity, or strong hydrogen bonding. But if these forces can be overcome by the introduction of strong polymer-solvent interaction, the second stage of solution can take place. Here the gel gradually disintegrates into a true solution. Only this stage can be materially speeded by agitation. Even so, the solution process can be quite slow (days or weeks) for materials of very high molecular weight.
Polymer Texture and Solubility
Solubility relations in polymer system are more complex than those among low molecular weight compounds, because of the size differences between polymer and solvent molecules, the viscosity of the system, and the effects of the texture and molecular weight of the polymer. In turn, the presence or absence of solubility as conditions (such as the nature of the solvent, or the temperature) are varied can give much information about the topic.
From what has already been said, it is clear that the topology of the polymer is highly important in determining its solubility. Crosslinked polymers do not dissolve, but only swell if indeed they interact with the solvent at all. In part, at least, the degree of this interaction is determined by the extent of crosslinking. Lightly cross linked rubbers swell extensively in solvents in which the unvulcanized material would dissolve, but hard rubbers, like many thermosetting resin, may not swell appreciably in contact with any solvent.
The absence of solubility does not imply crosslinking, however. Other feature may give rise to sufficiently high intermolecular forces to prevent solubility. The presence of crystallinity is the common example. Many crystalline polymer, particularly nonpolar ones, does not dissolve except at temperatures near their crystalline melting points. Because crystallinity decrease as the melting point is approached and the melting point is itself depressed of the solvent, solubility can often be achieved temperature significantly below the melting point. Thus linear polyethylene, with crystalline melting point Tm = 135 oC, is soluble in many liquids at temperatures above 100 oC, while even polytetraflouromethylene Tm = 325 oC, is soluble in more of the few liquids that exist above 300 oC. More polar crystalline polymers, such as 66-nylon Tm = 265 oC, can dissolve at room temperature in solvent that interact strongly with them (for example, to form hydrogen bonds).
Other polymers:
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