Polymer Host Phenomena

Several explanations have been proposed to describe these effects. Sasakawa and coworkers explained their results by a conformational trap argument (Lange and BSssler, 1982 Zboinski, 1983). Differences in trap densities were proposed as due to differences in rotational mobility of the dopant molecules in various polymers. Borsenberger concluded that the effect of the polymer was largely related to the prefactor mobility. It was argued that the effect of the polymer was related to differences in polymer ionization potentials. 

Yuh and Pai argued that the role of the polymer was related to the activation energy. Borsenberger and Bassler explained their results on a model based on dipolar disorder. According to the model, a is determined by the dipole moment of both the dopant molecule and the polymer repeat unit. The effect of the polymer host is then related to the difference in dipole moments of the dopant molecule and the polymer repeat unit as well as the dopant concentration. Most recent studies have been described by dipolar disorder arguments. 

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Gels swollen in binary solvents have been the subject of many investigations for their ability to modify the polymer-solvent interaction.4 7 Several authors8 10 have reported that gels made from PNIPA, swollen in aqueous solutions of aromatic compounds, collapse at aromatic concentrations above a certain threshold. This phenomenon has been attributed to the approach of the solubility limit, of the host molecule in water.9... 

At one time very few polymer pairs were believed to be miscible but over the last twenty years a host of new miscible pairs have been identified As a relatively new field, the phenomenon of miscibility and the new materials derived from it will certainly have many as yet undiscovered applications. 

The interesting polymer-solubility behaviour led us to compare this phenomenon with classical LCST effects. In our case, because of the reversible complex formation between the polymer P20 and CD, the optical effect is based on supramolecular interactions. This means that the discovered pseudo-LCST behaviour is a result of non-covalent interactions between the CD host and polymer guest. Furthermore, in this system competitive inhibition or control of the LCST is possible by addition of other suitable guest molecules of low molecular weight, for example, potassium 1-adamantylcarboxylate. CD complexes these molecules preferably and the polymer precipitates. This special effect cannot be observed in regular LCST systems. 

Compatibility with the host polymer plays a principal role in application of oligomeric HAS [13,284]. This phenomenon was studied in PP doped with poly(2,2,6,6-tetramethyl-4-piperidyl acrylate-co-n-octadecyl acrylate) having Mn between 5000 and 116000. The light stabilizing effect diminished with increasing mol. wt. of the stabilizer [300]. 

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