Stability, internal’ structural factor

In fact, the polymer is quite stable with respect to precipitation. Once isolated it can be kept in aqueous solution indefinitely (37). This stability is presumably kinetic in origin. Since all evidence points to a different internal structure for the polymer from all crystalline ferric oxide or hydroxide phases, the reorganization required for precipitation would be expected to have a high activation energy. Addition of base to pol5maer solutions does produce an immediate precipitate, presumably by cross-linking the polymer particles. In hydrolyzed ferric nitrate solutions with less than 2.5 base equivalent per mole of iron the eventual precipitates observed are probably formed directly from low molecular weight components. The low rate of dissociation would then be another factor in polymer stability. 

Pelton and coworkers showed that the size of PNIPAAm microgels decreases by a factor of 10 if sodium dodecyl sulfate (SDS) is used in the polymerization procedure [61]. Lyon s group used SDS for stabilization of PNIPAAm microgels prepared with PEG diacrylates of different PEG chain length [62], To investigate the influence of polymerization conditions on internal structure of PNIPAAm microgels, SDS was used in batch and semibatch polymerization processes [63],... 

Structural factors of an intramolecular process increasing the stability of only the photoacid side will decrease photoacidity. It follows that the reasons for the increased photoacidity of photoacids which undergo internal conversion from the locally excited, less polar state to the polar ifj state should be found in the photobase side of the photoacid-photobase equilibrium rather than in the photoacid side. 

G. Ruckensteiner, J. Burczeck, U. Ludwig, Factors Affecting the Thermal Stability of the Internal Structure When Burning Limestone , Zement Kalk Gyps 6,1995. 

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