Functional Copolymers of Polyvinylpyrrolidone
Sammanfattning: In many ways, polyvinylpyrrolidone (PVP) has a unique combination of chemical and physical properties. Unlike most polymers it is soluble in water as well as a number of organic solvents. PVP also has excellent film forming properties, outstanding chemical stability, complexing ability, low toxicity, and good adherence to many different substrates. PVP is therefore useful in numerous practical applications. In general, the inherent properties of PVP are utilized without modifications. However, the polymer lacks reactive functional groups, a limiting factor in many situations. Due to large differences in radical reactivity between 1-vinylpyrrolidin-2-one (NVP) and most other monomers, composition drift during copolymerization makes it very difficult to introduce functional groups or crosslinks in a controlled manner. Composition drift is best avoided by using monomers of equal reactivity. Attaching functional moieties to the alpha-position of NVP does not significantly alter the reactivity of the N-vinyl bond in a copolymerization. To use this approach, several functional monomers based on NVP itself were synthesized. From these NVP-derivatives, a number of functional PVP-based copolymers have been prepared. The copolymers are mainly intended for use as polymeric support materials in organic synthesis applications. Both soluble and crosslinked polymers were prepared for this purpose. The results from the soluble polymers show that the properties can be adjusted in terms of functionality, solubility, and molar mass. These polymers were suggested as attractive materials for drug delivery systems and phase-selectively soluble polymer supports for catalyst (or reagents). The unusual solubility profile of PVP was also successfully conveyed to crosslinked polymers. Lightly crosslinked beads of PVP could be prepared with useful loading capacities of functional groups and extensive swelling in several organic solvents as well as water. Naturally, this behaviour is very useful since the beads can be utilized as support materials in multi-step reaction sequences where several solvents of widely different polarity are used. This ability was demonstrated in the 5-step solid-phase synthesis of 5-(2,4,6-trimethoxy-phenyl)-cyclohexa-1,3-dienecarboxylic acid using polymer-bound cationic iron carbonyl complexes. In summary, the versatility of polyvinylpyrrolidone has been extended further since its properties can be easily tuned using copolymerization.
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