Polymers, functional oxazoline based

Another pyrrolidone-based phosphine has been incorporated into amphiphilic, water-soluble diblock co-polymers based on 2-oxazalone derivatives (Scheme 61). The synthesis involved the initial preparation of a diblock co-polymer precursor with ester functionalities in the side chain. This was achieved by sequential polymerization of 2-methyl-2-oxazoline to form the hydrophilic block that provides water solubility, and subsequently a mixture of ester-functionalized oxazoline 147 and 2-nonyl-2-oxazoline, the latter increasing the hydrophobicity of the second polymer block. Having made the backbone, the ester functionalities were converted into carboxylic acids giving polymer 148, which was then reacted with the phosphine ligand to give the desired supported material, 149. This was used in asymmetric hydrogenation reactions with success. 

Neither of the two base polymers (A and B) contain reactive groups. Most hydrocarbon polymers, such as polyethylene PE, PP, PS and copolymers thereof, are in this situation. In such cases, different compatibilization methods can be envisioned. The first one is to add two reactive polymers (C and D) which are mutually reactive and are miscible with A and B, respectively. The resulting copolymer will be of type C-D. The second one is to hmctionalize polymers A and B with different functional groups, which are mutually reactive. Take PE/PS blends as an example. When PE is functionalized with a carboxylic group and PS with an oxazoline group, they will be able to react with each other and form a desired compatibilizer [6]. 

Multifunctional initiators based on, for example, cyclotriphosphazine [106], silesquioxane [107], porphyrin [108] and bipyridine metal complex [109, 110] cores were also successfully used for the living cationic ring-opening (co)polymerization of 2-oxazolines, resulting in star-shaped (co)polymers. The use of polymeric initiators also allowed the construction of well-defined complex macro molecular architectures, such as triblock copolymers with a non-poly(2-oxazo-line) middle block that is used to initiate the 2-oxazoHne polymerization after functionalization with tosylate end-groups [111-113]. In addition, poly(2-oxazoline) graft copolymers can be prepared by the inihation of the CROP from, for example, poly(chloromethylstyrene) [114, 115] or tosylated cellulose [116]. 

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