SYNTHESIS AND PROPERTIES OF NOVEL LINEAR DENDRITIC BLOCK-COPOLYMERS - REACTIVITY OF DENDRITIC MACROMOLECULES TOWARD LINEAR-POLYMERS
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The reactivity of benzylic dendritic polyethers toward linear polymers was investigated using coupling reactions of preformed dendritic and linear blocks in solution and in the melt. It was found that the rate constants for the Williamson reaction of poly(ethylene oxide)s (PEO) or poly(ethylene glycol)s (PEG) with dendritic bromides of various sizes increased with the length of the linear block and the generation of the dendrimer. This anomalous behavior is attributed to the increased reactivity of the PEO and PEG alcoholate anions due to the solvation of the counterion by the linear block and to the conformation changes occurring after attachment of the first dendritic block to PEG. It was shown that the functional group at the focal point of the dendrimer preserves its accessibility and reactivity even in highly restrictive medium and is able to participate in transesterification reactions with PEO and PEG in the melt. Thus, block copolymers that differ by a single linking bond between the linear and dendritic blocks were formed. 1993, American Chemical Society. All rights reserved.