Syntheses and model complexation studies of well-defined crown terminated polymers

A TEMPO-based free radical initiator (4a) containing a dibenzo-24-crown-8 (DB24C8, 2a) moiety was synthesized. A similar initiator (4b) based on bis(m-phenylene)-32-crown-10 (BMP32C10, 1b) was also synthesized. The crown-based initiators were used to prepare crown ether terminated polystyrenes of narrow molecular weight distribution (PDI). The DB24C8-terminated polymer 5 was demonstrated to form a pseudorotaxane complex (18) with dibenzylammonium hexafluorophosphate (17), but because of its small cavity, 5 cannot complex bulky N,N'-dialkyl-4,4'-bipyridinium (paraquat or viologen) salts. On the other hand, the BMP32C10-terminated polymer 11 complexed N,N'-bis(p-tert-butylbenzyl)-4,4'-pyridinium bis(hexafluorophosphate (paraquat salt, 23) strongly, but did not interact with dibenzylammonium hexafluorophosphate (17) to a detectable extent. Therefore, these new polymeric hosts are capable macromolecular building blocks for supramacromolecular chemistry using pseudorotaxane complexation, and furthermore, both show selectivity; the DB24C8 polymer is selective for secondary ammonium ion complexation, and the BMP32C20 polymer is highly selective for paraquat recognition. Future work will involve application of these new functional polymers to preparation of star, graft, and block structures by self-assembly.