Synthesis and Characterization of PNIPAm Core Cross-Linked Star Polymers and Their Functionalization with Cyclodextrin

Poly(N-isopropylacrylamide) (PNIPAm) core cross-linked star (CCS) polymers (s-(PNIPAm)(n)) are synthesized by arm-first ATRP method. The related synthesis conditions are investigated and optimized. By varying cross-linker N,N-methylenebisacrylamide (BIS) concentration, PNIPAm CCS polymers with about 47, 86, and 211 arms are synthesized. Then, under ATRP condition, the living sites at the core of s-(PNIPAm)(n) reacting with a monovinyl -cyclodextrin (-CD) monomer afford -CD functionalized s-(PNIPAm)(n) (CDF-SPNIPAm). The structures of the star polymers are characterized. The results indicate that in CDF-SPNIPAm, the ratio of -CD units to PNIPAm arm numbers could be up to 0.6:1. The fluorescence spectra of star polymer/ANS (8-anilino-1-naphthalenesulfonic acid ammonium salt hydrate) systems prove that the -CD moieties of CDF-SPNIPAm are available for including guest molecules. By using pH-sensitive adamantyl (Ada)-terminated poly(4-vinylpyridine) (Ada-P4VP) (synthesized by ATRP strategy) as a model guest macromolecule, the host-guest complexation between -CD units of CDF-SPNIPAm and adamantyl groups of Ada-P4VP is confirmed via 2D NOESY H-1 NMR and DLS measurements. The results indicate that the presence of the Ada-P4VP arms provides temperature-responsive star polymers with pH sensitivity. Therefore, the -CD-functionalized star PNIPAm could provide host macromolecular platform for constructing novel miktoarm star polymers.